Palaeontology VOLUME 38 • PART 1 • MAY 1995 Published by The Palaeontological Association • London Price £45-00 THE PALAEONTOLOGICAL ASSOCIATION (Registered Charity No. 276369) The Association was founded in 1957 to promote research in palaeontology and its allied sciences. COUNCIL 1995-1996 President : Dr R. A. Fortey, Department of Palaeontology, Natural History Museum, Cromwell Rd., London SW7 5DB Vice-Presidents : Dr J. A. Crame, British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 OET Dr J. E. Dalingwater, School of Biological Sciences, Williamson Building, The University, Manchester Ml 3 9PL Treasurer: Dr T. J. Palmer, Institute of Earth Studies, University of Wales, Aberystwyth, Dyfed SY23 3DB Membership Treasurer: Dr M. J. Barker, Department of Geology, University of Portsmouth, Burnaby Road, Portsmouth POl 3QL Institutional Membership Treasurer: Dr J. E. Francis, Department of Earth Sciences, The University, Leeds LS2 9JJ Secretary : Dr M. P. 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Non-members may subscribe, and also obtain back issues up to three years old, at cover price through Blackwell Publishers, Journal Subscription Department, Marston Book Services, P.O. Box 87, Oxford OX2 0DT, UK. For older issues contact the Marketing Manager. US Mailing: Second class postage paid at Rahway, New Jersey. Postmaster: send address corrections to Palaeontology, do Mercury Airfreight International Ltd, 2323 EF Randolph Avenue, Avenel, NJ 07001, USA (US mailing agent). Cover: This specimen of Calymene blumenbachii from the Wenlock of Dudley is mounted in gold, forming the centrepiece of a nineteenth century brooch presented to the Natural History Museum by Miss E. Begg. THE ORIGIN OF ALGAL-BIVALVE _ AUG u PHOTO-SYMBIOSIS ^^KARlE-b by TERUFUMI OHNO, TETZUYA KATOH Cliui TERUFUMI YAMASU Abstract. The photo-symbiotic bivalves Fragum fragum and Fragum loochooanum burrow in sediments and supply light through a posterior shell gape to zooxanthellae within their internal soft parts. This newly discovered mode of photo-symbiosis in bivalves can be termed sciaphilous (shade loving), and the hitherto known one, in which bivalves expose mantles or transparent shells out of the sediment to harvest light, as heliophilous (sun loving). Fragum unedo, also examined here, is heliophilous. Sciaphilous photo-symbiosis in F. fragum is enabled by the zooxanthellae’s low compensation point of photosynthesis (50 //Einstein m-2 s^1), a point far lower than the ambient light intensity of their habitat. The zooxanthellae’s pre-adaptation to low light intensity might have played an important role in originating the zooxanthella-bivalve symbiosis. Sciaphilous photo-symbiosis allows bivalves to profit from photo-symbiosis without risking predation or epibiont attachment, and thus may have been common among fossil photo-symbiotic bivalves. The disproportionately rapid increase in the length of the posterior shell gape and the very rapid decrease of the angle between the posterior and ventral valve margins during the growth of two sciaphilous Fragum species, which ensure effective light harvesting by the zooxanthellae, can be used as criteria in searching for fossil sciaphilous microbial-bivalve photo-symbiosis. Symbiosis between bivalves and contained photosynthetic zooxanthellae has been known since the detailed study by Yonge (1936). This occurs in the genera Tridacna (Yonge 1936), Hippopus (Yonge 1936) and Corculum (Kawaguti 1941), all of which are Indo-Pacific tropical shallow-water dwellers. Symbiosis between non-photosynthetic organisms and photosynthetic microbes will be termed photo-symbiosis hereafter. The symbiotic unicellular, brown-coloured algae, traditionally called zooxanthellae, are currently placed in the dinoflagellate genus Symbiodinium (Blank and Trench 1986). This same genus is harboured within all the modern hermatypic corals. Although Yonge (1936) observed zooxanthellae contained within cells (phagocitic blood-cells) of the animals, the zooxanthellae are more commonly located intercellularly in the host bivalve’s soft tissues (Trench et al. 1981). With the exception of Tridacna crocea Lamarck, which bores in reef coral, all the taxa above are epifaunal. The hitherto known living photo-symbiotic bivalves, both epifaunal and infaunal, place their hypertrophied mantle edges (Hippopus and Tridacna , including T. crocea) or transparent windows on extremely flat posterior valve surfaces (Corculum cardissa (Linnaeus); Vogel 1975; Watson and Signor 1986) above the sediment surface in order to expose part of the animal to sunlight. This life habit can be termed heliophilous (sun loving). All the known photo-symbiotic bivalves belong to the superfamilies Cardiacea and Tridacnacea, which are closely related to each other. The majority of the bivalves of the superfamily Cardiacea adopt an infaunal mode of life. Thus the ancestors of the photo-symbiotic bivalves mentioned above were most probably infaunal bivalves. This raises the question of how the symbiotic relationship originated between the infaunal ancestors of these bivalves and the light-demanding photosynthetic zooxanthellae. Photo-symbiosis has been inferred in fossil bivalves (Philip 1972; Vogel 1975; Loriga and Benini 1977; Skelton 1979; Thiele and Tichy 1980; Yancey and Boyd 1983; Skelton and Wright 1987; Seilacher 1990) as well as among fossil brachiopods (Cowen 1970, 1982). This inference is based on | Palaeontology, Vol. 38, Part 1, 1995, pp. 1-21, I pl.| © The Palaeontological Association PALAEONTOLOGY, VOLUME 38 features of their shell morphology, shell microstructures and their palaeoecology, which are similar to those of living photo-symbiotic bivalves or hermatypic corals. Recently, Kawaguti (1983) and Yamasu (1988a, b ) have reported new examples of zooxanthella- bivalve symbiosis in Fragum fragum (Linnaeus) and Fragum unedo (Linnaeus). Umeshita and Yamasu (1985) found another example in a third species, Fragum mundum (Reeve). In contrast with the highly specialized shell forms of other known photo-symbiotic bivalves, the shell shape of the Fragum species is similar to other non-symbiotic cardiid bivalves, except for their long and straight posterior margin as well as the angular corner formed where the posterior and ventral valve margins meet. This suggested that a detailed investigation of bivalves belonging to the genus Fragum could provide us with information about the initial stage of zooxanthella-bivalve symbiosis. Further, information on the zooxanthella-symbiosis of the genus would also contribute to a safer basis for inferring the existence of photo-symbiosis among fossil bivalves. For these reasons, three living specimens of strawberry cockles, F. fragum , F. unedo and F. loochooanum Kira, were examined on the basis of their ecology, anatomy, distribution of zooxanthellae within their soft tissues, shell form and shell microstructure. For F. fragum, shell transparency and photosynthetic activity of symbiotic zooxanthellae were also examined. The present investigation reports the finding of the new life mode for photo-symbiotic bivalves, in F. fragum and F. loochooanum , which may be termed sciaphilous (shade loving). The adaptive significance and origin of photo-symbiosis in bivalves, as well as the criteria for inferring sciaphilous photo-symbiosis in fossil bivalves, are discussed. MATERIALS AND METHODS Habitats of the examined bivalves The majority of the observations of the life habits of the three species of Fragum , as well as the collection of materials for the further studies, were carried out by numerous scuba dives on the shallow sand flat of Amitori Bay in front of the Okinawa Regional Research Centre, Tokai University, Iriomote Island, Okinawa Prefecture, Japan, between November 1988 and November 1991. The substratum consists of light grey silty coarse sand. The sand grains are mainly calcareous bioclasts. The flat is exposed during the low tides of Spring and late Autumn, when the tidal range is largest. At average high tides, it is covered with about 2 m sea water. The mean monthly temperature fluctuates between 22 °C in February and 29 °C in July (from data for the period May 1977 to December 1989; Okinawa Regional Research Centre 1990). On test-dives to the deeper part of the bay, a few living individuals with zooxanthellae were also found at a depth of 20 m in muddy sand substrata. They were not incorporated into the material of the present study. Additional samples of living F. unedo were collected from the adjacent sandy flats within the bay and from the sandy flat at the mouth of Sakiyama Bay, which is located about L5 km south of the centre and separated from Amitori Bay by a small peninsula. For the study of shell allometry, F. unedo specimens collected from the Kabira Bay on Ishigaki Island, which is located about 50 km from Amitori Bay, were incorporated. The specimen for Plate 1, figures 5 and 8 was collected at Bise, Okinawa Island, Okinawa Prefecture. All the examined specimens, except for those photographically documented in the field study, are stored in the Museum of the Department of Geology and Mineralogy, Faculty of Science, Kyoto University (JCT00014-JCT00019). Burrowing rate index The collected samples were kept in a laboratory aquarium filled with a sufficient thickness of silty coarse sand from their natural habitats before measurement of burrowing rate indexes. The samples were provided with running sea water and received ambient light from windows. The burrowing of OHNO ET AL.: PHOTO-SYMBIOSIS 3 the cockles was recorded by a video-camera. Burrowing periods (time between erection of shells and complete burrowing of the posterior shell margin), and number of rocking motions during burrowing were determined from video-images. Mass (wet weight) and shell length of the samples were also measured. For each individual, burrowing rate index (BRI), defined by Stanley (1970), was calculated according to the following equation: BRI [mass (g)]1/3 burrowing period (s) x 100. Shell transparency of Fragum fragum Measurements were carried out using a spectro-photometer (Hitachi Type 3400). The shell surface is exposed to a light source. Behind it is a hole 3 mm in diameter in an opaque board. The light transmitted through the shell and the hole is then gathered and measured using a photo-multiplier equipped with an integrating sphere. Measurements of the photosynthesis-irradiance profile of the zooxanthellae of Fragum fragum The cockles were collected on the sandy flat in Amitori Bay in October, 1990 and kept in an aquarium for several days under the same conditions as the samples for the measurement of the burrowing index, and then examined for the photosynthetic activity of the zooxanthellae. Zooxanthellae in the cockles were isolated from the mantle tissues by squeezing them in sterilized and filtered sea water. The sea water with liberated zooxanthellae was then passed through a nylon mesh (50 pm) to remove tissue fragments, and then centrifuged at 1200 g for 10 min to separate bacteria and various small particles which were left in the supernatant. The red precipitate of zooxanthellae was then suspended in filtered sea water and placed in a 3-0 ml vessel with a rotating platinum electrode, fitted with a circulating water-jacket to keep a constant temperature of 20 °C. The light beam from a 350 W incandescent lamp was passed through two infrared-absorbing filters (Hoya, HA-30) and a diaphragm, to attenuate the light intensity in a step-wise fashion, and then focused on the vessel. Light intensity at the surface of the vessel was monitored with a Licor Quantum Sensor. Both Oa concentration in the vessel, as monitored by the platinum electrode, and the light intensity were automatically recorded. SCIAPHILOUS LIFE MODE AND POSTERIOR MANTLE EDGES More than two hundred living F. fragum were observed on the tidal flat in front of the Okinawa Regional Research Centre. Their population density here seldom exceeds one or two individuals per square metre, although an exact determination was not carried out. On burrowing, the valves become completely immersed in the sediment, with the flattened posterior valve slopes just beneath the thin sediment cover (PI. 1, fig. 3; Text-fig. 1b). The posterior shell gape is covered by partly fused mantle edges (PI. 1, figs 1 and 2; Text-figs 1a and 2). From both posterior valve margins, mantle edges extend laterally. They are furnished with numerous tentacles, and are moderately hypertrophied, especially ventral to the inhalant siphon. The tentacles secrete mucus and sand grains adhere around them. Consequently, the extended mantle edges and tentacles are covered by sand grains (PI. 1, fig. 9). Therefore in the natural life position of F. fragum, it is only the exhalant and inhalant siphons and a part of the posterior mantle edges covering the shell gape that are continuously exposed through the sediment (PI. 1, fig. 3; Text-fig. 1b). These exposed soft parts covering the posterior shell gape are spotted with transparent and non-transparent patches and are as a whole semitransparent (PI. 1, fig. 2). Large transparent patches commonly occur around the exhalant and inhalant siphons. More than eighty living F. loochooanum were observed. They have a life habit rather similar to F. fragum , and burrow completely into the sediment. Their very weakly hypertrophied lateral 4 PALAEONTOLOGY, VOLUME 38 expansions of posterior mantle edges, together with numerous tentacles (Text-fig. 1a), are covered by the sediment (PI. 1, fig. 6; Text-fig. 1b). Therefore, only the posterior mantle edges covering the posterior shell gape, including the inhalant and exhalant siphons, are continuously exposed through the sediment. Transparent and non-transparent patches spot these exposed soft parts and make them semitransparent. Large transparent patches occur on the mantle edges covering the notches of the marginal crenulations along the posterior valve margins in addition to those around the exhalant and inhalant siphons. This species does not fix sand grains around its tentacles. Five living F. unedo were available for observation. They bury their valves completely in the sediment. Their posterior mantle edges are furnished with tentacles and are strongly hypertrophied, especially ventral to the inhalant siphon. Here, they form fan-shaped lobes (PI. 1, fig. 7; Text-figs 1a-b). The lobes continue as broad fleshy stripes along the rest of the posterior margin. These hypertrophied mantle edges are spread over the surface of the substratum (PI. 1, fig. 7; Text-fig. 1b). The mantle edges covering the posterior gape, including inhalant and exhalant siphons, are thick and less transparent. Most of the individuals show a negative reaction to shade and draw back their posterior mantle edges when a shadow crosses over them. All the examined samples of these three species contain zooxanthellae within their soft tissues. Therefore, their coexistence with zooxanthellae is not purely fortuitous but very probably symbiotic. F.fragum and F. loochoocinum adopt infaunal life habits and do not extend their mantle margins and valves out of the sediment, except for the regions around the inhalant and exhalant siphons. Furthermore, F. fragum apparently deliberately minimizes the exposure on sediment by mucus secretion from the tentacles and adhesion of sediment grains around them. This previously unrecognized photo-symbiotic life mode, in which the host bivalves do not expose their mantle edges to the light, except for small areas stretched between the posterior shell gape, can be called sciaphilous (shade loving; Text-fig. 7). In contrast, all the hitherto known living photo-symbiotic bivalves, both epifaunal and infaunal, can be termed heliophilous (sun loving), because they put their hypertrophied mantle margins or transparent shells out of the sediment to expose them directly to the light. F. unedo, which is infaunal and extends its hypertrophied mantle margins and tentacles out of the sediment, belongs to this latter category. EXPLANATION OF PLATE 1 Figs. 1-5, 8-9. Fragum fragum. 1-2, with moderately expanded mantle edges and tentacles. 1, illuminated from above. 2, illuminated from below in dark room. Mantle edges covering the shell posterior gape are more transparent than the semi-transparent valves. Non-fused part of the mantle edges meet together along the dark line running along the middle of the shell gape from the inhalant siphon to the ventral margin. Both x 1-7. 3, in natural life position, posterior part of the shell covered with foraminiferal sand, x 3-3. 4, zooxanthellae in the mantle tissue, x c. 600. 5, soft parts : gills and mantle covering the inner shell surface, especially near the posterior gape, containing abundant zooxanthellae, are dark coloured. Condensation of zooxanthellae, partly caused by the contraction of muscles, has darkened the pallial lines. The bottom wall of the supra-branchial chamber (triangular white area in the middle of the photograph) contains fewer zooxanthellae than the area of the foot surface (upper left of the bottom wall of the supra-branchial chamber), which faces the bottom wall in life, x 1-4. 8, soft parts: abundant zooxanthellae darken both the outer and the inner gill demibranchs. In contrast, the posterior mantle edges are spotted with transparent flecks (dark in the photo) and white flecks, and contain very few zooxanthellae. The distal half of the L-shaped foot, and the mantle covering the anterior part of the shell interior, both located rather distant from the posterior shell gape from which light penetrates into the shell interior, are white and contain very few zooxanthellae, x 1-9. 9, the posterior slopes of shells are covered with sand grains, adhering to them because of the presence of mucus secreted by the tentacles. Fig. 6. Fragum loochooanum in natural life position. Only the posterior gape is visible through the sediment, x 4-3. Fig. 7. Fragum unedo in natural life position with strongly expanded mantle edges lying on the sediment, x 1-7. PLATE 1 OHNO et al Fragum 6 PALAEONTOLOGY, VOLUME 38 text-fig. 1 . Sketch of three Fragum species, a. Mantle edges fully expanded, b. Exposure of mantle edges through sediment cover (sediment is stippled). ACTIVE BURROWING ABILITY As a measure of locomotion ability, the burrowing time and burrowing rate index (BRI) were determined for ten individuals of F. fragum , six individuals of F. loochooanum and one individual of F. unedo (Table 1). For the Cardiacea, to which Fragum also belongs, Stanley (1970) reported BRI values for seven species. Following Stanley’s statement that temperature has a minor effect on BRI value within the range 20-30 °C, a comparison of BRI values between the present species and Stanley’s six species was made, all measured within this temperature range. Stanley’s seventh species, Dinocardium robustum shows an exceptionally large BRI value of 5 (measured at 18 °C) in comparison with his other six species. Three of Stanley’s (1970) species have a BRI value of 1, and of the other three, one species has a value of 0-9, another 0 5, and the last 04. Thus F. fragum (mean BRI = 0-7) burrows as effectively as Stanley’s six cardiacean species without symbiotic zooxanthellae. For F. unedo only one measurement is available (BRI = 0 4) which does not allow us to draw any conclusion, although it is comparable to the BRI values of Stanley’s six cardiaceans. F. loochooanum has a very low BRI value (mean BRI = 0 075) in comparison with the above discussed species. Perhaps the BRI value underestimates locomotive activity of small sized animals, which cannot use weight, for example, to help in cutting themselves into the sediment. If locomotive activity is measured in terms of burrowing period, F. loochooanum (114 s) burrows far faster than F. fragum. BIVALVE ANATOMY Mantle edges When the three examined strawberry cockle species open their valves, the mantle edges cover the shell gape along its whole length (Text-fig. 2). They are fused between the beak and the inhalant siphon. Along the rest of the gape, they are not fused, yet meet tightly together. The ventral mantle edges as well as the anterior mantle edges are thin, except for the rather thick ventral mantle edges near the angular postero-ventral shell corner. OH NO ET AL.: PHOTO-SYM BIOS IS 7 table 1. Burrowing index of three Fragum species. Abbreviations: M, mass; L, length; BP, burrowing period; R, number of rocking motions; BRI, burrowing rate index; std., standard deviation. The centre referred to is the Okinawa Regional Research Centre. M (g) L (mm) BP (s) R (times) BRI Fragum fragum* (n = 10) 1-86 14 4 891 3 0 14 3-24 17-0 129 4 1-15 3-44 17-4 231 3 0-65 3-89 17-9 115 3 1-37 4-48 19 2 316 4 0-52 4-54 18-9 305 4 0-54 4-89 190 1347 4 013 6-36 20-3 543 6 0-34 6-49 22-7 824 6 0-23 10 99 24-5 103 4 2-16 Mean 502 1913 480-4 4-1 0-72 SD 2-39 2-73 Fragum loochooanunrf 395-1 1-0 0-62 (n = 6) 016 7-1 50 4 0-076 0-24 8-6 129 4 0-073 0-25 8-5 122 5 0-074 0-27 8-5 124 5 0-076 0-29 8-6 160 4 0077 0-39 9-7 100 4 0-075 Mean 0-27 8-5 114-2 4-3 0-075 SD 007 0-75 33-7 0-5 0001 Fragum unedo% (« = 1) 6-86 25-1 484 1 1 0-40 * Samples from the sandy bottom in front of the centre; collected between 26 and 29 Oct. 1990; measured on 30 Oct. 1990 at water temperature of 26 8 °C. t Samples from the sandy bottom in front of the centre; collected between 26 and 31 Oct. 1990; measured on 5 Nov. 1990 at water temperature of 26-2 °C. $ Sample from sandy flat at the mouth of Sakiyama Bay; collected on 31 May 1989; measured on 2 June, 1989 at water temperature of 25 9 °C. As already described, the mantle edges along the posterior valve margins show considerable variation between the sciaphilous and the heliophilous species. In brief, the sciaphilous F. fragum and F. loochooanum have less hypertrophied, less extensively laterally expanded, and more transparent posterior mantle edges than the heliophilous F. unedo. It is difficult to estimate quantitatively the proportion of the incident light that is transmitted through the mantle edges covering the posterior gape of the sciaphilous F. fragum and F. loochooanum. In F. fragum, however, they are more transparent than the semitransparent posterior slope of their valves (PI. 1, fig. 2). Soft parts within the shell interior The anatomy of the soft parts within the shell interior is quite similar in all three Fragum species. The description below is mainly based on F. fragum (PI. 1, figs 5 and 8; Text-fig. 2). PALAEONTOLOGY, VOLUME 38 text-fig. 2. Anatomy of Fragum fragum. Inner surface of the bottom (anterior side) of the supra-branchial chamber is densely stippled. Mantle covering the inner surface of the shell is weakly, but regularly, stippled. Ventral and anterior mantle edges are irregularly stippled. Arrows on inner and outer demibranchs indicate the direction of ciliary grain transportation. Abbreviations: A, anus; AA, anterior adductor muscle; AME, anterior mantle edge; DP, dorsal partition of supra-branchial chamber; ES, exhalant siphon; F, foot; FG, food groove (inner marginal food groove of ctenidium); ID, inner demibranch; IS, inhalant siphon; LP, labial palp; MF, ventral end of mantle fusion; OD, outer demibranch; PA, posterior adductor muscle; PC, pericardium; PME, posterior mantle edge; PPR, posterior pedal retractor muscle; SBC, supra-branchial chamber; SP, sagittal partition connecting posterior adductor muscle and dorsal partition of supra-branchial chamber; VME, ventral mantle edge; VP, ventral partition of supra-branchial chamber. Just under the posterior shell gape there is an elongated tube separated ofif by a thin membrane (supra-branchial chamber; Purchon 1955) running parallel to the posterior valve margins. Its dorsal end reaches to the foot, yet the membrane is not fused with the latter but is separated by a very narrow slit. The tube is bipartite ventral to the exhalant siphon, where a thin membrane divides a lower (anterior) chamber, with attachment of demibranchs, from the upper chamber. Dorsal to the exhalant siphon it is tripartite. Here, there is a hollow between the mantle edge and the posterior adductor muscle. The anus opens in this hollow. Below it, a thin membrane separates two chambers, each with attachment areas for outer and inner demibranchs, respectively. The upper of the two chambers has a saggital partition. The three examined species have inner and outer gill demibranchs which hang from the lateral wall of the supra-branchial chamber. The inner demibranchs are considerably larger than the outer demibranchs and have food grooves along their free edges (inner marginal food grooves of ctenidium). The inner demibranchs are connected by a OHNO ET AL.: PHOTO-SYMBIOSIS 9 pair of labial palps to the mouth on the ventral side of the foot. The palps, considerably smaller than those illustrated in Clinocardium nut tali (Stasek 1961), are located at about one-third of the length of the inner demibranchs from their dorsal ends. Each of the labial palps is composed of two small triangular lobes. The adductor muscles are located near the beak. The foot is large and L-shaped. DISTRIBUTION OF ZOOXANTHELLAE Zooxanthellae (PI. 1, fig. 4) are contained intercellularly among the tissues of the strawberry cockles. Their brown colour makes it easy to determine their occurrence and relative abundance within the cockle tissues. In the two sciaphilous species, F.fragum and F. loochooanum. the zooxanthellae are contained in the innermost part of the hypertrophied lateral expansions of the posterior mantle edges, but in only small quantities. Their tentacles, as well as the mantle covering the posterior margins, both of which are more or less transparent, do not contain abundant zooxanthellae. The ventral mantle edges contain abundant zooxanthellae just near the corner where the posterior and ventral margins meet. The zooxanthellae content of the mantle edges gradually decreases towards the anterior mantle edges. In the shell interior of these sciaphilous species, the thin membranes of the supra-branchial chamber contain zooxanthellae, but not very abundantly. The surfaces of the gill demibranchs are strongly dark brown coloured (PI. 1, figs 5 and 8). On the outer surfaces of the demibranchs, the brown colour fades gradually towards the beak. The inner sides of the demibranchs are brown coloured, especially strongly along the line of their attachment to the supra-branchial chamber wall. Weak brown coloration is also observed on the foot facing the floor of the supra-branchial chamber. The membrane covering the posterior adductor muscle is strongly brown coloured. Abundant zooxanthellae also exist within the mantle lining the shell interior: in the smallest species, F. loochooanum , the whole surface is coloured dark brown; in F. fragum the coloration is more vivid along the posterior valve margins and posterior part of the ventral margin. The hypertrophied and laterally expanded mantle edges of the heliophilous F. unedo , which are exposed to light on the sediment surface, harbour a large number of zooxanthellae under their thick, almost non-transparent tissue. Zooxanthellae are also abundant in the ventral mantle edge just near the corner where it meets with the posterior mantle edge. Their abundance gradually decreases towards the anterior mantle edges. In the shell interior, the thin membrane of the walls and floor of the supra-branchial chamber contains a large number of zooxanthellae. The coloration of the gills and the mantle lining the shell interior is much weaker than the two sciaphilous species. In particular, the anterior part of the mantle lining the shell interior is almost white and contains very few zooxanthellae. In summary, the sciaphilous F. fragum and F. loochooanum farm the zooxanthellae mainly within their internal soft tissues, whereas the heliophilous F. unedo farms them chiefly in its exposed and hypertrophied posterior mantle edges. In the two sciaphilous species, the mantle edges covering the posterior shell gape and supra-branchial chamber, which aligns the gills just beneath and parallel with the posterior shell gape, are semi-transparent. They ensure the penetration of light to the gills and other internal soft tissues with abundant zooxanthellae. The heliophilous F. unedo also has a long supra-branchial chamber. This species, however, uses it as an area for farming the zooxanthellae rather than as a device for ensuring light supply to the gills. The light for the zooxanthellae within the tissues of the supra-branchial chamber is supplied from the inhalant and exhalant siphons. ACTIVE GRAIN TRANSPORTATION ON THE GILL SURFACE Transportation of grains by ciliary action (Text-fig. 2) was monitored by sprinkling fine grinding powder over the gill surfaces of F. fragum. On each outer demibranch grains are transported from the ascending branch to its free edge, and then on, over the descending branch on to and along the 10 PALAEONTOLOGY, VOLUME 38 ctenidial axis. On the inner demibranch, grains are transported on both the descending and ascending branchs to the food groove along its free edge. The action of cilia in the food groove then transports tine particles, via the labial palps, to the mouth. In one specimen it takes about a minute for the grains to cross the brightest part of the descending lamella of the inner demibranch from the ctenidial axis to the food groove, even after three hours have elapsed since the beginning of dissection. Excess grains are sorted by the labial palps, mixed with mucus to form small round balls and then expelled from its pointed end. The above construction of the gill as well as the manner of fine grain transportation on it closely resembles that of Clinocardium nuttali described by Stasek (1961). The similar construction of the gills and the labial palps of the three examined Fragum species suggests that these species actively transport and sort grains on the gills and labial palps, as observed in F. fragum , which in turn indicates that the three examined Fragum species retain active filter feeding. SHELL FORM AND ALLOMETRIC GROWTH Shell form In accordance with the diagnosis of the genus Fragum (Keen 1980), the three examined Fragum species have fairly inflated valves, flattened posterior valve slopes, well defined umbonal ridges along the intersection of the posterior and ventral valve slopes, as well as an angular postero-ventral corner of the valve margins. The posterior valve margin is very long and almost straight except near the beak. It meets with a more or less straight ventral margin and forms an angular corner. In the present study the angle of this corner is referred to as the PV-angle. In some specimens the umbonal ridge protrudes weakly at the shell margin postero-ventrally. In this case the margin ventral to it is weakly concave near the angular corner. Allometric growth The sciaphilous F. fragum and F. loochooanum show a very conspicuous disproportionate increase in the length of the posterior gape (PGL) in comparison with the increase in shell length (L) as expressed by the rapid increase in PGL/L ratio (Text-fig. 3a; Table 2). In the heliophilous F. unedo , on the other hand, this tendency is not present. The angles between posterior and ventral margins (PV-angle) of the two sciaphilous species are far smaller than that of the heliophilous one, when compared for the same L value (Text-fig. 3b). The average PV-angle of the largest specimens (L = about 25 mm) of F. fragum is 20 degrees smaller than that of F. unedo of comparative L value. The average for F. loochooanum is smaller by about 10 degrees than that of F. unedo , for comparable shell sizes (L = 10 mm). Furthermore, the PV-angle decreases very rapidly with increased shell length (L) in the sciaphilous F. fragum and F. loochooanum (Text-fig. 3b; Table 2). The heliophilous F. unedo also shows this tendency, but weakly. The strongly disproportionate increase in the length of the posterior shell gape (PGL) during the growth of F. fragum and F. loochooanum leads to a rapid enlargement of the area of the posterior shell gape through which light penetrates into the shell interior. The rapid decrease in the PV-angle during shell growth keeps an increasingly larger area of the ventral mantle edges near the angular postero-ventral corner in a short distance from the posterior shell gape. Thus the allometric growth of these two shell characters ensures a light supply to the areas rich in zooxanthellae in the soft tissues of the shell interior and along the shell margins of the two sciaphilous species. The heliophilous F. unedo farms its zooxanthellae mainly in its hypertrophied mantle edges exposed above the sediment. Therefore, for this species the above mentioned two shell characters are not so important and allometry is weakly developed. OHNO ET AL.\ PHOTO-SYMBIOSIS A text-fig. 3. Allometric shell growth of Fragum species. A, Posterior gape length (PGL)/length (L) ratio plotted against length (L). b. Angle between posterior and ventral valve margins (PV-angle) plotted against length (L). (Registration numbers of samples: Fragum fragum = CTO0014; F. loochooanum = CTO0015; F. unedo = CTO0016). Parameters of reduced major axes are listed in Table 2. TRANSMISSION OF LIGHT THROUGH THE SHELL The shell of F. unedo is thick and non-transparent. In contrast, F. fragum and F. loochooanum have rather thin and semi-transparent shells. The shell of F. fragum transmits more light than that of F. loochooanum. The shell structure and the transmission of light through the shell was examined for F. fragum. The shell of F. fragum is composed of a mosaic of transparent and non-transparent domains of mm order. The shell consists of an outer layer of needle-shaped crystallites radiating in a fan-shape PALAEONTOLOGY, VOLUME 38 12 table 2. Reduced major axis (T = aX+b) related to allometric shell growth of Fragum species. Abbreviations: L, shell length (mm); n , number of samples; PGL, posterior gape length (mm); PVA, angle between posterior and ventral valve margins (PV-angle) (degrees); r, correlation coefficient; n.s., not significant. For the definition of the reduced major axis, see Agterberg (1974, p. 122). Y X a b r Level of significance F. fragum PGL/L L 0-0157 0-7169 0-78813 P < 0-001 (n = 109; CTO0014) PVA L -1-0707 95-0033 0-80577 P < 0-001 F. loochooanum PGL/L L 0-0331 0-5551 0-38645 P < 0-001 (n = 80; CTO0015) PVA L -2-4040 108-4430 0-41084 P < 0 001 F. unedo PGL/L L 0-0061 0-6233 0-18729 n.s. (n = 19; CTO0016) PVA L -0-7236 113-1170 0-70156 P < 0-01 °0~^ 400 500 600 700 800 Wave length [nm] text-fig. 4. Transmission of light through the posterior slopes of Fragum fragum shells. A, the smallest specimen (shell length = 221 mm; CTO0017); b, the largest specimen (shell length = 31-5 mm; CTO0018); c, a medium-sized specimen (shell length = 15-8 mm; CTO0019). towards the growth margin and an inner layer of crossed-lamellar structure. These two shell layers show no microstructural modifications producing different transparency, thus the transparency must be achieved by factors other than microstructure. The posterior slope is the most transparent part of the shell of F. fragum. In Text-figure 4, the transmission/wavelength curves of this part are shown for three specimens of different sizes. The most transparent sample is the smallest one, but the least transparent sample is a medium sized specimen. Therefore the shell transparency of F. fragum may have considerable individual variability. The transparency of the posterior slope is between 13 and 18 per cent, for the least transparent specimen and between 14 and 22 per cent, in the most transparent one for light with wavelengths in the range 400-500 nm. As the wavelength increases to 800 nm this value increases to 27 per cent, in the least transparent specimen and 36 per cent, in the most transparent one. The needle-shaped crystallites of the outer shell layer radiate and those of the crossed lamellae in the inner shell layer are differently orientated from one lamella subunit to another. Therefore the light penetrating into the shell of this species will be scattered by these variously orientated crystallites and illuminates the shell interior uniformly. This is in contrast with the transparent windows of the photo-symbiotic bivalve Corculum cardissa. In the latter, bundles of fine needle-like OH NO ET A L.\ PHOTO-SYMBIOSIS 13 crystallites radiate inwards from the shell external surface to form windows (Watson and Signor 1986), which transmit light effectively, with minimum dispersion, into the shell interior where there are abundant zooxanthellae. A direct comparison of the shell transparency of Corculum cardissa and F.fragum is not possible because Watson and Signor (1986) do not give the size of their measured shells. However, the lower transmission values of the present three specimens compared with the samples studied by Watson and Signor (maximum light transmission value of 40 per cent, at 620 nm) does not contradict our impression that the transparency of the shell in Corculum cardissa is higher. The shell transparency of F. fragum , as well as of Corculum cardissa , is relatively low up to a wavelength of 500 nm, where the photosynthetic pigments (peridinin) of zooxanthellae have a strong absorption peak (Jeffrey and Haxo 1968). Corculum cardissa additionally exhibits a relatively low transparency around 675 nm (Watson and Signor 1986), close to where a second peak of the zooxanthellae’s action spectrum exists (at 672 nm; Scott and Jitts 1977; Dustan 1982). Therefore the shells of these two bivalves are not perfectly adapted to transmit light in the optimal wavelengths for the zooxanthellae’s photosynthesis. PHOTOS YNTHESIS-1 R RADIANCE PROFILE OF ZOOXANTHELLAE The photosynthesis versus irradiance curve was measured for the zooxanthellae extracted from F.fragum (Text-fig. 5). This curve indicates that the compensation light level of photosynthesis of text-fig. 5. Photosynthesis-irradiance profile of zooxanthellae extracted from Fragum fragum. the zooxanthellae is 50 //Einstein m 2 s ' (an Einstein equals Avogacfro’s number - 6 02 x I023 of quanta). Above this light level, zooxanthellae can produce organic matter in excess of their respiration. With increasing irradiance intensity, the rate of photosynthesis gradually increases until it attains a maximum value of about 80 //mol O, mgChl 1 h 1 at an intensity of 400- 500 //Einstein m 2 s_1. The daily variation in light intensity at a depth of 2 m on a sunny day is shown in Text-fig. 6. The measurement was carried out in front of the Okinawa Research Centre at Amitori, the habitat of the three examined Fragum species, on 6 Nov. 1991. Even during late Autumn, the light intensity greatly exceeds the compensation point of the zooxanthellae of F. fragum (50 //Einstein nr2 s-1) for at least 9 hours each day (08.00 to 17.00 hours). Because of the tide, the sandy flats where the three Fragum species live are submerged to a water depth of about two m only during spring high tides. At other times the water depth is less. The light intensity at the sea bottom will therefore, in general, be greater than that shown by the curve of Text-figure 6. 14 PALAEONTOLOGY, VOLUME 38 2 m water depth in Autumn sunny day ). Time DISCUSSION Sciaphilous photo-symbiosis in Fragum and its advantages Fragum loochooanum adds a new fourth example of symbiosis with zooxanthellae ( Symbiodinium ) in the genus Fragum. The present study also reveals that F. fragum and F. loochooanum have adopted a new and previously unrecognized life mode among photo-symbiotic bivalves, i.e., sciaphilous (shade loving) photo-symbiosis, in which they do not expose their soft tissues and shells out of the sediment (Text-fig. 7). F. fragum even seems to hide itself actively by adhering sand grains to its posterior shell slope by extensively secreting mucus (PI. 1, fig. 9). The mucus is probably derived from the zooxanthellae’s photosynthetic product, as in the two slugs studied by Trench et al. (1972). In the warm shallow seas of the present day, epifaunal bivalves are susceptible to bivalve-eating predators (Vermeij 1977, 1987, p. 167), or suffer from uncomfortable epibiont growth (Stanley 1970, pi. 1 16, figs 10 and 1 1 ; Dorjes 1978, p. 130). F. fragum and F. loochooanum are well protected from predation and epibiont attachment. Their active locomotion ability (Table 1) also allows them to escape from these disadvantages. Therefore these two sciaphilous bivalves enjoy the benefit of photo-symbiosis without trading their security. Symbiodinium To enable photosynthesis in a wide range of daily and seasonal as well as depth-dependent fluctuations of light intensity, marine algae can evolve molecular level adaptations. Shade adaptation is one such, and has been observed in a wide range of marine algae (Falkowski and Owens 1980). It is achieved by increase in number and/or size of photosynthetic units per algal cell (Falkowski and Owens 1 980 ; Falkowski and Dubinsky 1981). Some dinoflagellates also increase the amount of their light-harvesting pigment-protein complex (peridinin-chlorophyll-a proteins) when cultured under low light (Prezelin 1976). It is this shade adaptation which enables the zooxanthellae within F. fragum to photosynthesize with the limited amount of light coming through the host’s narrow shell gape. In fact, the compensation point of photosynthesis of the zooxanthellae of F. fragum (Table 3) is about one- quarter of that of the zooxanthellae of epifaunal and heliophilous Tridacna maxima (Roeding) (Scott and Jitts 1977), and about one-twentieth of the maximum intensity of the ambient light of the cockle’s habitat measured on a sunny Autumn day (Text-fig. 6). The photosynthesis irradiance OH NO ET A L:. PHOTO-SYMBIOSIS 15 CL LU 3 < LL T. maxima H. hippopus T. crocea F. unedo ECOLOGICAL TYPES OF RECENT PHOTO-SYMBIOTIC BIVALVES HELIOPHILOUS F.fragum F. loochooanum SCIAPHILOUS text-fig. 7. Life habits of photo-symbiotic bivalves. table 3. List of reported Ic ( = compensation point) values (in //Einstein m 2 s *). Host species Remarks Ic Authors Measured on hosts Hermatypic coral Stylophora pistillata Light adapted c 250 Falkowski and Dubinsky (1981) Shade adapted c 30 (estimated from their fig. 2) Stylophora pistillata Light adapted 127 Porter et al. (1984) Shade adapted 26 ibid. Anthopleura elegantissima Starved c 30 Fitt and Pardy (1981) (estimated from their fig. 1 ) Bivalve Tridacna maxima c 160-240 Trench et al. (1981) (estimated from their fig. 17) Measured on zooxanthellae extracted from host bivalve Tridacna maxima c 230 Scott and Jitts (1977) (estimated from their fig. 6) Fragum fragum 50 Present study 16 PALAEONTOLOGY, VOLUME 38 curve for the zooxanthellae of F. loochooanum is not available. However, we suggest that the same behaviour of zooxanthellae is essential for the sciaphilous photo-symbiosis of this species. Symbiodinium belongs to the ‘naked’ dinoflagellate order Gymnodiniales, which has a very sparse fossil record (Sarjeant and Downie 1974; Norris 1978; Williams 1978). Circumstantial evidence, however, suggests that it has a long symbiotic history. The changes in the relative importance of sponges and corals during the Middle Triassic-Late Jurassic interval probably coincided with the development of a symbiotic relationship between zooxanthellae ( = Symbiodinium) and corals (Fagerstrom 1987, p. 292). Since then, some of the Symbiodinium may have become successfully shade adapted, either as they accompanied hosts exploiting deeper and darker habitats, or because their built-in flexibility enabled them to photosynthesize in very low light intensity allowing corals to exploit darker habitats. In fact the present day shade-adapted Symbiodinium of the hermatypic coral Stylophora pistiliata shows a compensation point of about 30 //Einstein nT2 s^1 (Falkowski and Dubinsky 1981) which is even lower than that of the zooxanthellae living in F. fragum (Table 3). Besides bivalves, Symbiodinium is present in a wide range of hosts such as the jellyfish Cassiopea , and numerous species of hermatypic corals (Trench and Blank 1987). The genus’s ability to overcome the self-defence system of a wide variety of invertebrate host taxa may also be related to its long symbiotic history. Scarcity of photo-symbiosis The zooxanthellae’s shade adaptation makes all shallow sea bivalves potential hosts. Yet, among living bivalves, symbiosis with zooxanthellae is confined to the genera Tridacna , Hippopus , Corculum and Fragum. Microfragum festivum (Deshayes), belonging to the subfamily Fraginae and closely related to Fragum and Corculum , or Pinna sp., which exposes a considerable part of its transparent shell out of the sediment, do not harbour zooxanthellae in their soft tissues (personal observation), although they are living in the same sand flats as the three examined Fragum species. These observations suggest that the scarcity of zooxanthella-bivalve photo-symbiosis may not be the result of insufficient observation but is reality. Smith (1991) also pointed out that very few animals are involved in symbiosis with photosynthetic microbes. He considered that costs imposed upon the animal hosts, including those of mechanisms for control of symbiont cell division and regulation of symbiont population size and location, might make photo-symbiosis less economic than the greatly prevalent herbivory for gaining access to photosynthetically-fixed carbon. Palaeontological implications The recognition of sciaphilous photo-symbiosis in F. fragum and F. loochooanum with shade adapted zooxanthellae has several palaeontological implications. Firstly, the photo-symbiosis in this genus and other extant photo-symbiotic bivalves seems to have initiated as a sciaphilous one. Secondly, a sciaphilous origin of photo-symbiosis seems applicable also to some fossil photo- symbiotic bivalves. Finally, several fossil bivalve taxa are now becoming candidates for being (sciaphilous) photo-symbiotic bivalves. In the following we discuss these points in some detail. Sciaphilous origin of extant photo-symbiotic bivalves. The sciaphilous F. fragum and F. loochooanum do not show any indication that they once had mantle edges similarly expanded like those of F. unedo. Thus they seem to retain a more ancestral form than the latter. Yet they harbour zooxanthellae in their inner soft tissues. Therefore it seems that the photo-symbiosis in the genus Fragum was initiated by the association of shade (pre-)adapted Symbiodinium and an ancestral infaunal bivalve which was not pre-adapted for light harvesting for symbionts. As mentioned earlier, the symbiotic relationship between Symbiodinium and hermatypic corals was initiated between the Middle Triassic and Late Jurassic, which predates the known range of the genus Fragum (Miocene-Recent) by at least about 80 My. It is probable that some Symbiodinium OHNO ET AL:. PHOTO-SYMBIOSIS 17 c HELIOPHILOUS ( EPIFAUNAL ~ ZDC SCI A PH I LOUS INFAUNALC;: j HYPOTHESIZED HISTORY OF ALGAL-BIVALVE PHOTO-SYMBIOSIS text-fig. 8. Highly simplified hypothesized history of zooxanthella-bivalve photo-symbiosis (figure of bivalve in ellipse after Stasek 1961). table 4. Features related to the sciaphilous life mode of Fragum fragum and Fragum loochooanum. 1. More or less transparent mantle edges covering the posterior shell gape allows light penetration into the shell interior. 2. Long and rather transparent supra-branchial chamber aligns the gills with abundant zooxanthellae just beneath and along the posterior shell gape, through which light penetrates. 3. The rapid increase in the length of the straight shell posterior gape during shell growth increases the area of light penetration. 4. The rapid decrease in the angle between the posterior and ventral valve margins (PV-angle) during shell growth keeps soft parts with abundant zooxanthellae near the shell gape. PALAEONTOLOGY, VOLUME 38 species might have successfully shade adapted prior to the initiation of the photo-symbiosis with Fragum. Like Fragum , other extant photo-symbiotic bivalves ( Tridacna , Hippopus and Corculum) either belong to, or are closely related to, the superfamily Cardiacea, the majority of the members of which are infaunal. Thus the ancestors of these photo-symbiotic bivalves were also most probably infaunal. If so, the above stated scenario may also be applied to the origination of photo-symbiosis of these bivalves. The varied geological ranges of these photo-symbiotic bivalves (Tridacna since Miocene; Stasek 1961; Hippopus since ?Miocene, but with certainty in Recent; Stasek 1961; and Corculum in Recent; Keen 1980) suggests that the establishment of zooxanthella-bivalve photo- symbiosis took place several times. Once photo-symbiosis is established in a sciaphilous form, the selection pressure would favour the tendency to optimize the benefits of the symbiosis. There is not a unique solution in optimizing (Text-fig. 8). F. fragum and F. loochooanum sustained their sciaphilous life mode, which would minimize the danger of predation. Infaunal F. unedo evolved hypertrophied mantle edges and exposes them widely on the sediment surface to collect more light. Tridacna , Hippopus and Corculum shifted to epifaunal life. The former two expose their mantle tissues out of the shell to collect light, whereas Corculum makes its shell transparent to illuminate algae nesting in their soft parts which are protected within the host’s valves. Indeed the acquisition of photo-symbiosis with zooxanthellae led to a strong radiation in bivalve morphology and ecology. Sciaphilous origin of fossil photo-symbiotic bivalves. When considering the origin of photo-symbiosis in bivalves, earlier studies have emphasized the bivalve’s adaptations for supplying light to the photosynthetic microbial symbionts. Yonge (1936) suggested infection of zooxanthellae in the siphonal area of tridacnids as the starting point for the photo-symbiosis. Cowen (1982) postulated that symbiosis can only develop in a host that is pre-adapted by tissue exposure to light. Skelton (1979) also suggested pre-adaptation of bivalves for the establishment of the inferred photo- symbiosis in an extinct radiolitid rudist bivalve, Radiolites cf. angeoides (De Lapeirouse). The latter’s extremely narrow valve gape and its small body/mantle cavity ratio were interpreted as indicating atrophy of the gills and the loss of effective filter feeding. Skelton further suggested that the species developed expanded and tentacled mantle margins to make up for its ineffective filter feeding. These tentacled mantle margins, which were expanded out of the shell for collecting food particles, were later infected by the zooxanthellae. An alternative interpretation of the evolution of photo-symbiosis in this species may be a sciaphilous origin, i.e. the infection of shade adapted microbes within the internal soft tissues of the ancestor of this species. Then the expanded mantle margins of this rudist can be interpreted simply as the result of optimizing light harvesting, followed by the loss of efficient filter feeding. Because this scenario ensures nutrition of the bivalve by photosynthetic products, we can further curtail an evolutionary stage of food collection with expanded and tentacled mantle margins (Skelton 1979). For such a feeding method, it is necessary to conceive a probably very complicated mechanism for smooth transportation of the collected food particles through a very narrow gape and for passing over then to the labial palps or mouth. In future, the initiation of photo-symbiosis in this rudist bivalve and other inferred fossil photo-symbiotic bivalves should not be viewed only as the result of the bivalve’s pre-adaptation, but the possibility of their origination in a sciaphilous form should also be considered. New candidates of fossil photo-symbiotic bivalves. Because sciaphilous photo-symbiosis allows host bivalves to enjoy the benefit of symbiosis without the dangers of predation or epibiont attachment, many fossil photo-symbiotic bivalves, if they ever existed, are likely to have adopted, or even clung to, this option of symbiosis. F. fragum and F. loochooanum show certain morphological features related to their sciaphilous photo-symbiosis with zooxanthellae (Table 4). Among them, rapid increase in the PGL/L ratio as well as a rapid decrease in PV-angle during shell growth (Text-fig. 3; Table 2) can be preserved in OHNO ET AL PHOTO-SYMBIOSIS 19 fossil shells. These two features together with the occurrence of fossils from shallow sea sediments would be helpful criteria in the search for sciaphilous photo-symbiosis among fossil bivalves. Some promising fossil candidates may be expected among the trigoniid bivalves which adopted a life mode similar to the present day cardiids. in warm shallow marine sandy habitats during the Mesozoic (Stanley 1978). Indeed, a specimen of the Bajocian Trigonia denticulate! Ag. in our possession has an overall shell form quite similar to that of F. fragum and F. loochooanum. Furthermore, it would be interesting to see if the ancestors of Opisoma Stoliczka (Chavan 1969, N572 and fig. E72, 4) have a similar form to F. fragum or F. loochooanum. The shell morphology of this Lower Jurassic astartid bivalve has an overall resemblance to that of the living photo- symbiotic bivalve Corculum cardissa. These fossil bivalves tempt us to examine them and related species in detail, although their geological age suggests that their symbiotic photosynthetic microbes are not necessarily identical or related to the present day Symbiodinium. Acknowledgements. This study was enabled by the generous support of Tokai University, which offered us the facilities of the university’s Okinawa Regional Research Centre at Iriomote Island and provided us with habitat data. Drs H. Yokochi and H. Kono and Mr H. Sunagawa kindly helped us during field studies at the centre and provided us with information on the fauna of the area and constructive discussions. Mr A. Matsumoto of the Nikon Optics Company, Yokohama, kindly made the measurements of the shell transparency. Professor K. Chinzei of the Department of Geology and Mineralogy, Faculty of Science, Kyoto University supported us financially and provided vigorous discussion. Professors S. Kuroiwa and H. Tabata (Kyoto University), Professor J. Hohenegger (Institut fur Palaontologie, Universitat Wien) as well as an anonymous referee gave useful discussion and constructive suggestions for the improvement of the manuscript. This study was partly financed by grant aid from the Ministry of Education, Science and Culture awarded to the authors (04264107 ; B05454003), to Professor K. Chinzei (02404008) as well as grant aid from the Ito Science Foundation (Tokyo) awarded to T. Ohno. REFERENCES agterberg, F. p. 1974. Developments in geomathematics, 1. Geomatliematics, mathematical background and geo- science applications. Elsevier Scientific Publishing, Amsterdam, xvi + 596 pp. blank, r. j. and trench, r. k. 1986. Nomenclature of endosymbiotic dinoflagellates. Taxon , 35, 286-294. chavan, a. 1969. Superfamily Crassatellacea Ferussac, 1822. N562-N583. In moore, r. c. (ed. ). Treatise on invertebrate paleontology. Part N. Volume 2 {of 3), Mollusca , 6. Bivalvia. 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TERUFUMI OHNO Department of Geology and Mineralogy Faculty of Science Kyoto University, 606, Kyoto, Japan TETZUYA KATOH Department of Botany Faculty of Science Kyoto University, 606, Kyoto, Japan TERUFUMI YAMASU Department of Biology Typescript received 7 September 1993 Division of General Education Revised typescript received 8 June 1994 University of Ryukyus, 903-01, Okinawa, Japan THE TETHYAN BIVALVE ROUDAIRIA FROM THE UPPER CRETACEOUS OF CALIFORNIA by m. x. kirby and l. r. saul Abstract. The Tethyan genus Roudairia is described for the first time from North America. A new species, Roudairia squiresi , occurs in the shallow-marine, basal beds of the San Francisquito Formation (uppermost Maastrichtian) at Warm Springs Mountain, Los Angeles County, California. The earliest representatives of the genus Roudairia are from the Cenomanian of north and west Africa. The genus later migrated westward to the western Tethyan Realm and into California during the latest Cretaceous. The presence of R. squiresi suggests warm water in California at the end of the Cretaceous. The taxonomic status of two closely related genera, Cicatrea and Veniel/a , in relation to Roudairia , remains unclear. Flowever, among these three related taxa, there are at least two distinct generic groups present. The first is represented by Veniella and the second by Roudairia. Specimens from Africa and Madagascar, previously ascribed to ' Cicatrea ' cordialis , belong in the second group. Whether Cicatrea cordialis from India also belongs in this second group cannot be determined until additional specimens provide better morphological data. Several specimens of a new species, Roudairia squiresi , were collected from basal beds of the San Francisquito Formation on Warm Springs Mountain, in the San Gabriel Mountains, Los Angeles County, southern California (Text-fig. 1). Turritellid gastropods associated with R. squiresi at Warm Springs Mountain indicate a very late Maastrichtian age for the basal San Francisquito Formation (Saul 1983). The basal San Francisquito Formation at Warm Springs Mountain is part of a shallow-marine phase of a transgressive sequence that continued across the Cretaceous/Tertiary boundary into the Palaeocene (Kooser 1980; Kirby et al. 1991). A fragment of a left valve that resembles R. squiresi was found in undifferentiated Upper Cretaceous rocks at Dip Creek, south shore of Lake Nacimiento, San Luis Obispo County, central California (Text-fig. 1). Associated Turritellid gastropods and an ammonite indicate a latest Maastrichtian age (Saul 1983). Roudairia has not previously been reported from North America. One species is known from the Upper Cretaceous of Jamaica (Trechmann 1927), and four species are known from the Upper Cretaceous of Peru (Briiggen 1910; Lisson 1925; Olsson 1934, 1944). A closely related genus, Veniella Stoliczka, 1870, is present in Western Interior and Gulf Coast, North American deposits of Turonian to Maastrichtian age. Another closely related taxon, Cicatrea Stoliczka, 1870, is from the Upper Cretaceous of India. The palaeobiogeographical distributions of Roudairia , Veniella , and Cicatrea are clouded by difficulties in determining their generic and specific characters. Many of the pioneering reports of species assignable to these genera failed to note important morphological features and were vague as to stratigraphical position. Dartevelle and Freneix (1957) considered Roudairia and Cicatrea to be synonyms of Veniella , and therefore placed their species in Veniella. They indicated the biogeographical provenance of these species, but did not reassess completely their stratigraphical positions. A complete review is beyond the scope of this paper, but the work of Dartevelle and Freneix (1957), which delineates characters of four widely occurring species, " Cvprina {Cicatrea)' cordialis Stoliczka, 1870, ‘ Trigonia' auressensis Coquand, 1862, Roudairia drui Munier-Chalmas, 1881, and ‘ Cyprina' forebesiana Stoliczka, 1870, assists in assigning the first three of these species to Roudairia and the fourth to Veniella. | Palaeontology, Vol. 38, Part 1, 1995, pp. 23-38, 2 pis.] © The Palaeontological Association 24 PALAEONTOLOGY, VOLUME 38 text-fig. 1. Locality maps showing (a) Dip Creek, (b) Warm Springs Mountain, and (c) California. This paper describes the stratigraphy and depositional environments associated with R. squiresi , discusses the Late Cretaceous palaeobiogeography of the genus Roudairia, compares the generic characters of Veniella and Cicatrea with those of Roudairia , and concludes with the description of R. squiresi. STRATIGRAPHY AND DEPOSITIONAL ENVIRONMENTS The most complete specimens of R. squiresi are from the lowermost San Francisquito Formation at Warm Springs Mountain (Text-fig. 2). The San Francisquito Formation ranges in age from late Maastrichtian to late Palaeocene (Dibblee 1967; Kooser 1980, 1982). At Warm Springs Mountain, the formation was deposited on a granite-gneiss basement that is cut by dykes of early Maastrichtian age (Joseph et al. 1982). The San Francisquito Formation represents a marine- transgressive sequence that consists of shallow-marine deposits grading upsection into deeper submarine-fan deposits (Kooser 1980; Kirby 1991). The lower part of the formation contains a conformable section across the Cretaceous/Tertiary boundary (Kirby et al. 1991), as defined by the Turritella zonation of Saul (1983). Roudairia squiresi was found 5 m below this boundary (Text-fig. 2). Eight unabraded valves, including one right valve, three left valves, two articulated specimens, and one fragment, were found in a feldspathic sandstone at Warm Springs Mountain (Kirby 1991). The single-valved specimens had probably been transported a short distance, whereas the articulated specimens were most likely in situ. The specimens were associated with the gastropods Turritella webbi Saul, 1983, Turritella chaneyi orienda Saul, 1983, Anchural sp., and with the bivalves Cucullaea sp. nov., Brachidontesl sp. nov., and Callistalox fragilis (Gabb, 1869). Turritella webbi , Turritella chaneyi orienda , and Brachidontes are characteristic of a shallow-marine environment (Keen 1971; Saul 1983). KIRBY AND SAUL: TETHYAN BIVALVE ROUDAIRIA 25 Submarine Channel Offshore LACMIP Locality 14312 Transition Zone Granite-Gneiss Basement Pebble Conglomerate Dark-gray Mudstone Feldspathic Sandstone > / /j NNN] Granite-Gneiss h 40 m 20 m 0 m text-fig. 2. Stratigraphical section of the basal San Francisquito Formation, Warm Springs Mountain, California, showing chronostratigraphy, lithology, depositional environments, and stratigraphical position of Roudairia squiresi type locality (LACMIP locality 14312) (after Kirby 1991). Note transgressive nature of stratigraphical section. Feldspathic sandstone crops out from the base of the San Francisquito Formation to 47 m above the base of the formation (Text-fig. 2). The sandstone is silty, very fine- to medium-grained, and poorly sorted. Although mostly structureless, the sandstone contains indistinct planar bedding locally. Bioturbation is very abundant. Fossiliferous lenses, up to 210 mm thick, are present throughout the feldspathic sandstone. These lenses are inferred to be storm-lag deposits (Kirby 1991). Abundant bioturbation indicates deposition below fair weather wave base, and storm-lag deposits indicate deposition above storm wave base. Both these features indicate deposition of the feldspathic sandstone in the shallow-marine, transition zone (Kirby 1991). These transition-zone deposits are part of a shallow-marine, transgressive sequence that grades upsection into offshore deposits. The underlying granite-gneiss basement and an overlying submarine-channel conglomerate stratigraphically bound the sequence (Text-fig. 2). This 110 m thick sequence is between 68-5 Ma and 63-8 Ma in age, based on the Turritella zonation of Saul (1983). Deposition of this transgressive sequence probably resulted from both basinal subsidence and eustatic transgression. 26 PALAEONTOLOGY, VOLUME 38 90° text-fig. 3. Palaeobiogeographical distribution of Cicatrea and Roudairia species on a Maastrichtian palaeogeographic map (Ziegler et al. 1982). Cretaceous palaeobiogeographical names after Kaufmann (1973). Plotted occurrences range from the Cenomanian to the Maastrichtian. Key to species: Cc = Cicatrea cordialis (Stoliczka 1870); Ra = R. auressensis (Coquand 1862) (Dartevelle and Freneix 1957); Rb = R. brasiliensis Maury, 1930; Rbr = R. briiggeni (Lisson 1925) (Olsson 1944); Rc = R. cordialis (Stoliczka 1870) (Douville 1904; Boule and Thevenin 1906; Dartevelle and Freneix 1957); Rd = R. drui Munier-Chalmas, 1881 (Rennie 1930; Dartevelle and Freneix 1957); Re = R. elongata Naldini, 1948; Ri = R. intermedia (Brtiggen 1910) (Dartevelle and Freneix 1957; Willard 1966); Rj = R. jamaicensis Trechmann, 1927; Rp = R. peruviana Olsson, 1934; Rpa = R. pampaensis Leanza and Hiinicken, 1970; Rs = R. squiresi sp. nov. (this paper). Symbols indicate the age of the oldest specimens found at each locality; A = Cenomanian; ▼=Turonian; ■ = Campanian; • = Maastrichtian; ♦ = Late Cretaceous. A fragment of a left valve resembling R. squiresi was found at Dip Creek. This fragment was found associated with turritellid gastropods and other shallow-water molluscs in very coarse- grained, conglomeratic sandstone and conglomerate beds. Grove (1986) interpreted these sandstone and conglomerate beds to be turbidites that were deposited in deep water. Taliaferro (1944) referred the Dip Creek strata to his ‘Dip Creek formation’. But Durham (1968) mapped outcrops along the north shore of Lake Nacimiento as unnamed Upper Cretaceous and Lower Tertiary rocks. Grove (1986) used this designation for the outcrops along the south shore of Lake Nacimiento. Confident assignment of the Dip Creek section to a formation can only be done after detailed geological mapping in the Lake Nacimiento area is undertaken (V. M. Seiders, pers. comm. 1992). PALAEO BIOGEOGRAPHY The genus Roudairia has a South Temperate to Tethyan distribution (Text-fig. 3. Cretaceous palaeobiogeographical names as defined by Kauffman 1973.) The genus Veniella , which as plotted by Dartevelle and Freneix (1957, text-fig. 3) included Cicatrea and Roudairia , has a South Temperate to North Temperate distribution. Text-figure 4 shows the biogeographical distributions of Cicatrea , KIRBY AND SAUL: TETHYAN BIVALVE ROUDAIRIA 27 Location Ag® California | Peru WI & GC USA Jamaica Argentina Brazil N. Africa | W. Africa S. Africa Madagascar India Maastrichtian R R V R R V R V R V C Campanian R V R V R R V R V R V c Santonian/ Coniacian R V V R V V V c V Turonian R V V R V V V Cenomanian R V R V text-fig. 4. Location of Cicatrea spp. (C), Roudairia spp. (R), and Veniella spp. (V) through time (based on Stoliczka 1870; Meek 1876; Douville 1904; Boule and Thevenin 1906; Trechmann 1927; Maury 1930; Rennie 1930; Olsson 1934, 1944; Naldini 1948; Dartevelle and Freneix 1957; Willard 1966; Leanza and Hunicken 1970). Note that ages are not to scale. WI = Western Interior. GC = Gulf Coast. Roudairia , and Veniella through time. The earliest record of Roudairia is from the Cenomanian of north and west Africa (Naldini 1948; Dartevelle and Freneix 1957; Cooper 1978). Specimens from these areas range in age from Cenomanian to Maastrichtian. Willard (1966) reported Roudairia from the Turonian of Peru. In the Coniacian, Roudairia is found in Peru and west Africa (Olsson 1934, 1944; Dartevelle and Freneix 1957). In the Campanian, Roudairia is reported from Peru, Jamaica, Brazil, north Africa, west Africa, and south Africa (Trechmann 1927; Maury 1930; Rennie 1930; Olsson 1934, 1944; Dartevelle and Freneix 1957). In the Maastrichtian, Roudairia is reported from California (this paper), Peru, Argentina, north Africa, west Africa, and Madagascar (Douville 1904; Olsson 1934, 1944; Dartevelle and Freneix 1957; Leanza and Hunicken 1970). Abbass ( 1962) described a new species of Roudairia from the Danian of Egypt. If his new species, Roudairia awadi , is indeed a Roudairia , then Roudairia evidently survived the Cretaceous/Tertiary mass extinction and lived on into the Palaeocene. His description and figures of R. awadi , however, permit doubt as to whether his specimens actually belong to Roudairia. The palaeobiogeographical distribution of Roudairia suggests that the genus evolved either in the northern part of the South Temperate Realm or in the Tethyan Realm before or during the Cenomanian. The genus later migrated westward to the western Tethys during the Late Cretaceous. Roudairia squiresi, or one of its antecedents, migrated from Central or South America into California in the Maastrichtian (Text-figs 3-4). The migration of the Tethyan Roudairia into the northeastern Pacific at this time suggests the presence of warm water in California at the end of the Cretaceous. PALAEONTOLOGY, VOLUME 38 Roudairia squiresi of California is most similar to Roudairia peruviana Olsson, 1934, which is present in the Maastrichtian Monte Grande Formation and undifferentiated rocks of Campanian to Maastrichtian age in northern Peru (Olsson 1934, 1944). Roudairia peruviana is older than R. squiresi. Roudairia jamaicensis Trechmann, 1927, from the Campanian of Jamaica (Trechmann 1927), is less similar to, and is also older than R. squiresi. The present findings extend the palaeobiogeographical range of Roudairia from Jamaica and Peru northward to California (Text- fig. 3). The age range of Roudairia in the eastern Pacific is extended to the latest Maastrichtian (Text-fig. 4). SYSTEMATIC PALAEONTOLOGY Abbreviations. The following abbreviations are used with catalogue and locality numbers mentioned in the text : CIT, California Institute of Technology; CSUN, California State University, Northridge; LACMIP, Natural History Museum of Los Angeles County, Invertebrate Paleontology Section; PRI, Paleontological Research Institution; UCLA, University of California, Los Angeles. CIT and UCLA collections are currently at the Natural History Museum of Los Angeles County, Invertebrate Paleontology Section. Phylum mollusca Linnaeus, 1758 Class bivalvia Linnaeus, 1758 Order veneroida Adams and Adams, 1856 Family arcticidae Newton, 1891 Genus roudairia Munier-Chalmas, 1881 Type species. Roudairia drui Munier-Chalmas, 1881 from the Campanian and Maastrichtian of Tunisia. Diagnosis. Inflated arcticid bivalves of trigonal to subquadrate outline with a strongly carinate posterior; sculpture of undulating ribs on the flank. Hinge of right valve with three cardinals and four laterals: 1 at the ventral hinge border, anterior to 3a; 3a dorsal to 1 ; 3b bifid; AI short, subtrigonal; AIII elongate. Hinge of left valve with two cardinals and two laterals; 2b obscurely bifid; 4b elongate, thin; All chevron-shaped; PI I elongate with transverse striations on both sides. Posterior adductor muscle scar bordered anteriorly by a strong myophoric flange. Discussion. A number of problems with respect to the appropriate generic name for the specimens from Warm Springs Mountain cannot be solved solely on the basis of the Warm Springs Mountain specimens. Of the three generic taxa, Veniella Stoliczka, 1870 (type species Venilia conradi Morton, 1833), Cicatrea Stoliczka, 1870 (type species ‘ Cyprina' ( Cicatrea ) cordialis Stoliczka, 1870), and Roudairia Munier-Chalmas, 1881, the specimens from Warm Springs Mountain are least like Veniella. Dartevelle and Freneix (1957) reviewed the status of the generic names Veniella , Cicatrea , and Roudairia. They considered Cicatrea and Roudairia to be synonyms of Veniella because: (1) the separation of Veniella and Roudairia required well-preserved adult hinges; (2) ‘ Cyprina ' forbesiana Stoliczka, 1870, was considered by Vokes (1954) to have a left valve hinge like Roudairia and a right valve hinge resembling Veniella ; and (3) some species, such as the Indian Cicatrea cordialis , combine the hinge of Veniella and the external shape and sculpture of Roudairia. Although the types species of Roudairia and Veniella are sufficiently dissimilar to be recognized as representatives of distinct supraspecific taxa, Dartevelle and Freneix (1957) believed that ‘ Cyprina ’ forbesiana and Cicatrea cordialis bridge this morphological gap. Vokes (1954) suggested that Veniella is a North American Late Cretaceous group, but he considered Cicatrea cordialis , from India and Madagascar, to be closer to Veniella than to Roudairia. The following discussion outlines what is known of the generic characters of Veniella , Roudairia , and Cicatrea. The type species of Veniella , V. conradi , has been illustrated by Vokes (1954). Characters of the genus are discernable from his illustrations and from well-preserved specimens of the type species from the Ripley Formation of Tennessee (PI. 2, figs 2-4). Exteriorly, the shell has a strong posterior KIRBY AND SAUL: TETHYAN BIVALVE ROUDAIRIA 29 angulation. Commarginal sculpture anterior to the angulation consists of irregularly developed ridges, the strongest of which are flanged. In the right valve, V. conradi has three cardinals, one anterior lateral All I, and two posterior lateral teeth (PI. 2, fig. 2). In the left valve, V. conradi has two cardinals, one elongate to somewhat triangular anterior lateral All, and one posterior lateral tooth (PI. 2, fig. 3). Veniella conradi lacks an internal myophoric flange bordering the anterior side of the posterior adductor muscle scar. The Treatise on invertebrate paleontology illustration of the left valve of V. conradi is misleading (Casey 1969, p. N651, text-fig. El 29, 6a). Cardinal 2b is never so bifid in mature specimens as depicted (see ontogenetic hinge changes in Vokes (1954, text-figs 1-4, 6-9)) and the adductor muscle scars are discrepant in size and shape. The posterior adductor muscle scar is actually larger and rounder than the semicircular anterior adductor muscle scar. The nominal type species of Roudairia , R. drui , has been variously synonymized with the prior Opis undatus Conrad, 1852, and Trigonia auressensis Coquand, 1862. But Dartevelle and Freneix (1957, p. 141) rejected the synonymy of R. drui with Roudairia undata and Roudairia auressensis , and listed several characters, including a second posterior carina present in R. undata and finer, more uneven ribbing in R. auressensis , that separate these two species from R. drui. Roudairia drui has been recognized from several horizons and locations (Text-fig. 3), and not all of these specimens are conspecific (Dartevelle and Freneix 1957). This confusion and the poor preservation of some of the material has made generic characters of Roudairia difficult to determine. Exteriorly, R. drui has a carinate posterior angulation accentuated by a strongly raised keel. Roudairia drui is higher than long, and squarely truncated posteriorly. Commarginal ribbing on the anterior portion of the shell is strong and even near the beaks, but becomes more uneven ventrally. The commarginal ribs, although over-steepened, do not give rise to flanges. Vokes (1954) discussed the hinge teeth based on illustrations in Quaas (1902) and Pervinquiere (1912). The hinge of R. drui differs from that of V. conradi in having a chevron-shaped anterior lateral All in the left valve and a pustular anterior lateral AI in the right valve. In contrast, V. conradi has an elongate trigonal All in the left valve and lacks AI in the right valve. Dartevelle and Freneix (1957) did not indicate whether R. drui has an internal myophoric flange along the anterior side of the posterior adductor muscle scar or not. But Quaas’ figure ( 1902, pi. 24, fig. 22) of a left valve of R. drui indicates that such a flange is present. Abbass (1962) described several Roudairia species from Egypt. Regrettably, he did not refer to Dartevelle and Freneix (1957), nor did he indicate the relationship of his Egyptian taxa to those discussed by Dartevelle and Freneix (1957). In order to settle discrepancies between Abbass (1962) and Dartevelle and Freneix (1957), we would need to examine and compare Abbass' specimens with those described by Dartevelle and Freneix (1957). The type species of Cicatrea , Cyprina (Cicatrea) cordialis Stoliczka, 1870, has been recognized in various parts of Africa, as well as in India and Madagascar (Dartevelle and Freneix 1957) (Text- fig. 3). Discussions of the validity of Cicatrea (Douville 1904; Vokes 1954) refer to Stoliczka’s figure (1870, pi. 10, fig. 2) of a left valve hinge to define generic characters. Dartevelle and Freneix (1957) did not figure a hinge for this species and did not have any available for study. Although they did not mention an internal myophoric flange, illustrations of specimens identified as C. cordialis by Dartevelle and Freneix (1957) clearly show the presence of an internal flange bounding the anterior side of the posterior adductor muscle scar. Exteriorly, C. cordialis has a high keel along the strong posterior angulation. This keel is particularly pronounced near the beaks. Commarginal sculpture on the anterior portion of the valve is even and roundly ripple-ribbed near the beaks. The commarginal ribs evanesce ventrally. Stoliczka’s figure (1870, pi. 10, fig. 2) of the left valve hinge gives the impression of a double exposure. Two hinges appear to be present, one superposed on the other. One hinge is offset higher and to the left of the other hinge. Compared to Veniella and Roudairia , Stoliczka’s figure is peculiar in having no upright, flanged posterior end to the nymph. Although broad ligament grooves are indicated, the usual nymph flange is not. Stoliczka (1870) did comment on its absence. If two valves are superposed, one set of the ligament grooves and subumbonal pits would be above and to the left of the other. Cardinal 2b is drawn as a moderately broad triangle and is more like 2b of V. conradi than of R. squiresi and R. peruviana. This broadly triangular cardinal 2b is somewhat surprising as C. cordialis is more elongate with a strong forward 30 PALAEONTOLOGY, VOLUME 38 twist to the shell. In V. conradi , mature shells of greater elongation and forward twist have a narrower, more elongate 2b, but shorter shells have a more trigonal 2b. The left anterior lateral All is also peculiar. It is more equantly triangular than that of V. conradi and is drawn with the hint of a basal dimple suggesting the possibility of a socket for AI. If C. cordialis should be shown to have AI, then its hinge formula would be the same as that of Roudairia. Stoliczka (1870, p. 199) said that the base of cardinal 2b is united to the top of All by a low rib. In R. squiresi and R. peruviana , a ridge drops from the tip of All toward the base of 2b, but it encircles the socket for 1 and does not join 2b. Additionally, Stoliczka wrote (1870, p. 199), "a distinct rib is seen in front of the anterior muscular impression, it has the appearance of an anterior lateral tooth, but has in reality nothing to do with hinge-teeth’. If this figure (Stoliczka, 1870, pi. 10, fig. 2) were drawn from superposed impressions of two shells, the ’distinct rib’ would be the anterior margin of the upper, more leftward specimen. Roudairia squiresi has a raised anteroventral margin to the anterior adductor muscle scar, but this margin is not sufficiently raised to have the appearance of a tooth. Drawings of C. cordialis credited to Douville are in Boule and Thevenin (1906, text-figs 4-6). The drawings are based on rock moulds from Madagascar. Their text-figure 6 of the left hinge greatly resembles Stoliczka’s figure 2 ( 1870, pi. 10) in shape and position of hinge-teeth 2, 4 and All, except that in Douville’s text-figure 6, All is depicted as having a chevron-shape with a well-developed socket for AI in its base. Douville’s figures (Boule and Thevenin 1906, text-figs 4-6) do not depict any nymph or ligament groove. Their omission may have been caused by incomplete rock moulds. If Stoliczka’s left hinge (1870, pi. 10, fig. 2) is drawn accurately, then the hinge of Cicatrea differs from that of Roudairia in the absence of an alate nymph and in having both 2b and All broadly triangulate. But Douville’s tooth All (Boule and Thevenin 1906, text-fig. 6) is more like that of Roudairia and his right valve hinge (Boule and Thevenin 1906, text-fig. 4) shows a well-developed AI similar to that of Roudairia but much more elongate than that seen in R. squiresi or R. peruviana. Differences between illustrations of the Indian C. cordialis of Stoliczka and the Madagascan C. cordialis of Douville permit doubt as to whether they are both the same species, especially as the Indian specimens are probably of early Senonian age rather than the Maastrichtian age of the Madagascan specimens. Despite the comments of several palaeontologists (Douville 1904; Boule and Thevenin 1906; Rennie 1929; Cox 1952; Vokes 1954; Dartevelle and Freneix 1957), the generic characters of Cicatrea remain ambiguous. Adequate material from the type locality of C. cordialis is necessary to determine how closely Stoliczka’s figure (1870, pi. 10, fig. 2) depicts the features these palaeontologists have variously reinterpreted. Based on available illustrations, specimens assigned to C. cordialis by Douville (Boule and Thevenin 1906) and Dartevelle and Freneix (1957) are herein referred to Roudairia. In summary, the present taxonomic status of Veniella , Roudairia , and Cicatrea remains unclear due to the lack of well-preserved specimens of Cicatrea. Based on previous work (Boule and Thevenin 1906; Vokes 1954; Dartevelle and Freneix 1957), there are at least two distinct generic groups present. The first group, represented by Veniella , is characterized by uneven commarginal EXPLANATION OF PLATE 1 Figs 1-7. Roudairia squiresi sp. nov. LACMIP locality 14312, Warm Springs Mountain, California; San Francisquito Formation. 1-5, LACMIP 12204, holotype; left valve; 1, exterior showing strong carina on posterior angulation and rounded ripple ribs developed near beak; 2, anterior showing lunule and development of rounded ripple ribs near beak; 3, posterior, shell removed to show mark of internal myophoric flange on rock cast and posterior adductor muscle scar (rough area to right of myophore impression); 4, interior showing myophoric flange and position of adductor muscle scars; 5, hinge, nymph broken, posterior lateral PII, cardinal 4b elongate slender, cardinal 2b elongate trigonal with faint medial groove, anterior lateral All chevron-shaped. 6-7, LACMIP 12205, paratype; right valve; 6, hinge, nymph nearly complete, anterior laterals AI and AIII, cardinal 1, 3a, and 3b, 3b bifid, posterior laterals PI and Pill; 7, exterior showing strong carina on posterior angulation. All figures x 1 and coated with ammonium chloride. PLATE 1 KIRBY and SAUL, Roudairia 32 PALAEONTOLOGY, VOLUME 38 text-fig. 5. Left and right valve hinge areas of Roudairia squiresi with the hinge teeth labelled. ribbing on the anterior margin that tends to develop flanges, by an angulate but not carinate posterior angulation, by the absence of the anterior-lateral tooth AI, and by the absence of an internal myophoric flange on the anterior side of the posterior adductor muscle scar. The second group, represented by Roudairia , is characterized by even commarginal ribbing which commonly becomes roundly ripple-ribbed on the anterior portion of the shell near the beaks and which evanesces toward the ventral margin in large specimens, by a strongly carinate posterior angulation that is accentuated by a keel, by the anterior-lateral tooth AI, and by an internal myophoric flange bordering the anterior side of the posterior adductor muscle scar. The specimens from Africa and Madagascar previously described as Cicatrea belong in this second group. The Indian specimens described as Cicatrea may also belong in this second group. But until better preserved specimens of Cicatrea from India are available, the relationship of Cicatrea to Veniella and Roudairia will remain unclear. The specimens from Warm Springs Mountain are distinct from V. conradi. They are externally more similar to R. drui and C. cordialis. Internally, they are more similar to R. drui. Previous workers (e.g. Douville 1904; Olsson 1934; Vokes 1954) have used various stratagems to avoid replacing the more commonly used and better-based Roudairia Munier-Chalmas, 1881, with the enigmatic and ill-defined Cicatrea Stoliczka, 1870. Although the similarity of the Warm Springs EXPLANATION OF PLATE 2 Fig. 1. Roudairia squiresi sp. nov. LACMIP 12209, paratype; articulated specimen, anterior view; LACMIP locality 14316, Warm Springs Mountain, California; San Francisquito Formation. Figs 2-4. Veniella conradi (Morton). 2, LACMIP 1221 1, hypotype; right valve, interior view showing hinge, muscle scars, and lack of internal myophoric flange bordering posterior adductor muscle scar; LACMIP locality 8063, Coon Creek, Tennessee; Ripley Formation. 3-4, LACMIP 12212, hypotype; left valve; LACMIP locality 8063, Coon Creek, Tennessee; Ripley Formation; 3, interior view showing hinge, muscle scars, and lack of myophoric flange bordering posterior adductor muscle scar. 4, exterior with commarginal flanges developing into distant rib crests. Figs 5-8. Roudairia peruviana Olsson. 5-6, PRI 3716, holotype; right valve; Monte Grande, Peru; Monte Grande Formation; 5, exterior with strong carina on posterior angulation and rounded ripple ribs near beak; 6, hinge, lunular margin and anterior portion of hinge damaged, nymph broken. 7, PRI 4825 (exterior figured by Olsson, 1944, pi. 2, fig. 7), hypotype; left valve, interior view, hinge damaged but shows nymph, cardinal teeth 4b and 2b, and chevron-shaped anterior lateral AIL also myophore along posterior muscle scar; Monte Grande, Peru; Monte Grande Formation, specimen not coated. 8, LACMIP 12210, hypotype; right valve, hinge with well- preserved nymph, anterior laterals AI and AIII, cardinals 1, 3a and 3b, 3b widely bifid, posterior laterals PI and PIII; UCLA locality 5261, north of Tortuga, Paita Peninsula, north-western Peru; ‘ Baculites beds’. All figures x 1 and coated with ammonium chloride, except where noted otherwise. PLATE 2 V KIRBY and SAUL, Roudairia , Veniella 34 PALAEONTOLOGY, VOLUME 38 Mountain specimens to Cicatrea is unclear, they are in shape, sculpture, internal myophoric flange, and hinge most similar to Roudairia. Roudairia squiresi is the first species of this group to be found in North America. Roudairia squiresi sp. nov. Plate 1, figures 1-7; Plate 2, figure I 1991 Roudairia peruviana ? Olsson, 1934; Kirby, p. 133, pi. 3, figs 6, 7. Derivation of name. The species is named for Richard L. Squires whose work on Eocene molluscs of the eastern Pacific has greatly improved our understanding of Tethyan migrations into California. Holotype. LACMIP 12204; San Francisquito Formation (uppermost Maastrichtian); FACM IP locality 14312, Warm Springs Mountain, Fos Angeles County, southern California, USA. Paratypes. Five specimens: LACMIP 12205-12206 from LACMIP locality 14312; LACMIP 12207-12208 from UCLA locality 1591; LACMIP 12209 from LACMIP locality 14316; all from San Francisquito Formation (uppermost Maastrichtian); Warm Springs Mountain, Los Angeles County, southern California, USA. Diagnosis. A large Roudairia of nearly equant proportions, but with the beaks curled well forward, sculptured near the beaks by ten to fourteen undulatory commarginal ribs that evanesce ventrally, with a strong posterior carina along the posterior angulation. Cardinals 3b and 2b relatively narrow and posteriorly directed (Text-fig. 5). Description. Shell large, higher than long, subquadrate, inflated, thick; beaks strongly enrolled, strongly prosogyrous ; lunular margin nearly straight ; anterior end broadly rounded ; ventral border nearly straight with a slight sulcus to the anterior of the posterior carination and a little rostrate at the carination; posterior border nearly straight, rounding into dorsal border; lunule large, depressed, bounded by an inscribed line; no escutcheon; posterior carination high, alate near the beaks, abruptly carinate at the ventral border; paralleled anteriorly by a shallow sulcus. External sculpture of about ten to fourteen strong, broad, undulatory, commarginal ribs on beak, diminishing in height ventrally, extending from anterior slope break to sulcus anterior to carina. Entire surface marked by uneven commarginal growth lines. Ligament groove deep, arched behind strong alate nymphs. Hinge of right valve with short, strong 1 at the hinge border anterior to 3a (Text-fig. 5); short, ventrally directed 3a; strong, bifid, posteriorly directed 3b; anterior laterals AI and AI1I low; AI short subtrigonal; AIII elongate, paralleling the valve margin; socket for All chevron-shaped; PI and PHI elongate with PI longer; PIII paralleling the valve margin; socket for PII deep. Hinge of left valve with 2b elongate, narrowly trigonal, obscurely bifid, postero ventrally directed; 4b elongate, thin, posteriorly directed, dorsal to bifid socket for 3b; anterior lateral All chevron-shaped around shallow socket for AI, anterior to very deep socket for 1 ; PII elongate, strong, with transverse striations on both sides. Adductor muscle scars strongly marked, anterior impressed and bounded by raised rim, posterior impressed and bounded along anterior side by a strongly raised myophoric flange beginning near the beak and extending to ventral edge of muscle scar. Measurements. LACMIP 12204 height 700 mm, length 700 mm, inflation 350 mm; LACMIP 12205 height 69 0 mm, length 66-5 mm incomplete, inflation 29-6 mm. Remarks. Roudairia squiresi is similar to Roudairia peruviana Olsson, 1934, and to Roudairia jamaicensis Trechmann, 1927. These Roudairia are large and very trigoniiform, have strong, undulatory, commarginal sculpture on the flanks near the beaks that evanesce well before the ventral margin, have a strong posterior carina along the posterior angulation, and have an inscribed lunule. Internally, they have a strong myophoric flange bordering the anterior side of the posterior adductor muscle scar. The anterior left lateral All is strongly hooked and forms a chevron, the right anterior lateral AI is present, and the socket for All is chevron-shaped (Text-fig. 5). KIRBY AND SAUL: TETHYAN BIVALVE ROUDAIRIA 35 Roudairia squiresi differs from R. peruviana (PI. 2, figs 5-8) from the Maastrichtian of Peru in being less upright, having the beaks curled more forward, having a shallower sulcus anterior to the carina, and having commarginal ribs that are greater in number, narrower, and closer together. Roudairia squiresi contrasts with R. jamaicensis from the Campanian of Jamaica in being less elongate and having coarser and more pronounced commarginal ribbing. Trechmann figured a mature left valve and an immature right valve of R. jamaicensis (1927 , pi. 2, figs 1-2). The immature right valve is more elongate than similar sized specimens of R. squiresi and has finer and less pronounced ribbing. Although Trechmann’s figure (1927, pi. 2, fig. 1) of a mature left valve appears to be relatively higher, his measurements indicate that mature specimens are also more elongate than high, whereas in R. squiresi , height and length are more nearly equal. Veniella conradi (Morton 1833) is less trigoniiform. It has distant, flanged commarginal sculpture and a strong posterior angulation that does not bear a raised carina like that of R. squiresi. Veniella conradi lacks the internal posterior myophore, its lunule is not inscribed, anterior lateral All is elongate, trigonal, and the right anterior lateral AI is not present (PI. 2, figs 2-4). Vokes (1954, text-figs 6-9) illustrated the changes in the left cardinal 2b of V. conradi from juvenile inverted V-shaped to compressed trigonal, obscurely bifid adult. The obscurely bifid character of 2b in R. squiresi suggests that it too results from the compression of a widely bifid, inverted V-shaped, juvenile tooth. The ligament of R. squiresi is enlarged below the beak similar to many large venerids (e.g. Dosinia ponderosa (Gray 1838)). A similar subumbonal ligamental pit may be the structure that caused Stoliczka (1870) to describe the ligament of Cyprina ( Cicatrea ) cordialis as lying in a double groove. In R. squiresi , this elongate pit encroaches on the anterior end of the nymph, notching it just behind the beak, and creating exteriorly a pattern of shell and notches similar to that seen in Stoliczka’s figure lb (1870, pi. 10). Only a few specimens of R. squiresi have been found, including eight nearly complete large valves from Warm Springs Mountain. A fragment of a left valve from UCLA locality 6525 on Dip Creek, San Luis Obispo County, central California, consists only of the anterior part of the hinge, the lunule, and a suggestion of undulatory commarginal ribbing. The fragment is too incomplete to identify with certainty, but is probably R. squiresi. Stratigraphical range. Uppermost Maastrichtian. Geographical distribution. Warm Springs Mountain, Los Angeles County, and Dip Creek, south shore of Lake Nacimiento, San Luis Obispo County, central California, USA. Acknowledgements . We thank: P. Hoover of the Paleontological Research Institute for the loan of A. A. Olsson’s type and figured specimens from Peru; Sean Connell and R. L. Squires of the California State University, Northridge, who collected some of the specimens at Warm Springs Mountain; M. McIntyre and M. Wickman of the Angeles National Forest for allowing access to Warm Springs Mountain and granting permission to collect specimens; and Hayes Graphics for their computer and copy support. Photographs of the specimens were taken by J. De Leon, Natural History Museum of Los Angeles County. Discussions with G. Kennedy and E. Wilson were fruitful. This paper has benefited from a review by R. . Squires and two anonymous reviewers. REFERENCES abbass, h. l. 1962. A monograph on the Egyptian Cretaceous pelecypods. 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Journal of the Washington Academy of Sciences, 44, 36^44. willard, B. 1966. The Harvey Bassler collection of Peruvian fossils. Fehigh University, Bethlehem, Pennsylvania, 255 pp. ziegler, a. m., scotese, c. R. and barrett, s. F. 1982. Mesozoic and Cenozoic paleogeographic maps. 240-252. In brosche, p. and sundrmann, j. (eds). Tidal friction and the Earth's rotation , II. Springer-Verlag, Berlin, 345 pp. APPENDIX Cited fossil localities 1591UCFA: north-flowing tributary to Warm Springs Canyon; approximately 24 km west of Warm Springs Camp; approximately 1372 m north and 671 m west of Warm Springs Mountain; Warm Springs Mountain quadrangle, 1958, Eos Angeles County, California. Collected by: R. W. Webb, G. Young, and E. H. Quayle, 6/17/1941. San Francisquito Formation, uppermost Maastrichtian. 5261UCFA: ‘ Baculites beds’ north of Tortuga, Paita Peninsula, northwestern Peru. Collected by: A. G. Fischer. Maastrichtian. 6525UCFA: south-side of Fake Nacimiento; poorly-sorted conglomeratic sandstone cropping out at narrows of Dip Creek; fossils collected from outcrops on east-side of Dip Creek; about elevation 232 m; 427 m south and 61 m west of the northeastern corner. Section 30, Township 25 South, Range 10 East, Lime Mountain quadrangle, 1948, San Luis Obispo County, California. Collected by: R. B. Saul and L. R. Saul, 12/31/1977. Undifferentiated Cretaceous rocks, uppermost Maastrichtian. 8063LACM1P: (= CIT 703) Dave Week’s place, on Coon Creek; 5 6 km south of Enville; 121 km north of Adamsville, McNairy County, Tennessee. Collected by: W. P. Popenoe, 1929. Ripley Formation, Maastrichtian. 14312FACMIP: ( =CSUN 1447 O) fine-grained feldspathic sandstone 45 m above nonconformity between granite-gneiss basement and overlying San Francisquito Formation; elevation 1015 m; 442 m north and 152 m west of forest lookout tower on summit of Warm Springs Mountain; Warm Springs Mountain quadrangle, 1958, Los Angeles County, California. Collected by: M. X. Kirby, 2/2/1990. San Francisquito Formation, uppermost Maastrichtian. 38 PALAEONTOLOGY. VOLUME 38 14316LACMIP: (= CSUN 1 145) feldspathic sandstone; elevation 1061 m; 396 m north and 335 m east of forest lookout tower on summit of Warm Springs Mountain; Warm Springs Mountain quadrangle, 1958, Los Angeles County, California. Collected by: S. Connell and R. L. Squires, 1988. San Francisquito Formation, uppermost Maastrichtian. M. X. KIRBY Department of Geological Sciences California State University, Northridge Northridge California 91330, USA Present address: Department of Geology University of California, Davis Davis, CA 95616 L. R. SAUL Invertebrate Paleontology Section Los Angeles County Museum of Natural History 900 Exposition Boulevard Los Angeles California 90007, USA Typescript received 18 July 1993 Revised typescript received 20 April 1994 A NEW PLOURDOSTEID ARTHRODIRE FROM THE UPPER DEVONIAN GOGO FORMATION OF WESTERN AUSTRALIA by JOHN A. LONG Abstract. A new plourdosteid arthrodire, Mcnamaraspis kaprios gen. et sp. nov., is described from the Late Devonian (Frasnian) Gogo Formation of Western Australia. Mcnamaraspis is characterized by its very short spinal plate, larger pectoral fenestra and inferognathal with several distinct trenchant cusps. The anterior surface of the nasal capsule is covered by a hemispherical bone not previously recorded in placoderms. This is interpreted as an ossified annular cartilage, and, together with the interpretation of the suborbitalis muscle being present in arthrodires, supports the hypothesis that placoderms are more closely related to chondrichthyans than to osteichthyans. Mcnamaraspis is placed as the sister taxon to Torosteus in the family Plourdosteidae. The Plourdosteidae is redefined. Interrelationships of plourdosteids and relationships to other eubrachythoracid arthrodires are discussed. The superb three-dimensional preservation of the Gogo fishes is now well documented as many of the placoderms and osteichthyans from the fauna have been formally described (Miles 1971, 1977; Miles and Young 1977; Miles and Dennis 1979; Dennis and Miles 1979a, 6, 1980, 1981, 1982; Dennis-Bryan and Miles 1983; Dennis-Bryan 1987; Long 1988a, b, c, 1990, 1994; Gardiner and Miles 1990). New seasons of held work at Gogo from 1986 to 1992 have yielded many new species, including the arthrodire described in this paper. As the bones are uncrushed and the armour of the placoderms can be accurately reconstructed, descriptions of new material can be kept concise by leaving the photographs, tables and illustrations to show main morphological features and proportions. The new arthrodire described herein is essentially similar to Torosteus (Gardiner and Miles 1990) in its general anatomy, so only different features or new anatomical data are here described in detail. The plourdosteid arthrodires were a widespread group during the Late Devonian, being found in Canada ( Plourdosteus\ Vezina 1986, 1990), Russia (Janiosteus\ Ivanov 1988), China ( Panxiosteus ; Wang 1991) and Australia (Harry toombsia ; Miles and Dennis 1979; Kimberleyich thys ; Dennis- Bryan and Miles 1983; Torosteus ; Gardiner and Miles 1990). They appear to have displaced the earlier coccosteid arthrodires that are commonly found in Middle Devonian faunas, particularly in the Old Red Continent of Euramerica (Denison 1978, 1984; Dineley and Loeffler 1993). The hypothetical presence of annular cartilages in placoderms was one of several characters used by Stensio (1963) to argue for a close relationship between placoderms and chondrichthyans, despite the absence of any fossil evidence. The new form described here shows, for the first time, the presence of ossified annular cartilages in a placoderm. Comparisons are made with the nasal structures of extant fishes and its bearing on placoderm affinities is discussed. In addition, aspects of the soft anatomy of the head are reconstructed from the structures preserved on the visceral surface of the skull roof and cheek. Throughout the work the words ‘length’, ‘breadth’ and ‘height’ are abbreviated to as ‘L\ ‘B’ and ‘H’ respectively. Indices are expressed as ratios multiplied by 100. Institutional abbreviations are: BMNH, Natural History Museum, London, UK; WAM, Western Australian Museum, Perth, Australia. (Palaeontology, Vol. 38, Part 1, 1995, pp. 39-62, 1 pl.| © The Palaeontological Association 40 PALAEONTOLOGY, VOLUME 38 SYSTEMATIC PALAEONTOLOGY Class placodermi McCoy, 1848 Order arthrodira Woodward, 1891 Infraorder brachythoraci Gross, 1932 Family plourdosteidae Vezina, 1990 1990 Torosteidae, Gardiner and Miles, p. 162. Diagnosis. Eubrachythoracid arthrodires with moderately broad heads that lack both internasal and extrascapnlar plates; the postorbital plates and paranuchal plates are in extensive contact; the visceral surface of the skull-roof has well-developed, prominent postocular processes, and the lateral consolidated area has well-defined, triangular depressions; cheek unit loosely attached to skull-roof and submarginal plate free, well-defined spiracular notch present; parasphenoid with posterior depression immediately behind buccohypophysial foramen and with median hypophysial vein foramen present; trunk shield with a posterior lateral plate that deeply inserts into the ventral margin of the posterior dorsolateral plate; posterior ventrolateral plate has a prepectoral lamina contacting the anterior lateral plate. Remarks. Vezina (1990) erected the family Plourdosteidae, to include Plourdosteus , Panxiosteus , Harrytoombsia , Kimberleyichthys , Janiosteus and Eldenosteus , based on fifteen characters, although few of these are unique to the referred taxa. Soon after Vezina’s paper was published, Gardiner and Miles (1990) proposed the family Torosteidae, to include Plourdosteus , Torosteus , Harrytoombsia and Kimberleyichthys , based on fourteen characters, some of which were in agreement with Vezina’s definition of the family Plourdosteidae, but again containing few unique characters within the subset of referred taxa. With the description of a new genus, obviously well-preserved, and exhibiting features of both familial diagnoses, it is here appropriate to redefine the family Plourdosteidae, and place Torosteidae in synonomy with this family. The characters used in the definition are all regarded as synapomorphies unique to the referred taxa (as known). In addition, the feature of the well-developed lateral consolidated area with triangular muscle attachment areas has been included, following on from comparisons made on the cheek anatomy of arthrodires in this paper. Other characters used by Vezina (1990) and Gardiner and Miles (1990) which characterize members of the group, but are not unique to the family Plourdosteidae, include: trilobate centrals; loss of internasal plate; skull roofing bones with sinuous suture lines and broad overlap areas; inferognathal plate with well-developed median cusps; postnasal plate large and seen in dorsal view; spinal plate may project laterally from trunk armour; posterior median ventral plate enlarged, being only a little longer than broad. The posterior lateral plate participates in the pectoral fenestra of one coccosteid, Watsonosteus , although this genus is regarded as one of the most specialized end members of that lineage and not related to the plourdosteids as it lacks all the defining skull characteristics of the latter group. The most characteristic feature of the posterior lateral plates of plourdosteids is that they possess a dorsal process that inserts deeply into a narrow cavity within the ventral margin of the posterior dorsolateral plate. This arrangement also occurs in EXPLANATION OF PLATE 1 Figs 1-8. Mcnamaraspis kaprios gen. et sp. nov. Holotype, WAM 86.9.676. 1, head shield in dorsal view, x 1-5; 2, headshield and cheek bones in left lateral view, x 15; 3, left inferognathal in mesial view, x 2; 4-5, right posterior superognathal in 4, mesial and 5, lateral views, x3; 6-7, right anterior superognathal in 6, posterior and 7, anterior views, x3; 8, right articular in lateral view, x 3. All specimens whitened with ammonium chloride. PLATE I LONG, Mcnamaraspis 42 PALAEONTOLOGY, VOLUME 38 Eastmanosteus calliaspis (Dennis-Bryan 1987), but it appears to be a characteristic feature of all plourdosteids and is thus considered to have been acquired independently by Eastmanosteus , a dinichthyid (Long 1987). The genus Eldenosteus is currently being restudied by Heidi-Marie Johnstone and David Elliot at Northern Arizona University, based on new finds. It is excluded from comparison with other plourdosteids until descriptions of its anatomy are published. Genus mcnamaraspis gen. nov. Derivation of name. In honour of Dr Ken McNamara, Western Australian Museum, for his contributions to palaeontology. Type species. Mcnamaraspis kaprios sp. nov., only known species. Diagnosis. A plourdosteid arthrodire having a head shield slightly broader than long, with a nuchal plate thirty- nine per cent, of the skull length; inferognathals with two prominent anterior cusps; trunk shield with short spinal plate, nineteen per cent, as long as the median dorsal plate, and having greater contact with the interolateral plate than with the anterior ventrolateral plate; pectoral fenestra very large, being longer than the flank length of trunk shield. Remarks. The unusually short spinal plate separates this genus readily from all other plourdosteids (Text- fig. I). Mcnamaraspis kaprios sp. nov. Plate 1; Text-figures 1-14, 16-17 1988« 'a genus of plourdosteid arthrodire new to science’. Long p. 442, fig. 6. 1990 Torosteus pulchel/us , Gardiner and Miles pp. 175, 180. 1991 new genus of plourdosteid. Long, pp. 421, 425, pi. 4 C, D. Derivation of name. Greek ‘kaprios’, like a boar, alluding to the well-developed lower jaw tusks on the inferognathal. Holotype. WAM 86.9.676, an almost complete armour, including upper and lower gnathal elements, parasphenoid and partially ossified nasal capsules, wanting only the posterior ventrolateral plates and the left anterior ventrolateral plate (Text-figs 1-4, 6-14; PI. 1). Diagnosis. As for the genus. Other material. BMNH P52553, a small skull and partial trunk shield, examined and measured by the author (Text-fig. 5). Type locality. Bugle Gap (near locality 101 of Miles 1971), about 100 km east of Fitzroy Crossing, Western Australia. Gogo Formation (lower Frasnian). Collected by the author in August 1986. Description Head shield. The head shield (PI. 1 ; Text-figs 2-5) closely resembles that of both Harrytoombsia (Miles and Dennis 1979) and Torosteus (Gardiner and Miles 1990), but differs principally in the shape of the nuchal plate (Nu) which is shorter in length, has a strongly indented posterior margin, and a weakly convex anterior margin. Skull roof bones generally have sinuous and irregular sutures and relatively broad overlap surfaces. The cheek unit is clearly visible on the skull in dorsal view (Text-fig. 3), and the orbital notches (orb) are also well defined. The nuchal plate on the holotype occupies only thirty-seven percent, of the skull roof length (Text-fig. 4), and LONG: AUSTRALIAN ARTHRODIRE 43 text-fig. 1 . Mcnamaraspis kaprios gen. et sp. nov., holotype, WAM 86.9.676. Armour in left lateral view. Scale bar represents 10 mm. has a B/L index of 166 (for P52553 the nuchal is thirty-six per cent, of estimated skull length, B/L index of 162, Text-fig. 5). The nuchal has a weakly convex anterior margin, in contrast to the concave or indented anterior margins of all other plourdosteids. The paranuchal plate (PNu) has extensive contact with the postorbital (PtO), as in other plourdosteids, and the marginal plate (M) is strongly indented into the postorbital plate. The postorbital plate is significantly larger than the marginal. The postmarginal (PM) has a very small externally-ornamented area, most of the plate forming the posteriolaterally-facing subobstantic margin (soa). The pineal plate (P) is as long as the T-shaped squat rostral (R), the prepineal length of the skull 44 PALAEONTOLOGY, VOLUME 38 text-fig. 2. Mcnamaraspis kaprios gen. et sp. npv.. holotype, WAM 86.9.676. a, left side of cheek and skull roof in medial view, x2; b, head shield and cheek bones in ventral view, x I 5; both whitened with ammonium chloride. being twenty-five per cent, of the skull length. The postnasal plates (PN) both contact the rostral mesially and there are small accessory postnasal ossifications mesial to the postnasal bones in contact with the rostral (Text- fig. 6, acc. PN). The visceral surface of the skull-roof shows all the regular morphological landmarks seen in eubrachythoracid arthrodires (Text-figs 2, 7). Of particular interest are the robust postocular processes (pt.o.pr) which have smaller, secondary processes here termed the ‘hyoid processes’ (pr.hy), developed LONG: AUSTRALIAN ARTHRODIRE 45 text-fig. 4. Mcnamaraspis kaprios gen. et sp. nov., holotype, WAM 86.9.676. Head shield fully restored with cheek bones, in dorsal view. Scale bar represents 10 mm. posterior to them. The width between the postorbital processes is 16 mm, narrower than for any other place where dermal bone encloses cartilaginous neurocranium. The triangular area .posterolateral to these processes and bounded mesially by the lateral consolidated area (lcp) and anteriorly by a short ridge (ri, the 46 PALAEONTOLOGY, VOLUME 38 text-fig. 5. Mcnamaraspis kaprios gen. et sp. nov., BMNH P52553. Camera lucida sketch of head shield in dorsal view. Scale bar represents 5 mm. text-fig. 6. Mcnamaraspis kaprios gen. et sp. nov., holotype, WAM 86.9.676. Camera lucida sketch of left and right anterior margins of the head shield showing position of accessory postnasal bones. Scale bar represents 1 mm. ‘postsuborbital crista' of Carr 1991, p. 381). It is a well-defined depression (tri) for muscle attachment coming from the dorsal region of the cheek unit, and is discussed further below. The cheek plates (PI. 1; Text-figs 1, 8), of both sides are well-preserved and resemble the pattern seen in Torosteus except for the narrower suborbital process on the suborbital plate (SO). The submarginal plate (SM) is elongate and contacts the marginal and postmarginal plates, leaving a spiracular notch (spir) between the postorbital plate and the dorsal margin of the suborbital plate. The anterior end of this notch is closed by short contact between the suborbital and postorbital plates, unlike the open spiracular notch in Torosteus and Harry toombsia. The postsuborbital plate (PSO) has a well-developed subcutaneous pit and cuspate sensory- line groove (psoc), but the suborbital plate lacks the subcutaneous pit seen in other plourdosteids. The LONG: AUSTRALIAN ARTHRODIRE 47 text-fig. 7. Mcnamaraspis kaprios gen. et sp. nov., holotype, WAM 86.9.676. Head shield and left cheek bones in ventral view. Scale bar represents 10 mm. text-fig. 8. a, Mcnamaraspis kaprios gen. et sp. nov., holotype, WAM 86.9.676; camera lucida sketch of right suborbital plate in dorsal view, b, Torosteus tuberculatus , holotype, WAM 40.4.262; left suborbital plate in dorsal view. Scale bar represents 5 mm. 48 PALAEONTOLOGY, VOLUME 38 text-fig. 9. Mcnamaraspis kaprios gen. et sp. nov., holotype, WAM 86.9.676. a, right articular in mesial view; b-c, parasphenoid in b, ventral view; and c, dorsal view; d-e, left side of ethmoid ossification in d, anterior view; and E, lateral view; f-i, annular cartilages from both sides of nasal capsules in f, h, anterior view; and G, i, posterior view, a-e are x 3 ; f-i x 4. text-fig. 10. Mcnamaraspis kaprios gen. et sp. nov., holotype, WAM 86.9.676. Camera lucida sketch of parasphenoid in A, ventral view; and b, dorsal view. Both x 2-73. suborbital plate has a well-defined dermal process eminating from near the dorsal end of the orbital margin, along the mesial edge. This process (Text-figs 2, 7-8, pr) occurs in all other Gogo plourdosteids and is discussed more fully below. The dentition is characteristic for the genus in that the inferognathal (PI. 1, fig. 3; Text-fig. 1, ig) has three strong mesial ‘teeth’, two large anterior biting cusps, a trenchant crest with cutting edges on both labial and lingual edges, and well formed posterior teeth at the rear of the biting division of the inferognathal. The anterior superognathal (PI. 1, figs 6-7; Text-fig. 1, asg) has three biting cusps, a large trenchant median cusp and two sharp smaller cusps developed on the posteroventral corner of the biting margin. The posterior superognathal (PI. 1, figs 4-5; Text-fig. 1, psg) is remarkably thin compared with those of Harrytoombsia, hypv LONG: AUSTRALIAN ARTHRODIRE 49 text-fig. 1 1. Mcnamaraspis kaprios gen. et sp. nov., holotype, WAM 86.9.676. a, trunk shield in right lateral view, x L5; b, enlargement, showing right spinal plate, x 3. Torosteus and Kimberleyichthys , and has a characteristic sharp cusp directed posteroventrally from its centre. The dorsal process of the posterior superognathal is well-developed, but the greatest width of the bone is still only 06 of its length, this being shorter than for the other Gogo plourdosteids. The parasphenoid (Text-figs 9b, c; 10) has a pentagonal shape with a weakly convex posterior margin, although in all other respects it is not unlike that of Torosteus pulchellus (Gardiner and Miles 1990, fig. 24). The dorsal surface (Text-fig. 7b) has a well-defined rectangular rim separated from the ventral surface by an extensive prehypophysial shelf (sh). The central area is strongly depressed for the buccohypophysial foramina (fb.hy), with a robust median longitudinal crest separating them. Paired posterolateral processes (pl.pr) are developed. The opening for the median hypophysial vein (hypv) is well-defined. No extrascapular plate was found in the specimen, and, as all other parts of the anterior of the skeleton were preserved, it is reasonable to assume that an extrascapular plate was lacking from the armour as in other plourdosteids. The trunk shield (Text-figs 1, 3, 11-13) is missing only the posterior ventrolaterals and the left anterior ventrolateral plates. The presence of an enclosed pectoral fenestra (f. pec.) is demonstrated by the overlap area on the posterior lateral plate (PL) for the postpectoral lamina of the posterior ventrolateral plate. The pectoral fenestra was very large relative to the size of the lateral wall of the trunk shield, more so than for any other plourdosteid. The anterior lateral plate (AL) is characteristic for the genus within plourdosteids in having a nearly pointed dorsal margin, well-defined semicircular embayment for the overlap of the submarginal plate (the post branchial lamina), short spinal overlap margin, and an extensive, straight margin bordering the pectoral fenestra. The most diagnostic feature of the trunk shield is the very short spinal plate (Text-figs 1, 11b, 13, Sp) which is only twenty-one per cent, of the length of the medial dorsal plate, compared with thirty to thirty-six per cent, in Torosteus species. The spinal (Sp) has no posteriorly facing lamina as in Torosteus, and is embayed with a small posterior notch (n). The contact margin between the spinal and the interolateral (IL) is more than twice as long as the contact margin between the spinal and anterior ventrolateral plates (AVL). The median dorsal (MD), anterior dorsolateral (ADL) and posterior dorsolateral (PDL) plates show no special features; their shapes are shown in Text-figures 1-3, 1 1 and 12. Their proportions are incorporated into the measurements for the trunk shield (Table 1). The posterior lateral (PL) plate is strongly bent, and is much narrower than for Torosteus or Harry toombsia. 50 PALAEONTOLOGY, VOLUME 38 Mcnamaraspis kaprios gen. holotype, WAM 86.9.676, of trunk shield in ventral view, x 1-5. text-fig. 13. Mcnamaraspis kaprios gen. et sp. nov., holotype, WAM 86.9.676. Anterior half of trunk shield in ventral view. Scale bar represents 10 mm. The anterior and posterior median ventral plates (Text-figs I 1-13, AMV, PMV) are of similar length, the latter being about a third broader than the anterior median ventral plate. The interolateral plate is similar to that in other plourdosteids, such as Torosteus and Harrytoombsia and shows no special features apart from the well-defined anterior ventral shelf (Text-fig. 13, ant. s.a.). LONG: AUSTRALIAN ARTHRODIRE 51 Table I. Measurements of Mcnamaraspis kaprios Holotype, WAM 86.9.676. 1. Skull roof length - 56-3 mm 13. Length of inferognathal - 38-5 mm 2. Breadth skull-roof - 57-7 mm 14. Length of biting division of inferognathal 17-7 mm 3. Breadth of skull across posteromesial angles - 4 1 -2 mm 15. Breadth of trunkshield - 64 mm 4. Depth of headshield - 35 mm 16. Depth of trunkshield - 63 mm 5. Prepineal length - 1 3-9 mm 17. Length of rostrocaudal flank of trunkshield 26-5 mm 6. Length of orbit - 14 mm 18. Length of pectoral fenestra - c. 30 mm 7. Nuchal length - 20-9 mm 19. Median dorsal plate length - 43-8 mm 8. Length of lateral articular fossa - 5-3 mm 20. Median dorsal plate breadth - 35-2 mm 9. Depth of lateral articular fossa - 2-7 mm 21. Length of spinal - 9-4 mm 10. Angle between lateral articular fossa and headshield - 30° 22. Angle between spinal and midline of armour - 13° 11 Length of cheek - 40-5 mm 23. Anterior ventrolateral plate length - 44-8 mm 12. Length of postorbital division of cheek - 24-9 mm 24. Length of spinal division of anterior ventrolateral plate - 8-75 mm exc.n text-fig. 14. Mcnamaraspis kaprios gen. et sp. nov., holotype, WAM 86.9.676. Annular cartilage in a, anterior view; and b, posterior view. Scale bar represents 1 mm. NEW ANATOMICAL FEATURES FOR ARTHRODIRES The well-preserved holotype exhibits a number of features never described before in arthrodires or for placoderms in general, or which have only been alluded to in previous descriptions. These include: the first occurrence of annular cartilages; the development of muscle attachment areas for the opercular regions; the presence of bony processes on the suborbital plates; and the presence of additional postocular processes on the visceral surface of the skull roof. Annular cartilages. The specimen shows preservation of two perichondrally ossified irregular hemispheres (Text-figs 9f-i; 14) which were attached to the front of the snout. As the anterior part of the ethmoid bone was preserved it is possible to fit one of these bones over the front of the cavity for the nasal capsule. The neat fit of the hemispherical bone over the nasal cavity, and the presence of a small slit-like opening for the naris in the bone, suggests that it was an ossified cover to the nasal capsule. In chondrichthyans, an annular cartilage rings the nasal cavity and covers the front of the 52 PALAEONTOLOGY, VOLUME 38 nasal capsule (Stensio 1963). Although Stensio preferred to restore the annular cartilage in the snouts of arthrodires, there was no fossil evidence for this bone being present in any of the placoderms that he studied. The new Gogo specimen provides the first evidence of an annular cartilage being developed in placoderms. Why only these genera show the feature is not known, but it does not preclude the possibility that it was present as unossified cartilage in other placoderms, and ossified in only a few cases, such as in Mcnamaraspis. In its external shape, viewed anteriorly, the annular cartilage bone is lacriform (Text-fig. 14). The external surface is smooth and strongly convex with a small sloping slit, presumably for the incurrent naris (inc.n). The excurrent naris (exc.n) is represented by a notch in the ventral margin of the annular cartilage. This notch is well defined when the bone is fitted over the anterior face of the nasal capsule. The visceral surface (Text-fig. 14b) shows a large cavity around the incurrent naris (cav) and a series of depressions (dep), ridges (ri 1-3) and grooves (gr 1, 2), which in life may have braced a sinuous folded cartilage structure, much like the complex annular cartilage seen in many elasmobranchs (e.g. Isurus punctatus\ Stensio 1963, fig. 33). The function of this structure would have been to direct the flow of water from the incurrent naris around the olfactory organ, and out through the excurrent notch. In many sedentary elasmobranchs the annular cartilage is highly specialized, allowing for communication between the nasal openings and the mouth (Bell 1993), and therefore the primitive condition is seen in most free-swimming sharks. Mcnamaraspis , having been an active free-swimming predator, also exhibits a simple, unspecialized annular cartilage not too unlike that of modern pelagic sharks such as Isurus. As the annular cartilage of Mcnamaraspis did not develop nasoral grooves, the flow of water in and around the olfactory organs, situated anterior to the roseate cribrosal bone, was most likely functional purely in olfaction, without any likelihood of involving respiration. It has been suggested that some placoderms. like the antiarch Botliriolepsis , had paired lung-like structures (Denison 1941) and thus it could be argued the nasal capsules and their surrounding soft tissues may have secondarily developed respiratory specializations, although this has not been alluded to in any descriptions of the rostral bones or preorbital recesses of that genus (e.g. Stensio 1948; Young 1984). Suborbital bone - orbital autopalatine process. The additional small process found on the inside orbital margin of the suborbital bone in Mcnamaraspis (pr. Text-figs 7-8) has also been identified by the author in several other Gogo plourdosteids ( Harrytoombsia , Torosteus pulchellus , T. tuberculatus) but is absent from Eastmanosteus , Incisoscutum , all the camuropiscids and the two new, undescribed forms of Gogo ‘coccosteomorph arthrodires’ currently being studied by workers at the Natural History Museum, London. The process was termed the ‘mesial process’ by Gardiner and Miles (1990) who suggested that it ‘was probably for a branch of the adductor mandibulae muscle’. The process emanates from near the top of the orbital margin of the suborbital plate in Mcnamaraspis , and in the middle of the orbital margin in Torosteus. The process is situated more ventrally than the dermal articular ridge on the mesial margin of the suborbital plate of Buchanosteus (Young 1979, p. 333) and did not take part in any connection with the skull roof. When the cheek unit and jaw cartilages are articulated to the skull roof it is clear that the process aligns well with the posterior margin of the ossified division of the autopalatine and would have most probably have served as a bracing point or attachment point for a lateral ligamentous connection from the autopalatine to the suborbital plate. This is well demonstrated in the holotype of Torosteus pulchellus (Gardiner and Miles 1990, fig. 20) where the process can be seen emanating from the suborbital plate lateral to the posterior margin of the autopalatine. The strap-like palatoquadrate would have passed directly lateral to the process, and thus it could not have served as an attachment point for adductor mandibulae muscles. These muscles are here reconstructed as in Squalus (Text-fig. 15) inserting dorsally on the ventral concave surface of the palatoquadrate (Text-fig. 16). Thus the small mesial process can be termed ‘an orbital autopalatine process’ of the suborbital bone. This character would appear to be a strong synapomorphy uniting these Gogo taxa, and possibly may characterize the whole plourdosteid group if it can be identified within the other non-Australian genera. LONG: AUSTRALIAN ARTHRODIRE 53 text-fig. 15. Squalus acanthias, outer muscles of the head and pharynx (after Gans and Parsons 1964). adductor mandibulae spiracular slit / spiracular muscle / / levator hyoideus levator arcus palatini cucullans hyoideus constrictor dorsalis superficial constr ctor dorsalis text-fig. 16. Mcnamaraspis kaprios gen. et sp. nov. Attempted reconstruction of soft anatomy of the cheek and jaw regions. Scale bar represents 10 mm. Reconstructing jaw and opercular musculature. The lateral consolidated area of the skull roof is divided by a ridge (ri. Text-fig. 8) which separates the suborbital vault (suo.v) from a large triangular ventrally facing depression (tri). When the cheek unit is articulated with the skull roof this depression is adjacent to the postsuborbital plate, thus showing that it would have served as an attachment area for musculature that inserted on the visceral surface of the skull roof dorsal to the palatoquadrate. The adductor mandibulae muscles would have passed ventrally from the 54 PALAEONTOLOGY, VOLUME 38 text-fig. 17. Mcnamaraspis kaprios gen. et sp. nov. Restoration of living fish, tail based on Coccosteus cuspidatus (Miles and Westoll 1968) and Torosteus (WAM 91.4.32). palatoquadrate to insert along the mesial face of the inferognathal, as is normal of most fishes. Therefore I suggest that the triangular depression on the lateral consolidated area of the skull roof probably served as an attachment site for the levator palatoquadratini muscle (l.p. mus. Text-fig. 16), as occurs in this position in many osteichthyan and elasmobranch fishes (Text-fig. 15; Edgeworth 1935; Gans and Parsons 1964; Lauder and Liem 1983). This muscle would have facilitated movement of the cheek unit for respiration. Immediately posterior to the triangular depression is a smaller, less well-defined area where the lateral consolidated region tapers to the posterolateral corner of the skull roof. This weakly depressed area of dermal bone may have served as an attachment area for the smaller opercular muscle emanating from the perichondral ossification of the submarginal plate, here called an epihyal element. This ossification is only seen in one Gogo specimen, the holotype of Torosteus pulchellus (WAM 88.2.7) and may well be interpreted alternatively as an opercular cartilage as argued by Young (1986, p. 39). If so, the hyomandibular element, not perichondrally ossified in any Gogo arthrodire, would have to be reconstructed between the palatoquadrate and the epihyal/opercular cartilage element. For the purposes of reconstruction here the small ossification of the submarginal seems more likely to be an opercular cartilage, as it is situated adjacent to the weakly depressed area on the skull roof here interpreted as a suitable attachment site for the opercular muscle (Text-fig. 16). However, the true ‘epihyal’ element may well be situated posteroventral to the opercular cartilage as suggested by Young (1986). With regard to the adductor mandibulae in arthrodires, the presence of a slender suborbital division of bone on the suborbital plate would suggest that the suborbitalis muscles were well- defined, extending forwards and possibly meeting in a midline raffe. These muscles, along with the LONG: AUSTRALIAN ARTHRODIRE 55 levator palatoquadratini, serve to protract and retract the palatoquadrate in chondrichthyans (Edgeworth 1935), and in arthrodires would have worked with the opercular muscle to move the cheek unit during respiration. Changes in water volume within the buccal cavity may have been regulated by these suggested lateral movements of the dermal cheek unit, forming a simple buccal pump mechanism. This degree of mobility of the cheek unit is not seen in many arthrodires, as several groups have the cheek fixed rigidly to the trunk shield (e.g. camuropiscids, brachydeirids, selenosteids, etc.). In these forms, and other placoderms lacking a separate cheek complex, expulsion of water from the gill chamber would have been achieved by vertical movements of the head shield working in conjunction with gill arch muscles to force water out the branchial opening behind the submarginal plate. Postocular processes and hyoid process. The robust postocular processes of the plourdosteids are better developed than for any other arthrodire and most probably represent an adaptation for bracing or supporting the cartilaginous endocranium during the powerful bite. In addition to the robust anterior postocular process seen in Mcnamaraspis , there are a pair of smaller, delicate processes immediately posterior to the larger postocular processes. These smaller processes 1 have termed the ‘hyoid processes’ (pr.hy. Text-figs 7, 16) as they correspond well with the position of the ramus hyoideus nerve emerging from the anterior region of the posterior postorbital process of the braincase (as in Buchanosteus ; Young 1979), and presumably continuing down to the hyomandibular. These hyoid processes are also observed in Torosteus and Harry toombsia. Text- figure 16 shows an attempted reconstruction of some aspects of the soft anatomy of Mcnamaraspis based on the new morphological observations discussed above. Text-figure 17 shows an attempted reconstruction of Mcnamaraspis as a living fish with the tail restored after Coccosteus cuspidatus (Miles and Westoll 1968). The axial skeleton of the body from the trunk to the anal fin is preserved in one of the Gogo plourdosteids ( Torosteus sp., WAM 91 .4.32) showing these bones to be almost identical with those of Coccosteus. PHYLOGENETIC IMPLICATIONS Relationships of plourdosteids within the eubr achy thor acids. The following discussion of arthrodire interrelationships deals only with the higher eubrachythoracids, defined as a inonophyletic group by Lelievre et cd. (1987), Carr (1991) and Lelievre (1991). The eubrachythoracid arthrodires are defined by having: (1) separate autopalatine and quadrate ossifications of the palatoquadrate; (2) development of a continuous thickening across the posterior margin of the head shield; and (3) the supraorbital vault developed as part of the lateral consolidated arch which is bounded posteriorly by a posterior supraorbital crista (Carr 1991). Lelievre (1991) also used the position of the orbits as lateral on the headshield and the development of a suborbital blade on the suborbital plate, although Carr dismissed these on the grounds that they also occur in more primitive arthrodires such as Buchanosteus and to some extent in forms like Antineosteus. Carr (1991) recognized two main subgroups within the eubrachythoracids - coccosteomorphs and pachyosteomorphs. The coccosteomorph arthrodires are defined as inonophyletic by sharing: (4) a preorbital plate embayment in the central plate; (5) reduction in medial contact between the preorbital plates; (6) spinous posterior margin on median dorsal plate; (7) posterior lateral plate with well-developed ventral lamina; (8) posterior ventrolateral plate with well-developed postpectoral lamina; (9) parasphenoid perforated by a foramen for the median hypophysial vein. Within the coccosteomorph group I recognize the following inonophyletic groups: Incisoscutidae and Camuropiscidae (Denison 1984; Long 19886, 1994; Carr 1991) and the Plourdosteidae (Vezina 1990; =Torosteidae Gardiner and Miles, 1990). The following synapomorphies define the clade containing the Plourdosteidae + Incisoscutidae -(-Camuropiscidae: (10) paranuchal sutures with postorbital plate, excluding contact between marginal and central plates; (11) anteroventral wings of the anterior lateral plate in contact with the interolateral plate (Long 19886, Carr 1991). The Incisoscutidae and Camuropiscidae are united by the following synapomorphies (from Long 19886, 56 PALAEONTOLOGY, VOLUME 38 1994): (12) spindle-shaped (" trullate ’) body form with elongate head shield; (13) cheek unit attached firmly to lateral margin of skull roof, precluding movement; (14) durophagous dentition; (15) parasphenoid having a rhombic, elongated shape. The plourdosteid group is defined by at least three other synapomorphies discussed in the text: (16) well-developed paired postocular processes; (17) the presence of an orbital autopalatine process on the suborbital bone; (18) a posterior lateral plate that forms part of the margin of the pectoral fenestra and is deeply inserted into the posterior dorsolateral plate. The deep insertion of the posterior lateral plate into the posterior dorsolateral plate was noted by Carr (1991) as a synapomorphy uniting Eastmanosteus calliaspis and the dinichthyids, in addition to four other synapomorphies, listed below. As the plourdosteid group is also well-defined by at least three synapomorphies (listed above) it is parsimonious to regard this feature as a parallelism between plourdosteids and the group Eastmanosteus calliaspis + dinich- thyids. The interrelationships of the pachyosteomorph, dinichthyid and aspinothoracid arthrodires have been discussed in depth by Carr ( 1 99 1 ) and Lelievre (1991). Synapomorphies used by Carr to define these groups are as follows. Pachyosteomorphs share: (19) loss of the paranuchal embayment on the central plate; (20) reduction of contact between the nuchal and central plates; (21) formation of lateral contact between the suborbital and preorbital plates; (22) loss of the groove for the ventral portion of the main lateral line canal on the anterior dorsolateral plate. Eastmanosteus calliaspis and the dinichthyids (as defined by Carr 1991) are united by the following synapomorphies: (23) position of the posterior margin of pineal plate posterior to orbits; (24) presence of a contact face for the posterior superognathal on the linguiform process of the suborbital plate; (25) presence of a groove for the main lateral line canal on the posterior dorsolateral plate; (26) presence of anterior and lateral cusps on the anterior superognathal. In Carr’s analysis Heintzichthys and Gorgonichthys do not share any derived features with the dinichthyids, and in the light of new descriptions of Heintzichthys the analysis of dinichthyid interrelationships by Long (1987) is now redundant. Heintzichthys and Gorgonichthys share two derived features: (27) an anterior superognathal with an enclosed lateral face; and (28) the loss of adsymphysial denticles on the inferognathal bone. The Aspinothoracidi (Stensio 1959) are defined as a monophyletic group by the following synapomorphies from Carr (1991): (29) reduction of the lateral consolidated part of the head shield; (30) the anterior shift of the junction between the preorbital, central and postorbital plates to a new position over the orbit; (31) loss of the spinal plate; (32) closure of the angle between the postorbital and otic branches of the infraorbital canal, associated with the enlargement of the orbits. Finally, the selenosteids are defined by the presence of: (33) an enlarged orbit; and the following characters defined by Lelievre et al. (1987) -(34) denticulated gnathal plates; (35) loss of dorsal process on posterior superognathal plate; and (36) the development of an ethmoid crest. This scheme leaves out many of the poorly known higher eubrachythoracids which require more complete material before their affinities can be resolved. Interrelationships of plourdosteids. The taxonomic position of Mcnamciraspis as one of the plourdosteids can be demonstrated by the presence of characters (16)-(18) above. Gardiner and Miles (1990) united the Gogo plourdosteids with Flour dosteus canadensis on the strength of several general features in their family Torosteidae, but also noted the well-developed postocular processes as a synapomorphy of the group. Well-developed postocular processes are also known in some, but not all, dinichthyids (e.g. present in Dunkleosteus terreli; Heintz 1932; absent in Eastmanosteus calliaspis based on observation of Gogo specimens). In this respect they are regarded as a convergent feature in dinichthyids, a monophyletic group, if Heintzichthys and Gorgonichthys are excluded, as defined by Carr (1991). Whether an orbital autopalatine process occurs on the suborbital plate of Plourdosteus is not yet known, although as similar specializations occur on the inner surface of the skull roof (such as the presence of a well-defined triangular depression mesial to the lateral consolidated area, the development of a hyoid process behind the postocular processes, based on observation of BMNH LONG: AUSTRALIAN ARTHRODIRE 57 PACHYOSTEOMORPHI COCCOSTEOMORPHI Aspioothoracidi C4, A PLOURDOSTEIOAE i text-fig. 18. A, cladogram of higher eubrachythoracid interrelationships (after Carr 1991). b, cladogram of plourdosteid interrelationships. Synapomorphies are listed in text. P60583), and the suborbital is of similar robust form, it is predicated that it should also be present in this genus. Within the plourdosteid group several taxa share a number of derived features with polarity assessed by comparison with the coccosteid and dinichthyid outgroups. For example, the sizes of the marginal and postorbital plates are very similar in coccosteids and dinichthyids, and this is seen also in Kimberleyichthys , with increasingly larger postorbitals and smaller marginals in other plourdosteids. Thus the presence of very large postorbital plate relative to the size of the marginal plate may be an autapomorphy of Panxiosteus , but is of variable size range in other plourdosteids. The marginal plate is strongly indented into the postorbital plate in all plourdosteids except Panxiosteus and Plourdosteus , although this character is also of dubious phylogentic value as it is variable within coccosetids and dinichthyids. The large trilobate centrals of coccosteids and dinichthyids are also present in Plourdosteus , Janiosteus, Panxiosteus and Kimberleyichthys , but the posterior lobe is reduced in Mcnamaraspis, Torosteus and Harrytoombsia , here considered to be a synapomorphy (A) uniting these taxa. The parasphenoids are known in the Gogo forms and I l 3 PACHYOSTEOMORPHI 58 PALAEONTOLOGY, VOLUME 38 Plourdosteus (Vezina 1990), but are not useful in refinement of plourdosteid relationships as they are of more or less uniform morphology. The trunk shield is known in all the taxa save Janiosteus and only partially in Panxiosteus and Kimberleyichthys. The most variable features are the shape of the posterior lateral plates and the extent of their external ornamentation. The loss of dermal ornamentation on these plates is seen in Mcnamaraspis, and to some degree in Harrytoombsia and Toros tens pulchellus, but the primitive condition of having extensive areas of dermal ornamentation is retained in Kimberleyichthys , Torosteus tuberculatus and Plourdosteus. In this respect, although the character is quite variable it lends support to the hypothesis that Mcnamaraspis , Torosteus and Harrytoombsia form an apomorphic subgroup within the Plourdosteidae. The extreme reduction of the spinal plate is an autapomorphy of Mcnamaraspis within the Plourdosteidae that is paralleled within the Coccosteidae in the similar development of a large pectoral fenestra and short spinal in Watsonosteus. Text-figure 18 summarizes the position of the plourdosteids within the higher eubrachythoracids, and shows an hypothesis of interrelationships of plourdosteids, based on the above discussion. Placoderm relationships. The presence of annular cartilages in placoderms, based on the single specimen of Mcnamaraspis , demonstrates another similarity between placoderms and elasmo- branchs, as suggested by Stensio (1963), although the exact form of the annular cartilages of Mcnamaraspis differs in many features from those of elasmobranchs. In elasmobranchs the annular cartilage is a complex folded cartilage of variable morphology that encircles both the incurrent and excurrent nares, whereas in Mcnamaraspis it is an ossified single unit with only one narial opening, and thus only borders the space for the excurrent naris. Non-ossified cartilaginous annular cartilages were probably present in all arthrodires, based on the similar morphology of the cribrosal bones and shapes of the nasal regions (where preserved). The function of the annular cartilage, to divide the incurrent and excurrent nares from the common opening of the nasal capsule, and direct the flow of water around the olfactory organ, appears to be similar in both chondrichthyans and Mcnamaraspis. The convoluted folds of bone on the inner surface of the ossified annular cartilages shows clearly the direction of flow from the incurrent naris, around the outer surface of the olfactory organ, and out via the slit in one corner of the cartilage, this being interpreted as the excurrent naris. This character lends weight to the hypothesis of placoderms being more closely related to chondrichthyans (Stensio 1963; Goujet 1984), rather than being a sister group to osteichthyans (Forey 1980; Gardiner 1984). Young (1986) reviewed the evidence for placoderm relationships and argued that there was insufficient evidence for direct comparison of osteichthyan skull roof patterns with those of placoderms, and that other listed ‘synapomophies’ of placoderms and osteichthyans were often manifestations of a single character, such as the capacity to ossify the perichondrium. Young also preferred new interpretations of placoderm morphology and concluded that placoderms were either the sister group to all gnathostomes, or the sister group to chondrichthyans. The new observations that the arthrodires sometimes possessed an annular cartilage and that the suborbitalis division of the adductor mandibulae was probably developed as in chondrichthyans lend further support to the hypothesis that placoderms and chondrichthyans are sister groups. Resolution of such higher taxonomic problems will seemingly rest on new discoveries of well- preserved placoderms from sites such as Gogo, where pertinent new anatomical information is coming to light with each season’s fieldwork. Acknowledgements . Collection of material from Gogo in 1986 was funded through Grant No. 3364-86 from the National Geographic Society, and the preparation work, carried out in the Geology Department, University of Western Australia, was funded through a Queen Elizabeth II Award, during 1986-87. For helpful discussion on Gogo arthrodires and access to collections 1 thank Dr Peter Forey, Dr Kim Dennis-Bryan, Dr Roger Miles (Natural History Museum, London), Professor Brian Gardiner (Kings College, Fondon), and Dr Gavin Young (Bureau of Mineral Resources, Canberra). I thank also Dr Philippe Janvier for information on Panxiosteus, and Dr Herve Felievre (Museum of Natural History, Paris) for discussion on arthrodires and access to material. Travel to London in 1992 to undertake research on the Gogo fishes was funded through LONG: AUSTRALIAN ARTHRODIRE 59 the exchange scheme of the Australian Academy of Sciences and the Royal Society of London. Sincere thanks to Mrs Kate Trinasjic for editorial assistance with manuscript preparation, and to Ms Kristine Brimmel, W.A. Museum, for photography of specimens and the bromides. REFERENCES bell, m. a. 1993. Convergent evolution of nasal structure in sedentary elasmobranchs. Copeia , 1993, 144-158. carr, r. h. 1991. 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Zoological Journal of the Linnean Society, 69, 43-85. 1981. A pachyosteomorph arthrodire from Gogo, Western Australia. Zoological Journal of the Linnean Society, 73, 213-258. 1982. A eubrachythoracid arthrodire with a snub-nose from Gogo, Western Australia. Zoological Journal of the Linnean Society, 75. 153-166. dennis-bryan, k. 1987. A new species of eastmanosteid arthrodire (Pisces: Placodermi) from Gogo, Western Australia. Zoological Journal of the Linnean Society , 90, 1-64. — and miles, r. s. 1983. Further eubrachythoracid arthrodires from Gogo, Western Australia. Zoological Journal of the Linnean Society, 67, 1-29. dineley, d. and loeffler, E. 1993. Biostratigraphy of the Silurian and Devonian gnathostomes of the Euramerica Province, 104-138. In long, j. a. (ed.). Palaeozoic vertebrate biostratigraphy and biogeography. Belhaven Press, London, 369 pp. edgeworth, f. h. 1935. The cranial muscles of vertebrates. Cambridge University Press, London, 493 pp. forey, p. l. 1980. 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A new dinichthyid fish (Placodermi: Arthrodira) from the Upper Devonian of Western 60 PALAEONTOLOGY, VOLUME 38 Australia, with a discussion of dinichthyid interrelationships. Records of the Western Australian Museum , 13, 515-540. long, j. A. 1988a. Late Devonian fishes from the Gogo Formation, Western Australia. National Geographic Research , 4, 436-450. — 1988/5. A new camuropiscid arthrodire (Pisces: Placodermi) from Gogo, Western Australia. Zoological Journal of the Linnean Society , 94, 233-258. — 1988c. New information on the Late Devonian arthrodire Tubonasus from Gogo, Western Australia. Memoirs of the Association of Australasian Palaeontologists , 7, 81-85. — 1990. Two new arthrodires (placoderm fishes) from the Upper Devonian Gogo Formation, Western Australia. Memoirs of the Queensland Museum , 28, 51-63. — 1991. The long history of Australian fossil fishes. 337—428. In vickers-rich, p., monaghan, j. n., baird, r. f. and rich, t. h. (eds). Vertebrate palaeontology in Australasia. Pioneer Design Studios with Monash University Publications Committee, Melbourne, 1437 pp. — 1994. A second incisoscutid arthrodire (Pisces, Placodermi) from the Late Devonian Gogo Formation, Western Australia. Alcheringa , 18, 59-69. McCOY, f. 1848. On some new fossil fish from the Carboniferous Period. Annals and Magazine of Natural History , 2. 1-10, 115-133. miles, R. s. 1971. The Holonematidae (placoderm fishes): a review based on new specimens of Holonema from the Upper Devonian of Western Australia. Philosophical Transactions of the Royal Society of London , Series B, 263. 101-234. — 1977. Dipnoan (lungfish) skulls from the Upper Devonian of Western Australia. Zoological Journal of the Linnean Society , 61, 1-328. and dennis, k. 1979. A primitive eubrachythoracid arthrodire from Gogo, Western Australia. Zoological Journal of the Linnean Society, 66, 31-62. and westoll, t. s. 1968. The placoderm fish Coccosteus cuspidatus Miller ex Agassiz from the Middle Old Red Sandstone of Scotland. Part 1 . Descriptive morphology. Transactions of the Royal Society of Edinburgh, 67, 373-476. — and young, G. c. 1977. Placoderm interrelationships reconsidered in the light of new ptyctodontids from Gogo, Western Australia. In Andrews, s. m., miles, r. s. and walker, a. d. (eds). Problems in vertebrate evolution. Linnean Society Symposium Series 4, 123-198. stensio, e. a. 1948. On the Placodermi of the Upper Devonian of East Greenland. 2. Antiarchi: subfamily Bothriolepinae. With an attempt at a revision of the previous described species of that family. Meddelelser om Gronland 139, Palaeozoologica Groenlandica, 2, 1-622. — 1959. On the pectoral fin and shoulder girdle of the arthrodires. Kungliga Svenska Vetenskapakademiens Handlingar , 8. 1-229. — 1963. Anatomical studies on the arthrodiran head. Part 1. Preface, geological and geographical distribution, the organisation of the arthrodires, the anatomy of the head in the Dolichothoraci, Coccosteomorphi and Pachyosteomorphi. Taxonomic appendix. Kungligar Svenska Vetenskapakadamiens Handlingar , 4 (9) 2, 1-419. vezina, d. 1986. Les plaques gnathales de Plourdosteus canadensis (Placodermi, Arthrodira) du Devonien superieur du Quebec (Canada): remarques sur la crosissance dentaire et la mecanique masticatrice. Bulletin de la Museum National d Histoire Naturelle, Paris, 4 ser., 8, 367-391. 1990. Les Plourdosteidae fam. nov. (Placodermi, Arthrodira) et leurs relations phyletiques au sein des Brachythoraci. Canadian Journal of Earth Sciences, 27, 677-683. wang jun-qing. 1991. A fossil Arthrodira from Panxi, Yunnan. Vertebrata Palasiatica , 29, 264—275. woodward, A. s. 1891. Catalogue of the fossil fishes in the British Museum (Natural History), 2. British Museum (Natural History), London, 567 pp., 16 pis. — 1986. The relationships of the placoderm fishes. Zoological Journal of the Linnean Society, London, 88, 1-57. young, G. c. 1979. New information on the structure and relationships of Buchanosteus (Placodermi: Euarthrodira) from the Early Devonian of New South Wales. Zoological Journal of the Linnean Society, 66, 309-352. — 1984. Reconstruction of the jaws and braincase in the Devonian placoderm fish Bothriolepis. Palaeontology, 27, 625-661. JOHN A. LONG Western Australian Museum Francis St., Perth Western Australia 6000 Typescript received 6 December 1993 Revised typescript received 24 February 1994 LONG: AUSTRALIAN ARTHRODIRE 61 ABBREVIATIONS USED IN FIGURES aal anterior apronic lamina of the M marginal plate interolateral plate MD median dorsal plate acc.PN accessory postnasal bone Mk Meckel’s cartilage add.mand adductor mandibulae muscle Mm mentomeckelian bone ADL anterior dorsolateral plate n notch AL anterior lateral plate n.prof.V profundus nerve (V) AMV anterior median ventral plate Nu nuchal plate ant.s.a. anterior smooth area of ventral oa.AVL area overlapped by AVL lamina of interolateral plate occ occipital sensory-line canal groove ar. Qd articulation area of quadrate op. Ill opercular muscle Art articular bone orb orbit ASG anterior superognathal P pineal plate Aut autopalatine bone pap occipital para-articular process AVL anterior ventrolateral plate PDL posterior dorsolateral plate C central plate Pi pineal depression and fossae cav cavity of spinal plate PL posterolateral plate ch.pr.sv. channel for dorsal aspect of pl.pr posterolateral process on para- supravagal sphenoid Chy ceratohyal PM postmarginal plate cr.pr carinal process pmc postmarginal sensory-line canal CSC central sensory canal groove d.end.e external opening of endolympha- PMV posterior median ventral plate tic duct PN postnasal plate dep depression PNu paranuchal plate dp.m.cu cucullaris depression PP posterior pit-line groove d.prp dermal preorbital process of skull- p.pr posterior process of nuchal plate roof formed by preorbital plate pr orbital autopalatine process on Ehy epihyal or opercular cartilage suborbital plate exc.n excurrent naris pr.dt detent process of quadrate fb.hy paired buccohypophysial foramen p.rec posterior rectus muscle f.pec pectoral fenestra pr.hy hyoid process on visceral surface gr 1 groove 1 of skull roof gr2 groove 2 PrO preorbital plate gr.a.com transverse ventral groove PSG posterior supergnathal gr. SM groove on suborbital plate for PSO postsuborbital plate submarginal plate psoc postsuborbital sensory groove Hym hyomandibular PtO postorbital plate hy m hyoideus muscle pt.o.pr ventral postocular process hypv foramen for hypophysial vein pt.u paired pits on visceral surface of ifo infraorbital branch of sensory-like nuchal plate canal groove Qd quadrate bone IG inferognathal R rostral plate IL interolateral plate r.ext.hyVII ramus hyomandibularis VII nerve inc.n incurrent naris ri oblique premedian ridge of head ioc.pt supraorbital branch of infraorbital shield canal ril, ri2 ri3 ridges on visceral surface of ioc.sb supraorbital branch of infraorbital annular cartilage canal r.pr depression on visceral surface of lc main lateral line canal groove rostral plate lcp lateral consolidated area of skull sh prehypophysial shelf on para- roof sphenoid 1pm us levator palatoquadrini muscle SM submarginal plate laf lateral articular fossa SO suborbital plate ling.pr linguiform process of suborbital soa subobstantic region of head shield plate soc supraorbital sensory canal 62 PALAEONTOLOGY, VOLUME 38 /sore supraoral sensory canal Sp spinal plate spir spiracular recess subl.pr sublingual process suo.v supraorbital vault sup.ob superior obliquus muscle th.n nuchal thickening th.pre pre-endolymphatic thickening tri triangular depression on visceral surface of skull roof vsl ventral sensory pit-line groove DECAPODS IN AMMONITE SHELLS: EXAMPLES OF I NQU 1 LI N ISM FROM THE JURASSIC OF ENGLAND AND GERMANY by R. fraaye and M. JAGER Abstract. Inquilinism is that association in which one organism lives within another, using the host as a place of refuge. Four specimens are described from the Jurassic of England and Germany which illustrates ammonite inquilinism by decapods. The inquiline use of ammonite shells in the geological record, and its ecological and taphonomical implications are discussed. Lobsters are heavily armoured decapod crustaceans that generally inhabit holes and crevices of marine rocky and coralline environments. During Mesozoic times ammonites not only provided a food source for decapod crustaceans and other benthic organisms, they were also perfect places of shelter on otherwise fine-grained sea floors. Several fossil groups have been found preserved inside ammonite body chambers. This mode of preservation is referred to as inquilinism , a term used to describe those associations in which one animal lives within another, using the host (before or after death) as a place of refuge. Although this mode of preservation has been recorded in the literature, its taphonomic implications have virtually been neglected. A specimen of the erymid lobster Palaeastacusl sp. found in the body chamber of a harpoceratid ammonite from the Lower Toarcian Posidonia Shales of Dotternhausen, southern Germany, is described and illustrated herein. In addition, three specimens of the lobster Eryma dutertrei Sauvage, 1891, preserved in the body chambers of large perisphinctid ammonites are recorded from the Portland Limestone Formation (Portlandian) of southern England. The poor record of inquiline preservation of organisms in ammonite body chambers is probably due to the fact that they have not received enough attention rather than because they are rare. The occurrence of ammonite inquilinism in the Posidonia Shales of southern Germany is incompatible with a stagnant basin model, but agrees well with Seilacher’s (1990, pp. 123, 126-128) modified model: euxinic stagnant water conditions for most of the time, episodically interrupted by turbidity currents caused by storms. Whereas benthic life was impossible for most organisms during times of stagnant conditions, episodical storm-events brought oxygen down to the sea-floor and made life possible for some months or so. A co-evolutionary relationship between ammonites and the inhabitants of their empty shells is postulated. AMMONITE BODY CHAMBER CONTENTS In comparison with many studies of ammonite taphonomy (e.g. Roll 1935; Lehmann 1976; Seilacher et al. 1976; Brenner and Seilacher 1978; Seilacher 1982a, 19826; Tanabe et al. 1984; Maeda 1987, 1991 ; Neugebauer and Hudson 1987), few studies have dealt with the contents of body chambers. Three types of preservation have been distinguished so far. (1) Ernst (1967) and Maeda (1991) record post-mortem accumulations of echinoids and small ammonite shells transported into large ammonites. (2) The preservation of in situ ammonite remains. Fossil jaws preserved in situ in diagenetically compressed ammonites have been reported (e.g. Lehmann 1976; Morton 1981; Seilacher 1982a; Tanabe et al. 1984). Fossil crop/stomach remains of ammonites are rare in most deposits and | Palaeontology, Vol. 38, Part 1, 1995, pp. 63-75. | © The Palaeontological Association 64 PALAEONTOLOGY, VOLUME 38 preserved only in especially favourable environments. Nixon (1988, p. 650) lists only four examples of in situ crop/stomach remains in Jurassic ammonites. Riegraf et al. (1984, pi. 1, fig. 7) found nearly twenty specimens with crop and/or stomach remains in the Lower Toarcian Posidonia Shales of south west Germany. Recent finds of several compressed harpoceratid ammonites with preserved crop/stomach contents in the Toarcian black shales of southern Germany provide new data on their diet (Jager 1991; Jager and Fraaye work in progress). These new observations confirm the convictions of Nixon (1988) and Tshudy et al. ( 1989) that some, if not all, ammonites were potential predators and/or scavengers of decapod crustaceans. (3) Inquiline preservation. The fossil record of marine Jurassic sediments indicates that enormous numbers of empty ammonite conchs littered former sea floors. These ammonites supplied food for (nekto)benthic scavengers. There is an extensive literature on shell fracturing tentatively ascribed to crustaceans (Boucot 1990, p. 168). Examples of fractures of Jurassic ammonites presumed to have been produced by decapod crustaceans were recorded by, amongst others. Roll (1935), Seilacher and Wiesenauer (1978), Riegraf et at. (1984) and Jager (1991). Lehmann (1976, p. 1 35) illustrated the lobster Eryon breaking up an ammonite conch with its chelae in search of soft parts. Amongst the favourite prey animals of recent and fossil cephalopods are decapod crustaceans (Nixon 1988; Jager and Fraaye work in progress). Empty ammonite shells have the potential to shelter the small (nekto)benthic animals common on the soft Jurassic sea floors, and as such Jurassic decapod crustaceans may have been, at least in part, dependent on ammonites for food and shelter. A review of the literature illustrates many examples of inquiline preservation. A fine example is that of Stewart (1990), who recorded several fish genera found preserved in Upper Cretaceous inoceramid bivalves. An example of probably inhabitation of a Cenomanian crab (Diaulax oweni Bell in Dixon, 1850) with an ammonite was mentioned by Wright and Collins (1972, pi. 10, figs. 1 a~b). Unfortunately, the preparation of the crab has destroyed the in situ preservation (J. S. H. Collins, pers. comm.). A second example of a decapod crustacean preserved inside an ammonite body chamber was recorded from the Upper Cretaceous Chalk of northern Germany by Ernst (1967). A concretion containing a body chamber of a scaphitid ammonite filled with faecal pellets illustrated by Bishop (1981, p. 390, fig. K) is another example of Cretaceous ammonite inquilinism. The first example of ammonite inquilinism from the Jurassic was recorded by Krause (1891, pi. 12, figs 1-2), who described a very well-preserved lobster within a large ammonite of the genus Gravesia from the Upper Jurassic (Tithonian) of Germany. Another example of Jurassic ammonite inhabitation was described briefly by Jager (1990) from the Toarcian Posidonia Shales of Dotternhausen, southern Germany. Inside two compressed body chambers of harpoceratid ammonites fishes assignable to Pholidophorus were found. A further four specimens illustrating Jurassic ammonite inquilinism by decapod crustaceans, in three different types of preservation are described below. AMMONITE INQUILINISM IN THE LOWER TOARCIAN POSIDONIA SHALE Geological setting The bituminous Lower Toarcian Posidonia Shale is well-known for the excellent preservation of marine reptile, fish and crinoid skeletons found within it (Hauflf and Hauflf 1981). The facies is widespread not only in southern Germany, but also in northern Germany, England, France and Luxemburg (see map in Riegraf et al. 1984, p. 26). In Dotternhausen near Balingen, 70 km south- south-west of Stuttgart and 70 km south-west of Holzmaden, the Posidonia Shale (which is around 9 m thick here) is quarried by the Rohrbach Zement factory to produce cement. In Dotternhausen, the range of fossil species and kinds of preservation is nearly the same as at Holzmaden. The Posidonia Shale is a bituminous shale, compressed to around 5 per cent, of its original thickness, although limestone layers and concretions display little or no compression. The high content of pyrite and of organic hydrocarbon, the fine lamination of the sediment and the poverty of autochtonous benthos are strong arguments for stagnant water conditions during deposition of FRA A YE AND JAGER: DECAPODS IN AMMONITES 65 text-fig. 1. Stratigraphical profile, biostratigraphy and lithostratigraphical marker horizons of the Lower Toarcian of Dotternhausen (after Riegraf 1985, text- fig. 4), with the stratigraphical position of Pala- easlacusl sp. (RZC 0062). thouarsense fibulatum Nagelkalk- S banke region of fine ammonites Ni commune 8 Inoceramen-'* bank falciferum Oberer Stem-* Steinplatte -► elegans Unterer Stein Op exarafum elegantulum Fleins "* semicelatum clevelandicum pal turn 1m the Posidonia Shale. From the uppermost part of the Semicelatum Subzone till the lower half of the Fibulatum Subzone, benthic life was totally or nearly totally absent in most horizons, although an impoverished fauna is found in several horizons (Riegraf et al. 1984). The layers around the ‘ Inoceramenbank ’ at the boundary of the Falciferum/Commune Subzone, represent such horizons with a very impoverished, but not totally absent benthic fauna; some foraminiferan and ostracod species are present (Riegraf 1985, p. 45, fig. 22). In many layers of the Posidonia Shale, epizoans (mostly serpulids and oysters) often are fixed to the ammonite shells and, as the shell is compressed, the epizoans on the opposite side are also visible being distinctly pressed into the periostracum (Seilacher 1982a). From such specimens Kauffman (1978) developed his ‘benthic island’ model but, according to the results of Riegraf et al. (1984), Riegraf (1985) and Seilacher (1990), these findings seem to represent ‘islands in time’ (periods of sufficient oxygen content at the sea-floor) rather than islands in space. Many details of ammonite preservation in the Posidonia Shale have been published by Seilacher et al. (1976) and Riegraf et al. (1984, p. 52). Usually, the phragmocone is compressed to a paper- thin layer, the living chamber often compressed to a thickness of 1-2 mm. The calcareous shell layers are normally dissolved (this is the reason why septa are visible in few specimens only), but the periostracum is beautifully preserved as a golden brown leaf. Some shells are broken into disarticulated pieces (probably by the action of decapods or fish), but in most specimens the whole periostracum is preserved (though often with cracks, formed during compression) including the delicate rostrum of the apertures of Harpoceras and Hildoceras. The excellent preservation of many fossils points to rather low water energy, though current- alignment was recognized by Brenner and Seilacher (1978). The siphuncle is often preserved as a whitish band, and in an estimated 25 per cent, of Harpoceras and Hildoceras specimens’ aptychi are still present in the living chamber. Preservation of presumed crop and/or stomach contents is not uncommon (Riegraf et al. 1984; Jager and Fraaye, new data). Ammonites are present in every horizon of the 9 metre thick Posidonia Shale facies in Dotternhausen. In a section a few decimetres thick in the lowermost part of the Commune Subzone, 66 PALAEONTOLOGY, VOLUME 38 between the ‘Inoceramenbank’ and the 'Nagelkalkbanke' (Text-fig. 1), complete specimens are relatively easy to extract because of the fissility of the shale. Thus in this part of the section ammonites are intensively sampled. Ammonite taxa present (from most to less frequent) are Dacty/ioceras commune , Harpoceras falciferum (diameter of adult macroconchs normally 200-300 mm), Hiodoceras ex gr. douvillei/ sublevisioni, Phylloceras heterophyllum , Phymatoceras cf. escheri. Material Decapod crustaceans are rare in the Posidonia Shale except for chelae (propodus plus dactylus) of the swimmer Uncina posidoniae Quenstedt 1850 in the 'Fleins' layer and remains of Coleial sp. in the living chamber of ammonites (Jager and Fraaye, new data) in the lower part of the Commune Subzone. Other remains of decapod crustaceans are rare in the Posidonia Shale of southern Germany, but are found in several horizons. They were described by Beurlen (1928, 1930, 1944), Kuhn ( 1952) and Haufif and Hauff (1981) and include well-preserved, complete specimens of Uncina posidoniae , eight species of Proeryon , two Coleia species, one Glyphea, one Palaeopagurus (as Erymastacusl ), one stomatopode? and one macrure. It is not clear yet how Proeryon , which according to its dorsoventrally compressed shape is a typical bottom-dweller, could have managed to live during anoxic conditions, although it may have lived upon floating trunks or have been washed in, although one would expect poorer preservation. A new specimen (Rohrbach Zement Collection no. 0062) illustrated in Text-figures 2-4 has been determined as Palaeastacus ? sp. (R. Forster, pers. comm.). According to Forster (1966, p. 126) Palaeastacus Bell in Dixon, 1850 is a genus of the family Erymidae. The stratigraphically lowest examples of isolated chelae of Palaeastacus are from the lower Sinemurian, while remains of the carapace and more or less complete specimens range from the Upper Jurassic to the Upper Cretaceous. The new specimen is lying inside the anterior half of the body chamber of an adult macroconch of Harpoceras falciferum (Text-fig. 2). The ammonite shell diameter is approximately 270 mm. Though the living chamber is compressed to 1 mm, it is obvious that the crustacean really lies inside the ammonite shell, not at a level above or below. The aptychi are missing. Remains of the siphuncle are preserved. On the ammonite shell at least five oysters (oy.) and four serpulids (serp.) are fixed, probably on both sides of the ammonite, but this is not quite clear. The anterior part of the crustacean is directed towards the aperture of the ammonite, the chelae lying at least 40 mm behind the aperture (which is not preserved). The telson is directed towards the phragmocone. Around the crustacean, and nearly filling the ammonite body chamber, are areas which seem to be composed of masses of elliptical to subspherical bodies. These have an approximate maximum diameter of 1 -5-2-0 mm, are compressed and indistinct, and are here interpreted as crustacean coprolites. Although the Palaeastacus ? is almost complete (remains of the chelae, feet, abdomen and telson are visible) and the parts of the skeleton are lying close together, the disarticulation and compression of the skeletal parts makes proper description difficult. The anterior half of the decapod seems to be composed of two chelipeds and a few other fragments, most of them probably fragments of thoracopods. Nothing distinct is visible of the carapace which perhaps is lying underneath the chelipeds ('underneath' is applied according to the present state of the shale slab). The slab was not found in situ , and it is therefore unknown which is the upper and which the lower surface. In both chelipids, dactylus (d), propodus (p) and carpus (c) are lying close together, with only minute traces of disarticulation. One merus (m) is present. The two chelae are lying nearly parallel to each other and close together, with the dactyli touching each other. The chelae are covered with very strong spines, especially at the border. The carpi are triangular and spiny, but the spines are not quite as strong as in the propodi. The meri of the chelipeds are not properly distinguished from the leg fragments (1). Only one slender rectangular remnant seems to be a merus, but it is not clear to which of the chelipeds it belongs. Between the anterior and the posterior half of the crustacean there is an area, approximately 1 5 mm long, where only few skeletal remains are FRAAYE AND JAGER: DECAPODS IN AMMONITES 67 text-fig. 2. Palaeastacus ? sp. RZC 0062; preserved in body chamber of Harpoceras falcifenim ; large areas with elliptical coprolites indicated with black arrows; Posidonia Shales, Lower Toarcian; Dotternhausen, Germany; x 0 88. preserved. In the abdomen, five (or perhaps six) of the somites (s) are articulated to each other and clearly visible (Text-fig. 3). Together they are nearly 50 mm long. The telson is disarticulated from the abdomen. After 25 mm of free space, only one large plate of the telson (t) can be identified. 68 PALAEONTOLOGY, VOLUME 38 text-fig. 3. Palaeastacusl sp. RZC 0062; preserved in body chamber of Harpoceras falciferum, showing details of the spiny chelae and the abdomen; Posidonia Shales, Lower Toarcian; Dotternhausen, Germany; x 1-5. Ecological interpretation According to Forster (1966, p. 153) Erymidae preferred muddy soft-bottoms in relatively shallow water near the coast. They probably dug themselves into the mud or hid under stones for resting, for moulting or for protection. Erymidae were probably carnivorous or carrion feeders. Perhaps the fractures in ammonite body chambers, which sometimes look as if they were made by a ‘tin-opener’ (Riegraf et at. 1984, p. 58, fig. 15; Jager 1991, figs 3-4), were made by the strong chelae of Palaeastacusl. However, Palaeastacusl is too rare to have been responsible for all such ammonite destruction. The Palaeastacusl is too large and too complete to be the crop and/or stomach contents of the ammonite (as are many specimens of small and disarticulated Coleial sp. to be described in a later paper (Jager and Fraaye, new data), their interpretation as a moulted skeleton in Jager (1991, p. 33) probably being wrong). On the other hand the crustacean was not large enough to be able to walk around while within the ammonite shell in the manner of a hermit crab, which, moreover, would have a less calcified abdomen. Though the skeleton of Palaeastacusl should have been sheltered inside the ammonite shell against destruction, disarticulation is more distinct than in specimens found loosely in the sediment. This was the main reason why Jager ( 1991, p. 33) interpreted the Palaeastacusl as a moult. In fossil crustaceans, moulted skeletons are often recognizable by the splitting of the carapace and by an approximate right angle between the longitudinal axes of the carapace and the abdomen (Forster 1966, p. 154). In the Palaeastacusl , however, the carapace is poorly visible, and the right angle may be due to compression. Thus, it cannot be decided if it is a moult or a dead crustacean. The area FRAAYE AND JAGER: DECAPODS IN AMMONITES 69 text-fig. 4. Palaeastacusl sp. RZC 0062; preserved in body chamber of Harpoceras falciferum; outline of skeletal elements partly idealized, because some of the outlines are hardly visible in the original; for explanation of abbreviations see text; Posidonia Shales, Lower Toarcian; Dotternhausen, Germany; x 0-33. with only few skeletal remains between the anterior half and the abdomen is an argument for breakage between carapace and abdomen during moulting. Interpreting the small spherical structures as decapod coprolites, the animal must have lived for a relatively long time inside the body chamber (Text-fig. 4). This means that anoxic conditions at the sea-floor must have been interrupted for this period. AMMONITE INQUILINISM IN THE PORTLAND LIMESTONE FORMATION Geological setting The Isle of Portland is a natural peninsula about 6 km long, near Weymouth, on the southern coast of England. The specimens described below were collected in the ARC Broadcraft Quarry, north- east of the village of Easton during a one-week field trip in March 1990. The Portland Group consists of a lower Portland Sand Formation and an upper Portland Limestone Formation. The Portland Sand Formation grades down into the black shale sequence of the Kimmeridge Clay. The Portland Limestone Formation is overlain by evaporitic limestone-marl sequence known as the Purbeck Group. The Portland Group represents a regressive sequence (Townson 1975). The Portland Sand Formation consists mainly of clay-, silt- and sandstones, accumulated in a marine environment below wave base. The Portland Limestone Formation starts with a 3 m thick Basal Shell Bed. This bed contains a rich biota of mainly bivalves, gastropods and serpulids. The upper 25 m of the Portland Limestone Formation consists of cherty limestones deposited in an open shelf environment that pass up into shallow-water cross-bedded oolitic grainstones. Some levels within the cherty part of the Portland Limestone Formation are rich in large perisphinctid ammonites whose diameter often exceeds 0-5 m. The grainstones yield numerous 70 PALAEONTOLOGY, VOLUME 38 oncolitic algae, bivalves and gastropods. The lower Purbeck Group finally grades through stromatolitic levels with silicified tree trunks into fossil soils and lagoonal limestones. Two specimens described below were collected from the lower part (Galbcmites (Kerberites) kerberus Zone) of the Portland Limestone Formation. The environment was thought by Townson (1975) to have been moderately deep and tranquil marine. A third specimen (Collection Geo Centrum Brabant, no. MAB k. 0049) of a Glaucolithites sp. with two partially preserved chelae of Eryma sp. coincident with the body chamber was discovered in the Portland Clay Member, a few metres below the Basal Shell Bed, forming the topmost Portland Sand Formation ( Glaucolithites glaucolithus Zone). Material The first specimen (Collection Geo Centrum Brabant, no. MAB K0047) was found in a fragment of an ammonite body chamber 250 mm maximum length, 1 50 mm maximum width. The preservation of the segments of the lobster is very good. There are no signs of post-mortem transport and only a few compactional cracks are present. The axis of the lobster body runs parallel with the ammonite coiling (Text-figs 5-6). The lobster is embedded within an elongate concretion of slightly banded, light grey chert. This concretion in its turn runs parallel with the outline of the body chamber. Observations and experimental data from modern marine environments, and from the common Holocene subfossil decapods from concretions along the coasts of south-eastern Asia and northern text-fig. 5. Eryma dutertrei Sauvage. MAB K0047; embedded within chert concretion in perisphinctid ammonite body chamber; Portland Limestone Formation, Portlandian; Broadcraft Quarry, Portland, England; x0-8. FRAAYE AND JAGER: DECAPODS IN AMMONITES 71 text-fig. 6. Eryma dutertrei Sauvage. MAB K0047; schematic sketch showing chert concretion and preservation of decapod segments in perisphinctid ammonite body chamber; Portland Limestone For- mation, Portlandian; Broadcraft Quarry, Portland, England; x 05. text-fig. 7. Eryma dutertrei Sauvage. MAB K0047; schematic sketch of cross section of perisphinctid body chamber, showing position of chert concretion, bioclasts and epibionts; Portland Limestone For- mation, Portlandian; Broadcraft Quarry, Portland, England; xO-5. Australia indicate that concretions may form very rapidly around decaying decapod crustaceans (Schafer 1951 ; Moore 1969; Plotnick 1986). The process involves locally increased pH, a result of ammonia produced during organic decomposition, and bacterial sulphate reduction. In relatively pure, fine-grained carbonate rocks, chert nodules may develop in or around fossils or burrows, suggesting a possible association with organic micro-environments. The aggregation of silica into nodules apparently takes place during recrystallization of biogenic silica (often sponge spicules). Articulated skeletal remains indicate that the formation of chert concretions was associated with anaerobic decay of organic matter immediately following burial. The field and laboratory studies of Schafer (1951) and Plotnick (1986) indicate that the decay of soft tissues and the reduction in cuticule rigidity led to the loss of physical integrity of decapod specimens between a few weeks and several months. Size and shape of concretions are strongly influenced by the type of organic remains they grow in or around (Bishop 1981). The large carapace is covered with fine granules, the density of which decreases towards the rostrum. Unfortunately, most of the cephalic portion is covered by the right cheliped obscuring the cervical, gastro-orbital and hepatic regions. The characteristic intestinal margin is well-preserved. The long branchiocardiac and short postcervical grooves run parallel and are slightly disturbed by compressional cracks. Of the right chela, only the ischium, merus and proximal part of the carpus are visible. The chela is covered with very coarse granules; their density decreases laterally. Some large tubercles appear on the lateral part of the merus and proximal part of the carpus. The long finely granulated and denticulate movable and fixed fingers of both chelipeds are equal in size. Other thoracopods are only partially visible in the chert concretion. The abdomen consists of four more or less equal-sized somites between the considerably smaller first and sixth somites. The posterior margin of each somite overlaps the anterior margin of the adjacent one. The somites are covered with coarsely spaced granules and some tubercles. The tuberculation increases in strength 72 PALAEONTOLOGY, VOLUME 38 posteriorly and extends to the telson. The relatively long uropods are faintly striated. The few preserved cuticule fragments show tubercles of various sizes. The ammonite has only part of its body chamber preserved as a composite mould on which several oysters are attached. The size of the epibiont oysters increases towards the venter of the ammonite (Text-fig. 7). Its body chamber is filled with a bioclastic wackestone, the majority of the bioclasts being small bivalves and serpulids. The body chamber contains the lobster described preserved within a chert concretion. The second specimen (Collection Geo Centrum Brabant, no. MAB K0048) was found in an almost complete perisphinctid ammonite 380 mm in diameter. The incomplete carapace of the crustacean is split along the dorsal midline. Only the right chela and a few disassociated segments of the abdomen and pereiopods are present (Text-fig. 8). The same displacement and splitting of the text-fig. 8. Eryma dutertrei Sauvage. MAB K0048; schematic sketch showing molting remains in ammonite body chamber; Portland Limestone Formation, Portlandian; Broadcraft Quarry, Port- land, England; x 1. carapace are seen for example, in the Jurassic Glyphea and the Cretaceous Hoploparia and Onopareia and are recognized as indicative of a moulting position. The gastric and antennal regions of the carapace are missing because it was fractured along the cervical groove. The branchiocardiac, postcervical and inferior grooves are distinct and match the description of Eryma dutertrei Sauvage, 1891 in Forster’s (1966, p. 117) revision of the erymids. Except for the chert concretion, the infilling of the ammonite body chamber is the same as specimen MAB k0047 except that in this case several little gastropods and some plant remains are also present. The intense upper-side erosion and covering with oysters and other bivalves show that the ammonite acted as a benthic ’island’ for a relatively long time. DISCUSSION If ammonite inquilinism was a common feature, bite traces on ammonite shells produced by, for example, sharks and reptiles are not necessarily the result of hunting on living ammonites. It is possible that these predators may have hunted the animals which lived, hid or moulted within empty ammonite conchs. By grabbing and shaking, the predators could have forced these inhabitants out of their refuge. Several groups of organisms develop extreme adaptations to specialized habitats (Boucot 1990). It is likely that, in addition to decapod crustaceans, other (nekto)benthic groups (e.g. fishes, dwarf FRA A YE AND JAGER: DECAPODS IN AMMONITES 73 ammonites) adapted an ammonite inquiline mode of life, simply because on offshore fine-grained Mesozoic sea floors there were no other suitable hiding places. We therefore concur with Ernst (1967) and Matsumoto and Nihongi (1979), who respectively explained certain accumulations of thin shelled echinoias and small heteromorph ammonites in larger ammonites as in situ cave dwellers. Some examples of post-mortem accumulations recorded by Maeda ( 1991 ) could also have been ammonite inhabitants. Post-mortem drift is not consistent with the fact that in the same sediments the jaw apparatus of the ammonites are comparatively often preserved within the body chambers (Hirano 1991). Maeda (1991) also recorded considerable amounts of plant remains, disarticulated crinoid stalks and inoceramid shells to have accumulated in body chambers of large ammonites. Lehmann (1975), Lehmann and Weischat (1973) and Riegraf et al. (1984) noted accumulations of crinoid ossicles and inoceramid shells within Jurassic ammonites. There are several modern examples of crustaceans which store pieces of animal material and seagrass leaves in their burrows as bacterial horticultures (Bromley 1990). Were ammonites ideal dining rooms for decapod crustaceans or did the decapods have their own horticultures, or both? And were these horticultures plundered by other (nekto)benthic animals such as fishes and echinoids? 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Journal of Paleontology, 63, 621-626. wright, c. w. and collins, j. s. h. 1972. British Cretaceous Crabs. Monograph of the Palaeontographical Society, 126, 1 114. RENE FRAAYE Geo Centrum Brabant St. Lambertusweg 4 5291 NB Boxtel The Netherlands Typescript received 24 February 1993 Revised typescript received 20 November 1993 MANFRED JAGER Rohrbach Zement D-7466 Dotternhausen Germany J DISCONTINUITY IN THE PLIO-PLEISTOCENE EURASIAN WATER VOLE LINEAGE by D. NERAUDEAU, L. VIRIOT, J. CHALINE, B. LAURIN Cliul T. V AN KOLFSCHOTEN Abstract. A supposed lineage extending from Mimomys occitanus - M. ostramosensis to Arvicola terrestris through at least seven species has been widely accepted. The early part of the lineage, from M. occitanus to M. ostramosensis , has been shown mathematically to be a good example of phyletic gradualism. But the transition from M. ostramosensis to M. savini is somewhat hypothetical. A new morphological analysis of the type population of M. savini (West Runton, England) has demonstrated that this species cannot be derived from M. ostramosensis , but must stem from another parent species, possibly M. coelodus or Cromeromys irtyshensis. There are, in fact, two distinct lineages characterized by different line a sinuosa and occlusal morphologies, the first corresponding to M. occitanus - M . ostramosensis, and the second to Cromeromys savini - A. terrestris. Phyletic gradualism is demonstrated by a new graphic presentation of both lineages. This changed phyletic relationship has no biostratigraphical repercussions. Voles (Arvicolidae, Rodentia) figure abundantly in the Plio-Pleistocene fossil record (Chaline 1972, 1987). Among the 140 lineages identified for the period, the Eurasian water vole lineage is of major evolutionary and biostratigraphical interest. This lineage extends from Mimomys occitanus - M. polonicus - M. pliocaenicus - M. ostramosensis - M. savini to Arvicola terrestris. The part of the lineage that runs from M. occitanus to M. ostramosensis has been used for quantitative testing of phyletic gradualism on a European scale (Chaline and Laurin 1986; Viriot et al. 1990; Chaline et al. 1993). The only remaining hypothetical aspect of the lineage is the transition from M. ostramosensis to M. savini (Viriot 1989; Kolfschoten 1990«, 1993), in part because of the sparse fossil populations. Although the transition seemed plausible in a stratophenetic approach to the development of the lineage, no quantitative test had been made. The purpose of this paper is to carry out this quantitative test, focusing on an abundant and previously unstudied population of Mimomys savini from the type locality. MATERIAL To test the transition between the Mimomys occitanus - M. ostramosensis lineage and M. savini , the following species and populations have been subjected to morphometric analyses: Mimomys occitanus occitanus from Sete (Herault, France); Mimomys occitanus hajnackensis from Wolfersheim (Germany); Mimomys polonicus from Rebielice Krolewski 1 and 2 (Poland); Mimomys polonicus from Commenailles (Bresse Valley, France); Mimomys ostramosensis from Montousse 5 (Pyrenees, France); Mimomys savini from West Runton, Upper Freshwater Bed (England); Mimomys savini from Kortchevo (Russia). THE M. OCCITANUS - M . OSTRAMOSENSIS CH RONOMORPHOCLIN E The water vole lineage (Text-fig. 1) was progressively pieced together as new fossil populations were discovered (Flinton 1926; Heim de Balsac and Guislain 1955; Chaline and Michaux 1969, 1974, 1975;Kretzoi 1969; Chaline 1974, 1984;Janossy and Meulen 1975). The first species to be described [Palaeontology, Vol. 38, Part 1, 1995, pp. 77-85.) © The Palaeontological Association 78 PALAEONTOLOGY, VOLUME 38 Time (M.y.) text-fig. 1 Phyletic gradualism in the Mimomys occitanus - M. ostramosensis lineage, showing the major evolutionary trends: increased hypsodonty related to a higher tinea sinuosa\ appearance of cementum in the re-entrant angles, and disappearance of the enamel islet. Continuous growth only occurs between Mimomys savini and Arvicola terrestris cantiana (after Chaline 1987, modified). was M. pliocaenicus (Forsyth Major 1902) from Castelfranco in Italy, followed by M. savini (Hinton 1926) from West Runton in England and M. stehlini (Kormos 1931). The lineage was completed by the description of M. occitanus (Thaler 1955), M. polonicus (Kowalski 1960), and M. si/asensis (Janossy 1974), which was shown to be synonymous with M. occitanus by Chaline and Laurin (1986). Janossy and Meulen (1975) described an evolved stage of M. pliocaenicus under the name of M. ostramosensis. Finally, Weerd (1978) rounded off the lineage by describing a primitive M. occitanus as M. davakosi. Quantitative analysis, restricted to the M. occitanus - M. ostramosensis part of the lineage, using morphometic methods (Chaline and Laurin 1986) showed that evolution involved ( 1 ) morphological NERAUDEAU ET A L.\ PLIO-PLEISTOCENE WATER VOLES 79 text-fig. 2. Nine occlusal measurements (A) and six jugal measurements (B) of the Mimomys first lower molar used for multivariate analysis. changes in the occlusal surface of the first lower molar ( Mimomys ridge, enamel islet), (2) appearance of cementum in the re-entrant angles, and, above all, (3) a rapid, though irregular, increase in the rate of hypsodonty conveyed by the increased height of the linea sinuosa on the crown sides and (4) by the non-appearance of roots (Text-fig. 1). Digital image processing applied to area quantification (Viriot et al. 1990), likewise confined to the M. occitanus - M. ostramosensis part of the lineage, showed that while the anterior part of the occlusal surface was becoming simpler the posterior part was increasing in complexity. The lineage M. occitanus - M. ostramosensis is a chronomorphocline that stretches from Western Europe (Spain and England) to Siberia and even China (Zheng and Li 1986; unpublished observations by Chaline at the Beijing Institute of Palaeontology and Palaeoanthropology). This vast range means that the lineage is a yardstick in Eurasia for establishing a high-resolution biostratigraphy of the Pliocene and Lower Pleistocene (Chaline 1989; Chaline and Farjanel 1990). THE MIMOMYS SA VIN I - A RVICO LA TERRESTRIS LINEAGE Hinton ( 1926) first suggested the transition from M. savini to Arvicola. The gradual transition from M. savini to A. terrestris cantiana and thence to A. terrestris terrestris has likewise been demonstrated (Heim de Balsac and Guislain 1955; Koenigswald 1980; Kolfschoten 1990a, 19906). Zazhigin ( 1980) described M. intermedins (= M. savini ) under a new genus Cromeromys , created for the Siberian species irtyshensis. Quantitative studies of the A. terrestris cantiana - A. terrestris terrestris lineage showed a relative variation in the thickness of the anterior and posterior walls of the tooth triangles (Koenigswald 1980; Heinrich 1982; Kolfschoten 1990a, 19906, 1992). When converted into index form, this gradual change found an application in quantitative biostratigraphy. Although the evolution is 80 PALAEONTOLOGY, VOLUME 38 gradual, it is not always linear, at least not in north-western Europe. The thickness index displays a clinal variation from north to south across Europe, and southern populations have a more primitive appearance with a lower index (Rottger 1986). Where advanced populations became extinct in the north during the late Middle Pleistocene, they were replaced by more primitive populations which migrated from southern areas thus altering the progressive variation over time by a reversal in the thickness index (Kolfschoten 1990a, 1992). A NEW POPULATION ANALYSIS OF MIMOMYS SAVINI A bivariate study of variability in M. savini was conducted independently of the remainder of the lineage (Pasquier 1972). This species supposedly formed a transition with the Arvicola genus but had never figured in a general quantified analysis. Analysis of a fairly abundant, previously unstudied population from the type locality of the Freshwater Bed, West Runton, England) provides insight into the question. A new multivariate analysis was performed using the classic biometric parameters (Text-fig. 2). It clearly shows that there is a trend from M. occitanus occitanus to M. ostramosensis (Text-fig. 3), and text-fig. 3. Multivariate analysis based on Text-figure 2 measurements. The morphological variability of M. savini does not fit in with that of M. ostramosensis as could have been expected if M. savini derived from M. ostramosensis and continued the sequence M. occitanus - M. ostramosensis. Differences concern the anterior complex morphology (parameters 1-3) and the tinea sinuosa (especially parameters 11 13). There is a clear discontinuity between the two lineages (O, M. occitanus occitanus ; * , M. polonicus; □, M. pliocaenicus; #, M. ostramosensis ; A, M. savini). that the morphological variability of M. savini (none occlusal and six lateral characters) does not fit in with that of M. ostramosensis as could have been expected if M. savini were descended from M. ostramosensis. NERAUDEAU ET AL.: PLIO-PLEISTOCENE WATER VOLES TIME (M.y.) = Arno* text-fig. 4. Linea sinuosa changes in the M. occitanus - M. ostramosensis lineage compared with the M. savini-A. terrestris cantiana sequence. The jugal views correspond to mean values of populations calculated for each species for parameters 10-15. It is clear that the gradual evolution of the linea sinuosa in M. occitanus - M . ostramosensis does not continue in M. savini. There is a discontinuity suggesting that M. savini derives from another Mimomys lineage, perhaps from M. coelodus. The linea sinuosa variations observed in jugal view (Text-fig. 4) show that the pattern of change from M. occitanus to M. ostramosensis involves a distinct upturn of folds 1 and 5 towards the top of the crown and a more limited upward extension of folds 2, 3 and 4 which recede from front to back. This is obviously a gradual evolution. When these data are compared with M. savini , however, a major difference can be seen in the pattern of the linea sinuosa. While folds 1 and 5 rise towards the top of the crown, folds 2, 3 and 4 remain very low. M. savini does not derive from M. ostramosensis but probably from another Mimomys lineage. The occlusal morphology of the anterior complex of M. occitanus hajnackensis, M. polonicus , M. ostramosensis and M. savini has been quantified by digital image processing. This computerized technique describes the geometry of objects in a bidimensional space (for details, see Viriot 1989, Viriot et al. 1990 and Viriot et al. 1993). It is well understood that, in the course of M, occlusal evolution in the Eurasian water vole lineage, the greatest changes took place in the anterior 82 PALAEONTOLOGY, VOLUME 38 complex. This anterior complex can be broken down into three parts: triangle 4, triangle 5 and the anterior loop. The percentage of the area occupied by these three parts with regard to the total area of the anterior complex can be quantified (Text-fig. 5). From M. occitanus hajnackensis to M. 10 60 Triangle 4 text-fig. 5. Evolutionary trends in the anterior complex of the Mj from M. occitanus to M. savini described by digital image processing. Overlapping clouds from M. occitanus hajnackensis to M. ostramosensis characterized by a decrease in the area occupied by the anterior loop to the profit of triangles 4 and 5. Discontinuity of the M. savini plot with an increased area of the anterior loop at the expense of triangle 4 (O, M. occitanus hajnackensis; * . M. polonicus ; #, M. ostramosensis; A, M. savini). ostramosensis , the area occupied by the anterior loop decreases gradually to the profit of both triangles 4 and 5. Then, if we look at the passage from M. ostramosensis to M. savini , the process is reversed and the area occupied by the anterior loop increases at the expense of triangle 4 alone. There is a clear discontinuity between the Mimomys part of the lineage and the Arvicola part, which includes M. savini. THE POSSIBLE ORIGIN OF THE SA VINI LINEAGE According to the present knowledge of Mimomys species, two possible origins can be attributed to the savini lineage. First, Rabeder (1981, text-fig. 8 1— 2b), noticed that the linea sinuosa of Mimomys coelodus displays only a minor upturn of fold 2 as in some M. savini. Moreover, in Zazhigin’s figures (Zazhigin’s 1980, text-figs 25-8, 9), the linea sinuosa of M. coelodus has small upturns of the three intermediate folds NERAUDEAU ET AL.\ PLIO-PLEISTOCENE WATER VOLES 83 as in other M. savini. Finally, according to Kretzoi (1954), the holotype of M. coelodus coming from the Kislang fauna (Hungary), is closely related to M. intermedins , a species previously synonymized with M. savini. Therefore, M. coelodus is a species with hypsodont molars, with a M, displaying a well-developed enamel islet and no Mimomys ridge (Text-fig. 6a-b). Therefore, M. coelodus is a text-fig. 6. Holotypes: a-b, M. coelodus-, a, occlusal view; b, jugal view (after Rabeder 1981). c-d, C. irtyshensis', c, occlusal view; d, jugal view (after Zazhigin 1980). possible ancestor of M. savini. However, the relationship between M. coelodus and the larger late Biharian voles has not yet been investigated properly and remains hypothetical, while the taxonomic status of M. coelodus is unknown. The second hypothesis corresponds to Zazhigin’s opinion, that M. savini should be regarded as part of the Cromeromys lineage, known from Late Pliocene deposits from Western Siberia and Transbaikalia, and from Early and Middle Pleistocene deposits from Eurasia. Indeed, the linea sinuosa of Cromeromys irtyshensis , the type species (Zazhigin 1980, fig. 24-1-8), looks very much like those of M. coelodus and M. savini (Text-fig. 6c-d). Moreover, the larger voles from West Runton, referred to as C. intermedius and related to C. irtyshensis, are often assigned to M. savini (Kretzoi 1969, Zazhigin 1980), according to their characteristic M:!. As M. savini can no longer be placed within the lineage of the genus Mimomys (type species Mimomys pliocaenicus ), it must be assigned to Cromeromys savini (Hinton, 1910). In summary, the discontinuity between the lineages M. occitanus - M. ostramosensis and C. savini - A. terrestris implies that the first lineage, which displays gradual morphological evolution, ends with M. ostramosensis. The lineage is replaced stratigraphically and, it seems, ecologically by that of C. savini , which is of uncertain origin, which gradually leads to A. terrestris cantiana and which continues to the present day with A. terrestris terrestris. This discontinuity between the two lineages was masked by the fact that C. savini succeeds M. ostramosensis in the same stratigraphical sequences. The phylogenetic re-arrangements introduced here do not change the biostratigraphical significance of C. savini. Acknowledgements. The authors thank the Harrison Zoological Museum of Sevenoaks (Kent) for lending previously unstudied material of the Mimomys savini type population, to Dr A. Nadachowski who made it possible for us to obtain the material, to A. Van der Meulen and D. F. 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VAN KOLFSCHOTEN Typescript received 23 June 1993 Revised typescript received 21 June 1994 Institute of Prehistory Reuvensplaats 4 PO Box 9515 2300 RA Leiden, The Netherlands COMPOSITION AND DISTRIBUTION OF THE INOCERAMID BIVALVE GENUS ANOPAEA by J. A. CRAME and S. R. A. KELLY Abstract. Anopaea is a distinctive Late Jurassic-Early Cretaceous inoceramid bivalve genus. Traditionally recognized by its elongate-pyriform outline and impressed antero-ventral sulcus, it is now apparent that it also has a distinctive hingeline. In each valve the thickened shell material of the hinge region terminates in a prominent fold, the anterior buttress; this often takes on the appearance of a small anterior 'ear'. Some fifteen taxa are now assigned to the genus and a further seven are probable members. The bulk of these forms fall withm the Late Tithonian-Early Albian. A. callistoensis sp. nov., from the Late Tithonian-?Early Berriasian of the Antarctic Peninsula, and a probable new species from the Berriasian of the South Shetland Islands, are described. Inoceramus constrictus , from the Early Albian of Queensland Australia, can now be referred to the genus. It can be confirmed that, with only a very small number of exceptions, Anopaea was restricted to Late Jurassic-Early Cretaceous extra-Tethyan localities. In this sense it may be regarded as a genuine bipolar taxon, although amphitropical is perhaps a more accurate term. Problems of generic discrimination remain at the forefront of taxonomic investigations into the widespread late Palaeozoic-Mesozoic bivalve family Inoceramidae Giebel, 1852. This is particularly so for the prolific Cretaceous representatives and there is currently an urgent need to clarify the definitions and status (i.e. taxonomic rank) of a wide variety of available names. One genus that would appear to be relatively stable is Anopaea Eichwald, 1861. Although still poorly known at the time of publication of the Treatise (Cox 1969), its status has subsequently been confirmed and its distribution extended to a variety of Late Jurassic-Early Cretaceous extra-Tethyan localities (e.g. Pokhialainen 1974; Crame 1981; Kelly 1984; Dhondt 1992). Its unusual form and essentially bipolar distribution have ensured that it is the focus of continued attention. Nevertheless, despite the distinctive form of this genus (to be discussed in detail below), instances have been recorded of apparent transitions to the ubiquitous Inoceramus. These are perhaps most prevalent in the informal 'Inoceramus' anglicus and 'I', neocomiensis groups (e.g. Pokhialainen 1969«, p. 125; Saveliev 1962, pi. 2, fig. la; Crame 1985, p. 488). Of equal concern is the fact that some features of the Anopaea shell have never been explained satisfactorily. Foremost among these is the 'concave appendix, similar to the ear-like appendix of Aucella [= Buchia], situated in front of the beaks’ (Eichwald 1865, p. 481). A similar 'anterior ear’ was noted by Etheridge, Jr (1901, p. 25) on a specimen of Inoceramus [= Anopaea ] constrictus. How could an apparently bona fide member of the Inoceramidae have a Buchia- like appearance? It is the intention of this study to redefine the diagnostic features of Anopaea using new material collected recently from the Antarctic Peninsula region and existing collections from Australia. With a firmer understanding of what constitutes membership of the genus, both its stratigraphical and geographical distribution can be reviewed. This in turn may help to constrain the nature and timing of bipolar events associated with the Jurassic-Cretaceous boundary (Crame 1993). DISTINGUISHING FEATURES OF ANOPAEA Anopaea is a small to medium sized bivalve (typically 50-80 mm in length) with a distinctive elongate-pyriform (i.e. pear-shaped) outline; the posterior is typically high and rounded, and the IPalaeontology, Vol. 38, Part 1, 1995, pp. 87-103, 2 pis.) © The Palaeontological Association PALAEONTOLOGY, VOLUME 38 A B C E F anterior buttress inner aragonite umbo lunuie anterior sulcus r i — 7 ligament ligament ridge pit nacreous layer anterior buttress text-fig. 1. Key morphological features of Anopaea. a, external view of a right valve; b, anterior view of a whole specimen; c, external view of a left valve; d, idealised cross-section through the hinge and ligament area (N.B. orientation of prisms in prismatic calcite layer is schematic only); e, left valve hinge area; F, right valve hinge area; G, exploded anterior view to show buttresses at the anterior terminations of the ligament areas. anterior narrow and pointed (Text-fig. 1). It is equivalve, or very nearly so, and moderately inflated. In front of the prominent beak in each valve there is a deep cordiform lunuie and a variably developed anterior sulcus can be traced from the umbonal region to the antero-ventral margin. Here, the latter feature may form a deep embayment which effectively divides the shell into anterior and posterior 'lobes’. Possession of a multivincular ligament, thin prismatic shell layer and regular commarginal ornament provide a ready link to the Inoceramidae. Unfortunately, details of the musculature remain poorly known; general shell form strongly suggests an endobyssate mode of life (Crame 1981, fig. 2). EXPLANATION OF PLATE 1 Figs 1-8. Anopaea callistoensis sp. nov., Late Tithonian-Early Berriasian?, Fossil Bluff Group, eastern Alexander Island. 1, KG. 3404. 268, paratype, internal mould of a right valve with traces of shell material, x F5. 2, KG. 3404. 187b, paratype, internal mould of a left valve, x F5. 3, KG3404.435, paratype, internal mould of a juvenile right valve, x 1-5. 4, KG.4209.14, paratype, internal mould of a right valve, x 1. 5, KG. 3404. 190, paratype, internal mould of a left valve, x F5. 6, KG. 4209. 87, paratype, internal mould of a right valve, x 1. 7, KG.3404.183, holotype, internal mould of a right valve with traces of shell material, x 1. 8, KG.3404.185, paratype, internal mould of a right valve, x 1. PLATE 1 : yi ■ CRAME and KELLY, Anopaea 90 PALAEONTOLOGY, VOLUME 38 To date, the only region of the Anopaea shell which has not been described adequately is the hingeline. Apart from the fact that it seems to be characterized by comparatively small rounded ligament pits, virtually nothing is known about it. However, some recently collected specimens from the Antarctic Peninsula region (described formally below as Anopaea callistoensis sp. nov. and A. sp. nov?) bear reasonably well preserved hingelines and form the basis, together with a revision of the Australian species Anopaea constricta (Etheridge, Jr), of a new reconstruction of this critical region of the shell. The sketches presented in Text-figure 1 are based upon a series of camera lucida drawings of specimens of the two new Antarctic species and the revised Australian form. Perhaps the most striking feature to emerge from study of this new material is that some specimens do indeed show a small antero-dorsal Buchia- like ear (e.g. Text-figs 3a-b, d-e, 5a; PI. 1, fig. 8). It is present in both left and right valves and takes the form of a rounded, buttress-like fold of shell material that is directed strongly inwards (i.e. towards the plane of commissure; Text- fig. 1). There is no evidence that the buttresses were true ears, in the sense that they are associated with byssal notches, or that they articulated with the other valve. Instead, it would appear that these features represent the anterior termination in each valve of a strip (or shelf) of thickened shell material running along the hingeline. Following the terminology of many Russian workers, such a structure should be referred to as the ligamentat (e.g. Pokhialainen 1969 b, 1972). On internal moulds this shelf commonly has a shallow, concave cross-profile (Text-figs 1, 3). The net effect of two opposing shelves of thickened shell material would have been to increase the interumbonal distance (Text-fig. 1 G). This in turn would have permitted, at least to some extent, the development of more inflated shells; as in endobyssate arcids, it may well be that the development of more inflated forms was a strategy to promote greater stability (Savazzi 1987). It is still unclear whether the material comprising the thickened hingeline is formed consistently from one particular shell layer. Examination of a series of specimens of A. constricta (see below) revealed this region to be composed of a thickened prismatic calcite layer (Text-fig. 1d-f; PI. 2, fig. 6). It would appear that the ligament was mounted directly on this layer, as perhaps it is in most unequivocal members of the Inoceramidae (Crampton 1988). It is also apparent that, as in other true inoceramids, this prismatic calcite layer was in turn superimposed upon a thickened inner aragonitic layer (sheet nacre) which is particularly prominent in the umbonal region (Text-fig. 4a, C). Nevertheless, on one of the two small specimens assigned below to Anopaea sp. nov?, it is the inner aragonitic layer, rather than the outer calcitic one, which is considerably thickened in the hinge region (Text-fig. 4a). Although somewhat altered now, this appears to comprise sheet nacre up to 250 pm thick (Text-fig. 4a). Unfortunately, the ligament pits are missing on this specimen, but it cannot be discounted that they were mounted directly upon this aragonitic layer. Resolution of the composition of this important taxonomic feature must await the discovery of well preserved specimens. Using an amended diagnosis for the genus Anopaea (see systematic section below), it has been possible to reassess critically those inoceramids which should be assigned to the taxon. The results of this survey are presented in Table 1, where two main categories are recognized : a group of species which can be assigned with some certainty to the genus, and a group of forms whose status is in some way questionable. Other taxa of less certain affinity are probably best attached with a degree of uncertainty to Inoceramus ; in particular, the taxonomic position of1/’, deltoides Crame (1985) and its allies cannot yet be resolved. The two new Antarctic species are described formally in the following systematic section, where the opportunity is also taken of redescribing the Australian Albian form, A. constricta (Etheridge, Jr). All the Antarctic material is stored in the collections of the British Antarctic Survey, Cambridge, EJK. CRAME AND KELLY: INOCERAMID BIVALVES 91 table I. Taxonomic re-appraisal of the genus Anopaea. Abbreviations: BAS, British Antarctic Survey, Cambridge; CIRGEO, Centro de Investigaciones en Recursos Geologicos; DVTGU, Dal'nevostochnoye Territorial’noye Geologicheskoye Upravleniye; NHM, Natural History Museum, London; NZGS, New Zealand Geological Survey; SVKNII, Severo-Vostochnogo Kompleksnogo Nauchno-Issledovatel'skogo Instituta. Taxon Type material Range and occurrence References and notes Late Volgian, central Kelly (1984) Russian Platform; Late Volgian and Ryazanian, eastern England 1. Valid taxa Anopaea brachowi (Rouillier, in Rouillier and Vossinsky, 1849) Anopaea sphenoidea Gerasimov (1955) Anopaea strambergensis (Boehm, 1883) Anopaea callistoensis sp. nov. Anopaea sp. nov? Anopaea gerasimovi Kapitza (1978) Anopaea pivanensis Kapitza (1978) Anopaea sawasovi Kapitza (1978) The original of /. lobatus Auerbach and Lrears (1846, pi. 7, fig. 1 ) is held in the Museum of A. P. and M. A. Pavlow, Moscow. It is designated herein lectotype of I. lobatus Auerbach and Lrears, 1846 and of I. brachowi Rouillier (1849) Holotype: Geological Survey of the Central Areas, Moscow, Gerasimov Collection, No. 1086 (Gerasimov 1955, pi. 20, fig. 2); 3 paratypes (Gerasimov 1955, pi. 20, figs 3-5) Holotype: Unnumbered specimen figured by Boehm (1883, pi. 67, figs I and 3) is designated herein as the lectotype Holotype: BAS, Cambridge, KG.3404.183; paratypes - as listed in this paper (BAS, Cambridge, P.2151.1-3) Holotype: DVTGU, Khabarovsk, No. 12M/I Holotype: DVTGU, Khabarovsk, No. 12/1 Holotype: DVTGU, Khabarovsk, No. 12/3 Late Volgian, Russian Platform and eastern England Tithonian, Stramberger Schichten, Carpathian Alps Late Tithonian-?Early Berriasian, Alexander Island, Antarctica Early Berriasian, South Shetland Islands, Antarctica Berriasian, Lower Priamur (Primorskiy), Russian Led. Berriasian, Lower Priamur (Primorskiy), Russian Led. Berriasian, Lower Priamur (Primorskiy), Russian Led. Kelly (1984) Boehm’s (1883, pi. 67, figs 1-3) three specimens almost certainly belong to Anopaea ; however, he noted (Boehm 1883, p. 594) that these specimens are atypical and may have come from elsewhere This paper This paper Kapitza ( 1978) Kapitza (1978) Kapitza (1978) 92 PALAEONTOLOGY, VOLUME 38 TABLE 1. (coni.) Taxon Type material Range and occurrence References and notes Anopaea stempeli Kapitza ( 1978) Anopaea sp. indet. Anopaea amurensis Kapitza (1978) Anopaea trapezoidalis (Thomson and Willey, 1972) Anopaea sp. nov. aff. mandibula (Mordvilko, 1949) Anopaea sp. nov. Anopaea constricta (Etheridge, Jr., 1892) 2. Taxa of less certain affinity Anopaea? stoliczkai (Holdhaus, 1913) Anopaea? verbeeki Boehm (1904) Anopaea? windhouweri Boehm (1904) Anopaea? sp. nov. Holotype: DVTGU, Khabarovsk, No. 12/2 (Single right valve. No. 1/11440) Holotype: DVTGU, Khabarovsk, No. 12/4 Holotype: BAS, Cambridge, KG. 18.31a; 4 paratypes, KG. 18.31b-e (BAS, Cambridge, KG. 1682.37) (C1RGEO, Buenos Aires, PI 1467) Holotype: Queensland Museum, Brisbane, FI 7/ 124 1 Holotype: unnumbered specimen figured by Holdhaus (1913, pi. 98, fig. 10a); as this now appears to be lost, a neotype may need to be designated from topotypes held in NHM, London (BPM 5051, 7198, 77198, 7199 and LL 24167) Holotype: unnumbered specimen figured by Boehm (1904, pi. I, fig. 4a, b), by monotypy Holotype: unnumbered specimen figured by Boehm (1904, pi. 1 , fig. 3), by monotypy (Three specimens figured by Fleming [1958, figs 12, 14 and 15]; from boulders derived from NZGS Iocs. S62/523, 525 and 526) Berriasian, Lower Priamur (Primorskiy), Russian Fed. Berriasian, Mangyshlak, Russian Fed. Late Valanginian, Lower Priamur (Primorskiy), Russian Fed. ?Hauterivian-Barremian, Alexander Island, Antarctica Albian, Alexander Island, Antarctica Early Albian, James Ross Island, Antarctica Early Albian, Queensland, Australia Tithonian, southern Tibe Tithonian, Indonesia Tithonian, Indonesia Tithonian, New Zealand Kapitza (1978) Bogdanova (1988) Kapitza (1978) Crame and Howlett (1988) Crame (1985) Medina and Buatois (1992) This paper Lack of a clearly defined antero-ventral sulcus and more rounded nature of some specimens cast some doubts upon affinity to Anopaea ; Crame (1981) Known from only one incomplete specimen (which may now be lost) Known from only one incomplete specimen (which may now be lost) Inoceramus n. sp. A, ?aff. everesti Oppel may be an Anopaea ; Anopaea n. sp. is incomplete; Fleming (1958) CRAME AND KELLY: INOCERAMID BIVALVES 93 TABLE 1. (cont.) Taxon Type material Range and occurrence References and notes Anopaea? mandibula (Mordvilko, 1949) Holotype: not yet traced Early Albian, Mangyshlak, Russian Fed. " Although there are indications that this species is close to Anopaea (Saveliev 1962) there are also resemblances to Inoceramus coptensis Casey. The latter form may, in turn, be close to Birostrina salomoni (d'Orbigny) (J. S. Crampton, pers. comm. 1993) Anopaea? mandibulaformis (Pokhialainen, 1969n) Holotype: SVKNII, Magadan, No. 289 Late Berriasian-Early Valanginian, Myrgal region, Russian Fed. By no means an obvious Anopaea ; Pokhialainen ( 1969u, pi. 3, fig. 3) Anopaea? attenuata Eichwald (1965) Holotype: unnumbered specimen figured by Eichwald (1865, pi. 21, fig. 4a), by monotypy ‘Neocomian’, Russian Platform Possibly a juvenile; some juveniles of A. callistoensis sp. nov. have this narrow, elongated form SYSTEMATIC PALAEONTOLOGY Order pterioida Newell, 1965 Family inoceramidae Giebel, 1852 Genus anopaea Eichwald, 1861 Type species. Inoceramus lobatus Auerbach and Frears, 1846 non Munster in Goldfuss and Munster, 1835; subjective synonym of I. brachowi Rouillier, 1849. Emended diagnosis. Small-medium sized, elongate-pyriform inoceramid with deep cordiform lunule; equivalve, or almost so; antero-ventral sulcus usually well developed; opistodetic hinge based on thickened shell layer (or ligamentat); on internal moulds this thickened layer is represented in each valve by a concave gutter; ligamentat terminates in an anterior, ear-like buttress. Included species and geographical range. See Table 1 . Age-range. Late Tithonian-Early Albian. Anopaea callistoensis sp. nov. Plate 1, figures 1-7; Text-figures 3a-b, d-e, 4b v. 1981 Anopaea sp. nov.(?) Crame, p. 213, pi. 2, figs e-j [Late Tithonian, Himalia Ridge Formation, Callisto Cliffs, Alexander Island, Antarctica]. v. 1988 Anopaea sp. nov.? Crame and Howlett, p. 15, fig. 6a [Late Tithonian, Himalia Ridge Formation. Planet Heights, Alexander Island, Antarctica]. 94 PALAEONTOLOGY, VOLUME 38 Type material. Holotype: KG. 3404. 183 (PI. 1, fig. 7; internal mould RV). Paratypes: KG. 2802, 30, 40, 43a, b, 53, 58, KG. 3404. 162, 167, 178, 183a, b, 184, 185, 186, 187a, 188, 189, 190, 191, 193, 194, 195a, b, 196, 197, 198, 268, 432, 433a, b. 434, 435, KG.4209.12, 13, 14, 19, 38, 39, 40, 42a, 43, 44, 45, 46, 47, 48, 59, 60a, b, 67, 85, 86, 87, 88, 89, 101, 104, 105, 122, 123, 124, 125, 126, 139, 142. All specimens from the Fossil Bluff Group of eastern Alexander Island (Text-fig. 2). At locality KG. 2802 (western Callisto Cliffs, 71° 0T S; 68° 03' W), the specimens were obtained from the 91-99 m level in the measured section (Himalia Ridge Formation); at KG. 3404 (northern Planet Heights, 71° 02' 50" S; 68° 36' 30" W) the specimens were obtained from approx, the 109-1 18 m level in the measured section (Himalia Ridge Formation); at KG. 4209 (central Offset Ridge, 71° 38' S, 68° 39' W) the specimens were obtained from the 132-204 m level in the upper part of the Atoll Nunataks Formation to lower part of the Himalia Ridge Formation. Occurrence. As for the type material. Associated macrofossils suggest that, at the two more northerly localities (KG. 2802 and 3404; Text-fig. 2), the species has a Late Tithonian age (Butterworth et al. 1988; Crame and Howlett 1988); at the more southerly locality (KG. 4209) it may range into the Early Berriasian. Precise placement of the Jurassic-Cretaceous boundary using macrofossils alone is not yet possible in Antarctica. Derivation of name. After Callisto Cliffs, eastern Alexander Island. Diagnosis. Weakly to moderately inflated Anopaea with subrectangular posterior and variably developed anterior sulcus; distinctive ornament of fine growth lines superimposed on low, commarginal folds. CRAME AND KELLY: INOCERAMID BIVALVES 95 Description. This species is equivalve (or very nearly so) and has the typical Anopaea outline, as described in the introductory section. Most specimens have the familiar elongate-rectangular form, with the length (L = anterior to posterior extremities) considerably in excess of the height (H = maximum dimension perpendicular to length). A sample of 25 specimens gave the following measurements (in mm): x L = 44-72 (SD = 21-04, range = 16-0-92 0); x H = 34-0 (SD = 11-93, range = 13 0-62 0); x H/L = 0-81 (SD = 0-21, range = 0-52— 1 -47). A few juveniles have a much more erect profile (e.g. KG. 3404. 435; PI. I, fig. 3), but even in these there are still clear indications of the characteristic high, rounded posterior and narrower, pointed anterior. text-fig. 3. Hinge region and anterior buttress of Anopaea. a-b, d-e, Anopaea callistoensis sp. nov.; a, KG. 3404. 193, internal mould of a right valve exhibiting a prominent anterior buttress, x 3; b, KG. 3404. 191, internal mould of a right valve, showing the concave shelf corresponding to the ligamentat and its abrupt anterior termination in a buttress, x 3; D, KG. 3404.434, internal mould of a right valve, showing a concave shelf and anterior buttress overhanging a deep lunule, x 3; e, KG.3404.187b, internal mould of a left valve, showing a prominent anterior buttress, x 3. c, A. trapezoidalis (Thomson and Willey), KG.18.31d, internal mould of a bivalved specimen, viewed from the left; the prominent shelf formed by the ligamentat can be seen along the hinge of the right valve, x 1. The valves are weakly to moderately inflated, with the maximum degree of convexity occurring in the umbonal and central regions; some specimens show a considerable degree of flattening towards the postero- dorsal and ventral margins. The umbones are prominent, prosogyrous and rise slightly above the hingeline. On the antero-dorsal side of the umbo there is a steep descent to the lunule, which is always well developed (PI. 1, figs 1-8; Text-fig. 3). The antero-ventral sulcus is usually only weakly impressed. It can be traced on the holotype (KG.3404.183; PI. 1, fig. 7) from the antero-ventral margin to almost the umbo, but on other specimens it is barely more than an indentation on the ventral margin (e.g. PI. 1, fig. 1). The best preserved hingelines are straight and a number clearly show the distinctive concave cross-profile (i.e. in dorso- ventral section; Text-fig. 3). The anterior termination of the hingeline in both valves is marked by a small, protruding buttress; on a number of specimens these features have a distinctive ‘ear-like’ appearance (PI. 1. fig. 8; Text-fig. 3a-b, d-e). As stated previously, it is believed that the two buttresses simply rested against each other, for neither appears to have crossed the plane of commissure. Nevertheless, on two poorly preserved specimens, which may both have been distorted slightly (KG. 3404. 196, KG. 4209. 104), there are 96 PALAEONTOLOGY, VOLUME 38 indications that the left buttress rested partly within the right. How widespread a phenomenon this may have been is not known at present. The ornament on both internal and external moulds comprises a series of prominent commarginal folds with superimposed secondary growth lines (PI. 1, figs 1-8). The primary folds generally have a wavelength of 2-4 mm, but on the ventral margins of the largest specimens they reach 6-7 mm across; they have acute to well text-fig. 4. SEM photomicrographs of the shell structure of Anopaea. a, Anopaea sp. nov?, P.2151.3, detail from the postero-dorsal region of a right valve from the South Shetland Islands; contact between the inner nacreous (upper two-thirds of photograph) and outer prismatic calcite layer shown, x280. b, A. callistoensis sp. nov., KG.3404.188, outer prismatic calcite shell layer from the postero-dorsal region of a right valve, x 90. c-d, A. constricta (Etheridge, Jr, 1901), F. 21077. c, inner nacreous shell layer from the umbonal region of a right valve, x 2000; d, FI 3 17, outer prismatic calcite shell layer from the postero-dorsal region of a right valve, x 1 70. b and d are perpendicular sections, a and c are slightly oblique. rounded cross-profiles. The secondary growth lines are superimposed across the entire width of the valve but are at their clearest on the primary folds. Here they are regularly and evenly spaced, often on a sub-millimetre scale (PI. 1, figs 6-7). Traces of a thin, simple prismatic shell layer are found on a number of specimens; in the postero-dorsal region of KG.3404.188 it reaches slightly in excess of I mm in thickness (Text-fig. 4b). CRAME AND KELLY: INOCERAMID BIVALVES 97 text-fig. 5. Anopaea sp. nov?, Berriasian, Byers Group, Livingston Island, South Shetland Islands, a, P.2151.1, internal mould of an incomplete right valve, showing a blunt, rounded anterior buttress overhanging a deep lunule; b, P.2151.2, internal mould of an incomplete right valve. Both x3. Remarks. As remarked previously (Crame 1981, p. 213), there is considerable similarity between this taxon and the approximately coeval Russian species, Anopaea brachowi (Rouillier) and A. sphenoidea (Gerasimov) (Table 1 ). The resemblance is perhaps strongest with the latter, although A. callistoensis sp. nov. can be distinguished by its subrectangular posterior, and less regular commarginal folds. There may also be some overlap with A. windhouweri Boehm from the Tithonian of Indonesia (Crame 1981, p. 213). However, this species is based on a single specimen and efforts to trace it have so far proved unsuccessful. The range of Berriasian species described by Kapitza (1978) from the Far East of the Russian Federation (Table 1) is clearly distinct from this new form, as is A. sp. nov? from the South Shetland Islands, to be described below. A specimen of Anopaea from Tithonian-Berriasian strata of the Nordenskjold Formation, northeastern Antarctic Peninsula is not sufficiently well preserved to compare in detail with the Alexander Island material (Kelly and Doyle 1988). Anopaea sp. nov? Text-figures 4a, 5a-b Material. Internal moulds of two small RV (P.2151.1, 2); external mould RV with shell material (P.2151.3, counterpart of P.2151.2). Locality P.2151 is on the northern face of Point Smellie, Byers Peninsula, Livingston Island, South Shetland Islands (62° 38' 55" S; 61° 09' 15" W) (Text-fig. 2). This locality is at approximately the 350 m level in a composite section through the President Beaches Formation of the Byers Group (Crame et al. 1993). Occurrence. As for material. Associated macro- and microfossils indicate a Berriasian age for this locality; dinoflagellate cyst taxa in particular suggest that this can be refined to Early Berriasian (Crame et al. 1993). Description and remarks. These two small right valves are almost certainly juveniles. The ventral regions of both of them are incomplete, but the dimensions can be estimated at 24 mm (L) by 18 mm (H) for P. 2151. 1, and 19 mm (L) by 13 mm (H) for P. 2151.2. Despite their small size, both these forms are quite distinct from the smallest specimens of A. callistoensis sp. nov. and would appear to represent the basis of a new taxon. The hinge region of both specimens is well defined, showing the characteristic concave cross-profile (i.e. in a dorso- ventral section) and anterior termination in a distinct buttress (Text-fig. 5). Although there are no indications of an antero-ventral sulcus, it is clear that both specimens have a narrow, pointed anterior region. Traces of regular commarginal ornament characterize P. 2151.1, but on P. 2151. 2 and P. 2151. 3 the pattern is much more irregular (Text-fig. 5). 98 PALAEONTOLOGY, VOLUME 38 Part of the reason for more irregular ornament on the smaller of the two specimens is that it bears traces of a thickened inner shell layer, which is particularly apparent on P.2151.3. This originally aragonitic layer is approximately 250 //m thick, and perhaps more than this in the hinge region where it is especially prominent (see above). It has a distinctive laminated-foliated texture (Text-fig. 4a) but was originally sheet nacre in composition. Although no unequivocal pits can be detected along the hinge of P.2151.3, it would seem possible that this was the layer on which the ligament was mounted. If this observation is correct, it would mean that in some taxa, or possibly the juveniles of some taxa, the ligament was not mounted on the outer prismatic shell layer (see above). The outer prismatic shell layer is far less prominent on specimens P.2152 and P.2151.3. Anopaea constrict a (Etheridge, Jr, 1901) Plate 2, figs 1-6; Text-figures 4c-d v. 1872 Inoceramus allied to I. problematicus d’Orbigny : Etheridge, p. 344, pi. 22, fig. 4 [refigured here, PI. 2, fig. 1 ; QM FI 241 ; anterior missing therefore appears like Inoceramus ]. pv. 1878 Inoceramus carsoni M’Coy; Etheridge, Jr, p. 109 [Only the reference to Inoceramus allied to I. problematicus d'Orbigny; see Etheridge, Jr, 1872; i.e. QM F1241], vp. 1892 Inoceramus carsoni M’Coy; Etheridge, Jr (in Jack and Etheridge, Jr), p. 463 [Only QM F1241]. v. 1901 Inoceramus etheridgei Etheridge; Etheridge, Jr, p. 22 [QM F1241]. *v. 1901 Inoceramus constrictus sp. nov. Etheridge, Jr, p. 24, pi. 2, fig. 7 [GSQ FI 3 17]; pi. 3, fig. 6 [GSQ FI 3 16] [Rolling Downs Formation, Albian; Hughenden and Marathon Stations, Queensland]. 1928 Inoceramus constrictus Etheridge, Jr; Heinz, p. 144 [Rolling Downs Formation, Hughenden and Marathon Stations, Queensland]. pv. 1966 Inoceramus sutherlandi M'Coy; Ludbrook, p. 157 [Only the reference to Inoceramus allied to I. problematicus d’Orbigny; see Etheridge, Jr, 1872, i.e. QM F 1 24 1 ]. pv. 1968 Inoceramus constrictus Etheridge, Jr; Day, p. 394, pi. 46, figs 1-8 [Ranmoor Member, Early Albian, Queensland]. 1969 Inoceramus constrictus Etheridge, Jr; Day, p. 151 [Tambo fauna, Albian, Queensland]. 1981 Inoceramus constrictus Etheridge, Jr; Crame, p. 216 [Early Albian, Queensland, Australia], v. 1990 Inoceramus cf. sutherlandi M’Coy; Rozefelds et al. p. 687 [QM F 1 24 1 ] . Type and other material. Etheridge, Jr (1901, pi. 2, fig. 7 and pi. 3, fig. 6) figured two syntypes, of which the latter is designated herein as lectotype (= GSQ FI 3 16), and the former as paralectotype (= GSQ FI 3 17). Both specimens are from the Early Albian Ranmoor Member of the Rolling Downs Formation, Queensland; the lectotype is from a locality behind the Hughenden Hotel, Hughenden, Flinders River (Text-fig. 2), and the paralectotype from Marathon Station, Queensland (Day 1968). Other material includes: QM FI 241 - originally figured as Inoceramus allied to I. problematicus d’Orbigny (Etheridge, Jr 1872); QM FI 6384, F21071, F21072, F21077; as for paralectotype. Occurrence. As for the type and other material. R. W. Day (pers. comm. 1991) believes that A. constricta is associated with Beudanticeras flindersi in a level immediately overlying the Dimitobelus dayi horizon of the Early Albian of Queensland, Australia. Diagnosis. Moderately inflated Anopaea with well-rounded posterior margin and strongly impressed anterior sulcus. EXPLANATION OF PLATE 2 Figs. 1-6. Anopaea constricta (Etheridge, Jr); Early Albian, Ranmoor Member, Rolling Downs Group, Queensland, Australia. 1, QM FI 241, internal mould of a right valve, original of Inoceramus allied to I. problematicus , d’Orbigny, Etheridge, 1872, p. 344, pi. 22, fig. 4. 2, QM F21072, internal mould of a left valve, with traces of shell material. 3, QM F16384, internal mould of left and right valves in butterfly position. 4, QM F21071, internal mould of a right valve, with traces of shell material. 5-6, GSQ F 1 3 1 7, paralectotype; 5, internal mould of a right valve; 6, the same specimen viewed from the inside and showing detail of the hingeline. Figs 1-5 x 1 ; Fig. 6x2. PLATE 2 CRAME and KELLY, Anopaea 100 PALAEONTOLOGY, VOLUME 38 Description. The five best preserved specimens (GSQ F 1 3 1 7, QM F16384, F21071, F21072, F21077) show this species to range in length (L) from 50 to 110 mm and height (H) from 39 to 60 mm; mean H/L = 0-734. The same specimens show the typical Anopaea form, with perhaps the most striking feature being a deeply impressed antero- ventral sulcus (PI. 2, figs 2-5); on all specimens this can be traced clearly into the earliest growth stages. As Etheridge, Jr (1901, p. 25) indicated, the maximum degree of inflation occurs immediately posterior to the sulcus, in the central regions of the valve. On the largest specimen (QM F16384), the postero- dorsal region is considerably flattened. Specimens QM F21071, F21072 and GSQ FI 3 17 display well preserved hingelines. On specimen GSQ FI 3 17, six ligament pits are preserved in a 15 mm strip of hinge immediately posterior to the beak (PI. 2, fig. 6). Initially, the ligament pits are somewhat narrow and elongate but they broaden posteriorly until the fifth and sixth are comparatively large, oval features measuring 3x1-5 mm. The pits bear fine horizontal striations and are clearly mounted on the prismatic shell layer (PI. 2, fig. 6). As this ligament surface is inclined at a steep angle to the plane of commissure, it would appear that the ligament must have been partially external (Text- fig. Id). On specimen GSQ F 1 3 1 7 (RV), the anterior end of the ligament region terminates in a prominent tongue- like buttress composed of prismatic calcite (PI. 2, fig. 6). This feature has a length of approximately 4 mm and maximum width (in a dorso-ventral sense and close to its base) of nearly 2 mm; it curves gently towards the left valve but does not appear to have projected across the plane of commissure. The tongue-like appearance is enhanced by a concave upper surface (which is essentially dorsal in aspect) flanked by two sharply defined ridges. There are steep descents on all flanks of the buttress, and on the innermost border there is a small, but distinct, notch. It is unclear at present whether this may represent a point of contact with the left valve buttress. Traces of a thin ( < 1 mm) prismatic shell layer are preserved on the flanks of most specimens and there are also remnants of an altered inner nacreous layer (Text-fig. 4c-d). The ornament pattern on internal moulds is of broad commarginal folds (> 5 mm), with minor folds superimposed (PI. 2, figs 1-5). Remarks. Without doubt, this taxon is a bona fide member of the genus Anopaea. Its general form and style of ornament would seem to set it apart from most other species, although there is perhaps some overlap with A? mandibula (Mordvilko) and its allies. Anopaea sp. nov. aff. mandibula from the Antarctic Peninsula (Table 1) also exhibits a persistent antero-ventral sulcus (Crame 1985, text- fig. 9b), but in general both this form and A. mandibula sensu stricto (e.g. Saveliev 1962, pi. 5, figs 1-1 1) have finer and more closely spaced ornament. DISTRIBUTION AND PHYLOGENETIC POSITION Following the taxonomic reappraisal of Anopaea , it is possible to review its distribution in both time and space. The first occurrences in the stratigraphical record can now be confirmed as Tithonian (or Volgian in the Boreal realm), and in all probability this can be refined to the Late Tithonian (Table 1). At this time the genus was represented by the very distinctive A. brachowi and A. sphenoidea in localities such as the Russian Platform and eastern England, and the not dissimilar A. callistoensis sp. nov. in the Antarctic Peninsula. There are also further probable Tithonian occurrences of Anopaea in the Carpathian Mountains, southern Tibet, Indonesia and New Zealand (see below). New earliest Cretaceous (Berriasian) localities for the genus include the South Shetland Islands, Mangyshlak and the Far East of the Russian Federation (Lower Priamur) (Table 1). In the latter region the genus can also be extended into the succeeding Valanginian stage. Thereafter, however, the Early Cretaceous record of Anopaea is somewhat sketchy. Anopaea trapezoidalis from the Antarctic Peninsula occurs in strata that are judged to be younger than Valanginian but pre-Aptian in age; nevertheless, no diagnostic Hauterivian or Barremian fossils are yet known from the Fossil Bluff Group of Alexander Island (Crame and Howlett 1988). The next definite datum for the genus is the Albian, with a possible occurrence in Mangyshlak, and definite occurrences in Antarctica (both Alexander Island and James Ross Island) and Queensland, Australia; there is a strong probability that all these occurrences can be referred to the Early Albian. As has been remarked on previously, it is rather striking how the bulk of these occurrences fall within the Late Jurassic-Early Cretaceous extra-Tethyan regions; Anopaea may be said to have had CRAME AND KELLY: INOCERAMID BIVALVES 101 an essentially bipolar distribution (Crame 1993, and references therein). However, it is necessary to qualify this statement, for a few records may in fact be from Tethyan localities. In particular, A ? strambergensis occurs in the Stramberger Schichten in association with a Tethyan fauna, although Boehm (1883, p. 594) noted that the two specimens of this species were of somewhat atypical lithology; they may have originated from another bed, or possibly not from Stramberg at all. The Berriasian Mangyshlak record is also from a region of interdigitating Boreal and Tethyan facies, but it is clear that in this instance the specimen of Anopaea sp. indet. occurs in association with a Buchia bivalve assemblage (Bogdanova 1988). Lower latitude occurrences of the genus in the Southern Hemisphere include A ? stoliczkai , if this is indeed a true member of the genus, and A ? verbeeki and A? windhouweri from Indonesia. It can be concluded that, with a small number of exceptions, Anopaea had an essentially amphitropical distribution from at least the Late Tithonian to the Early Albian. In this sense it would indeed seem to qualify as a bipolar taxon. What perhaps should also be emphasized here is that new evidence is coming to light which suggests that this was not a deep water inoceramid. Although it was once suggested that Anopaea may have achieved widespread distribution via a deep water route (Crame 1981, p. 216), this now seems less likely. Anopaea callistoensis sp. nov., for example, is known to occur in association with a molluscan assemblage which suggests comparatively shallow-water, nearshore environments (Crame and Howlett 1988). Similar environments are also indicated for the coeval boreal species, A. brachowi and A. sphenoidea (Kelly 1984). The combination of features, such as the elongate-pyriform outline, antero-ventral sulcus, cordiform lunule and anterior buttress, serves to distinguish Anopaea at least at the generic level. It is becoming increasingly apparent that the latest Jurassic-earliest Cretaceous interval was a time of major turnover in global inoceramid faunas, with the replacement of Retroceramus- dominated ones by Inoceramus sensu /u/o-dominated ones (e.g. Pokhialanen 1974; Crame 1985). Anopaea flourished briefly in the transitional phase between these two great faunas but appears to have become increasingly rare through the latter part of the Early Cretaceous. Indeed, should A? mandibula prove not to be a member of the genus, it may be that, by the early Albian, Anopaea was restricted to southern high latitudes. Acknowledgements. We thank: P. A. Jell and E. D. McKenzie (Queensland Museum) and S. M. Parfrey (Queensland Minerals and Energy Centre) for the loan of Anopaea constricta specimens; W. Werner (Bayerische Staatsammlung fur Palaontologie und Historische Geologie, Miinchen) for casts of A? strambergensis ; G. E. G. Westermann (McMaster University) and U. Lepping (Geologisches Institut der Albert-Ludvigs-Universitat, Freiburg im Brisgau) for their efforts in attempting to locate the types of A? verbeeki Boehm and A? windhouweri ; R. W. Day (Queensland Minerals and Energy Centre), J. S. Crampton (Institute of Geological and Nuclear Sciences, New Zealand) and N. J. Morris (The Natural History Museum, London) for valuable taxonomic discussions; K. Robinson (B.A.S.) for SEM micrographs; and P. Bucktrout and C. J. Gilbert (B.A.S.) for photography. Finally, we thank J. S. Crampton and an anonymous referee for their careful reviews of the manuscript. REFERENCES auerbach, j. and frears, h. 1846. Notices sur quelques passages de Fouvrage de MM. Murchison, E. de Verneuil et la Comte A. de Keyserling: Geologie de la Russie d’Europe et des montagnes de FOural. Byulleten Moskovskogo obshchestva , Ispytateley Prirody , Otdel Geologicheskiy, 35, 486-500. boehm, G. 1883. Die Bivalven des Stramberger Schichten. 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Geological Society of America and University of Kansas Press, Boulder, Colorado, 489 pp. crame, j.a, 1981. The occurrence of Anopaea (Bivalvia: Inoceramidae) in the Antarctic Peninsula. Journal of Molluscan Studies, 47, 206-219. 1985. Lower Cretaceous inoceramid bivalves from the Antarctic Peninsula region. Palaeontology, 28, 475-525. — 1993. Bipolar molluscs and their evolutionary implications. Journal of Biogeography, 20, 145-161. — and howlett, p. j. 1988. Late Jurassic and Early Cretaceous biostratigraphy of the Fossil Bluff Formation, Alexander Island. Bulletin of the British Antarctic Survey, 78, 1-35. — pirrie, D., crampton, J. s. and duane, a. m. 1993. Stratigraphy and regional significance of the Late Jurassic-Early Cretaceous Byers Group, Livingston Island, Antarctica. Journal of the Geological Society, London, 150, 1075-1087. crampton, j. s. 1988. Comparative taxonomy of the bivalve families Isognomonidae, Inoceramidae and Retroceramidae. 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[ Principal Mesozoic fossils of the central regions of the European part of the USSR. Part 1. Lamellibranchiata, Gastropoda, Scaphoda and Brachiopoda of the Jurassic deposits}. Gosgeoltekhizdat, Moscow, 379 pp. [In Russian], giebel, c. G. 1852. Allgemeine Palaeontologie : Entwuf einer systematischen Darstellung der Fauna und Flora der Vorwelt. Ambrosius Abel, Leipzig, viii + 413 pp. goldfuss, A. and munster, G. 1835. Petrefacta Germaniae. Volume 2, Dusseldorf, 69-140, pis 97-121. heinz, r. 1928. Uber die Kreide-Inoceramen Australiens und ihre Beziehungen zu denen Europas und anderer Gebiete. Beitrage zur Kenntnis der oberkretazischen Inoceramen VIII. Mitteilungen aus dem miner alogisch- geologischen Stattsinstitut in Hamburg, 10, 131-147. holdhaus, K. 1913. Fauna of the Spiti Shales (Lamellibranchia and Gastropoda). Memoirs of the Geological Survey of India Palaeontologica Indica, 4, 397-456, pis 94—100. kapitza, a. a. 1978. Novye vidy nizhnemelovykh inotseramid nizhnego priamur’ya [New species of Lower Cretaceous inoceramids from Lower Priamur]. 65-77, pis 4-6. In poyarkova, z. n. (ed.). Biostratigrafiya yuga dal'nego vostoka ( fanerozoy ) [ Biostratigraphy of the south of the Far East ( Phanerozoic )]. DVNTS AN SSSR, Vladivostok, 139 pp. [In Russian]. kelly, s. r. a. 1984. Bivalvia of the Spilsby Sandstone and Sandringham Sands (Late Jurassic-Early Cretaceous) of eastern England. Part 1. Monograph of the Palaeontographical Society , 137 (566), 1-94, i-xii, 20 pis. CRAME AND KELLY: INOCERAMID BIVALVES 103 — and doyle, p. 1988. The bivalve Aulacomyella from the Early Tithonian (Late Jurassic) of Antarctica. Antarctic Science, 3, 97-107. ludbrook, n. h. 1966. Cretaceous biostratigraphy of the Great Artesian Basin in South Australia. Bulletin of the Geological Survey of South Australia, 40, 1-223. Medina, f. a. and buatois, L. A. 1992. 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O kharaktere sochleneniya stvorok u inotseramid neokoma [On the characteristics of valve articulation in Neocomian inoceramids]. In shilo, n. a. (ed.). Inotseramy yury i mela severo-vostoka SSSR [Jurassic and Cretaceous inocerams from the Far East USSR], Trudy Severo-Vostoknogo Kompleksnogo Nauchno-IssledovateV skogo Instituta, 32, 118-123. — 1972. Sistematicheskoe polazhenie inotseramid neokoma [Systematic position of the inoceramids in the Neocomian], 57-65. In pergament, m. a. (ed.). Trudy Vsesoyuznogo Kollokvyuma po Inotseramam [Transactions of the All-Union Colloquium on inocerams], Vol. 1. Academia Nauk SSSR, Geologicheskii Institut, Moscow, 167 pp. [In Russian]. — 1974. Osobennosti rasprostraneniya inotseramid neokoma tikhookeanskoi oblasti [Spreading of the Neocomian Pacific inoceramids]. Trudy Instituta Geologii i Geofiziki, Sibirskoe Otdelenie, 80, 174—187. [In Russian], rouillier, c. 1849. In rouillier, c. and vossinsky, a. Etudes progressives sur la geologie de Moscou; quatrieme etude. Bvulleten Moskovskogo obshchestva, Ispytateley Prirody , Otdel Geologicheskiy, 22, 337-355. rozefelds, a. c., mckenzie, e. d. and mobbs, c. 1990. Type, figured and mentioned fossil invertebrates in the Queensland Museum. Memoirs of the Queensland Museum, 28, 665-713. savazzi, e. 1987. Geometric and functional constraints on bivalve shell morphology. Lethaia , 20, 293-306. saveliev, A. a. 1962. Al’bskiye inotseramidy Mangyshlaka [Albian inoceramids from Mangyshlak]. In saveliev, a. a. (ed.). Paleontologiclteskiy sbornik, 3 [Palaeontological Collection, 5]. Trudy Vsesoyuznogo Neftyanogo Nauchno-IssledovateV skogo Geologo- Razvedochnogo Instituta, 196, 219-254 [In Russian], Thomson, m. r. a. and willey, l. e. 1972. Upper Jurassic and Lower Cretaceous Inoceramus (Bivalvia) from south-east Alexander Island. Bulletin of the British Antarctic Survey, 29, 1-19. j. A. CRAME S. R. A. KELLY British Antarctic Survey Natural Environment Research Council High Cross Typescript received 9 September 1993 Madingley Road Revised typescript received 8 January 1994 Cambridge, CB3 0ET, UK DECAY AND FOSSILIZATION OF NON- M INERA LIZED TISSUE IN COLEOID CEPHALOPODS by AMANDA J. KEAR, DEREK E. G. BRIGGS ■ blood vessels intramuscular connectives inner tunic inner skin radial muscle VENTRAL text-fig. 1. Diagrammatic representation of coleoid mantle and tunic morphology, a, squid body, showing the position of outer tunic, mantle muscle and inner tunic; b, the layered structure of the tunic; c, a section through the skin and upper mantle, showing muscle morphology in relation to the anterio-posterior axis of the animal; radial and circular muscle and intramuscular connectives are marked; patterning on the muscle indicates fibre orientation, a-b re-drawn, with permission, from Ward and Wainright (1972). MATERIALS AND METHODS Recent coleoid cephalopod material was obtained from the Plymouth Marine Laboratory, UK. The squids Alloteuthis subulate) and Loligo forbesi (Teuthida : Loliginidae) and the cuttlefish Sepiola atlantica (Sepiolida; Sepiolidae) were trawled off Plymouth. The animals used for experiments were those which were brought up dead or dying in the nets, or died overnight in the stock tanks. Only the heads of Loligo (n = 16: dorsal mantle length 135-295 mm; body weight 1 1 T 7-587-9 g) were utilized in experiments. Whole Alloteuthis (n = 16: dorsal mantle length 60-85 mm) and Sepiola (n — 4: dorsal mantle length 15-20 mm) were utilized. Specimens were placed in 250 ml Kilner jars with 150 ml ( Alloteuthis , Sepiola) or 200 ml ( Loligo ) of seawater from the Plymouth Marine Laboratory’s research circulation (salinity 33-1 ppt; pH 7-63 + 0-06) and transferred to an incubator at 20 °C within 4 hours. These experiments correspond to the ‘slow diffusion’ type (lb) of Briggs and Kear (1993a, 1994). Specimens were inspected/sampled after 1, 2, 3, 4, 7 and 10 days and after 2, 3, 4, 6, 8, 10, 15, 20, 25, 30 and 50 weeks. Morphological changes were recorded without opening the jars or disturbing the carcass. Sampling for analysis involved decanting off the seawater and filtering or sieving the remains. More decay resistant organs (beaks, radula, statoliths, eye lenses, gladius, suckers) were removed and fixed in alcohol. Material was fixed for SEM using the glutaraldehyde- HMDS method (Nation 1983). The remains of the carcass were oven-dried at 105 °C to constant weight. The colour and pH of the seawater within the experimental vessel were noted. Crystalline material was removed from the carcass for analysis with the electron microprobe. Fossil coleoids which commonly preserve muscle fibres are likely to preserve other soft tissues. Exceptionally preserved material held in the collections of the Natural History Museum (NHM) and Bristol City Museum (BRSMG) was therefore examined (see Appendix). The investigation REAR ET 4L.:COLEOID CEPH ALOPODS 109 Table 3. Decay stages in AUoteuthis and Sepiola. After 1 day: Post-mortem The carcass is firm. The outer layer of mantle skin shows signs of disintegration while the chromatophores of the inner layer contract, giving the animal a pale appearance. The skin shrinks away from the mantle in places, revealing the muscle underneath, which turns opaque white. The ink behaves as a liquid. Some eggs escape down the funnel of a mature female Sepiola. After 2 days : Osmotic effects The muscle (arms, funnel, mantle, fins) becomes soft. The arms and mantle may be swollen. The swollen egg mass of mature Sepiola displaces and tears the mantle. After 3 days: Shrinkage The arms and eyes, and some of the outer layer of skm, begin to detach from the carcass. Pigment granules are scattered in the water. The muscles disintegrate if disturbed. The body and arms have shrunk, and contraction of the mantle reveals the edge of the ink sac, anus and spermatophoric duct. The gladius of AUoteuthis may protrude from the front of the mantle, but is structurally indistinguishable from fresh material (Text-fig. 3d). The gills may be swollen. The muscle of the head has shrunk, making the eyes appear disproportionately large. A bulge in the arm cone may represent the folded tentacles swollen in their “pouch”. The chitinous arm suckers may remain in place (Sepiola) (Text-fig. 3f) or be mainly detached due to decay of the attachment muscles (AUoteuthis). The ink solidifies. After 1 week: Disintegration begins The carcass shrinks further and collapses unless the shape of the mantle is maintained by reproductive material inside (in female AUoteuthis). Surviving pigment is very dark. The fins may detach, and the head drifts away from the mantle. The beaks and radula remain in the buccal mass, although the edges of the beaks may have disintegrated. The gladius becomes brittle. Few sucker rings are still attached. Retinal pigment may stain the eye lenses, beaks, and pen. The outer membranes of the ink sac disintegrate, but the ink remains a unit. The digestive gland may still be evident. The spermatophores of Sepiola survive as bunches of transparent tubes, some still containing sperm. The gills of AUoteuthis remain evident and possible nidamental glands are visible in females. In places a layer of white crumbly mineralized material is present beneath the pigment layer, but above the mantle muscle. Although the quantity was inadequate for analysis, the crystal form and occurrence are similar to magnesium phosphate that sometimes precipitated in decay experiments on the shrimp Palaemon (Briggs and Kear 1994). After 2 weeks The carcass has shrunk to several amorphous masses. The outline of the arms and the associated eye lenses remains evident. The ink and remains of mantle may survive as one unit (Sepiola) or the gonad alone is intact and three-dimensional (AUoteuthis). Other internal organs have completely decayed or are unrecognizable. Eggs are scattered. The beccublast cells appear white and fibrous and retain their original structure in AUoteuthis. A thin membrane peels away from the inner surface of the gladius (Text-fig. 3e). A white coating of mineralized material (probably MgP04) may be present on the upper surface of gonad and some muscle, as well as on the bottom of the jar. It occurs either as a thin structureless crust or as scattered crystal laths and needles. After 8-10 weeks The head and mantle disintegrate further, and muscle peels away from the pen in places. The arms may be recognizable. The eyes are visible as dark purple areas surrounding the lenses. The gonad remains three- dimensional only in AUoteuthis. focused on Belemnolheutis antiquus (Belemnitida: Belemnotheutidae) and Mastigophora brevipinnis (Teuthida: Mastigophoridae) from Christian Malford, Oxfordshire (Jurassic, Callovian), but material of Plesioteuthis prisca (Teuthida: Plesioteuthididae) and Trachyteuthis hastiformis (Teuthida: Trachyteuthidae) from Solnhofen (Jurassic, Tithonian); Loligosepia ( = Geoteuthis) sp. (Teuthida: Loligosepiidae) from Gloucestershire and Somerset (Jurassic, Upper Lias); and 110 PALAEONTOLOGY, VOLUME 38 Table 4. Decay stages in Loligo. After 1 week The head begins to swell. The outer muscle is stained pink. The sucker rings are fragile and detach easily (Text-fig. 3g). The eyes are represented by dark patches and may have separated from the carcass. The lenses remain intact and the brain cartilage is hard. The buccal muscles shrink and lose their shape when disturbed. The beaks pull out with no resistance; lip muscle tissue may remain attached to the lower beak. After 2 weeks Gas bubbles are present under the skin. The sucker rings, statoliths and eye lenses are stained pink by retinal pigment. The eyes and tentacles fall off and most of the sucker rings detach. The buccal muscle tissue disintegrates. The brain cartilage becomes soft and spongy and no neural tissue remains. After 3-4 weeks The head may float due to the presence of additional gas bubbles. The manus of the tentacles, the eyes and much of the muscle disintegrates. The untanned areas of the beaks are now stained. The anterior of the radula disintegrates. Dark purple-pink crystals of MgP04 form in the skin of the arms and around the shrinking brain cartilage. After 6 weeks The head disintegrates to an amorphous semi-liquid. The beaks disarticulate; some semi-liquid muscle adheres inside the hood area. Only the eyes, brain cartilage and arms are recognizable. Nearly all the sucker rings detach. After 10 weeks Only the arms, tentacles, and a few sucker rings are recognizable, but they disintegrate if disturbed. Many doughnut- and spiral-shaped crystals of magnesium phosphate (Table 5) occur loose and on the arms; they form on the sucker rings which may be embedded within them (Text-fig. 3h-i). Their purple colour is derived mainly from the retina, and to a lesser extent from the chromatophores. After 15-30 weeks A crumbly, largely amorphous mass containing crystals, either individual or clusters of needles up to 3 mm long, covers the bottom of the experimental vessel. Parts of the arms and tentacles may be recognizable. The brain cartilage has largely disappeared. The edges of the beaks decay. The radula disintegrates if disturbed. After 50 weeks The beaks and part of the radula are evident, together with crystals, in a mass of semi-liquid tissue. There is no trace of the suckers. Geopeltis simplex (Teuthida: Geopeltidae) from Boll, Wiirttemberg, Germany (Jurassic, Upper Lias) was also examined. Small pieces of phosphatized mantle were removed from specimens of the Christian Malford taxa Be/emnotlieutis antiquus (specimens NHM C.46898 and NHM C.2456) and Mastigophora brevipinnis (NHM 31362, NHM 46964 and NHM 62231) for investigation by scanning electron microscopy. Where possible, the orientation of the fragments relative to the anterio-posterior axis of the specimens was noted. Muscle fragments from Mastigophora brevipinnis (NHM 31362) were analyzed by electron microprobe. A specimen of Geopeltis sp. (University of Bristol, Geology Department, BRSUG 25602) from Black Ven, Charmouth, Dorset (Jurassic, Lower Lias) was sectioned and polished for analysis by light microscopy, SEM and electron microprobe. KEAR ET AL.\ COLEOID CEPHALOPODS 111 text-fig. 2. SEM micrographs of soft-tissue decay in slow diffusion conditions. A, Sepiola atlantica mantle at 1-5 days, fixed in HMDS for SEM examination. The muscle has largely decayed away, but collagenous tissues (tunics, intramuscular connectives) remain intact. The fibres in the upper portion of the picture have ‘unravelled’ during specimen handling. Scale bar represents 20 /mi. b, same specimen as a showing the cut edge of the mantle. Intramuscular connectives are visible, running between the inner and outer tunic layers. The collagen is covered with bacteria of 2-4-5 /mi in diameter; compare with phosphate spheres in fossil material in Text-fig. 4. Scale bar represents 20 /mi. c, Alloteuthis subulata after 4 weeks, oven dried. Fibrillar phase beccublast cells still insert on the upper beak. The fibrils still cluster into hexagonal clumps, which probably represents the original position of the cells. Scale bar represents 40 /mi. d, the rear edge of the upper beak crest in Alloteuthis subulata after 3 days. The polygonal imprints left by beccublast cells are evident. The chitin of the beak is undecayed at this stage. Scale bar represents 20 /mi. E, Loligo forbesi sucker surface after 3 weeks. The attachment muscles have decayed away, leaving polygonal imprints of chitinoblast cells similar to the beccublasts in d. Scale bar represents 10 /mi. RECENT COLEOIDS Death and decay stages In both experimental and aquarium conditions dead and dying Alloteuthis , Sepiola and Loligo lie on the bottom of the tank. They are ignored by their companions. In contrast, dying Sepia float at or near the surface in both aquarium and natural conditions, and are frequently attacked by conspecifics as well as being an easy target for epipelagic and aerial scavengers. Thus, the mode of dying affects the preservation potential of a given taxon. The tentacles are not normally extended at death and should therefore be concealed in undisturbed carcasses. Any tilting of the carcass head downwards during handling, however, can cause the tentacles to slide from their ‘pouch’, and they also hang down in this way in anaesthetized and dying Sepia. PALAEONTOLOGY. VOLUME 38 text-fig. 3. Decay of structural tissues in recent coleoids under conditions of slow diffusion, a, statolith from an undecayed Loligo forbesi. Scale bar represents 400 /mi. b, surface of Loligo statolith after 4 weeks. The statolith is exfoliating and individual aragonite rhombs are becoming loose. Scale bar represents 10 /mi. c, eye lens from Alloteuthis subulata after 3 days. The lens has been broken along the natural fracture plane to show the internal structure. Scale bar represents 200 /an. d, ventral side of Alloteuthis gladius after 3 days. A membrane covers the surface, obscuring detail of the structure beneath. Scale bar represents 20 /mi. e, ventral view of Alloteuthis gladius after 1 week. The thin membrane has peeled away and the chitin beneath is splitting along natural growth lines. Bacteria are visible on the gladius surface. Scale bar represents 20 /mi. f, sucker in situ on the arm of Sepiola atlantica after 1-5 days. The attachment muscles still hold the sucker ring in place. Scale bar represents 40 /mi. G, a detached sucker ring from Loligo after 1 week. No muscle tissue remains adhering to the chitin. Scale bar represents 400 //m. H, Loligo sucker removed from an arm after 10 weeks. The sucker has been overgrown by magnesium phosphate crystals in a spiral pattern. No organic component remains visible. Scale bar represents 400 /mi. i, close-up of h to show crystal structure. Scale bar represents 100 jum. Specimens illustrated in c to F were dehydrated in HMDS prior to SEM examination. KEAR ET A L.\ COLEOID CEPHALOPODS ] 13 text-fig. 4. SEM of muscle tissue from fossil coleoids. a, transverse section of Belemnotheutis antiquus (NHM C.2456) mantle muscle. Fibrous structure is clearly visible. The massive band at the top of the picture is a layer of varnish. Scale bar represents 40 /mi. b, close-up of a showing the 1-2 pm microspheres of calcium phosphate which make up the muscle fibrils. Scale bar represents 10 /mi. c, longitudinal section of the same specimen with the muscle fibres viewed end on. The massive band on the right is a layer of varnish. Scale bar represents 40 /un. d, close-up of c showing microspheres 1-2 //m in diameter. Scale bar represents 10 /mi. e, Belemnotheutis (NFIM C. 46898) mantle with two sets of muscle fibres meeting at 90°. Scale bar represents 40 /mi. F, Mastigophora brevipinnis (NHM 62231) muscle tissue from the digestive gland sheath. The collagenous sarcolemma is preserved but the fibrils themselves have decayed away. Scale bar represents 10 /mi. The flesh of Alio tent his , Sepiola and Loligo starts to become opaque before they stop respiring, indicating that histochemical changes in the mantle can occur prior to actual death. The flesh of Sepia is opaque in life. PALAEONTOLOGY, VOLUME 38 1 14 Table 5. Composition of mineral phases in fossil coleoids and decaying Loligo. Oxide weights based on electron microprobe analyses (total given as weight per cent, of sample mineralized). Ratio of calcium phosphate to CaC03 based on the assumption that all P205 is incorporated into ideal OH-apatite [Ca5(P04);!0H]. The CaO:P205 ratio is 1:1-32 (based on molecular weights, ignoring H and excess O). The remaining CaO is assumed to form CaCO.s. Specimen % by wt Na20 MgO SiO, A1.A PA so3 FO CaO CaO in phosphate Phos : carb (%) Geopelt is Pen layer 1 60-8 0-2 0-6 0-04 — 1-9 0-1 1-0 560 2-5 4-5 95-5 Pen layer 2 88 1 2-6 0-3 — 005 32-2 1-2 3-2 48-4 42-5 87-8 1 2-2 Pen layer 3 65 1 0-5 0-7 — — 1 1-7 0-4 1-5 49-5 15-4 311 68-9 Pen layer 4 88-0 1-3 0-3 — 002 318 1-0 4-0 49-4 42-0 85-0 15-0 Pen layer 5 70-8 0-7 0-6 — 0-01 16-9 0-7 1-7 49-3 22-3 45-2 54-8 Pen layer 6 95 1 0-8 0-4 — 0-02 33-9 1-4 4-8 53-5 44-7 83-6 1 6 4 Ink sac 83-2 1-5 0-3 — 0-01 30-4 1-7 3-2 45-8 40 1 87-6 12-4 Rock 56-5 0-3 0-8 21 0-83 2-2 0-5 0-2 48-9 2-9 5-9 94- 1 Mastigophora Radial 86 1 0-9 0-3 — — 32-5 0-5 1-9 49-6 42-9 86-5 13-5 Circular 85-6 1-0 0-3 — 0-02 32-4 0-4 1-6 49-5 42-8 86-5 13-5 Rock 75-9 0-4 1-7 34-8 17-54 0-8 2-9 — 10 4 1-1 10 6 89-4 Loligo (4w) Sucker crystal 58-2 0 1 20-6 — 002 37-4 01 01 0-1 0-1 — Table 6. Ultrastructural features preserved in fossil coleoids examined by light and electron microscopy. Species Outer tunic Inner tunic Radial muscle Circular muscle Intramuscular mesh Gladius structure Belemnotheutis Yes ? Yes Yes Yes Yes Geopeltis ? — Yes Yes — Yes Loligosepia Yes — Yes Yes — — Mastigophora Yes Yes Yes Yes Yes ? Plesioteuthis Yes — Yes Yes — Yes Trachyteuthis — — ? ? — Yes Degradation is very similar in carcasses of Allot euthis and Sepiola (Table 3). Only the head and arm crown portion of Loligo were utilized in decay experiments, and studies concentrated on the fate of the structural materials (chitin, collagen, crystalline protein, aragonite) and on the precipitation of minerals in and around the carcass (Table 4). Ultrastructural decay and preservation Muscular disintegration is rapid in all three coleoid species and ultrastructural detail is lost in as little as T5 days. The collagenous component of the muscle (tunic layers and intramuscular connectives) survives longer than the fibrils themselves (Text-figs 2a, b), and is probably responsible REAR ET AL. \ COLEOID CEPHALOPODS 115 text-fig. 5. SEM of collagenous connective tissues from fossil coleoids. a, two outer tunic layers from the ventral surface of Belemnotheutis antiquus (NHM C.2456) (see Text-fig. 1b). The fibres cross at an angle of 30-32°. The axis of the body bisects this angle in living species. Scale bar represents 100 pm. b, close-up of a to show the 0-25-0-5 //m microspheres of which the tunic fibres are composed. Scale bar represents 10 /nn. c, section through the inner tunic and overlying mantle muscle in Mastigophora brevipinnis (NHM 62231). A number of layers are visible. Scale bar represents 4 /nn. d, collapsed intramuscular connective fibres in Mastigophora (NHM 31362). The muscle tissue has vanished leaving only the collagenous support structures and scattered 1-2 pm spheres preserved (compare with Text-fig. 2b). Scale bar represents 40 pm. e, close-up of d; some isolated calcium phosphate spheres are visible adhering to the fibres. Scale bar represents 10 //m. F, close-up of surface texture of intramuscular connective fibre from d. The fibre is preserved in clusters of microcrystallites with a framboid-like texture. Scale bar represents 2 //m. 1 16 PALAEONTOLOGY, VOLUME 38 varnish muscle microspheres banded tunic layer microspherulitic layer chitinoblast layer massive gladius layer banded gladius layer chitinoblast layer muscle microspheres muscle sarcolemma text-fig. 6. For legend see opposite. KEAR ET A L. : COLEOID CEPHALOPODS 117 for the mantle and arms retaining their shape when undisturbed. Although no mineral phases were observed in mantle muscle, the structures and bacteria observed resemble those seen in fossil material (compare Text-figs 2b, 4 and 5). In just two specimens (n — 19) of Alloteuthis (one each in slow and no diffusion; see Briggs and Kear 1993«, 1994) the cells of the upper beak crest area retained some fine structure even after 4 weeks. A fibrous to ‘fluffy’ texture was evident under the binocular microscope, remaining white even after oven drying. When viewed with the SEM these fibres appear to insert directly onto the beak (Text-fig. 2c). They are 200 //m in length and seem to clump in distinct hexagons of about 70-100 pm diameter. Within these clumps are smaller bundles, about 10 /mi in diameter, which could mimic the pattern of beccublast cell imprint on fresh Alloteuthis beaks (Dilly and Nixon 1976). Individual fibrils are about 2 /mi in diameter and show no evidence of M or Z bands. They probably represent fibrillar phase beccublast cells (= muscle holdfasts; Dilly and Nixon 1976) rather than mandibular muscle itself. Analysis by electron microprobe revealed these fibres to be primarily organic, with no significant mineral phases. Their survival may reflect their structural nature and the protected position of the buccal mass. Decay of chitinous tissues In all taxa the beaks survive throughout the duration of the experiments with little alteration (Tables 3-4). SEM analysis shows that the rear edges of the beaks fracture and disintegrate at 10 weeks. Preliminary analyses with the electron microprobe demonstrate that fresh beaks ( Eledone , Todaropsis) have high levels of sulphur and calcium, and sometimes high silicon and chlorine. Potassium, magnesium and phosphate are present, but not in substantial quantities. Examination of Alloteuthis beak material after 4 weeks decay showed that sulphur, calcium and chlorine remain bound within the chitin of the beaks during this period. Other elements in the analysis (Mg, Si, P) decline. Only potassium increases over the 4 week period. Polygonal imprints of beccublast cells identical to those reported by Dilly and Nixon (1976) are evident on the outer surface of the beaks when the buccal muscle has decayed away (Text-fig. 2d). In untanned areas this pattern becomes distorted or obscured as decay progresses. Similar polygonal imprints occur on the outer surfaces of the suckers (Text-fig. 2e) presumably representing the imprint of ‘chitinoblast’ cells, the analogues of beccublasts. In all taxa examined, the radular ribbon is less decay-resistant than the radular teeth which often remain in place until disturbed. The anterior portion of the radula, which carries the old teeth, disintegrates earlier than the posterior portion with its young and newly formed ribbon and teeth. The gladius, despite being untanned, showed little disintegration. No trace was found, however, of the thin chitin of the oesophagus, buccal palps or stomach lining. Decay of calcareous tissues Detailed observations of decay were carried out on the statoliths of Loligo , as their larger size (1-2 mm) made retrieval and examination feasible (Text-fig. 3a). The statoliths show evidence of surface exfoliation after 1 week under slow diffusion conditions, and there is extensive loss of crystal rhombs in weeks 2-4 (Text-fig. 3b). During decay the statoliths become stained with the pigment released by the carcass, becoming progressively darker. The statoliths were not recovered beyond week 6. This could be due to their small size which makes them difficult to detect in the disintegrating carcass, their purple-pink colour which makes them impossible to distinguish from the many crystalline fragments which are associated with Loligo at this stage, or their complete disintegration or dissolution (vessel pH 7- 10-8-46). text-fig. 6. A section through the mantle muscle and inner tunic, the underlying gladius, and the muscle forming a sheath around the digestive gland of Mastigophora brevipinnis. a, SEM montage of specimen NHM 62231. Scale bar represents 40 pm. b, diagrammatic representation of the section in a. See text for details. 118 PALAEONTOLOGY, VOLUME 38 text-fig. 7. For legend see opposite. KEAR ET AL.: COLEOID CEPHALOPODS 119 Decay of eye lenses Initially the eye lenses and surrounding tissues form an intact unit. As early as week 1 the soft tissues have a spongy texture and an imprint is left by forceps tips if they are handled. Soft tissues may remain adhering to the lenses for up to 10 weeks. The eyes remain in situ more often in small carcasses ( Alloteuthis , Sepiola ) than in the large specimens ( Loligo ), but this is simply because the eyes of the small animals ‘rest' on the bottom of the jar and thus have firm support even when the surrounding soft tissue disintegrates. In contrast, Loligo eyes are positioned above the substrate at rest, and collapse with decay of the supporting tissues. The eye lenses themselves cleave along a natural fracture plane (Text-fig. 3c). This can occur as early as week 1 ( Alloteuthis ) or as late as week 50 (Loligo). This difference in timing may be a surface area-volume effect. Prior to full cleavage, a fracture is visible running round the lens (day 3 to week 30). Handling of the lenses often causes cleavage along this plane. FOSSIL COLEOIDS Musculature Morphology. Mantle muscle fibres were observed in Belemnotheutis , Mastigophora , Geopelt is. Loligosepia and Plesioteuthis. Both radial and circular muscle is preserved (Text-fig. 4) but the fibrils or fibres do not always survive. The radial muscles may be represented by raised ridges on the specimens, or they may be missing, leaving a gap between blocks of circular muscle. Where specimens have been conserved by coating in shellac, the varnish fills these gaps and obscures structure. In some specimens ( Belemnotheutis ; BRSMG Ca5242, BR.SMG Cd21) the ‘muscle’ pattern seen is an imprint of the fibres on the surrounding tissues (?tunic). Longitudinal muscle fibres were observed in Belemnotheutis (NHM C.2456), Mastigophora (NHM 62231) and Plesioteuthis (NHM 83731). In the latter two species these fibres are associated closely with the gladius. The muscles of the arms or tentacles have preserved fibres only in Belemnotheutis , in which they are longitudinal. In one specimen (NHM C. 46898) an arm has fractured to reveal longitudinal structure all the way through. The other fibre orientations reported in living coleoids (circular, oblique, helical; Kier 1982, 1988) were not observed. Ultrastructure. Muscle is preserved in two different forms in material from Christian Malford. The first involves replacement of the muscle by ?sheets of microspheres of 1-2 pm diameter (Text-fig. 4a-e; Allison 1988). The scale of the filaments preserved in this way indicates that they represent muscle fibrils (diameter 1-4+10 pi n; Ward and Wainright 1972) rather than whole fibres (diameter 51+2-1 pm ; Ward and Wainright 1972). This form is well represented in Belemnotheutis. The second way in which muscle tissue is preserved is the ‘sarcolemma’ form, first described in fish from the Cretaceous Santana Formation of Brazil (Martill 1990). The core of the fibres has vanished, leaving only the outer sheath of the sarcolemma intact (Text-fig. 4f). The ‘missing’ fibrils text-fig. 7. Anterior-posterior histological sections (silver staining) through the front portion of a juvenile Loligo pealei to show the gladius and associated tissues. Gaps between tissues are histological artefacts. Slides courtesy of Professor J. Z. Young, a, section through the anterior of the gladius at the rear of the head. The upper skin and tunic meet the central keel of the gladius and only a thin layer covers it. Radial and intramuscular fibres are present in the mantle. The layer of chitinoblast cells surrounding the gladius is clear, particularly ventrally. Scale bar represents 100 pm. b, skin and tunic sit directly on top of the keel of the gladius, which rests directly on the brain cartilage. Chitinoblasts surround the gladius, the ventral cells larger than the dorsal, which may be continuous with the inner tunic. Layering within the gladius is evident. Scale bar represents 100 /nn. c, section through the body. The gladius is now embedded within the mantle muscle, and associated with the muscular sheath which surrounds the digestive gland. The chitinoblasts are flattened but still visible in places. Scale bar represents 100 pm. 120 PALAEONTOLOGY, VOLUME 38 would have had a diameter of 2-7 //m each. Preservation of the sarcolemma, in the absence of fibrils, has only been observed in Mastigophora. Composition. Analysis of both radial and circular muscle fibres in Mastigophora shows them to be calcium phosphate. There is no difference in composition between the two muscle forms (Table 5). Connective tissue. The three main types of connective tissue associated with the mantle musculature in Recent squid (outer tunic, inner tunic and intramuscular fibres) are all preserved in Belemnotheutis and Mastigophora. The outer tunic is also preserved in Plesioteuthis and Loligosepia , and possibly in Geopelt is (Table 6). In Belemnotheutis the tunic still preserves the parallel rows of fibres in alternating sheets (Text- fig. 5a, c) which are bisected by the sagittal axis of the specimen at 15-16° (an angle of 27+ 1-0° is recorded in living Loligo and Lolliguncula ; Ward and Wainright 1972). The fibres in the tunics are preserved as microspheres, 0-25-0-5 //m in diameter (Text-fig. 5b). The number of sheets in the tunics varies, but at least three are present in Belemnotheutis. In Mastigophora (NHM 62231 ) there are four to five in the inner tunic, two to three in a tunic-like layer dorsal to the gladius, and one or two in a similar layer ventral to the gladius (layers ii, iv and vii respectively; Text-fig. 6). The intramuscular connective tissue fibres are best preserved in Mastigophora (Text-fig. 5d-f). These fibres are 5-10 pm in diameter and are fragmented into sections 20-150 pm long. The texture of these fibres is reminiscent of framboids, in that they consist of spheres composed of crystallites of < 01 //m (Text-fig. 5f). Ward and Wainright (1972) measured intramuscular connective tissue fibres of diameter 2-6 + 0-74 //nr in living material. A section through Mastigophora from Christian Malford In specimen NHM 62231 a section through the gladius and surrounding tissues revealed nine separate layers (Text-fig. 6). These are: (i) a muscle layer, about 70 //m thick, composed of microspheres of 1-2 pm diameter, texturally similar to the muscle preserved in other specimens, but with a lower order of information retained; (ii) a layer about 10 pm in total thickness, consisting of four to five sheets, representing the inner boundary tunic associated with the muscle layer (i) (Text-fig. 5c); (iii) another microspherulitic layer running parallel to the gladius, with a total thickness of about 60 pm. with bands of smoother material within it; (iv) a thin (c. 2-3 pm) layer of compacted microcrystallites or spheres similar to those evident in Belemnotheutis tunic (Text-fig. 5a-b); (v) a massive layer, thickness c. 40 pm, with a fracture reminiscent of the desiccation cracks in dried beak material; (vi) a layer about 80 //m thick, with a conchoidal fracture and banded structure. Some of the fractures from layer (v) run parallel to or into this, so it may be a different face of the same material. The bands look like growth lines, with finer lines visible within broad striation. Broad bands are about 1-2 pm and find bands about 0-3 pm thick. Layers (v) and (vi) represent the gladius. (vii) another layer, c. 3 pm thick, of tunic-style microspheres 0-25 to 0-5 //m in diameter; (viii) disorganized microspheres of 1-2 pm diameter representing muscle tissue with low order preservation that grades into layer (ix); (ix) sarcolemma style preservation. The sarcolemma sheaths appear to have a granular texture, composed of crystallites/grains about 0-1 //nr in size (Text-fig. 4f). ‘Muscle’-sized microspheres are scattered around, but not organized into fibres. The hollows in the sarcolemma ( = site of fibres) run parallel to the gladius. The combined thickness of layers (viii) and (ix) is about 200 pm. REAR ET AL. \ COLEOID CEPHALOPODS 121 Comparing the structures with living material (see Text-fig. 7), the Mastigophora specimen is interpreted as a section from the dorsal mantle to the muscular sheath of the digestive gland. Layers (i), (viii) and (ix) are undoubtedly muscle, the last two representing the digestive gland sheath which sits ventral to the gladius (Text-fig. 7c). The banded structure in layer (ii) is the inner tunic of the mantle muscle. Layer (iii) does not retain enough structure for a precise interpretation. It may represent either a second muscle band, or epithelial tissue associated with the secretion of the gladius. The mantle muscle is not split into two layers in modern coleoids, so the latter interpretation is more likely. Examination of recent material shows the presence of a layer of epithelial cells surrounding the gladius (Text-fig. 7). Under the light microscope these are similar in morphology to the odontoblasts associated with the radular sac (Nixon 1968), the beccublasts reported by Dilly and Nixon (1976) and the ‘chitinoblasts’ of Kear (1990). Because of their association with the gladius, layers (iv) and (vi) are suggested to be the remains of these chitinoblast cells. Layers (iii) and (iv). in combination, may be the dorsal chitinoblasts: (iii), responsible for chitin secretion; and (iv), the remains of the fibrillar material which anchors the mantle muscle to the pen. Complex layering of this type is also preserved in Belemnotheutis antiquus. In the tissues dorsal to the gladius of specimen NHM C.2456 twelve layers can be distinguished using the binocular microscope. The topmost two are identifiable as tunic layers (see Text-fig. 5a), and the third as muscle fibres (Text-fig. 4a-d). Layer (viii) shows very fine fibres running at 60° to the orientation of the muscle fibres and may be another tunic type layer. No structure was evident in the other layers. A section through Geopeltis from Charmouth An incomplete specimen (BRSUG 25602) of the loligosepiid Geopeltis , preserved in a nodule from the Lower Lias of Black Ven, Charmouth, Dorset, was studied. The form of the gladius identifies the specimen, which preserves the ink sac near the midline. text-fig. 8. Polished sections through the gladius and associated soft tissues of Geopeltis sp. from Charmouth, Dorset (BRSUG 25602). A, the edge of the rachis of the gladius, with layered structure clearly visible. Sparry calcite is present in the wider portion to the top of the photograph. Scale bar represents 500 /mv b, counterpart of the specimen. The thin layers of the gladius are to the right, with fibrous material overgrown by calcite immediately beneath. The other bands reveal no ultrastructure. Scale bar represents 100 pm. 122 PALAEONTOLOGY, VOLUME 38 The broad gladius is about 1 mm in total thickness. A layered structure is evident, with alternating brown and yellow-white bands. At the very edge of the gladius there are eight layers present (Text-fig. 8; compare with the cross sections of modern gladius material in Text-fig. 7). On the counterpart four layers were visible with the binocular microscope, and a further two revealed by the electron microprobe. Fibrous structure is visible within the surface layer (Text-fig. 8b); individual fibres have clearly defined edges with smaller fibrils running obliquely within them. This may represent the original structure of the gladius. Soft tissues are represented by white to brown material. On the part this ‘organic’ material appears to be slumped on and around the gladius, with no ultrastructure preserved. Sparry calcite is associated with this material. There appear to be two generations of diagenetic calcite present. On the counterpart there is fibrous structure within the ‘organic’ material (Text-fig. 8b) and it is layered, different layers showing different degrees of ultrastructural preservation and overgrowth by calcite. Similar layered structure is preserved in the gladius and muscle tissue of coleoids ( Trachyteuthis hastiformis , Plesioteuthis prisca) from the Solnhofen limestone (NHM 83730 and 83731). Six layers are evident in a section of Trachyteuthis under the binocular microscope: five of these are gladius and the sixth possibly mantle muscle. Striations, fibres and sub-layers are evident within the main bands of gladius material. This structure may reflect original morphology. In Plesioteuthis six gladius and two possible mantle muscle layers are visible. Composition of fossil material Analysis of muscle tissues from Mastigophora (Table 5) shows no difference in the composition of radial and circular muscle. Calcium phosphate and calcium carbonate (Table 5) were present in material from the gladius and ink sac of Geopeltis. In the gladius the proportions vary from almost pure fluorapatite (layers 2, 4 and 6), through a phosphate-carbonate mixture (layers 3 and 5), to high carbonate (layer 1). Material from the ink sac is also calcium phosphate (fluorapatite) with some carbonate, and a low organic content (Table 5). These compounds reflect diagenetic mineralization and not original gladius or ink composition. Beyermann and Hasenmaier (1973) demonstrated the presence of melanin in the preserved ink sacs of specimens of Geoteuthis from the Posidonienschiefer (Lias) of Germany using infrared spectrometry. The calcium carbonate in the gladius may be the diagenetic sparry calcite abundant elsewhere in the specimen. Hewitt and Wignall (1988) analysed a specimen of Trachyteuthis from the Kimmeridge Clay (Late Jurassic) of England and determined that it was composed of francolite. They interpreted this as implying an originally phosphatic composition, i.e. as a diagenetic replacement of a shell composed of chitin and brushite. Hirschler et cil. (1990) demonstrated experimentally that aragonite can be replaced by calcium phosphate. Analyses of fossil material (above) and experimental results (Briggs and Kear 1994) confirm that a range of original tissue compositions may be altered to calcium phosphate. Thus the ‘shell’ of Trachyteuthis may have been originally aragonitic in composition. DISCUSSION The precipitation of crystals A striking result of the decay experiments was the precipitation of crystals of magnesium phosphate, particularly in association with Loligo. Experiments run under the same conditions of slow diffusion on the crustaceans Crangon and Palaemon (Briggs and Kear 1994) commonly resulted in the formation of crystal bundles of aragonite. However, laths of magnesium phosphate formed on a Palaemon carcass that had decayed under these conditions for 75 weeks. The replication of soft tissue in calcium phosphate was much more prevalent in experiments run under different ‘closed’ conditions (Briggs and Kear 1994). Whether such soft tissue mineralization can be induced in similar experiments on coleoid cephalopods remains to be investigated. KEAR ET AL.: COLEOID CEPHALOPODS 123 Table 7. Habitat, post-mortem effects and preservation potential of living coleoid families. Data from Schafer (1972), Clarke et al. (1979), Clarke (1985), Nesis (1987), Lipinski and Jackson (1989), Croxall and Prince (1994). Jackson and Mladenov (1994) and this study. * Positive post-mortem buoyancy is assumed where the coleoid is ammoniacal, although data for all families are not available. Classification after Clarke (1988). Habitat Buoyancy Type Life Post-mortem* Sepiida Spirulidae Oceanic Midwater Shell Neutral Sepiidae Shelf Benthic Shell Neutral Positive Sepiadariidae Shelf Benthic Shell Neutral Sepiolida Sepiolidae Shelf Benthic Muscular Negative Negative Idiosepiidae Shelf Benthic Muscular Negative Teuthida Pickfordiateuthidae Oceanic Midwater Muscular Negative Loliginidae Shelf Midwater-benthic Muscular Negative Negative Lycoteuthidae Shelf-oceanic Midwater Ammonia Neutral Positive Enoploteuthidae Oceanic Midwater Ammonia Negative Ancistrocheridae Oceanic Midwater-benthic Ammonia Neutral Pyroteuthidae Oceanic Midwater 9 Negative Octopoteuthidae Oceanic Midwater Ammonia Neutral Positive Onychoteuthidae Oceanic Midwater-benthic Ammonia Neutral Positive Cycloteuthidae Oceanic Midwater Ammonia Neutral Positive Gonatidae Oceanic Midwater-benthic Oil Neutral ?Positive Psychroteuthidae Oceanic Midwater ? ?Negative ?Negative Lepidoteuthidae Oceanic Midwater Ammonia Neutral Positive Pholidoteuthidae Oceanic Midwater 9 Negative Architeuthidae Oceanic Midwater-benthic Ammonia Neutral Positive Histioteuthidae Oceanic Midwater Ammonia Neutral Positive Neoteuthidae Oceanic Midwater 7 Negative Positive Bathyteuthidae Oceanic Midwater Ammonia Neutral Positive Ctenopterygidae Oceanic Midwater 7 Negative Brachioteuthidae Oceanic Midwater 7 Negative Batoteuthidae Oceanic Midwater Ammonia Neutral Positive Ommastrephidae Shelf and slope Midwater-benthic Muscular Negative Both positive and Thysanoteuthidae Oceanic Midwater Muscular Negative negative records Chiroteuthidae Oceanic Midwater Ammonia Neutral Positive Mastigoteuthidae Oceanic Midwater Ammonia Neutral Positive Promachoteuthidae Oceanic Midwater 7 ?Negative Grimalditeuthidae Oceanic Midwater Ammonia Neutral Positive Joubiniteuthidae Oceanic Midwater Ammonia Neutral Positive Cranchidae Oceanic Midwater Ammonia Neutral Positive Vampyromorpha Vampyroteuthidae Oceanic Midwater Sulphate Neutral Octopoda Cirroteuthidae Oceanic Benthic Sulphate Neutral Stauroteuthidae Oceanic Benthic Sulphate Neutral Opistoteuthidae Oceanic Benthic Sulphate Neutral Bolitaenidae Oceanic Midwater Sulphate Neutral Amphitretidae Oceanic Midwater 7 7 Idioctopodidae Oceanic Benthic 7 7 Vitreledonellidae Oceanic Midwater Sulphate Neutral Octopodidae Shelf Benthic Muscular Negative Negative Tremoctopodidae Oceanic Midwater Muscular Negative Ocythoidae Oceanic Midwater Muscular Negative Argonautidae Oceanic Midwater Muscular • Negative Alloposidae Oceanic Midwater Sulphate Neutral 124 PALAEONTOLOGY. VOLUME 38 Differential survival of chitinous structures The thick, tanned a chitin of the beaks survived longest and with least damage in the experiments (for 50 weeks in Loligo). Buccal masses are routinely allowed to rot for a few days in a jar of sea or tap water to extract beaks for taxonomic purposes because this avoids damaging untanned areas (Clarke 1986; Kear 1990). The tanned portions of the radula (also a chitin; see Table 2) persisted longer than the untanned: the teeth may survive even when the ribbon has disintegrated. The pen (untanned f chitin) also suffered little damage, but the oesophageal cuticle (untanned a) and the stomach lining (untanned y) do not seem to survive. The suckers (ft chitin, untanned) also degenerated quickly but they are preserved in one specimen of Belemnotheutis (BRSMG Ca5240) from Christian Malford (Donovan and Crane 1992). Thus thicker, tanned chitinous structures have a higher preservation potential. Cephalopod beaks are robust as evidenced by their survival in the digestive tract of marine vertebrates (whales, seals, albatrosses). Sperm whales find them indigestible and regurgitate large quantities of beaks, which can be found covering the seafloor at certain localities (Clarke 1962). Aggregations of beaks have not been reported from the fossil record, even though the earliest record of sperm whales (Physeteridae) is lower Miocene (Stucky and McKenna 1993), and earlier marine vertebrates preyed on cephalopods (see e.g. Pollard 1968; Martill 1986). Isolated fossil examples, however, are known (e.g. Dzik 1986). Other decay resistant structures Traces of the brain cartilage (collagen) may last up to 20 weeks. As other collagenous tissues (tunics, sarcolemma) preserve well, the brain cartilage would also be expected to survive in fossil material Fischer and Riou (1982a) interpreted paired structures behind the eyes in Romaniteuthis gevreyi (Callovian of La Voulte-sur-Rhone) as brain cartilage. In other material, extensive preparation in the head region may be required to reveal the presence of the cartilage. The statoliths (aragonite) exfoliate during decay and eventually vanish. This disappearance may be real or an artefact of sampling technique. Isolated statoliths are found in the fossil record (Clarke and Fitch 1975; Clarke and Maddock 1988), but none has been reported associated with a body fossil. Possible explanations include: (1) isolated statoliths may have passed through the gut of a predator before reaching the seafloor; (2) exceptionally preserved fossils would need sectioning or extensive preparation to reveal the presence of statoliths within the head; and (3) the statoliths may have recrystallized during diagenesis. During decay the eye lenses eventually cleave and stain, but seem otherwise undamaged. They are preserved in coleoids from La Voulte-sur-Rhone (Fischer and Riou 1982a, 1982&) but have not been reported from Christian Malford. Eye lenses follow the same pattern of cleavage and are stained orange-brown when they undergo digestion by vertebrates (dogfish and albatross). In addition, digested eyes exfoliate, the various layers of the lens starting to peel away from the centre. This may represent a terminal stage of disintegration not reached during the course of our decay experiments. The influence of buoyancy on preservation potential In life, coleoids can be divided into two groups (Table 7): negatively buoyant (14 families; Clarke 1985) and neutrally buoyant (25 families; Clarke 1985). The muscular, active swimmers (Loliginidae, Ommastrephidae) which are the target for commercial squid fisheries are typical examples of negatively buoyant species. Living coleoids achieve neutral buoyancy by four different methods (Clarke el al. 1979; Clarke 1985). These are: (a) the use of gas-filled shells in ‘true’ cuttlefishes and Spirulidae; (b) substitution of sulphate ions by chloride ions within the body tissues of some oceanic octopods, e.g. Cirroteuthidae, and the Vampyroteuthidae; (c) storage of low density fats in the digestive gland in the Gonatidae; and (d) the accumulation of ammonium chloride ions in sixteen families of oceanic squid, e.g. Architeuthidae, Cranchiidae (Table 7). REAR ET AL.. COLEOID CEPHALOPODS 125 A freshly dead or dying coleoid may either sink or float. Observations from aquarium animals, decay experiments (Schafer 1972; Lipinski and Jackson 1989), and the mass mortalities associated with spawning (I l lex illecebrosus in Newfoundland, Loligo opalescens in California, and Loligo vulgaris reynaudii in South Africa) indicate that the majority of negatively buoyant animals remain so at death. Ommastrephids, however, have been observed floating after mass mortalities and stranded on beaches. These events represent death during the migration phase of the life cycle, not post-spawning mortality (M. R. Clarke, pers. comm.). The normally neutrally buoyant Sepia , with its large internal shell, floats in the early stages of decay (Schafer 1972; Lipinski and Jackson 1989; personal observations), indicating a rapid post- mortem shift to positive buoyancy. This may take place before the animal is dead; morbid animals lose their ability to regulate buoyancy. Subsequent loss of the ‘cuttlebone’ as Sepia decays allows the rest of the carcass to sink (Lipinski and Jackson 1989). Conversely, our experimental observations on Loligo heads indicate that negatively buoyant species may be buoyed up by decay gasses after a period on the sea floor (depending on the depth of water: see Allison et al. 1991). Kondakovia longimana is an ammoniacal squid (family Onychoteuthidae). Analysis of its tissues show that it contains almost double the ammonia found in other species which use this buoyancy mechanism (3294 mM compared with 199-6-206-9 niM in Moroteuthis of the same family) and that it has very loosely arranged bundles of muscle fibres, with the ammoniacal fluid filling the ‘gaps’ (Lu and Williams 1994). This tissue chemistry results in post-mortem positive buoyancy. Most records of Kondakovia are from predator stomachs (albatrosses, petrels, whales) and sightings of dead individuals at the sea surface. There are very few records of live captures (Lu and Williams 1994). As albatrosses are incapable of diving to great depths (6-12 m; Croxall and Prince 1994) they are assumed to be scavenging on Kondakovia floating at or near the surface (Lu and Williams 1994). The giant squid Architeuthis is occasionally found stranded or floating at the sea surface. Whilst some of these specimens are undoubtedly the regurgitations of sperm whales, several have been reported as still alive (Verrill 1880), showing that the ammoniacal Architeuthis was positively buoyant when dying. In animals that are neutrally buoyant at death and settle rapidly to the sea-floor the tentacles remain concealed within the cone of the arms. By contrast, in morbid and dying Sepia , or in carcasses that are handled, the tentacles slip out and hang loose in the water (Text-fig. 9). Hence, an exceptionally preserved animal which only displays four pairs of arms may have the tentacles concealed. Thus Plesioteuthis presumably had tentacles even though they have not been recorded. A morbid animal which floats will be spotted by scavengers (including cannibalistic conspecifics) very easily, and is also unlikely to get buried. In ‘sinking’ species an annual event such as a spawning mass mortality will attract scavengers in large numbers so carcasses are unlikely to be left undisturbed. Carcasses of Loligo opalescens are rapidly removed from the shelf spawning grounds into deeper water by currents (R. Starr, pers. comm.). A similar process may explain the mass accumulations of belemnite rostra in some localities (Doyle and MacDonald 1993). Species with the highest potential for fossilization are those benthic shelf species that remain negatively buoyant after death ( Octopus , Sepiola) or those which spawn in mid-water producing a neutrally buoyant egg mass and a negatively buoyant carcass (e.g. the Ommastrephidae) which may fall into anoxic bottom water. Table 7 categorizes the ecology of modern cephalopods and t heir post-mortem buoyancy. Belemnotheutis possessed a phragmocone and might be expected to mimic Sepia physiologically and be neutrally buoyant in life and positively buoyant after death. However, the occurrence of exceptionally preserved material seems to indicate that there was little or no positive phase, the carcass reaching the seafloor rapidly after death. The phragmocone may not have represented as large a proportion of the body in Belemnotheutis as it does in Sepia , so it may not have been capable of refloating the carcass. If the high proportion of living teuthids that become positively buoyant after death (Table 7) is paralleled in extinct genera, it requires an agent such as rapid burial and/or a soupy substrate (Martill 1993) to be invoked where the soft tissues of the fossil forms are preserved (Allison 1988). 126 PALAEONTOLOGY, VOLUME 38 C neritic squid, e.g. Loligo negatively buoyant carcass D oceanic squid -> positively buoyant carcass e.g. Kondakovia negatively buoyant carcass e.g. Pickfordiateuthis continues to sink text-fig. 9. Cephalopod habitats and buoyancy (before and after death), a, benthic octopods remain negatively buoyant after death and have a relatively high preservation potential, b, cuttlefish have positive post- mortem buoyancy and a low preservation potential, c, neritic squid have negative post-mortem buoyancy and a high preservation potential. Tentacles do not extend at death. D, oceanic squid families may have either positive or negative post-mortem buoyancy. In negatively buoyant families preservation potential is lower than for their neritic counterparts, and decay will commence before reaching the seafloor. The potential for fossilization is lower still in positively buoyant species. In both cases tentacles will extend during movement of the carcass through the water column. The influence of sex and maturity on preservation potential In our experiments the ovary maintained the three dimensional shape of the rear portion of the body, and may be responsible for holding the disintegrating mantle in place. Whilst spermatophores and sperm may survive some time (10 days in Sepiola ) they do not show the same cohesion. However, as it is energetically more expensive to produce eggs than sperm, females divert more of their resources to reproduction than males (an extreme case being the disintegration of the mantle in Moroteuthis ingens; Jackson and Mladenov 1994). In spent animals, therefore, males are more likely to be preserved than females. A further complication is that eggs, in common with other tissues, swell through osmosis as they decay. In a mature Sepiola carrying large eggs, this process tears the body apart. In Alloteuthis , of mid range maturity, the presence of an ovary enhanced the preservation of the body outline (see above). In an immature female (ovary undeveloped) or male, presumably a 'normal’ disintegration pattern would be seen. As determination of sexual maturity or gender in fossil coleoids is problematic (although sexual dimorphs can be recognized, e.g. Doyle 1985), such biases may be difficult to identify. REAR ET AL.: COLEOID CEPHALOPODS 127 Phylogenetic implications of ultrastructural preservation The discovery of a ‘modern’ mantle structure in Jurassic cephalopods which possessed a phragmocone (Belenmotheutis) and in those without ( Geopeltis , Loligosepia , Mastigophora , Plesioteuthis ) is of phylogenetic interest. It supports the view (Donovan 1977; Doyle et al. 1994) that the squid grade of organization had already evolved by the Jurassic. Other Jurassic and Cretaceous genera appear to have mantle tissue with a similar structure to that reported here, although they have not been examined using the SEM. They include Sueviteuthis (Toarcian), Teudopsis (Toarcian), Kelaeno (Tithonian), Leptotheuthis (Tithonian), Paraplesioteuthis (Tithonian), Trachyteuthis (Tithonian) and Dorateuthis ? (Santonian). The Phragmoteuthidae have been regarded as the stem group ancestral to these genera (Donovan 1977). A Toarcian Phragmoteuthid from Holzmaden, Bavaria, (in the Museo Civico di Storia Naturale, Milan) shows what appear to be packets of radial muscle, up to 3 mm long, under the optical microscope, in contrast with the longer bands in other fossil coleoids and in Recent squids. This is tentatively regarded as a more primitive condition. Squid mantle (Ward and Wainwright 1972) differs from octopus mantle (Gosline and DeMont 1985) in its detailed structure. The system of collagen tunics and intramuscular fibres in squids prevents longitudinal extension of the mantle during contraction of the circular muscles (Wells 1988). In octopods the same function is performed by longitudinal muscles, which are absent from the main part of the squid mantle. The octopod arrangement may permit greater flexibility of the mantle, at the expense of higher energy expenditure (Gosline and DeMont 1985). The possession of tunics and intramuscular collagen fibres links Belenmotheutis and Mastigophora to living Decabrachia (Teuthida, Sepiida and Sepiolida) rather than Octobrachia (Cirroctopoda and Octopoda). Belenmotheutis and the related Acanthoteuthis (Donovan and Crane 1992), both with phragmocone and ten undifferentiated arms, must stand close to the ten-armed forms from which the arm arrangements in living Octobrachia and Decabrachia were derived (Bandel and Boletzky 1988; Boletzky 1992). However, they had already evolved the decabrachia type of mantle. Mastigophora (number of arms unknown, without phragmocone) represents a further stage toward modern squids, whether or not it lay on or near the direct line of evolutionary descent. The presence of squid-type musculature in Belenmotheutis calls into question the current systematic placing of the genus in Belemnitida (Jeletzky 1966; Bandel and Kulicki 1988) accepted by Donovan and Crane (1992). The Belemnoidea (Aulacocerida, Belemnitida and Diplobelida) are now considered to have diverged from the ancestors of Phragmoteuthida and modern squids in the Late Palaeozoic (Doyle et al. 1994). The structure of the mantle musculature in typical Belemnoidea (i.e. with well-developed rostrum) is unknown. If Belenmotheutis is a belemnitid then the squid-type mantle structure had either evolved by the Late Palaeozoic, or evolved independently in Belemnitida and in Loligosepiida (which include Mastigophoridae) subsequently. Both these possibilities are unlikely, and the position of Belenmotheutis remains to be resolved. If the highly specialized mantle structure of squids evolved only once, as seems likely, then the monophyletic group of Recent squids and cuttlefish (Clarke 1988) can be extended back in time to include the fossil forms discussed in this paper. The mantle structure of the Octobrachia may have evolved from that of the squids or, more probably, they represent a separate monophyletic group. The presence of typical squid mantle structure in the Jurassic suggests that coleoid physiology had evolved by that time. Wells et al. (1992) contrasted the physiology of coleoids with that of Nautilus , which can survive in conditions of very low oxygen tension, whereas coleoids with their more active life style and high metabolic rate cannot. The fossil record of coleoids, apart from the Aulacocerida, before the Jurassic is almost non-existent, but coleoid organization probably began to evolve in Phragmoteuthida at least as early as the Late Permian, and had given rise to typical squids by the Late Norian (Triassic; Reitner 1978). 128 PALAEONTOLOGY, VOLUME 38 CONCLUSIONS Although the three coleoid species investigated, the squids Alloteuthis subulata and Loligo forbesi, and the sepiolid Sepiola atlantica, degraded in a similar series of stages and at comparable rates under experimental conditions (Tables 3, 4) a range of factors, including habitat and buoyancy (Table 7), will ensure a diversity of preservation potential among coleoids. The amount of phosphate required for the extensive mineralization of specimens from Christian Malford and other localities must have exceeded that available in the carcass itself. The additional source was presumably phosphate concentrations that built up in the sediment beforehand (Allison 1988; Martill 1988). Some decay is necessary to promote mineralization, and all the fossil specimens show evidence of degradation. The experiments on modern squid show that ultrastructural detail in muscle may be lost in as little as T5 days (under conditions of Alow diffusion’: Briggs and Kear 1993r/, 1994) although not all the muscle tissue decays at the same time. Experiments on mineralization indicate that the formation of calcium phosphate is more prevalent under ‘closed’ conditions where it takes some time to initiate after the onset of decay (two weeks in shrimp experiments: Briggs and Kear 1993 A 1994). Precipitation then builds up over a period of weeks. Detailed documentation of the ultrastructural detail preserved in phosphatized soft tissue (as opposed to the texture of mineralization) has previously been confined to taxa from the Lower Cretaceous Santana Formation of Chapada do Araripe, Brazil (Martill 1988, 1989, 1990; Wilby and Martill 1992) and the Upper Jurassic Cordillera de Domeyko of Chile (Schultze 1989). Coleoid cephalopods have not been reported from the Santana Formation and there are no SEM studies of the rare examples from the Cordillera de Domeyko (Schultze 1989). This investigation therefore demonstrates, for the first time, the range of tissues that may be preserved with ultrastructural detail in phosphatized fossil coleoids. This study emphasizes that this kind of preservation is not confined to a small number of Konservat-Lagerstatten, but is more widespread (see, for example, Briggs et al. 1993). It is becoming increasingly clear that there is considerable potential for informative histological studies of the soft tissues of a range of fossil organisms. Acknowledgements. We are grateful to: E. Brown, F. Frettsome and R. Swinfen of the Plymouth Marine Faboratory for provision of fresh cephalopod material; J. Z. Young for access to histological material; S. Powell for assistance with the SEM and photography; M. Simms for donation of the Fias Geopeltis\ P. Crowther for access to the Bristol City Museum collections; M. K. Howarth (Natural Flistory Museum) for permission to remove pieces of specimens for SEM ; and S. Baker and J. Cooper for facilitating access to the NHM collections. P. A. Allison, P. Doyle and D. M. Martill commented on an earlier draft. The Zoological Society of London granted permission to reproduce Text-figure 1a-b. This work was funded by NERC grant GR3/7235 to DEGB, and by the Department of Social Security and Bristol City Council Housing Department. 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DONOVAN Typescript received 21 December 1993 Revised typescript received 14 September 1994 Geology Department University of Bristol Bristol BS8 IRJ. UK APPENDIX: SPECIMENS EXAMINED FOR THIS STUDY NHM, Natural History Museum; BRSMG, Bristol City Museum; BRSUG, University of Bristol, Geology Department; *, material removed for examination by scanning electron microscopy; t, material removed for examination by electron microprobe. Species Repository Specimen number Locality Belemnotheutis antiquus NHM BRSMG BRSMG BRSMG Geopeltis simplex NHM Geopelris sp. BRSUG Loligosepia ( = Geoteuthis) NHM NHM NHM Mastigophora brevipinnis NHM BRSMG Plesioteuthis prisca NHM Trachyteuthis hastiformis NHM C2456*, C46898* Ca 5240 (Lectotype) Ca 5242 (Type specimen) Cb 7661, Cd 18a, b, Cd 21, Cd 22a, Cd 22b C580 25602f C5260 C9922 Cl 26 19 31362*f, 46964*, 62231* Cd 32, Cd 37, Cd 38a, b, Ce 17967a, b 83731, 83732, C1046, C46284a, C46847, C46869, C46880, C46886 83730 Christian Malford, Oxfordshire Christian Malford, Oxfordshire Christian Malford, Oxfordshire Christian Malford, Oxfordshire Boll, Wurtemberg, Germany Black Ven, Charmouth, Dorset Dumbleton, Gloucestershire Gloucestershire Near Ilminster, Somerset Christian Malford, Oxfordshire Christian Malford, Oxfordshire Solnhofen, Germany Solnhofen, Germany A NEW PALAEONTOLOGICAL TECHNIQUE DESCRIBING TEMPORAL SHAPE VARIATION IN MIOCENE BIVALVES by TRACY A. GLASSBURN Abstract. Principal components quantitative shape analysis (PC shape analysis) is demonstrated to be a rapid and effective palaeontological morphometric technique for quantifying shape. It allows easy interpretation, as morphology can be reconstructed from PC scores. Results of PC shape analysis have revealed that temporal patterns of shape variation in four Chesapeake Group (Miocene) taxa from Maryland are not congruent. Whilst there was a significant monotonic trend towards more disc-shaped valves in Dosinia acetabulum , there was no significant temporal trend in Lucina ( Stewartia ) anodonta valve shape. Whilst the evolutionary tempo in an Anadara lineage was more consistent with punctuated equilibrium, with interspecific changes controlling ultimate shape transformation and reversing intraspecific trends, the Astarte lineage had an evolutionary tempo not inconsistent with phyletic gradualism, where intraspecific trends were generally preserved during speciation. Presently, no universal method for measuring shape exists. Commonly, morphological techniques utilize measured distances between homologous landmarks as shape variables (reviewed in Bookstein et al. 1985). However, if there is a paucity of distinct homologous landmarks (e.g. with simple invertebrates) shape information will be limited. The development of automated image analyzers has led to the creation of better techniques for describing simple invertebrate shape by making use of a nearly continuous representation of an organism’s outline. Whilst the outline may not include all critical morphological features, our perception of differences in shape is based largely upon outlines (Scott 1980). Like Fourier (Schwarz and Shane 1969; Ehrlich and Weinberg 1970) and Eigenshape analysis (Lohmann 1983), the PC shape technique (Parks 1983, 1987) has been developed to process the large data sets generated by image analyzers. The major objective of this study was to develop the PC shape technique as a palaeontological tool for describing temporal variation in bivalve morphology. Miocene bivalve genera from southern Maryland were selected because the stratigraphy and palaeoecology of the Chesapeake Group and the taxonomy, taphonomy and palaeoecology of the genera have been studied extensively. The results are compared with earlier studies which describe evolutionary tempos of the same Chesapeake Group genera from Maryland. MATERIALS AND METHODS Study area and bivalve taxonomy Temporal variation in shape was characterized for eight Early to Late Miocene bivalve species, comprising Dosinia acetabulum (Conrad), Lucina ( Stewartia ) anodonta Say, Anadara subrostrata (Conrad), A. staminea (Say), A. idonea (Conrad), Astarte cuneiformis Conrad, A. thisphila Glenn and A. perplana Conrad (Table 1, Text-fig. 1). In a written communication to Kelley (1983a), Blackwelder recognized the congeners of Anadara and Astarte as being part of lineages with direct ancestor/descendant relationships. Taxonomies are based upon Glenn (1904) with revisions by Yokes (1957), Moore (1969) and Bretsky (1976). | Palaeontology, Vol. 38, Part. 1, 1995, 133-151. | ©The Palaeontological Association 134 PALAEONTOLOGY, VOLUME 38 table 1. Number of specimens sampled in each ‘zone’. ‘Zone’ Taxon 10 14 16 17 19 22 24 Anadara sp. A. subrostrata (Conrad) A. st amine a (Say) A. idonea (Conrad) 36 16 17 37 60 96 Astarte sp. A. cuneiformis Conrad A. thisphila Glenn A. per plana Conrad 45 3 7 36 3 32 Dosinia acetabulum (Conrad) 10 22 6 41 42 Lucina (Stewartia) anodonta Say 39 37 12 9 69 Species were identified and traced in the field in order to preclude the loss of samples through breakage during transport. Whole shells only were collected, and thus the study is biased towards better preserved bivalves. Furthermore, adult specimens within a narrow size range were sampled to limit ontogenetic effects. Fossils were collected from fifteen exposures located principally along the western shore of Chesapeake Bay (Text-fig. 2). The strata are part of the Chesapeake Group which is nearly continuously exposed for approximately 60 km, trending north-south, and coinciding roughly with the southerly dip direction of the unconsolidated siliciclastics. The Chesapeake Group in southern Maryland has been divided into three formations, designated the Calvert, Choptank and St Mary's formations (Shattuck 1904; Text-fig. 3). Shattuck (1904) subdivided the formations into twenty- four ‘zones’ based upon lithology and major shell beds. Difficulties in recognizing formation contacts (Dryden 1930; Gernant 1970; Blackwelder and Ward 1976) and the disputed assumption that all of the ‘zones’ are laterally continuous and synchronous has led to controversy surrounding the stratigraphical relationships and nomenclature. However, it was not an objective of this study to tackle stratigraphical problems within the Chesapeake Group and therefore, for the purpose of this study, Kidwell's (1988, 1989) classification scheme has been adopted (Text-fig. 3). The Miocene of southern Maryland records a period of regression during which marine, paralic and non-marine sediments were deposited within the Salisbury embayment (Gibson 1962; Gernant 1970; Kidwell 1988). The Salisbury embayment (which is an extension of the Baltimore Canyon trough) is a structural basin the depth and boundaries of which have varied with changes in tectonic and eustatic controlling factors (Newell and Rader 1982). Basin margin disconformities bracket ten transgressive-regressive cycles which commonly contain major shell beds at their base, representing condensed transgressive lag deposits (Kidwell 1984, 1986). The PC shape technique Fossil outlines were digitized using a Houston Hipad II digitizing tablet and stylus. Approximately 1 50-200 data points were recorded for each shell using fortran77 program, digitize, written by Parks (1983, 1987). Operator error, determined by digitizing the same set of shapes twice, was 0-5 per cent. Fossil outlines were rotated to a common orientation using one of two fortran77 programs, binpaxm or modrot3, developed and written by Parks (1983, 1987). Elongate genera were rotated using binpaxm which first calculated the principal eigenvector or axis of greatest length, according GLASSBURN: MIOCENE BIVALVES 135 text-fig. 1 . a, inferred life position of Lucina ( Stewartia ) anodonta Say according to Bretsky (1976). b, Anadara subrostrata (Conrad), c, inferred life position of Astarte thisphila Glenn according to Stanley (1970). D, inferred life position of Dosinia acetabulum (Conrad) according to Gernant (1970). 136 PALAEONTOLOGY, VOLUME 38 text-fig. 2. Map of the West Shore of Chesapeake Bay, Maryland with sampling localities: locality 1, Chancellor’s Point; 2, Langley’s Bluff; 3, Drumcliff; 4, Little Cove Point; 5, Calvert Cliffs State Park; 6, Camp Baybreeze; 7, Rocky Point; 8, Camp Conoy; 9, Flag Ponds Wildlife Reserve; 10, Calvert Beach; 11, Mataoka Cottages; 12, Kenwood Beach; 13, Gover- nor Run Beach; 14, Plum Point; 15, Randle Cliffs Beach. to the method of Tough and Miles (1983), and then positioned the principal axis in a horizontal orientation. This method worked well with elongate genera because the principal eigenvector was consistently orientated with respect to biological landmarks. However, with more rounded genera the principal axis was not consistently orientated. Thus the positioning of biological landmarks varied between specimens. In order to orientate consistently more rounded genera, modrot3 was used because it rotated outlines to place the beak directly above the calculated centre-of-gravity. After rotation, thirty-six radial lengths were calculated from the centre-of-gravity to thirty-six points interpolated around the margin at 10° intervals using a cubic curve fit procedure, with the first radial always connecting the tip of the umbo with the centre-of-gravity. The outlines were then rotated around the x and/or v axis according to a best least squares fit to an asymmetrical reference shape. In order to eliminate size effects the data were normalized by dividing an individual’s radials by its mean radial length. A x2 test was performed to verify that every variable (radial length) within a data set fitted a normal distribution at the 0 05 significance level. Data matrices containing thirty-six radial lengths of congeners were reduced by principal components analysis (using fortran77 program bmdp4m; Frane et al. 1985) to six to seven principal components (PC) each accounting for a variance greater than or equal to one (Table 2). The PCs cumulatively accounted for approximately 90 per cent, of total shape variation which was found to describe shape adequately (Text-fig. 4c). GLASSBURN: MIOCENE BIVALVES 137 Epoch Miocene Early Middle Late Age Burdigalian - Serravallian Tortonian Sequence with > Disconformities > , — PP-0 PP-1 Kidwell 1968, 1989 ^ Calvert Formation Choptank Fm St. Mary’s Fm PP-2 PP-3 CT-0 CT-1 SM-OSM-1 SM-2SM-3 § r. Lithologic “Zones" Shattuck 1904 4-9 10 11 12 13 14 15-16 17 18 A 1 5.5 10.5 19 20 21 22 23 24 Ma Kidwell 1989 17.5 16.5 8.2 Axis Rank Genus Anadara — x x x Dosinia x — text-fig. 3. Stratigraphy and age of Chesapeake Group sequence and homogeneous groups of taxa computed by multiple range analysis using canonical variate 1 (Axis 1) and 2 (Axis 2) scores; in Anadara groups - square is A. subrostrata, x is A. staminea and dot is A. idonea; in Astarte groups - square is A. cuneiformis, x is A. thisphila and dot is A. perplana. 138 PALAEONTOLOGY, VOLUME 38 PC 7 PC 6 PC 5 PC 4 PC 3 PC 2 PC 1 PC Loadings Dosinia Anadara Recreation of Astarte Shape PC 1 PC i Score (+3) Score (-3) Original Shape PC 6 PC 5 PC 4 PC 3 PC 2 PC 1 » » text-fig. 4. a, plots of Dosinia acetabulum and Anadara PC loadings, b, equation used to recreate shape from PC scores and loadings; reconstruction of two specimens of Anadara using PC scores +3 and —3. c, reconstruction of an Astarte fossil shape by the cumulative addition of PC 1 through PC 6 to average shape. table 2. Variance explained (expl.) and cumulative per cent, of variance (cum.%) for each PC having a variance ^ 1. Genus : Anadara Astarte Dosinia Lucina Variance: Expl. Cum.% Expl. Cum.% Expl. Cum.% Expl. Cum.% PC 1 19-23 53 18-96 53 14-87 41 13-31 37 2 5-53 69 5-39 68 5-65 57 9-29 63 3 3T2 77 4-59 80 4-24 69 3-73 73 4 1-96 83 1-57 85 2-89 77 2-52 80 5 1-43 87 1-48 89 2-07 83 1-58 85 6 119 90 115 92 1 45 87 1-33 88 7 1-08 90 Analysis of evolutionary trends PC scores for each individual were estimated by post-multiplying its standardized set of thirty-six radial lengths by the matrix of PC loadings. The scores essentially represent the amount of a PC that is contained in a shape. As PC 1 contributed the most to shape variation (Table 2), PC 1 score GLASSBURN: MIOCENE BIVALVES 139 frequency histograms at each stratigraphical level were plotted to reveal evolutionary trends in a single species or lineage. The histograms were presented with reconstructed end member shapes to facilitate the interpretation of morphological trends. Within a single lineage, if the direction of an intraspecific shape trend was retained with the transformation of that species into the next, phyletic gradualism was inferred. Morphological change within a lineage would also have to be equally influenced by inter- and intraspecific shape trends. In contrast, if interspecific trends varied markedly in direction from associated intraspecific changes, the punctuational model was implied. In addition, interspecific changes should control the ultimate shape transformation of a lineage. Kruskal-Wallis one-way analysis by ranks was used to determine whether there was a significant difference between PC 1 scores of stratigraphical populations within a genus. Morphological differences between stratigraphical populations of a genus were quantified using estimated PC scores as input variables in multi-group discriminant analysis (using fortran77 program bmdp7m; Jennrich and Sampson 1985). Mahalanobis distances were computed between stratigraphical population means and between each specimen and its corresponding stratigraphical population centroid. The percentage of individuals in each taxon correctly and incorrectly classified according to ‘zones’ of occurrence was reported as was the percentage of individuals in each lineage correctly and incorrectly classified according to species. Successful classification of stratigraphical populations and the placement of a high percentage of individuals into stratigraphically proximal ‘zones’ implied a gradual change, where mixing of individuals from proximal ‘zones’ was due to the existence of intermediate morphologies. Canonical variate 1 mean scores of stratigraphical populations, calculated by discriminant analysis, were plotted and the morphological meaning of trends was represented by the shape of individuals with canonical scores most closely approximating group means. Group centroids were used instead of individual canonical variate scores to make trends more easily recognizable. A non- parametric rank correlation technique was used to search through group centroids of all of the canonical variates of a taxa to find significant monotonic trends. Spearman’s rank correlation coefficient, C, was calculated to quantify the relationship between temporal order and the order of group centroids along a canonical variate axis. Multiple range tests (statgraphics software; Statistical Graphics Corporation 1988) were performed using canonical variate 1 and 2 mean scores of stratigraphical populations of congeners. The statistical technique employed least significant difference (LSD) of means at the 95 per cent, confidence level in order to determine the presence of homogeneous stratigraphical populations. The homogeneous groups were plotted against time and associated stratigraphical level in order to show the maximum time interval in which a significant change in canonical variate 1 and 2 score means and, thus, shape occurred. COMPARISON WITH ALTERNATIVE METHODS OF SHAPE ANALYSIS The need to quantify shape was recognized by Thompson (1915), who used cartesian coordinates to describe the shape of one organism as the distortion of another. Benson (1981) more recently developed a morphometric technique using a similar approach. However, rather than explaining shape change in terms of homogeneous plane strain, as in Thompson’s model, he examined the differential deformation of geometrical representations of homologous parts in relation to overall form. Both methods rely on the recognition of homologous points to compute morphological changes. Point to point measurements have been used widely in biometric studies, probably for reasons of instrumental limitations and past precedents, rather than theoretical considerations (Scott 1980). The development of alternative morphometric techniques to process outline information (e.g. Fourier, Eigenshape and PC shape analysis) has proven to be useful when describing simple invertebrate shape where there are few homologous points along the periphery. Both Eigenshape (Lohmann 1983) and PC shape analysis use multivariate statistics to reduce orientated fossil outline information to fewer principal components. One difference between PC shape and Eigenshape analysis is the method of representation of an organism’s outline. While PC 140 PALAEONTOLOGY, VOLUME 38 shape analysis uses equiangular radial lengths about an organism’s calculated centre of gravity, Eigenshape analysis uses net angular changes in direction at each step around a perimeter (preferred technique where there are re-entrants along a shape’s periphery). Another difference between PC shape and Eigenshape analysis is the calculation of principal components based upon covariances among shapes versus correlations among shapes. Whereas the first principal component in PC shape analysis describes maximum shape variation among organisms, the first Eigenshape describes the average shape of a group of organisms. More recently, users of Eigenshape analysis have started to use covariances among shapes in principal components analysis (e.g. Schweitzer and Lohmann 1990). A strength of multivariate shape methods, such as Eigenshape and PC shape analysis, is that the first k basis vectors (principal components) account for more variation in a data set than the first k basis vectors of other methods, such as the Fourier technique, whose basis vectors are the Fourier harmonics. The Fourier method characterizes shape using a harmonic Fourier series of the expansion of the radius as a function of the angle about the centre of gravity. The harmonics are computed from: CO R(6) = A0+ £ A n cos (n9 *!>,,), n=l where R is a radius vector measured from a shape's centre of gravity to a point on the periphery in the polar direction 9 , A0 is the mean radius of the shape, An is the amplitude and 0-75 3 4 -0-77 P > 0-075 4 2 -0-64 P > 01 Astarte 1 86 -0-20 P> 0-5 2 8 014 P = 0-75 3 5 0-49 P > 0-25 4* 1 -0-89 P < 0-05 Dosinia 1* 80 -100 P = 0-00 2 17 000 P = 1-00 3 2 -0-20 P < 0-75 4 i 010 P> 0-75 Lucina 1 100 -0-90 P > 0 05 table 6. PC coefficients for discriminant functions; canonical variates with significant monotonic trends are marked with an asterisk. PC Genus Axis 1 2 3 4 5 6 7 Anadara 1 -2-10 -0-28 0-13 — 0 13 0-28 -0-22 2 -0-04 0-93 -0-47 — 0-71 — 0 10 -0-64 3 002 0-07 -006 0-38 0-92 -0-42 4 0 13 -0-62 — 0-10 -0-77 0-34 -0-04 Astarte I -1-85 -0-35 -0-48 -009 2 0-17 -0-40 — 0 19 -1-00 3 -002 0-87 -0-54 -0-25 4* 0-26 -0-39 -0-80 0-36 Dosinia 1* -1-71 0-35 0-38 0-39 2 004 -0-44 1-03 -0-45 3 0-03 — 0-71 003 0-74 4 0-34 0-58 0-47 0-53 Lucina 1 — 1-51 Kruskal-Wallis one-way analysis by ranks (Table 3). The morphological transformation of the youngest species into a shape similar to that of the oldest species was apparent in plots of homogeneous group ranks (Text-fig. 3) and the canonical variate 1 and 2 group centroids of stratigraphical populations (Text-fig. 6b). Discriminant analysis classified a majority of individuals with their correct ‘zones’ (Table 4). Discriminant analysis successfully classified 97-9 per cent, of individuals to the A. thisphila species while only 46-9 and 79-2 per cent, of individuals were correctly placed into the A. perplana and GLASSBURN: MIOCENE BIVALVES 145 A 17 16 10 Anadara n i A. staminea staminea o A. subrostrata o 1 PC 1 B PC 1 text-fig. 7. Anadara. A, PC 1 score frequency histograms labelled with means and reconstructed end member shapes; vertical axis denotes number of individuals, b. Plot of PC 1 and 2 scores with reconstructed end member shapes; open circles are A. subrostrata , grey squares are A. staminea and black circles are A. idonea. A. cuneiformis species, respectively. More incorrectly classified individuals of A. perplana and A. cuneiformis were placed into stratigraphically distant 'zones’ versus levels sampled nearest the correct 'zone’. Mixing of distant stratigraphical populations was due to the transformation of the lineage towards older morphologies. The resemblance between A. perplana and A. cuneiformis shape was demonstrated by a large percentage of the misclassified individuals being placed in stratigraphical 'zones' corresponding with the other species. The middle species, A. tliisphila , had a larger percentage of misclassified individuals placed into ‘zones’ sampled nearest the correct 'zone’ suggesting that transformation from the youngest stratigraphical population of A. cuneiformis , through all stratigraphical populations of A. tliisphila , to the single stratigraphical population of A. perplana was characterized by mixing of intermediate forms. The presence of intermediate morphologies was further demonstrated with multiple range analysis, which placed the youngest stratigraphical populations of A. cuneiformis and A. tliisphila into two ranks instead of one (Text-fig. 3). Furthermore, PC 1 and canonical variate 1 trends were preserved in succeeding species transformations, which is not inconsistent gradual change. However, it can be argued that the transformation of two homogeneous populations of A. tliisphila into one population of A. perplana resulted from migration of an allopatric A. tliisphila population into the study area followed by the removal of the earlier population (Text-fig. 3). Canonical variate 4 had the only significant monotonic trend (Table 5). Canonical variate 4 was most highly influenced by PC 3 (Table 6) having a loading which defined a triangular component of shape (Glassburn 1987, p. 139). The negative Spearman’s rank correlation coefficient (Table 5) 146 PALAEONTOLOGY, VOLUME 38 indicates that older species have higher canonical variate 4 mean scores and thus, shapes generated by more negative PC 3 scores (because PC 3 has a large negative coefficient in the canonical variate 4 function; Table 6). As more cuneiform shapes would be generated with more negative Astarte PC 3 scores (Glassburn 1987, p. 139), the monotonic trend detected by rank correlation analysis of canonical variate 4 was from cuneiform shapes in older species to trigonal shapes in younger species. The PC which accounted for a majority of total shape variation (PC 1) made the greatest contribution to canonical variate 1, which accounted for 86 per cent, of variation between stratigraphical populations, indicating that temporal shape change had a major influence on overall shape variation. In contrast, canonical variate 4 which accounted for 1 per cent, of variation between stratigraphical populations was influenced predominantly by PC 3 accounting for just 12 per cent, of total shape variation. Thus, the most significant shape trend was from cuneiform to trigonal back to cuneiform shapes. However, there was a small, monotonic trend from cuneiform towards trigonal morphologies. The Anadara lineage PC 1 accounted for 53 per cent, of shape variation in the Anadara lineage (Table 2). PC 1 frequency histograms showed a dichotomy between inter- and intraspecific shape trends (Text-fig. 7a). Whilst intraspecific trends were from valve shapes with smaller to larger L/H ratios, interspecific trends, which determined the ultimate shape transformation, were from valve shapes with larger to smaller L/H ratios. Temporal shape change was significant according to Kruskal-Wallis one-way analysis by ranks, with the test statistic being nearly double that of the Astarte lineage (Table 3). The plot of PC 1 and 2 scores of the congeners of Anadara revealed the presence of at least five different morphological groups (Text-fig. 7b). The odd PC 1 and 2 score pattern was generated with no rotation of the PC loadings matrix. When one of five different rotation methods available in the PC program bmdp4m (Frane et al. 1985) was used the pattern was not observed. Thus the appearance of the PC 1 and 2 score pattern may be an artefact of the PC analysis technique. The evolution of all of the Anadara morphological groups was from negative PC 1 and 2 scores, generating elongate valves with straight ventral margins to positive PC 1 and 2 scores, generating rounder valves with smaller L/H ratios and curved ventral margins. Schoonover (1941) noted the presence of different morphological groups of A. staminea from different beds at the same locality and between different localities. She observed that variations in shell diameter resulted in variations in valve morphology where specimens with larger diameters had sharper angles at the junction of the anterior and dorsal, dorsal and posterior, and posterior and ventral margins whilst specimens with smaller diameters had outlines less squarely compressed anteriorly and posteriorly. Both Glenn (1904) and Sheldon (1916) noted that some of the variations of A. staminea were so distinctive that they had been incorrectly described as separate species. Therefore a preliminary study of geological factors which may have contributed to the presence of the different morphological groups was conducted. When the individual points were labelled according to valve area it was revealed that size did not contribute to the PC 1 and 2 pattern and thus the different morphological groups were not the result of ontogeny (Glassburn 1987, figs 8.37-8.40). Also, the five morphological groups do not represent geographical populations; for instance there were five morphological groups of A. staminea from ‘zone’ 19 sampled at two locations (Calvert Cliffs State Park and Camp Baybreeze; Glassburn 1987, fig. 8.40). Furthermore, the morphological group containing individuals of A. subrostrata , A. staminea and A. idonea had individuals sampled from localities spanning the entire length of the study area from Randle Cliffs Beach to Chancellor’s Point (Text-figs 2, 7b). This study cannot clarify whether or not the morphological groups are ecophenotypes, as they might have resulted from differences in local palaeoecology. A more extensive field investigation is required before the PC 1 and 2 pattern can be dismissed as merely an artefact of the shape technique. Discriminant analysis placed 67-2 per cent, of individuals into the correct stratigraphical level, but was much more successful classifying individuals according to species (Table 4). Thus, there was a GLASSBURN: MIOCENE BIVALVES 147 greater distinction between the morphology of species than stratigraphical populations. More incorrectly classified individuals were placed into stratigraphically proximal ‘zones’ rather than distant ‘zones’. However, mixing between proximally sampled stratigraphical populations was predominantly within species with only 2 per cent, of the misclassified individuals being the result of mixing between the youngest population of an ancestor species and the oldest population of its descendant. Non-parametric rank correlation analyses of canonical variate group centroids revealed no significant monotonic trends (Table 5). Plots of canonical variate 1 group centroids and canonical variate 1 and 2 homogeneous rankings revealed that the direction of species’ trends was not preserved with subsequent speciation (Text-figs 3, 6a). Furthermore, a greater amount of change occurred with speciation than with any intraspecific change. The canonical variate 1 plot revealed that overall morphological transformation of the lineage was from species with larger L/H ratios to valves with roughly equivalent lengths and heights. Canonical variate 1, which accounted for 71 per cent, of variation between stratigraphical populations, was most highly influenced by PC 1, which accounted for a majority of total shape variation; thus, variation between stratigraphical populations made the biggest contribution to total shape variation. However, speciation contributed the most to temporal variation. Comparison with earlier morphometric studies of the Maryland species The observed lack of congruent temporal patterns between Chesapeake Group bivalves was also noted by Kelley (1984). The morphological variation was probably not the result of shared ecophenotypic responses but the result of genetic variation. In common with the present study, Kelley (1983a, 19836, 1984) observed that the Anadara lineage had an evolutionary tempo consistent with punctuated equilibrium. The present study found that overall morphological transformation of the lineage was determined by interspecific trends which were from elongate shapes, with straight ventral margins, to rounder shapes, with curved ventral margins. Stanley (1970) describes two life modes for extant Anadara species: (1) an infaunal or epifaunal byssally attached life mode which preceded the development of (2) free burrowing forms. Species with byssally attached life modes, such as Anadara antiquata , are distinguished from free burrowers, such as A. ovalis and A. chemnitzi , by their more elongate shapes, where an elongate and flattened ventral margin provides a broader means of support for byssal attachment (Stanley 1970). The Anadara lineage in this study was composed of elongate forms, especially A. subrostrata , suggesting a byssally attached life mode. The supposition that the Anadara species in this study were byssally attached is supported by Gernant (1970), who described the Anadara species as semi- infaunal suspension feeders. The general transformation of the Anadara lineage was from forms more ideally suited to a byssally attached life mode towards shapes more reminiscent of burrowing forms. As in this study, convergence between youngest and oldest Astarte species’ morphologies was observed by Kelley (1983a) in seven out of eight measured characters and Schoonover (1941), who noted that A. perplana resembled some of the Randle Cliffs Beach A. cuneiformis specimens (Text- figs 5c, 6b). Furthermore, Schoonover (1941) observed that A. perplana had a smaller L/H ratio, being more trigonal in shape than A. cuneiformis , which supports the results of rank correlation analysis which revealed a monotonic trend in canonical variate 4 centroids from cuneiform valve shapes towards more trigonal forms (Table 5). In contrast to the present study, Kelley (1983a, 19836, 1984) reported an evolutionary tempo of punctuated equilibrium within the Astarte lineage. However, morphological intermediates between Astarte species were observed by Schoonover (1941) and Kelley (1983a) consistent with gradual change having occurred. In contrast to this study, Kelley (1983a) observed stasis within Dosinia acetabulum (Conrad). Disparities in evolutionary tempos observed between this study and Kelley’s (1983a, 19836, 1984) studies of the Astarte lineage and Dosinia acetabulum may have been due to differences in the 148 PALAEONTOLOGY, VOLUME 38 evolution of valve shape versus biometric parameters measured by Kelley (1983a, 1983/7, 1984). Probably, more significant is the difference in the temporal resolution of the two investigators’ studies. As results in this study were based upon specimens collected from fewer stratigraphical levels, apparent gradual trends may have resulted from consistent direction in punctuation events or sampling of a zigzagging stasis trend coincidentally resembling unidirectional change. In contrast to this study, Stanley and Yang (1987) found that stasis best described the evolutionary mode of Dosinici acetabulum. Their results were based upon calculations of the area of non-overlap of two populations' first eigenshapes as a percentage of the area of fossil eigenshape. However, discriminant analysis based on twenty-four morphometric variables, including aspects of valve shape, revealed some monotonic trends in D. acetabulum (Stanley and Yang 1987, fig. 17). Stanley and Yang (1987) state that D. discus , a US East Coast extant species, arose from D. acetabulum. D. discus is a rapid burrower preferring sandy substrates and has disc-shaped valves which it uses to slice vertically downward into the substrate (Stanley 1970). While this study reports that D. acetabulum valves gradually evolved from oblong to disc-shapes (Test-figs 4a, 5c), Stanley and Yang (1987) found that temporal shape variation in D. acetabulum was minor relative to geographical variation and that interspecific change within the ‘lineage’ containing D. acetabulum and D. discus was characterized by a speciation event or rapid phyletic change. The present study requires sampling from a wider geographical area and comparison between intra- and interspecific variation within the corresponding ‘lineage’ of D. acetabulum in order to support conclusions concerning evolutionary mode. The monotonic trend observed by the present study may be a minor trend in a larger time frame of zigzagging morphological stasis, or a bend in an anastomosing stream of change in which geographical variability was as great as temporal variability. Like the present study, Kelley (1984) found that stasis best described temporal shape variation in Lucina ( Stewartia ) anodonta Say. Only individuals of L. anodonta from ‘zone’ 24 could be distinguished from other stratigraphical populations, being smaller and more inflated than the earlier specimens (Schoonover 1941 ; Kelley 1984). Stasis in L. anodonta is supported by the species persistence from the Miocene to the Recent (Bretsky 1976). DISCUSSION There were many similarities in results using the PC shape technique and previous studies which used other morphometric techniques to describe temporal shape change within the same bivalve species. Furthermore, many aspects of temporal shape variation highlighted by the PC shape technique were also reported in a thorough study by Schoonover (1941) who made qualitative observations about temporal morphological changes. Although there were some discrepancies between evolutionary tempos and modes reported in this and previous studies the cause was most probably the difference in temporal resolution, where this study sampled from fewer stratigraphical horizons or from a more limited time span and geographical range. Limitations in the sampling scheme not withstanding the PC shape analysis technique proved to be a fast and simple way to characterize fossil outline shape. Its strength over qualitative assessment of temporal shape change is that it quantifies shape, providing a more objective way to compare shapes of different stratigraphical populations. The advantage of using PC shape analysis versus point-to-point measurement techniques, as with all image analysis techniques, is the speed at which morphological information can be collected. One doubt concerning the validity of morphometric techniques which process outlines is that comparisons are made between non-homologous points whereas techniques utilizing point-to-point measurements can target homologous points (Bookstein el al. 1982; Full and Ehrlich 1986). There are generally few homologous points present on the peripheries of simple invertebrates and outline processing techniques which compare points connected by equiangular radial lengths (e.g. Fourier and PC shape analysis) or equal chord lengths (e.g. Eigenshape analysis) can only be certain of achieving correspondence with respect to one homologous point if it is the initial point. GLASSBURN: MIOCENE BIVALVES 149 Although PC shape analysis performed calculations between non-homologous points, the first two PC loadings, accounting for greatest shape variation, were always orientated in relation to morphological landmarks (Text-fig. 4a). PC 1 loadings always contained two pairs of lobes with axes 90° to each other. One axis always connected the umbo with the ventral margin (defining shell height) and the other axis defined shell length. PC 2 loadings always contained two pairs of lobes orientated 45° to the lobes of the PC 1 loadings, with one axis connecting the lunule with the point of intersection between the posterior and ventral regions and the other axis connecting the point of intersection between the posterior and dorsal regions with the point of intersection between the anterior and ventral regions. Possibly more important than recording changes between limited homologous points present on a bivalve periphery is recording distortions in bivalve shape occurring to accommodate changes in shape or size of soft body parts. An interesting project for the future would be to use PC shape analysis to describe bivalve shape and the shape of muscle scars in order to determine how changes in the shape of the muscle attachment area impacts upon valve shape. SUMMARY 1. Cubic interpolation reduced 100-200 x—y coordinates of a properly rotated valve periphery to thirty-six radial lengths spaced at equiangular intervals. The thirty-six radial lengths were then used as variables in principal components analysis reducing the original data set to less than eight principal components accounting for approximately 90 per cent, of total shape variation (Table 2). PC scores were used as shape variables in discriminant analysis and non-parametric rank correlation analysis to determine whether significant intra- and interspecific shape trends existed. 2. Original shape was reconstructed by destandardizing results of matrix multiplication of PC scores with PC loadings (Text-fig. 4). 3. Phyletic gradualism was implied in a lineage where the direction of an intraspecific shape trend was retained with the transformation of that species into the next species and total shape change was equally influenced by intra- and interspecific trends. 4. Punctuated equilibrium was implied in a lineage where interspecific trend directions varied markedly from associated intraspecific trends and intraspecific temporal variation contributed much less than speciation to total shape change. 5. Discriminant analysis demonstrated that a species population in one stratigraphical level was measurably different in shape from a population in another stratigraphical level. If a high percentage of misassigned individuals were placed in proximal stratigraphical levels it indicated a mixing of morphological intermediates implying a gradual change. 6. The valves of Dosinia acetabulum (Conrad) evolved gradually from oblong to disc shapes (Text-figs 5a, 6c). 7. Stasis best described the temporal shape trend of Lucina (, Stewartia ) anodonta Say (Text-figs 5b, 6d). 8. The Astarte lineage evolved gradually from cuneiform to trigonal and back to wedge shapes (Text-figs 5c, 6b). 9. The Anadara lineage exhibited an evolutionary mode consistent with punctuated equilibrium. Intraspecific trends were from valves with smaller L/H ratios to more elongate shapes, whilst interspecific changes, controlling ultimate shape transformation in the lineage, were from elongate valves with straight ventral margins to valves with smaller L/H ratios and curved ventral margins (Text-figs 6a, 7). Acknowledgements. I thank Jim Parks for providing shape rotation and digitizing programs and for supervising. I thank David Hickey, Jim Parks, John Ferguson, Andy Gale, Earl Shapiro and two anonymous reviewers for reading the manuscript and offering suggestions for its improvement. Steven Cauller, Martin Mengel and David Cundall provided stimulating discussions and Andy Sage and David O'Grady assisted in 150 PALAEONTOLOGY, VOLUME 38 the field. David Bohaska of the Calvert Marine Museum enabled access to certain exposures. Paul Slusarewicz assisted with the production of some of the Text-figures. This research was supported by a grant from Jim Parks’ grain shape analysis project. REFERENCES benson, r. H. 1981. Form, function and architecture of ostracode shells. Annual Review of Earth and Planetary Sciences, 9, 59-80. blackwelder, B. w. and ward. l. w. 1976. Stratigraphy of the Chesapeake Group of Maryland and Virginia. Geological Society of America Southeast Section Field Trip Guidebook, 1-55. 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Analysis of two-dimensional shapes by principal components score descriptors: geological interpretations from sand grains, pebbles, benthic foraminifera and bivalve mollusks. Bulletin of the American Association of Petroleum Geologists , 71, 601-602. Schoonover, l. m. 1941. A stratigraphic study of the molluscs of the Calvert and Choptank Formations of Southern Maryland. Bulletins of American Paleontology , 25, 169-299. schwarz, h. p. and shane, k. c. 1969. Measurement of particle shape by Fourier analysis. Sediment ology, 13, 213-231. Schweitzer, p. n. and lohmann, G. p. 1990. Life-history and the evolution of ontogeny in the ostracode genus Cyprideis. Paleobiology , 16, 107-125. scott, G. h. 1980. The value of outline processing in the biometry and systematics of fossils. Palaeontology , 23, 757-768. shattuck, G. b. 1904. Geological and paleontological relations with a review of earlier investigations. Maryland Geological Survey Miocene Volume , 33-137. sheldon, p. G. 1916. 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GLASSBURN Department of Geology Lehigh University Bethlehem, Pennsylvania 18015 USA Present address : 1725 Robinhood Lane Typescript received 11 January 1994 Clearwater, Florida 34624 Revised typescript received 24 August 1994 USA THE ULTRASTRUCTURE OF SPORES OF COOKSONIA PERTONI by D. EDWARDS, K. L. DAVIES, J. B. RICHARDSON CUld L. AXE Abstract. The ultrastructure of spores isolated from sporangia of Cooksonia pertoni from Pridoli and Lochkovian rocks of the Welsh Borderland has been elucidated using both scanning and transmission electron microscopy. The Silurian material, attributable to C. pertoni subsp. synorispora , contains Synorisporites verrucatus while the Devonian C. pertoni subsp. apiculispora yields either Streelispora newportensis or Aneurospora sp. All three spore taxa show an exospore ( = exine) composed of two layers, both of which extend into the murornate and verrucate sculpture in Synorisporites verrucatus , into the papillae and proximal folds of Streelispora newportensis , and into apertural folds (where observed) in all three taxa. In contrast, only the outer layer occurs in the apiculate sculpture of the Devonian spores. The homology of the layers is briefly discussed in relation to extant vascular cryptogams. Such ultrastructural observations compare favourably with published descriptions of the same taxa recorded from dispersed assemblages using light microscopy. Similar ultrastructure has already been recorded in cf. Ambitisporites isolated from Pridoli Cooksonia pertoni from Long Mountain, Shropshire, thus providing support for the hypothesis that, while the gross morphology and spore structure of C. pertoni remained unchanged from the Silurian into the Devonian, spore sculpture evolved from smooth to verrucate to apiculate. The record of early land plants in Silurian and basal Devonian rocks is largely based on small fragmentary coalified fossils of simple morphology and lacking anatomical detail. Studies on the use of in situ spores in attempts to deduce relationships and to detect hidden diversity are in their infancy. Thus the morphologically simple taxon Cooksonia pertoni Lang has been shown to possess at least three different kinds of spore depending in part on its geological age (Fanning et al. 1988). These are the dispersed miospore genera Ambitisporites , Synorisporites and Streelispora/ Aneurospora, taxa that are united in their equatorially crassitate structure, but that differ mainly in the nature of their distal exines with sculpture being laevigate, verrucate or apiculate. From the relative ages of the megafossils and data from dispersed spore assemblages, it was inferred that laevigate spores (Ambitisporites) represent the ancestral state in C. pertoni , that apiculate spores are the most derived, and that the murornate-verrucate sculpture of Synorisporites verrucatus possibly represents an intermediate state in the Ambitisporites-Streelispora/ Aneurospora lineage. Streelispora/ Aneurospora is so written because limited numbers prevented a study and description of the proximal features of the in situ spores in all cases, and it is the presence or absence of proximal folds, that is used to distinguish the two genera in the dispersed record. In more recent work (Edwards et al. 1992) we have unequivocal evidence for in situ Streelispora newportensis in Lochkovian C. pertoni , and, in this study, for papillate apiculate equatorially crassitate spores lacking proximal folds, which can be more confidently assigned to Aneurospora than in previous studies, although there remain reservations on identification at specific level. Previous descriptions of the in situ spores employed light and scanning electron microscopy. Flere we report on ultrastructure as seen in sections viewed by transmission electron microscopy. LOCALITY DATA, MATERIAL AND TECHNIQUES All material is housed at the National Museum of Wales, Cardilf (NMW). (Palaeontology, Vol. 38, Part 1, 1995, pp. 153-168, 4 pls.| © The Palaeontological Association 154 PALAEONTOLOGY, VOLUME 38 Ludford Lane , Shropshire [SO 5122 7412]. Platyschisma Shale Member, Downton Castle Formation; tripapillatus-spicula Sporomorph Assemblage Zone; Pfidoli Series, Silurian. Two coalified discoidal sporangia (NMW 93.143G.1 and 2; PL 1, figs 1-5) containing Synorisporites verrucatus were recovered after bulk maceration, in 40 per cent, hydrofluoric acid, of a fossiliferous siltstone c. 1-6 m above the main bone bed at the famous locality at Ludford Lane Corner. This was the horizon that yielded the earliest terrestrial arthropods and stoma (Jeram el al. 1990) and is of early Pfidoli age. The discoidal structures resemble C. pertoni in shape, with each bearing a centrally placed ridge marking the attachment of the subtended axis. Except at this site and at the periphery, where spores are occasionally visible, the surface of each specimen is covered by an acellular sheet with irregular depressions, interpreted as the remains of the sporangial cuticle. We therefore have neither direct gross morphological nor anatomical evidence for affinity with C. pertoni. identification being based on overall shape of the spore-containing region and the fact that Synorisporites verrucatus has not to date been found in a sporangium of any other shape. Brown Clee Hill. Beneath small waterfall in stream section to the north of Brown Clee Hill, Shropshire; Ditton Group; lower middle part of micrornatus-newportensis Sporomorph Assemblage Zone; Lochkovian Stage, Lower Devonian. The sporangia were isolated by disaggregation of the grey siltstone in water and cleaned by brief immersion in 40 per cent, hydrofluoric acid. They come from the upper plant-bearing horizon in the stream (Edwards el ah 1994). Dispersed palynomorphs indicate an early Lochkovian age (lower middle micrornatus-newportensis Zone). Four samples containing Streelispora newportensis were sectioned. Two are unequivocal sporangia. The less compressed one (NMW 93. 143G.6) was initially almost intact distally, a fracture near the margin revealing cellular details of the sporangial wall and spores. In the second (NMW 93.143G.5) a short length of the subtending axis remains, but more of the distal wall has disappeared exposing the spores (PI. 1, fig. 7). The remaining two are more compressed with preservation reminiscent of that in the Silurian examples: NMW 93.143G.3 has an almost circular outline; NMW 93.143G.4 is more fragmentary with an irregular outline (PI. 1, fig. 6). M50 motorway [50 6650 2658 ]. Near 29-5 marker post on north side of motorway, Hereford and Worcester; St Maughans Formation; lowest part of micrornatus-newportensis Sporomorph Assemblage Zone; Lochkovian Stage, Lower Devonian (details in Edwards and Rose 1984). The sectioned example (NMW 93.143G.7) was a spore mass, more or less circular in outline (PI. 2, fig. 3), recovered from bulk maceration of a grey-green shale 2 m above the base of the St Maughans Formation. The distally apiculate, proximally papillate spores (PI. 2, figs 4-7), lacking any proximal folds, are assigned to Aneurospora sp. and are believed to be derived from a C. pertoni sporangium since no other Lower Devonian sporangium of this shape has yet been demonstrated to contain Aneurospora. EXPLANATION OF PLATE 1 Figs 1-5. Scanning electron micrographs (SEMs) of Cooksonia pertoni subsp. synorispora\ NMW 93.143G.1 ; Ludford Lane, Shropshire; Downton Castle Sandstone Lormation, Pfidoli Series (Upper Silurian). 1, lower side of sporangium showing spores at margins and site of axis attachment ; x 44. 2, close up of outer surface of sporangium wall; x 210. 3, spores (Synorisporites verrucatus) before acid treatment, with remnants of wall on left; x 1000. 4, proximal surface of spore after acid treatment; x 3450. 5, part of distal surface of spore after nitric acid treatment; x 5570. Fig 6-8. SEMs of C. pertoni subsp. apiculispora ; north Brown Clee Hill, Shropshire; Ditton Group, Lochkovian (Lower Devonian). 6, NMW 93.143G.4; incomplete sporangium with visible spores and short subtending axis disintegrating on lower surface; x 25. 7, NMW 93.143G.5; sporangium with traces of axis; x 55. 8, NMW 93.143G.3; apiculate sculpture on distal surface of Streelispora newportensis after nitric treatment; x 3200. PLATE 1 EDWARDS et a/., Cooksonia 156 PALAEONTOLOGY, VOLUME 38 All specimens were first examined untreated by SEM (Cambridge 360), to allow secure identification. In the early stages of the study, suitable material was then treated with fuming nitric acid to facilitate observations by LM but more importantly to remove pyrite prior to sectioning for TEM. This contrasts with methodology for dispersed spores, where only minimal nitric acid treatment is used to aid clearing. Indeed, our experiences with Ambitisporites, from a Pridoli Cooksonia pertoni from Long Mountain, Shropshire (Rogerson et al. 1993), indicated that valuable information was being destroyed by the concentrated acid treatment and our procedures were subsequently modified to include sectioning of untreated spores and examination by SEM after acid treatment. This was impossible on one of our original specimens (NMW 93.143G.5) where all material had already been used. In this study, therefore, sections were prepared from untreated spores where available and all material was subjected to fuming nitric acid for 30 minutes. Unlike the Ambitisporites spore masses from Long Mountain, those treated with nitric acid retained their integrity. Detailed techniques for sectioning for TEM are given in Rogerson et al. (1993). Essentially acid-treated and untreated specimens were dehydrated, embedded in Spurr resin, sectioned at 60-90 nm using an LKB Ultrotome 8801A and stained with 1 per cent, (w/v) potassium permanganate in 0-1 M phosphate buffer pH 6 followed by 2 per cent, (w/v) uranyl acetate and basic lead citrate. All sections were examined using a JEOL 100S TEM at an accelerating voltage of 80 kV. TERMINOLOGY To avoid confusion, particularly with conventional palynological descriptions, the terminology adopted in our ultrastructural studies (Rogerson et al. 1993) is repeated. Observations on extant pteridophytes reveal three components of the sporoderm (see e.g. Tryon and Lugardon 1991). These are: perispore , the acetolysis-sensitive peripheral envelope; exospore , the acetolysis-resistant component largely composed of sporopollenin (exine sensu Potonie and Kremp 1954); and the endospore, laid down immediately outside the cell membrane and, being composed predominantly of cellulose, considered unlikely to survive taphonomic processes. Similarly the perispore (or perisporium; see Traverse 1988) sensu stricto rarely persists in fossils, but the term is sometimes used by palynologists for a loosely attached outer layer showing no infrastructure. In this study, we use the term ‘peripheral layer’ for extra-exospore coalified material. The trilete mark is usually represented in TEM by a projecting apertural fold, mainly involving the exospore. A superficial suture is rarely visible in SEM. Variations within the exospore such as differences in texture, staining or structure are termed layers. DESCRIPTIONS OF IN SITU SPORES Synorisporites verrucatus Richardson and Lister , 1969 Dimensions, means and sample numbers from the two sporangia are presented in Text-figure 1 . A spore mass with abundant S. verrucatus recovered on bulk maceration from the type locality of C. pertoni at Perton Lane is interpreted as a possible coprolite because of its atypical shape and the EXPLANATION OF PLATE 2 Figs 1-2. Scanning electron micrographs (SEMs) of Streelispora newportensis before acid treatment showing papillae and folds; north Brown Clee Hill, Shropshire; Ditton Group, Lochkovian (Lower Devonian). 1, NMW 93.143G.4; x 3000. 2, NMW 93.143G.3; x 2080. Figs 3-7. SEMS of spore mass of C. pertoni subsp. apiculispora shape, containing Aneurospora sp. before acid treatment; NMW 93.143G.7; M50 motorway, Hereford and Worcester; St Maughans Group, Lochkovian (Lower Devonian). 3, spore mass; x 95. 4, group of spores; x 1575. 5, sculpture on distal surface; x 2650. 6, close up of proximal face with pitted appearance; x 3100. 7, proximal face with pronounced apertural folds and interradial papillae; x 2900. PLATE 2 EDWARDS et al., Streelispora , Cooksonia 158 PALAEONTOLOGY, VOLUME 38 CHARACTER TAXON Synorisporites verrucatus NMW 93.143G.1 NMW 93.143G.2 ex Ludford Lane ex Ludford Lane Dimensions of sporangium (mm) 1.48 x 1.01 0 89 x 0.95 min. mean max. min. mean max. Diameter of spore minus acid 14.00 19.76 22.06 16.80 23.04 27.20 (om) (n=23) (n=5) Diameter of spore plus acid 16 66 20.70 27.27 16.60 24.28 33.30 (Mm) (n=28) (n=12) Width of peripheral layer 0 025 0 12 0 33 0.025 0.10 0.20 (M^) (n=60) [minus acid] (n=27) [minus acid] Width of outer exosporal layer 0 10 0 27 1.10 0.04 0.05 0 08 (Pm) (n= 112) (n=66) Width of inner exosporal layer 0.33 1.15 2 60 0.44 0 96 1.93 (pm) (n=89) (n=49) Width of dark layer around lumen 0.030 0.033 0 060 0 020 0.040 0.130 (pm) (n=47) (n=40) Dimensions TEM Height 0.50 1.11 2 00 0.20 0 52 1.00 of distal (n=17) (n=5) sculpture data Width at 1.00 2.81 3.66 1.28 1.86 2.62 (pm) base (n=17) (n=5) SEM Height 0.68 1.08 1.59 1.57 1.99 3.15 (n= 1 0) (n-10) data Width at 0 90 1.36 1.59 2.10 2.50 3.15 base (n=10) (n=13) text-fig. I . Quantitative data for Svnorisporites verrucatus. presence of at least two further spore taxa. However, the ultrastructure of unequivocal S. verrucatus from the mass is consistent with that in the Ludford Lane samples. Under the scanning electron microscope, the spores look similar both before and after acid treatment (PI. 1, figs 3, 5). Untreated examples were usually visible at the edges of the mass, some still as components of tetrads (PL 1, fig. 3). Distal surfaces show typical verrucate to murornate EXPLANATION OF PLATE 3 Figs 1-6. Transmission electron micrographs (TEMs) of sections of Svnorisporites verrucatus ; 1-3, 5-6, NMW 93.143G.1 ; 4, NMW 93.143G.2; Ludford Lane, Shropshire; Downton Castle Sandstone Formation, Pfidoli Series (Upper Silurian) 1. sections through a number of spores, before nitric acid treatment, with extensive darker intersporal material; arrow indicates possible apertural fold; x 5840. 2, as for 1 but with possible aborted spores which are narrower and darker; arrow indicates pronounced black peripheral layer; x 9890. 3, as for 1 and 2 but with well developed black peripheral layer; narrow 'fuzzy' line marks position of lumen; x 16690. 4, narrow innermost layer of exospore following nitric acid treatment adjacent to lumen (light central area); x 27360. 5, remnant of membrane-like material or remains of aborted spores following treatment with nitric acid; x 350. 6, section through both surfaces of single spore after acid treatment, but with lumen barely visible as discontinuous white line; note prominent outer layer of exospore; x9170. Figs 7-10. TEMs of sections of Streelispora newportensis spores; NMW 93.143G.4; north Brown Clee Hill, Shropshire; Ditton Group, Lochkovian (Lower Devonian); see PI. 1, fig. 6, PI. 2, fig. 1. 7, number of spores before acid treatment; arrow indicates possible apertural fold ; x 9030. 8, proximal and distal surface of same spore after acid treatment showing pronounced outer layer of exospore which is thicker and extends into sculpture on distal surface; part of a second spore is seen top right; x 14370. 9, possible detached peripheral layer; x 21 190. 10, as for 8 but with dark innermost layer of exospore marking the lumen; x 30450. PLATE 3 EDWARDS el al., Synorisporites , Streelispora 160 PALAEONTOLOGY, VOLUME 38 sculpture (PI. 1, fig. 5); the proximal surface is smooth (PI. 1, fig. 4) as is the equatorial crassitate region. The trilete mark is prominent, each arm being represented by a ridge lacking sutures and extending to the equator. Interradial areas may be folded and always lack papillae (PI. 1, fig. 4). In contrast, TEMs look markedly different before and after nitric acid treatment. Untreated spores are tightly adhered in the spore mass (PI. 3, figs 1-3), but are encompassed by an intersporal matrix, readily distinguished from the very narrow darker region (= peripheral layer of Rogerson et at. 1993) immediately surrounding individual spores (PI. 3, figs 2-3). This intersporal region is more or less homogeneous apart from narrow ‘membranous’ lines, sometimes describing irregular flattened oval outlines, sometimes disjunct (PI. 3, fig. 2). These structures usually survive treatment with nitric acid, but the remainder of the intersporal matrix does not (PI. 3, fig. 5). The peripheral layer, present to varying degrees and of irregular thickness as it ‘follows’ the contours of the exospore, also disappears on acid treatment. In light microscopy it appears as a coalified layer, obscuring further detail. The wall surviving fuming nitric acid treatment is interpreted as the exospore and, in this state, comprises two or possibly three layers (PI. 3, figs 4, 6). An outermost dark electron-dense layer of more or less uniform thickness (termed outer exospore) surrounds a wider lighter homogeneous layer (under exospore), both of which are visible in the sculpture (PI. 3, fig. 6). Groups of circular to oval electron transparent cavities occur largely throughout the homogeneous layer but may extend into the outer exosporal layer (PI. 3, fig. 6). The innermost narrow dark layer immediately around the lumen is more variable in thickness and sometimes absent (PI. 3, figs 4, 6). It is more clearly defined and prominent in specimen NMW 93.143G.2 (PI. 3, fig. 4). In untreated specimens the lumen is represented by a dark line. Acid treatment induces separation of the spore walls so that the lumen becomes visible. The lumen also extends into the apertural fold (PI. 3, fig. 1), in which all layers of the exospore are visible. Streelispora newportensis ( Chaloner and Street) Richardson and Lister , 1969 Quantitative data from the four samples, all from north Brown Clee Hill, are presented in Text- figure 2. Scanning electron micrographs before and after acid treatment look similar. Intersporal variation relates mainly to proximal features; almost all show papillae, but associated folds may be variously orientated, i.e. not consistently periclinal, with additional folding sometimes present (PI. 2, figs 1-2). Distal ornament of coni varies only in size (PI. 1, fig. 8). In all specimens prior to nitric acid treatment, the outlines of individual spores are difficult to observe under TEM since spores are tightly adpressed and consequently difficult to section. Therefore, the existence of a peripheral layer is equivocal. However, less compressed untreated spores were occasionally observed under TEM. Such spores exhibit distinct layering of the exospore (PI. 3, fig. 7). After exposure to acid the spores separate and the profiles become well-defined. Traces of a thin dark layer (? peripheral layer) remain in one specimen, although this may also be an atypical example of sloughing of the outer exospore (PI. 3, fig. 9), and there is scant evidence for an intersporal mix. The exospore has two conspicuous layers with a narrow more electron-dense layer surrounding a wider homogeneous one (PI. 3, fig. 10). Both layers are present in the proximal folds (PI. 4, figs 1-3), apertural folds and papillae (PI. 4, fig. 2), but only the outer is seen in the ornament (PI. 3, fig. 8; PI. 4, figs 1, 5). A very dark line delimits the lumen (PI. 3, fig. 10), and may be associated with ovoid electron-dense bodies (0 66-2-00 pm x 0 50-0-66 / urn diameter). As in Synorisporites verrucatus , this line is not visible in all sections and varies in thickness. Aneurospora sp. The sporangium of C. pertoni shape (PI. 2, fig. 3) contained proximally tripapillate, equatorially crassitate, apiculate spores (PI. 2, fig. 7), assigned to Aneurospora in that proximal folding is lacking. Dimensions are given in Text-figure 2. A thin, darkly stained peripheral layer is apparent under TEM (PI. 4, fig. 9) and only partially disappears on exposure to acid (PI. 4, fig. 6). The exospore itself is two-layered (PI. 4, figs 6, 10—1 1) with the outer narrow electron-dense layer contrasting with the wide homogeneous inner, the latter being relatively wider than that in Streelispora. Both layers EDWARDS ET AL.\ COOKSONIA SPORE ULTRASTRUCTURE 161 CHARACTER TAXON Streelispora newportensis Aneurospora Pooled data for NMW 93 143G 3-6 ex Brown Clee Hill NMW 93.143G.7 ex locality DE 98 M50 Dimensions of sporangium/spore mass (mm) 1.43 x 1.0 (30.1 series) 1.95 x 1.87 (40.1 series) 1.14 x 0.68 (UF1566 series) 0.93 x 0.79 (55.6 series) 0.78 x 0.67 min. mean max. min. mean max. Diameter of spore minus acid (pm) 13.64 21.56 28.38 (n=32) 18.97 24.52 28.00 (n=22) Diameter of spore plus acid (pm) 15.00 22.81 31.20 (n=26) “ Width of peripheral layer (pm) 0.12 0.18 0.36 (n=5) 0.03 0.04 0.11 (n=34) Width of outer exosporal layer (pm) 0.06 0.25 0.55 (n=273) 0.03 0.06 0.12 (n=42) Width of inner exosporal layer (pm) 0.16 0.65 1.87 (n=205) 0.40 0.99 1.68 (n=42) Width of dark layer around lumen (pm) 0.02 0.04 0.12 (n=48) 0.05 0.11 0.35 (n=23) Dimensions of proximal fold (pm) Height 0.86 1.44 3.66 (n=9) Width at base 0.46 0.73 1.33 (n=9) - Width at apex 0.33 0.52 0.80 (n=5) “ Dimensions of proximal papilla (pm) Height 1.39 1.98 2.66 (n=8) 1.29 2.17 2.22 (n=7) Width at base 1.25 3.85 6.00 (n=8) 3.22 4.70 5.80 (n=7) Width at apex 0.62 2.87 4 00 (n=3) Dimensions of distal sculpture (pm) TEM data Height 0.33 0.77 1.20 (n=21) 0.25 0.43 0.95 (n=10) Width at base 0.73 1.44 2.13 (n=20) 0.25 0.72 0.93 (n=10) SEM data Height 0.45 0.82 0.93 (n=20) 0.51 0.63 1.02 (n=10) Width at base 0.69 1.01 1.39 (n=20) 0.51 0.83 1.02 (n= 15) text-fig. 2. Quantitative data for Streelispora newportensis and Aneurospora. 162 PALAEONTOLOGY, VOLUME 38 are present in the apertural fold and papillae (when present) with only the outermost layer in the distal coni (PL 4, fig. 1 1). TEMs reveal that the projecting coni frequently coincide with depressions in the exospore of adjacent spores. It is a possibility that the pitted appearance of the latter when observed under SEM (PI. 2, fig. 6) is due to the impaction of coni on neighbouring spores during compression, or may merely be due to localized corrosion. DISCUSSION Effects of nitric acid treatment Layering within the exospore. The striking differences noted in cf. Ambitisporites spores from Cooksonia pertoni sporangia before and after acid treatment allowed interpretation of observed ultrastructure in terms of the original chemistry of the peripheral layer and the exospore. However, it raised the possibility that the layering of the exospore, particularly prominent after staining, is actually produced by acid treatment (Rogerson et al. 1993). The same kind of layering, present in all the acid-treated spores in this study, demands similar assessment as a prerequisite for comparisons of exospore structure in extant and extinct embryophytes. Is the nitric acid accentuating original differences in the wall and their affinities for the stain, or is the layering merely reflecting the degree of penetration of the nitric acid (and hence chemical modification) into the spore wall? Evidence for the latter comes from the consistently peripheral position of the staining and its more or less uniform width. It could be argued that the minor variations relate to timing of the various procedures and/or degree of penetration of the resin. On the other hand, again based on a relatively small sample size, for Streelispora and Synorisporites , the thickness of the outer layer relative to that of the exospore is more or less constant. Further, in considering the apiculate ornament of Aneurospora and Streelispora , the area of staining is greater than that anticipated from the degree of penetration into the rest of the wall. Perhaps most importantly, the layering is not a feature of all spores treated with nitric acid (see e.g. Synorisporites downtonensis illustrated in Text- fig. 3a-b) and is frequently observed in non-treated spores. Further layering has been recorded and illustrated in specimens of Ambitisporites , Synorisporites, Streelispora and Aneurospora studied using light microscopy (Richardson and Ioannides 1973, p. 14). The differing intensity of staining observed between samples and occasional ‘reversed staining' effects may well reflect minor differences in procedures, but even where there is little or no contrast between layers, the outer consistently appears smoother and the middle more granular. EXPLANATION OF PLATE 4 Figs 1-5. Transmission electron micrographs (TEMs) of sections of Streelispora newportensis after fuming nitric acid treatment; 1-3, NMW 93.143G.4; 4-5, NMW 93.143G.6; north Brown Clee Hill, Shropshire; Ditton Group, Lochkovian (Lower Devonian). 1, number of spores stacked in sporangium; lumens are not visible, arrow indicates possible proximal fold; x 5940. 2, part of spore with papilla and fold in section on proximal surface and sculpture on distal; lumen is not visible; x 10490. 3, fold on proximal surface and some extrasporal material; x 20000. 4, possible equatorial thickening; note differing response of layers of the exospore to sectioning and ‘reversed’ staining of middle and outer layers; x 9200. 5, sculpture comprising outer layer of exospore; x 12400. Figs 6-11. TEMS of sections of Aneurospora sp. following concentrated nitric acid treatment, all except fig. 9 which is before acid treatment; note outer layer of exospore is here stained lighter than remainder of wall; see NMW 93.143G.7 (PI. 2); M50 motorway, Hereford and Worcester; St Maughans Group, Lochkovian (Lower Devonian). 6, outer and inner layers, lumen and possible peripheral layer; x 20570. 7, apertural fold, triangular area with extended ‘arms’ marks lumen; x4360. 8, poorly developed equatorial thickening; x 5960. 9, distal surface showing sculpture with peripheral layer before acid treatment; x 22000. 10, section through distal and proximal surface with some evidence of innermost exospore layer visible as a dark line around oblique lumen; x 22225. 11, distal surface with sculpture formed from outer layer only; some evidence for a particulate peripheral layer; x 27780. PLATE 4 EDWARDS et al., Streelispora , Aneurospora 164 PALAEONTOLOGY, VOLUME 38 text-fig. 3. a, SEM showing tetrads of Synorisporites downtonensis (NMW 93.143G.8), Ludford Lane, PfidoH Series, x 792. b, TEM of section of thick-walled spores after nitric acid treatment (NMW 93.143G.8), x 3352. Assuming then that the nitric acid is revealing information on wall layering, what is the basis for this response? Possibilities include chemical differences relating to polymerization of sporopollenin or physical differences involving variation in the original substructures on which sporopollenin is deposited. The differing responses of the exosporal layers of Aneurospora and Streelispora to the knife may well reflect differences in their physical properties. Thus, the inner layer appears chattered while the outer is unaffected (cf. PI. 3, fig. 7 ; PI. 4, figs 4-5). Whatever the cause, it is likely that differential compaction and homogenization during diagenesis would have obliterated any original fine structure, making comparisons with extant spores of limited value. Nevertheless, there are similarities with certain filicalean ferns, such as zonation with comparable dimensions (Lugardon 1990), and indeed Professor Lugardon, having seen our Ambitisporites material, was of the same opinion and wrote ‘elles (i.e. the layers) correspondent probablement a des resistance a l’acide en relation avec des variations chimique, ou physico-chimique de la sporopollenine a l’interieur d’une meme couche’. He believes that the layers in living ferns correspond to the variation in degrees of polymerization of sporopollenin as layers are deposited during maturation, but which usually, but not consistently, have disappeared in mature spores. Similar atlases are needed for mosses and hepatics. In a brief overview (Brown and Lemmon 1990), two-layered exines are recorded in certain hepatics, hornworts and Sphagnum although the bryopsid exine is described as typically homogeneous. Such comparisons made on the ‘nearest living match’ approach are over simplistic and certainly are not intended to reflect relationship. The likelihood that spore wall ultrastructure has remained static over four hundred million years must be debated. However, surveys of extant filicaleans and a few bryophytes do show that exosporal layering is present and that its significance has been addressed in extant cryptogams. Peripheral layer. Observations by light microscopy in Ambitisporites revealed the peripheral layer as an adhering coalified sheet, while its reaction with concentrated nitric acid indicated a different chemistry from the probably sporopollenin-impregnated exospore. Nitric acid had a similar effect EDWARDS ET AL.: COOKSONIA SPORE ULTRASTRUCTURE 165 in the present investigations although traces of the enveloping dark layer remain in Aneurospora and may be equivalent to a translucent ‘structureless’ layer sometimes visible in light microscopy. In contrast to the marked morphological differences noted by SEM in ‘before and after' treatments of in situ cf. Ambitisporites, there is little change in the spores discussed here. Intersporal matrix. This behaved in similar fashion to the peripheral layer, although traces of ‘membranous’ sheets remained after concentrated nitric acid treatment in Synorisporites. Size. Although nitric acid is sometimes cited as increasing the size of spores, we have noted only a small increase in maximum diameter ( < 5 per cent, in Synorisporites , 3 per cent, in Streelispora ), but the small size sample and difficulties of measurement limit confidence in the data. There are no noticeable changes in wall thickness but, in a number of cases, lumens become apparent as distal and proximal walls separate. There is also the suggestion, particularly from SEMs that the exospore becomes more supple with collapse between unsupported areas, thus enhancing features such as crassitudes and apertural folds, although these are also visible on untreated material. HOMOLOGY OF SPORE LAYERS AND ASSOCIATED STRUCTURES (Text-figure 4) Exospore The concentrated nitric acid-resilient component is interpreted as exospore. Apart from differences in electron opacity, producing the layering, it is apparently homogeneous, although the possibility that its original structure has been eliminated during diagenesis cannot be discounted. The general appearance is similar to that recorded in cf. Ambitisporites (Rogerson et al. 1993). The very dark narrow line around the lumen seen in Aneurospora and Synorisporites is not a consistent feature, but, where present, persists after nitric acid treatment. It might represent the remains of spore contents or even endospore. Layering in an otherwise homogeneous exospore is seen in illustrations of extant ferns (Lugardon’s 1990 Filicinees) and articulates and also in liverworts (Brown and Lemmon 1990) where associated with lamellar organization. A suture on the trilete mark has never been observed in sections of Ambitisporites , Synorisporites verrucatus , Streelispora newportensis and Aneurospora. Its apparent presence in preparations viewed by light microscopy may be due to the lumen projecting into the apertural fold. The electron-transparent circular to oval cavities noted in cf. Ambitisporites (Rogerson et al. 1993) are common in Synorisporites verrucatus , particularly after acid treatment where they may be localized towards the equator, less common in Streelispora newportensis and absent from Aneurospora sp. They occur in outer and inner layers of the exospore, and occasionally cross the junction between them. Similar structures are present in TEM preparations of Parka (Hemsley text-fig. 4. Schematic representation of exospore layers in Ambitisporites sp. (a), Synorisporites verrucatus (b, C), Aneurospora sp. (d) and Streeli- spora newportensis (e). x = inner exospore, y = outer exospore, z = peripheral layer. Scale bar repre- sents 0-52 /;m. 166 PALAEONTOLOGY, VOLUME 38 1989), and are called ‘bubble-like cavities’. It seems likely that they are artefacts of preparation or develop during preservation but we have no explanation for their formation. Peripheral layer and intersporal matrix The nature of the acid sensitive layer enveloping the exospore was somewhat inconclusively discussed above in relation to cf. Ambitisporites (Rogerson et al. 1993). It is comparable in position (Brown and Lemmon 1990) and reaction to concentrated nitric acid with the perispore recorded in mosses, ferns, Lycopodiaceae, and microspores of heterosporous lycophytes (Lugardon 1990) where it is deposited by condensation of tapetal particles onto one or several layers, after completion of the exospore. However, the perispore of extant plants is highly ordered, sometimes with taxon- specific surface patterning and seems to comprise a far more discrete layer than that recorded here. We therefore remain equivocal on the homology of the peripheral layer with the perispore. We are also uncertain of its relationship to the far more extensive intersporal ‘matrix’ recorded in Synorisporites which may be distinguished from the peripheral layers because of its more granular appearance and lighter staining. Like the peripheral layer it disappears on treatment with fuming nitric acid. The membrane-like structures which withstand acid treatment may well be the remains of aborted spores and have outlines consistent with this hypothesis. A further possibility is that they are similar to the ornamented sheets noted between spores of Uskiella spargens (Shute and Edwards 1989) and compare with sheets formed by fusion of Ubisch bodies in spermatophytes. The intersporal matrix may represent the remains of a periplasmodial tapetum, but more probably represents the locular fluid which bathes developing spores. Although a liquid has low fossilization potential, it may have been preserved in this case because of its colloidal or viscous nature, itself possibly due to the presence of more recalcitrant molecules as precursors of sporopollenin. COMPARISONS WITH RELEVANT DISPERSED SPORE TAXA It is of some interest to compare the ultrastructural detail presented here with structure recorded in the diagnoses of the dispersed spores which were originally based on light microscope observations. Thus, considering the emended diagnosis of the genus Streelispora , Richardson et al. (1982) described the exine as ‘two-layered (possibly three-layered)’ with ‘layers closely adpressed over most of the surface’ and contact areas ‘characterized by tangential folds and small radial folds of the outer thin exo-exinal layer’. For S. newportensis the papillate thickenings are considered part of a second and thicker underlying exo-exinal layer. Our observations confirm the layering, our outer and inner exospore being equivalent to the outer thin exo-exinal and underlying thicker exo- exinal layers respectively, but suggest that the inner exo-exinal layer also contributes to the folds (Text-fig. 4). From the nature of the proximal radial and tangential folds, as interpreted by light microscopy, it had been expected that the two layers were loosely attached on the proximal surface. However, none of the sectioned spores illustrated here show separation of the two layers with the outer, forming a fold. The major structural feature, ‘the more or less equatorial crassitude’, is surprisingly difficult to identify in our TEM sections, although it is present and best developed in spores from specimen NMW 93.143G.6 (PI. 4, fig. 4). Likewise it is not pronounced in TEMs of Synorisporites or Aneurospora. Indeed in their emended generic diagnosis for the latter, Richardson et al. (1982) described a subequatorial region which is ‘especially rigid and probably thickened so as to appear like a dark band (equatorial crassitude); the inner limits of it are often ill-defined and its width is also + variable even in the same specimen’. This description fits very well with our observations. In all four genera (. Ambitisporites , Synorisporites , Streelispora and Aneurospora ), viewed under the light microscope, the equatorial crassitude sometimes appears as more rigid than the adjacent distal area and retains its shape in various compressional states. In contrast, although, in the original description of Synorisporites verrucatus (Richardson and Lister 1969), the exine is described as homogeneous with the equatorial crassitude 2-3 pm wide, in later light microscope descriptions of better preserved Synorisporites (verrucatus and tripapillatus) and Ambitisporites , Richardson and Ioannides (1973, p. 277, pi. 5, fig. 5) showed a closely adherent EDWARDS ET AL.: COOKSONIA SPORE ULTRASTRUCTURE 167 diaphanous outer layer. This is now thought to be equivalent to the outer exospore seen in our TEM sections. EVOLUTION IN COOKSONIA SPORES Based on SEM studies and stratigraphical occurrences it was originally suggested that spores of Cooksonia pertoni all have a similar structure (i.e. equatorially crassitate) but that sculpture changed in time from smooth to verrucate to apiculate (Fanning et al. 1988). These TEM observations support the hypothesis as regards structure, and show how the distribution of the outermost layer varies with change in ornament. There is also a decline in total wall thickness excluding sculpture, although, because of the nature of its ornament, Synorisporites verrucatus spores appear to have larger amounts of sporopollenin than Ambitisporites. There is no evidence that the ornament in S. verrucatus , although superficially sometimes similar to surface wrinkling, was formed by contraction: the muri and verrucae were formed by additional material with resultant increase in surface area even though the actual diameter of the in situ spores of S. verrucatus is less than that for Ambitisporites sp. Although our in situ Aneurospora and Streelispora came from strata of differing age, their apiculate sculpture is similar and shows little intrasporangial variation. Minor differences in appearance between the two relate to quality of preservation. Considering the dispersed spore record, although the two genera form only a small numerical proportion of assemblages, there is a large number of integradational forms based mainly on the type and distribution of apiculate/granulate sculpture. The various types of sculptural forms and the proportions of the variants present change throughout the Lochkovian, but as yet we have insufficient numbers of megafossils with in situ spores to relate this to the evolution of subspecies of Cooksonia pertoni. A similar trend in exine morphology (namely, laevigate-verrucate-apiculate) has been recorded in dispersed spore representatives of a second structurally different miospore morphotype, although as yet the parent plants remain unknown. The trend is further exhibited by cryptospores, probably indicating a convergence in response to common environmental pressures in at least two major groups of land plants (Richardson and Burgess 1988). Finally, a peripheral layer has been demonstrated in all four taxa, and is most persistent in Aneurospora , where traces remain after nitric acid treatment, but is frequently absent in Streelispora. This leads to questions relating to the relative maturity of these in situ spores and the possibility that Cooksonia sporangia containing Aneurospora spores with their thinner peripheral layer (specimen NMW 93.143G.7, PI. 2, figs 3-7) are immature. Against the latter is the common occurrence of Aneurospora in the dispersed record. Acknowledgements. Our ultrastructural research was financed by NERC Research Grant GR3/7882 (PDRA K.L.D.). Such support is gratefully acknowledged. REFERENCES brown, r. c. and lemmon, b. e. 1990. Sporogenesis in bryophytes. 56-94. In blackmore, s. and knox, r. b. (eds). Microspores : evolution and ontogeny. Academic Press, London, x + 347 pp. edwards, d. and rose, v. 1984. Cuticles of Nematotliallus : a further enigma. 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L. and richardson, j. b. 1993. Identification of in situ spores in a Silurian Cooksonia from the Welsh Borderland. Special Papers in Palaeontology , 49, 17-30. shute, c. h. and Edwards, d. 1989. A new rhyniopsid with novel sporangium organization from the Lower Devonian of South Wales. Botanical Journal of the Linnean Society, 100, 11 1-137. traverse, a. 1988. Paleopalynology. Unwin Hyman, Boston, xxiii + 600 pp. tryon, A. F. and lugardon, B. 1991. Spores of the Pteridophyta: surface, wall structure and diversity based on electron microscope studies. Springer-Verlag, New York, x + 648 pp. D. EDWARDS K. L. DAVIES L. AXE Department of Earth Sciences University of Wales College of Cardiff Cardiff CF1 3 YE, UK Typescript received 29 June 1994 Revised typescript received 27 October 1994 J. B. RICHARDSON Department of Palaeontology Natural History Museum London SW7 5BD, UK LOWER DEVONIAN BIOSTRATIGRAPHY AND VERTEBRATES OF THE TONG VAI VALLEY, VIETNAM by TONG-DZU Y THANH, P. JANVIER, TA HOA PHUONG CUld DOAN NH AT TRUONG Abstract. A new vertebrate assemblage is described from the base of the Khao Loc Formation at Tong Vai, Dong Van district, Ha Giang Province, Vietnam. It includes the galeaspid Polybranchiaspis liaojaoshanensis , two acanthothoracid placoderms, and the sarcopterygian Youngolepis praecursor. This assemblage is quite similar to that of the Xitun Formation of Yunnan (Late Lianhuashanian to Early Nagaolingian) and can also be correlated with the vertebrate faunas which occur at the base of the Bac Bun Formation of the Bac Bo in Vietnam. New data on the morphology of P. liaojaoshanensis are provided on the basis of this material, with special reference to the structure and ornamentation of the exoskeleton. The Tong Vai valley is situated near the Chinese-Vietnamese border, west of the Quan Ba hamlet, on the Ha Giang-Yen Minh main road in the Dong Van district (Text-fig. 1). From Quan Ba, the road to Tong Vai runs through a pass in a mountainous area of limestone and sericite-bearing shales. The distance between Quan Ba and the Tong Vai valley is directly about 10 km (18 km by road). The Palaeozoic rocks of the Tong Vai valley and its surroundings were considered by Deprat (1915) to be Late Cambrian to Early Ordovician in age (see also the geological map of the Ma Li Po area in this work). Vassilevskaya (in Dovjikov 1965) regarded the 'Luong Kho Limestones’ of the Tong Vai valley as Ordovician, on the basis of poorly preserved brachiopods and ostracodes of 'Ordovician-Silurian aspect'. In 1973, Ta Thanh Trung and Hoang Anh Truong were the first to collect early Devonian fossils from this area. These included some brachiopods e.g. Lingulella dussaulti Patte) and a specimen of the galeaspid fish Polybranchiaspis sp. (Ta Thanh Trung 1978). Hoan Xuan Tinh (1976), chief engineer of the Geological Mapping Team for the Bao Lac sheet, correctly described, apart from a few inaccuracies, the stratigraphical sequence of the Early Devonian in the Tong Vai valley, and his description was later referred to in the 'Stratigraphy of Vietnam’ (Vu Khuc and Bui Phu My 1990). Of the five members he described, the first two may not belong to the Devonian, but rather represent terrigenous beds that Vassilevskaya (in Dovjikov 1965) referred to the Late Cambrian, and Deprat (1915) to the Ordovician. The description of the Polybranchiaspis-beanng levels in Hoang Xuan Tinh’s (1976) paper is quite different from the one made later by Ta Thanh Trung (1978), who collected the galeaspids from 'dark grey carbonate-bearing terrigenous deposits’. On the contrary, Hoang Xuan Tinh (1976) depicted his Polybranchiaspis- bearing third member of the Lower Devonian as a succession of opalescent, yellowish quartzitic sandstones, siltstones and mudstones, which he referred to as the ‘Bac Bun Suite’. To this author, the 'Bac Bun Suite’ comprised the Si Ka and Bac Bun formations first described by Deprat (1915) and later reviewed by Tong Dzuy Thanh (1967, 1982) and Tong Dzuy Thanh et al. (1986). According to Hoang Xuan Thinh’s description, his third member may be attributed to the Si Ka Formation, although, as will be mentioned below, such coarse terrigenous rocks do not seem to occur in the Lower Devonian of the Tong Vai valley. | Palaeontology, Vol. 38, Part 1, 1995, pp. 169-186, 3 pis.] © The Palaeontological Association 170 PALAEONTOLOGY, VOLUME 38 text-fig. 1. Locality Map; 1-4, location of invertebrate and vertebrate-bearing exposures of member 3 of the Tong Vai section. GEOLOGICAL SETTING In summer 1991, one of us (T.H.P.) made a field trip to the Tong Vai valley and recorded several fossiliferous localities which have since been investigated, in spring 1993, by Tong-Dzuy Thanh, Ta Hoa Phuong and Doan Nhat Truong in the frame of the project KT 04.6.1.1. of the Vietnamese Fundamental Research Program in Natural Sciences. Description The eastern slope of the Tong Vai valley consists of sericitized shales and dark grey limestones, dated, with reservations, as Late Cambrian (Dovjikov 1965). The rest of the area consists mainly of limestones and interbedded marls. The complete stratigraphical column in Tong Vai, from the Upper Cambrian to the Devonian, is still unknown because of tectonic complications. However, six successive members can be distinguished in the Devonian, without any breaks (Text-fig. 2). These are, from base to top: 1. The basal member consists of light grey, relatively thin-bedded (200 mm) and sometimes opalescent, striped limestones. They resemble the Upper Palaeozoic limestones widespread in the north of Vietnam. Sometimes, they display a schistosity to various degrees. The contact between these limestones and the underlying Upper Cambrian is not clear and the thickness of this member cannot be estimated precisely. A thickness of only c. 300-350 m can be observed, but the sequence may be thicker. They have yielded only scolecodonts and small rounded masses or organic matter (F. Paris, pers. comm.). TONG-DZU Y THANH ET AL.: DEVONIAN VERTEBRATES 171 Grey, recrystallized limestone with numerous indetermined remains of Amphipora and tabulate corals. Thamnopora polyforata Thin-bedded, dark-grey limestones Tabulate corals belonging to the Euryspirifer tonkinensis -fauna Thin-bedded, dark-grey limestones and mudstones with plant remains Thin-bedded, dark -grey limestones with interbedded marls and calcareous shales with Polybranchiaspis liaojaoshanensis and Howittia wangi Thin-bedded, dark-grey, reciystallized limestones with thin siliceous interbeds in the lower part Light-grey, striped limestones Sericitized shales Lower Paleozoic text-fig. 2. Stratigraphical section of the Early Devonian of the Tong Yai valley. 2. The second member begins with cherts and dark-grey, recrystallized limestones and dolomites. Further up, the cherts disappear and the upper part of the member consists only of recrystallized limestones and dolomites. The thickness of this member is c. 200 m. It has yielded only scolecodonts (F. Paris, pers. comm.). 3. The third member consists of marls with interbedded dark grey limestone and mudstone layers. Locally, lenses of calcareous shales occur, in particular in the middle part of the member, and these weather to a pink colour. Abundant vertebrate remains occur about 50 m above the base of this member. They are associated with ostracodes and occur in dark grey calcareous siltstones (see below for faunal list). 40 m upwards, on the road from the Tong Vai valley to Ban Thang (1, 2, Text-fig. 1), some brachiopods were collected in marls. They are referred by Duong Xuan Hao and Le Van De (1980) to Howellella ex. gr. crispa (Hisinger) and Hysterolites wangiformis Zuong. The latter species is Howittia wangi (Orientospirifer wangi Hou of Chinese authors). Other brachiopods occur near the top of this member, on a small hill on the roadside close to Luong Kho village (3, Text-fig. 1) and 172 PALAEONTOLOGY, VOLUME 38 were referred by Duong Xuan Hao to Hysterolites wangiformis ( Howittia wangi ) and Tadschikial aff. xuanbaoi Zuong. The latter is similar to the type material from the lowermost Lower Devonian of the lower Da River basin (northwestern Vietnam). From Ta Thanh Trung’s (1978) description, his Polybranchiaspis sp. and Lingulella dussaulti (Sample 2808/1) were certainly also collected in this member. The total thickness of this third member is c. 200 m. 4. The fourth member consists of thin-bedded black limestones intercalated with calcareous shales and mudstones, some of which are coal-bearing. It has yielded some undetermined plant remains which were collected from the mudstones. It is c. 50 m thick. 5. The fifth member consists of thin-bedded, dark grey limestones and marl lenses, which contain tabulate corals (in particular, abundant Favosites kolimciensis Rukhin) of the Euryspirifer tonkinensis- fauna. Its thickness is c. 80 m. 6. The uppermost member consists mainly of light grey recrystallized limestones with abundant traces of ramiform stromatoporoids. These limestones are very similar to the Middle Devonian Amphipora limestones formerly described by French geologists (‘Calcaires a Amphipora' ; Saurin 1956). The top of member 6 cannot be observed in the area of Tong Vai valley, because of faulting. Its observed thickness is c. 250 m. Discussion From Hoang Xuan Tinh’s (1976) account, one of us (Tong-Dzuy Thanh 1982; Tong-Dzuy Thanh el al. 1986) referred the Polybranchiaspis- bearing beds of the Tong Vai valley to the Si Ka Formation. The new field observations presented in this paper suggests a reinterpretation of the Devonian of this area. The fauna of the third member unquestionably belongs to the Howittia wangi assemblage, which defines the Bacbunian regional stage in the Bac Bo (northern Vietnam, formerly called the Tonkin). Its major representatives are Howittia wangi and Howellella ex gr. crispa , and the vertebrates are quite similar to those in the corresponding stratigraphical level of Dong Mo and Trang Xa (Tong-Dzuy Thanh and Janvier 1990). The only, minor, difference is the presence of the brachiopod Tadschikial aff. xuanbaoi , similar to the type material from northwestern Vietnam (Duong Xuan Hao and Le Van De 1980). There is some difference between the Tong Vai vertebrate fauna and that of more southernly localities, such as Trang Xa and Dong Mo (Tong-Dzuy Thanh and Janvier 1987, 1990). Although Youngolepis is present in both, no acanthothoracid material has been recorded from the latter two localities. Moreover, there is a marked difference in the structure and ornamentation of the exoskeleton of the galeaspid Polybranchiaspis from Tong Vai (see below) and those of the poorly preserved specimens from Dong Mo referred to by Tong-Dzuy Thanh and Janvier (1990, fig. 4) as ‘ Polybranchiaspis sp.’. In the latter, the ornamentation consists of simple, rounded tubercles devoid of a basal recess, which are aligned into ridges along the shield margin. Therefore it is probable that the Dong Mo galeaspid, although a polybranchiaspidiform, does not belong to the genus Polybranchiaspis , but to a form which is closer to Bannhuanaspis (Janvier et al. 1993) in exoskeletal structure. According to the observations of one of us (T. D. T.), the fourth member of the Tong Vai section is quite similar in lithology to the base of the Khao Loc Formation in the Ban Hinh-Khao Loc section, which is situated not far South of Tong Vai. It can thus be suggested that the limestone of EXPLANATION OF PLATE 1 Figs 1-3. Polybranchiaspis liaojaoshanensis Liu, Pragian, Khao Loc Formation, Tong Vai, Ha Giang Province, Vietnam. 1 , BT 1 70, head shield in dorsal view, photographed in immersion to show the pineal foramen (a) and elastomere cast of its incomplete counterpart (b); note the ostracodes surrounding the specimens. 2, BT 171, right side of a headshield in dorsal view, elastomere cast of natural impression. 3, BT 172, left side of a headshield in internal view, elastomere cast of the internal surface of the exoskeleton and the ornamentation of the posterior wall of the median dorsal duct. All x 2. PLATE 1 TONG-DZUY THANH et at Polybranchiaspis 174 PALAEONTOLOGY, VOLUME 38 member 4 and upwards can be attributed to the Khao Loc Formation (Pragian-Givetian), which is widespread in the Northwest of Ha Giang Province (Text-fig. 2). The limestones of the uppermost member of Tong Vai (member 6) can be correlated with the upper part of the Khao Loc Formation and the Ban Pap Formation. The latter formation is widely distributed in the North of Vietnam. This correlation is supported by the abundance of Amphipora , a guide fossil for the Middle Devonian limestone in the North of Vietnam. The red beds of the Si Ka Formation do not occur in the Tong Vai area. Instead, below the Bacbunian faunal assemblage (fishes and Howittia wangi), there is a thick series of limestones (members 1 and 2), which are devoid of stratigraphically significant fossils (only scolecodonts are found). They may be a lateral equivalent of the Si Ka Formation. The correlation of the Bac Bun and overlying Mia Le formations of the Bac Bo with the Nakaoling (Nagaoling) and Yukiang formations (or stages) or southern China have been proposed in our former papers (Tong-Dzuy Thanh 1982; Tong-Dzuy Thanh et al. 1986, 1988u, 6; Tong-Dzuy Thanh and Janvier 1987, 1990) on the basis of both vertebrate and invertebrate faunas. It is further supported by the new material described herein. The Bacbunian vertebrates in northeastern Vietnam are frequently found in association with invertebrates of the Howittia wangi assemblage or in beds which immediately underlie this assemblage. By comparison with the data provided by S. T. Wang (1991), the Bacbunian vertebrate assemblage (in Dong Mo, Trang Xa, Tong Vai and other Vietnamese localities) is very similar to that of the Xitun Formation of the Cuifengshan Group in eastern Yunnan (China). Moreover, the Lower Devonian succession in the northeastern Bac Bo, from the Sika to Bac Bun and Mia Le formations is closely similar to that from the Lianhuashan to Nakaoling and Yukiang formations of Guangxi, China (Yang et al. 1981). This striking resemblance is seen in both the lithology and the faunal assemblages. As a result of the greater faunal diversity in northern Vietnam, these formations can be precisely dated, in particular the Mia Le Formation, which is clearly Pragian in age (Tong- Dzuy Thanh 1982; Tong-Dzuy Thanh et al. 1988«). This has been recently confirmed by the discovery of dacryoconarids of the Nowakia zlichovensis and N. barrandei zones, and a rich conodont assemblage of the Perbonus- zone (determined by Pham Kim Ngan, Hanoi), in the base of the limestones which overlie the Mia Le Formation in the Dong Van - Ma Lu section (Ha Giang Province, near the Chinese-Vietnamese border). Here, in the uppermost beds of the Mia Le Formation, one of us (T.H.P.) discovered new dacryoconarids among which is the well-known Pragian species Nowakia arcuaria (H. Lardeux, pers. comm.). In conclusion, these data suggest that: (1) the Bac Bun Formation, which underlies the Mia Le Formation and contains the vertebrates described below, may be Late Lochkovian to Early Pragian in age; (2) the Bac Bo area of northern Vietnam and the Yunnan-Guangxi areas of southern China belong to the same palaeobasin, characterized by endemic fish faunas; (3) the Bacbunian vertebrate and invertebrate faunas of northern Vietnam display mixed features of the Yunnan and Guangxi assemblages; and (4) they correspond to a foreshore to near-shore palaeoenvironment. Further south, in the Phu Luong and Trang Xa area, the larger amount of detritic sediments in the Sika and Bac Bun Formations suggests an even more near-shore to deltaic type of environment. EXPLANATION OF PLATE 2 Figs 1-3. Polybranchiaspis liaojaoshanensis Liu, Pragian, Khao Loc Formation, Tong Vai, Ha Giang Province, Vietnam. 1, BT 173, incomplete headshield in dorsal view, elastomere cast of the specimen (a, x 2), close- up view of the median dorsal opening, lit from the left (b, x 3), and S.E.M. photograph of the elastomere cast of the anterior wall of the median dorsal opening (c, x 20; d, x 15), to show the denticles on the anterior wall of the duct. 2, BT 172 (same specimen as PI. 1, fig. 3), S.E.M. photograph of an elastomere cast of the ornamentation on the posterior wall of the median duct, partly folded against the internal surface of the exoskeleton, x 15. 3, BT 174, incomplete headshield in ventral view, elastomere cast showing the ventral rim of the dermal headshield and the internal surface of the dorsal exoskeleton, x 2. PLATE 2 TONG-DZUY THANH et al. , Polybranchiaspis 176 PALAEONTOLOGY, VOLUME 38 text-fig. 3. Polybranchiaspis liaojaoshanensis Liu. a, reconstruction of the headshield in dorsal view (based on several specimens from Tong Vai); b, distribution of the sensory-line canals. Abbreviations: iorb, infraorbital canal; mdo, median dorsal opening; mil, main lateral-line; orb, orbit; pif, pineal foramen; sorb, supraorbital canal; tcom, transverse commissural canal; til-4, transverse lateral canals. text-fig. 4. Polybranchiaspis liaojaoshanensis Liu. a, reconstruction of the exoskeleton around and inside the median dorsal opening; b, reconstructed sagittal section through the median dorsal opening and duct; c, vertical section through two tubercles of the exoskeleton (combined from several thin sections); d, vertical section through the exoskeleton and a sensory-line canal (combined from several thin sections). Abbreviations: brec, basal recess of exoskeleton; ctb, central tubercle; fpt, forward pointing tubercle of median dorsal duct; Itb, lateral, or secondary tubercle; md, median dorsal duct; mdo, median dorsal opening; pb, perichondral bone; sbap, subaponeurotic vascular canals; sic, sensory-line canal. SYSTEMATIC PALAEONTOLOGY The vertebrate material from the Tong Vai valley consists mainly of well preserved galeaspid headshields, as well as isolated placoderm plates and the cosmine-covered dermal bones and scales of a sarcopterygian. All the specimens come from the marls and shales of member 3, and are associated with smooth-shelled ostracodes. The material described herein is registered in the TONG-DZU Y THANH ET AL.\ DEVONIAN VERTEBRATES 177 text-fig. 5. Polybranchiaspis liaojao- shanensis Liu, reconstruction of the exoskeletal headshield. a, ventral view; b, lateral view. Abbreviations: bm , branchial notch; «, notch; orn , oral notch. collection of the Geological Museum (Bao Tang Dia Chat, here abbreviated BT), 6 Pham Ngu Lao Str., Hanoi. Casts are deposited in the collection of the Laboratoire de Paleontologie, Museum National d’Histoire Naturelle, Paris). Class galeaspida Halstead Tarlo, 1967 Order polybranchiaspidiformes Liu, 1965 Family polybranchiaspididae Liu, 1965 Genus polybranchiaspis Liu, 1965 The genus Polybranchiaspis was erected by Liu (1965) for the species P. liaojaoshanensis Liu, 1965 (erroneously spelled as P. liaojiaoshanensis by Liu 1975 and several subsequent authors) from the Cuifengshan and Xitun formations of Yunnan (China). Polybranchiaspis now comprises nine species (including the type species), all from Yunnan. Polybranchiaspis liaojaoshanensis Liu, 1965 Plates 1-2, Plate 3, figures 1,2; Text-figures 3-5 Type specimen. An almost complete headshield (Institute of Vertebrate Palaeontology and Palaeo- anthropology, Beijing, No. V.3027; Liu 1965, pi. 3, fig. 1), from the Cuifengshan Group at Qujing, Yunnan. A relatively large hypodigm is now also known from this locality. Some other Polybranchiaspis species, e.g. P. gracilis Cao, 1985, P. yunnanensis Cao, 1985, P. rhombicus Cao, 1985 and P. sinensis Cao, 1985, described from the same locality and formation, are probably reflections of intraspecific variation within P. liaojaoshanensis. Material. The material from Tong Vai consists of five more or less complete headshields (BT 170-175) and numerous exoskeleton fragments (not numbered). 178 PALAEONTOLOGY, VOLUME 38 Locality and horizon. All the specimens described are derived from the four fish-bearing exposures of the Tong Vai valley (1-4, Text-fig. 1), which correspond to the same shaly horizon in the basal part of the third member of the Tong Vai section (second member of the Khao Loc Formation proper; Text-fig. 2). Description. The headshield of the Polybranchiaspis species from Tong Vai is indistinguishable from that of P. liaojaoshanensis Liu from the Cuifengshan Formation of Yunnan (Liu 1965, 1975). On the basis of the photographs of the incomplete headshields discovered by Ta Thanh Trung (now deposited in the Geological Institute, Beijing), Tong-Dzuy Thanh and Janvier (1987) referred the Vietnamese specimens to P. cf. gracilis Cao, recorded from the same formation by Cao (1985). The latter was said to be characterized by posterolateral orientation of the foremost lateral transverse sensory-line canal (til. Text-fig. 3b). However, examination of large populations of P. liaojaoshanensis from Yunnan now suggests that P. gracilis lies within the range of variation of P. liaojaoshanensis. The exoskeleton of the Polybranchiaspis specimens from Tong Vai is well preserved (in contrast to previously described Chinese material) and has yielded new information about its structure and ornamentation. Most of the specimens have been prepared as impressions, by removing the exoskeleton with hydrochloric acid, and making elastomere casts (PI. 1, figs lb, 2-3; PI. 2, fig. 1 ; PI. 3, fig. 1). Ornamentation. In external aspect, the ornamentation of the exoskeleton of P. liaojaoshanensis shows relatively large but low, star-shaped tubercles (PI. 1, figs lb, 2-3; PI. 2, fig. la; PL 3, fig. la; Text-figs 3a, 4c-d, 5). These are smaller in the anterior part than in the posterior part of the dorsal surface of the shield. Also, in the posterior part of the shield, particularly on the median dorsal crest and along the lateral margins, they tend to become elongated, and even spine-shaped (Text-figs 3a, 5b). The tubercles on the ventral rim of the shield are very small (PI. 1, fig- 3; PL 2, fig. 3; Text-fig. 5a). They are irregular in shape, with a large median elevation, or central tubercle ( ctb , Text-fig. 4c), and four or five ‘branches’, each of which is made up by two or three smaller, lateral tubercles (PL 3, fig. la; Itb , Text-fig. 4c). These ‘branches’ may unite one tubercle with neighbouring ones. Although the sensory-line canals are closed over most of their course, their pattern can be traced as a result of the presence of double rows of smaller tubercles (PL 1, figs lb, 2; PL 2, fig. la; Text-fig. 3a). In internal view, each of these tubercles is hollowed by a shallow depression, or basal recess (PL 1, fig. 3; PL 3, fig. lb; tree. Text-fig. 4c), which often leaves a more or less polygonal impression on the surface of the internal natural mould of the exoskeleton. The perichondral layer of the endoskeleton, when still present, closes these polygonal recesses basally (PL 1, fig. 3; pb. Text-fig. 4c posteriorly to the orbit). This pattern has, for a long time, given the impression that the galeaspid exoskeleton was made up of small tesserae, like that of osteostracans (Halstead et al. 1979). Janvier (1981) also regarded this polygonal pattern as evidence for a honeycomb-like structure to the galeaspid exoskeleton, and compared it with the similar structure of the heterostracan exoskeleton. Both interpretations appear now to be incorrect. A vertical thin section through the exoskeleton of Polybranchiaspis (Text-fig. 4c-d) displays basically the same histological structure as in the Dong Mo 'Polybranchiaspis sp.’, Bannlmanaspis (Tong-Dzuy Thanh and Janvier 1990, pi. 1; Janvier 1990; Janvier et al. 1993) and Xiushuiaspis ( Changxingaspis , N. Z. Wang 1991), that is, an acellular, aspidine-like structure with horizontal incremental lines. There is no evidence for any type of dentinous tissue and one cannot distinguish any histological discontinuity between the tubercles. The walls of the basal recesses are made up of the same kind of laminar hard tissue as the tubercles. The relation of the structure in Polybranchiaspis to that in Bannlmanaspis (where there is no basal recess and where each tubercle seems to correspond to one exoskeletal unit, in particular in the posterior part of the shield) is unclear. If each of the star-shaped tubercles of Polybranchiaspis , with its basal recess, is regarded as a single dermal unit, then it may be regarded primitive, and comparable to, for example, a thelodont scale with its pulp cavity. Conversely, one may consider that the star-shaped tubercles of Polybranchiaspis are in fact compounds of much smaller units, represented by the central tubercle and the adjacent cusps on the radiating ridges. Then, each of these ‘primary’ tubercles would correspond to one single unit of Bannlmanaspis. The former hypothesis could be supported by the fact that a similar pattern (stellate or costulated tubercles with a large basal recess) occurs also in the Silurian galeaspid Hanyangaspis (N. Z. Wang 1986), which was regarded by Janvier (1981) and N. Z. Wang (1991) as the most generalized galeaspid on the basis of several other characters. The latter hypothesis could be supported by the fact that the structure of the exoskeleton of Bannlmanaspis is remarkably simple and passes progressively to the body squamation. Also the latter structure (small units, each corresponding to a single, simple tubercle) seems to be that seen in most other galeaspids, in particular the Eugaleaspidiformes. No major conclusions concerning the polarity of the character states in the galeaspid exoskeleton can reasonably be drawn from such sparse data, and a review of the exoskeletal structure in all other galeaspids is urgently needed. TONG-DZU Y THANH ET AL.. DEVONIAN VERTEBRATES 179 Sensory-line canals. The sensory-line canals of P. liaojaoshanensis are remarkably large and form prominent ridges on the internal surface of the exoskeleton, well beyond the base of the walls of the basal recesses (PI. 1, fig. 3; PI. 2, fig. 3; sic, Text-fig. 4d). The fact that their basal part is often 'unfinished’ suggests that they are partly lined by the perichondral bone lamella of the endoskeleton. The cast of the natural impression of the external surface shows that the sensory-line canals were closed over most of their length (PI. 1, figs lb, 2; PI. 2, fig. la). The supraorbital and lateral transverse canals were open only distally (PI. 1, fig. 2; PI. 2, fig. la; sorb, tll-4. Text-fig. 3b), and the infraorbital canal opened by only a few broad slits, lateral to the orbits (PI. 1, fig. 2; PI. 2, fig. la; iorb, Text-fig. 3b). In some specimens, the transverse commissural line opens in a few short slits (PI. 1, fig. lb; PI. 2, fig. la; tcom , Text-fig. 3b). There is no evidence of small sensory-line pores along the canals. This condition differs from that in all other vertebrates, and the function of such, almost entirely closed sensory-line canals remains unexplained. Subaponeurotic vascular plexus. The presence of a dense subaponeurotic vascular plexus below the exoskeleton of galeaspids has been recorded by Halstead et al. (1979) and described by N. Z. Wang (1991) in the Silurian genus Xiushuiaspis. It is here shown to be present also in P. liaojaoshanensis (PI. 1, fig. 3; PI. 3, fig. 2). This network of vascular canals lies between the exoskeleton and the underlying endoskeletal shield, but is lined with perichondral bone (sbap. Text-fig. 4c). It is thus situated within or just below the perichondral lamella which closes basally the basal recesses. Its structure is closely similar to that of osteostracans and gnathostomes. Median dorsal opening. The main defining characteristic of galeaspids is a large median dorsal opening ( mdo , Text-figs 3b, 4a-b) in the anterior part of the headshield, which is currently interpreted as the external opening of an inhalent duct (md. Text-fig. 4b), comparable in function, and perhaps homologous to the nasopharyngeal duct of extant hagfishes (Janvier 1984). The paired olfactory organs open into this duct immediately below its external opening. The duct communicates basally with the gill chamber. This median dorsal opening and its duct are known to be partly lined by a thin layer of exoskeleton (Wang and Wang 1982; Janvier 1984; Liu 1985). Some of the Polybranchiaspis specimens from Tong Vai display delicate details of the dermal ornamentation of the duct. In the anterior wall it consists of minute, tilted pyramid-shaped tubercles which point toward the exterior (PI. 2, fig. lb-d ; fpt, Text-fig. 4a-b). The latter are arranged in rows which are parallel to the margin of the median dorsal opening. In contrast, in the posterior wall of the duct, the ornamentation consists of irregularly arranged tubercles which are more similar to those of the external surface of the headshield, and pass posteriorly to small, independent platelets (PI. 1, fig. 3; PI. 2, fig. 2). However, even in this part of the duct, the tubercles are tilted toward the exterior. This new information is of great importance to the understanding of the functional interpretation of the median dorsal opening in galeaspids. It is well known that, in fishes in general, the apertures through which water passes from the exterior to the interior (margin of nasal opening, spiracle, etc.) are lined with minute tubercles or denticles which point toward the exterior, the role of which essentially is to repel ectoparasites (Patterson 1977). The presence of such externally pointing tubercles in galeaspids is thus evidence for an inhalent (and not exhalent, as suggested by Belles-Isles 1985) function of the median dorsal opening, and accords with the position of the olfactory cavities observed in other galeaspids (N. Z. Wang 1991). This condition can be directly compared with the forward-pointing denticles recently discovered inside the snout of some thelodonts, and which have been regarded by Brugghen and Janvier (1993) as evidence for an inhalent nasopharyngeal opening (but in a terminal position) in thelodonts. In Polybranchiaspis, the external margin of the median dorsal opening is lined by a prominent ridge, somewhat accentuated in our specimens by a slight dorsoventral flattening of the rest of the shield (PI. 2, fig. la-b). Pineal foramen. The pineal foramen seems to be a variable character in galeaspids. Liu (1965) described the pineal opening of P. liaojaoshanensis as very small, but Halstead et al. (1979) considered that there was no pineal opening, as in heterostracans. The Tong Vai specimens show a very clear, rounded pineal opening, which is variable in size but fairly large (PI. 1, fig- la; PI. 2, fig. la; pif. Text-fig. 3b), and surrounded by a crown of small tubercles. Orbit and orbital cavity. In one specimen from Tong Vai (PI. 1, fig. 3), the perichondral lining of the orbital cavity is partly preserved and appears almost hemispherical in shape, yet the posterior ventral myodome (or trigeminal chamber) cannot be observed. The orbits are almost circular in shape and protrude slightly above the level of the surrounding exoskeleton (PI. 1, fig- 2; PI. 2, fig. la). Although the exoskeleton is certainly thicker 180 PALAEONTOLOGY, VOLUME 38 around the orbits, there is no major change in the aspect of the ornamentation along the orbital margin, contrary to what is commonly observed in osteostracans. Absence of endolymphatic opening. In spite of the excellent state of preservation of the exoskeleton and ornamentation in our specimens, we have been unable to see any trace of the endolymphatic opening. To date, the latter has been observed only in the Silurian galeaspid Xiushuiaspis (N. Z. Wang 1991), where it lies in front of the posterior transverse commissural sensory-line canal (probably homologous to the unique commissural canal of Polybranchiaspis). We can thus conclude that there is no endolymphatic opening in P. liaojaoshanensis. Ventral rim. The ventral rim of the headshield is covered with minute stellate tubercles. Along the margin of the oralobranchial fenestra, at least seven branchial notches are visible in one of our specimens (PI. 2, fig. 3; brn. Text-fig. 5a), which is incomplete. Here again, no change in the aspect of the ornamentation is noticeable along the notch margin, and the exoskeleton passes to the smooth surface of the perichondral bone which lines the branchial fossae. Liu (1975) recorded twelve branchial notches in P. liaojaoshanensis from Yunnan, where the actual branchial fossae can be observed. It is probable that three or four of the branchial notches in our specimen are less marked, because they lie in the narrowest part of the rim, just behind the level of the orbit. At this level, the rim is recurved dorsally (i.e. toward the oralobranchial cavity), and this does not seem to be due to distortion. This branchial division of the rim ends, immediately behind the level of the orbits, in a well- marked notch («, Text-fig. 5a). Anteriorly, it is much broader, until it reaches the oral region. Only the lateral part of the oral notch is visible in our material ( orn , Text-fig. 5a). In one specimen (PI. 1, fig. 2), the external surface of the part of the exoskeleton which extends behind the orbits shows a series of seven or eight ‘waves’, corresponding to the position of the underlying branchial fossae. Remarks on galeaspid taphonomy. Owing to their extremely thin exoskeleton (c. OT-O-4 mm) and often weakly ossified endoskeleton, complete galeaspid headshields are preserved only in very low energy environments, such as in the third member of the Tong Vai section and at a few Chinese localities. Nevertheless, even in such quiet deposits, some headshields are broken, and seem to have broken always in the same way: the anterior rim of the median dorsal duct, or the lateral parts of the shield are detached from the central part (PI. 1, figs 2-3; PI. 2, fig. la). This suggests that there are areas of weakness in the headshield, in particular in the epibranchial region, where the roof of the oralobranchial chamber meets the dorsal exoskeleton. This is probably the reason why, in many galeaspids ( Asiaspis , Lungmenshanaspis , Pentathyraspis ), large fenestrations occur in this particular area, and have been interpreted as either dorsal ‘fields’ (by reference to those in osteostracans) or dorsal branchial openings (N. Z. Wang 1991 ; Pan 1992). In some well preserved specimens from Tong Vai, there are often small patches of exoskeleton which are missing in the epibranchial region, and this is presumably due to pre-preservational damage. These fenestrations are thus most probably artefacts of preservation. EXPLANATION OF PLATE 3 Figs 1-2. Polybranchiaspis liaojaoshanensis Liu, Pragian, Khao Loc Formation, Tong Vai, Ha Giang Province, Vietnam. 1, S.E.M. photograph of an elastomere cast of the external (a), BT 171, and internal (b), BT 172, surface of the exoskeleton, x45. 2, BT 175, headshield with exoskeleton removed and photographed in immersion, to show the subaponeurotic vascular plexus (sensory-line canals darker), x 5. Fig. 3. Acanthothoraci gen. et sp. mdet. 1, BT 167, Pragian, Khao Loc Formation, Tong Vai, Ha Giang Province, Vietnam. Natural cast of the right anterolateral and spinal plates (a, x 4), and S.E.M. photographs of an elastomere cast of the impression, showing a lateral stellate tubercle of the anterolateral plate (b, x 1 50) and some crescentiform tubercles of the postbranchial lamina (c, x 100). Figs 4-5. Acanthothoraci gen. et sp. mdet. 2, same locality and horizon as PI. 3, fig. 3. 4, BT 165, natural impression of the right anterior ventrolateral and spinal plates in ventral view (a) and elastomere cast of the latter (b), x 4. 5, BT 168, left anterolateral and anterior ventrolateral plates in lateral view, most of the bone missing, x 4. Fig. 6. Youngolepis praecursor Zhang and Yu, BT 169, Pragian, Khao Loc Formation, Tong Vai, Ha Giang Province, Vietnam. Right lower jaw in lateral view, x 3. PLATE 3 TONG-DZUY THANH et al., Devonian vertebrates 182 PALAEONTOLOGY, VOLUME 38 Superclass gnathostomata Cope, 1889 Class placodermi McCoy, 1848 Order acanthothoraci Stensio, 1944 The Tong Vai material includes a few placoderm plates which can be referred here to the presumably paraphyletic taxon Acanthothoraci (Goujet 1984), on the basis of their overall morphology and star-shaped ornamentation. They seem to belong to two distinct forms, based on slight differences in the shape of the anterolateral plate. Both forms are probably new, and differ markedly from all previously described acanthothoracids, but we consider that it is preferable to wait for the discovery of cranial material, to ensure a useful systematic analysis, before erecting new species. acanthothoraci gen. et sp. indet. 1 Plate 3, figure 3; Text-figure 6a Material. An anterolateral plate of the right side, associated with the spinal plate (BT 167). Locality and horizon. Exposure 2 (Text-fig. 1) of the Tong Vai valley, in a thin layer of black shale from the third member of the section (second member of the Khao Loc Formation). Description. We refer to this first form a complete anterolateral plate, associated with the spinal plate ( AL , SP, Text-fig. 6a), preserved as an impression of its external surface. The dorsal blade of the anterolateral plate is roughly square, and the postbranchial lamina is not clearly distinct from the rest of the plate, yet is covered with crescentiform tubercles (PI. 3, fig. 3c; pbrl. Text-fig. 6a) as in e.g. Romundina (0rvig 1975), Palaeacanthaspis and Kosoraspis (Stensio 1944; Denison 1978). The rest of the anterolateral plate is ornamented with large, scattered, star-shaped tubercles (PI. 3, fig. 3b). acanthothoraci gen. et sp. indet. 2 Plate 3, figures 4—5; Text-figure 6b-c Material. Impression of the anterior ventrolateral and spinal plates of the right side (BT 165); fragmentary impression of an anterior ventrolateral plate of the left side (BT 166); indeterminate plate fragment (BT 164), with the same ornamentation as BT 165; associated anterolateral and anterior ventrolateral plates of left side (BT 168). Locality and horizon. All specimens referred to this form come from exposure 1 (Text-fig. 1) of the Tong Vai valley and are from the shaly basal part of the third member of the section (second member of the Khao Loc Formation). Description. This second form is represented by the external impression of an anterior ventrolateral plate and the associated spinal plate ( AVL , SP, Text-fig. 6c), and two associated anterior ventrolateral and anterolateral plates ( AL , A VL, Text-fig. 6b). They all differ from the preceding form by their larger, more rounded and closely-set tubercles, as well as by the rounded shape of the dorsal blade of the anterolateral plate, and the medially directed postbranchial lamina (pbrl. Text-fig. 6b). Since the bone was very thin, the impressions of the internal and external surfaces are somewhat superimposed, and observation of the specimens in immersion reveals traces of the overlap areas. A clear overlap area for the anterior dorsolateral plate, and possibly the posterolateral plate, is visible in the anterolateral plate (Text-fig. 6b). There seems also to be an overlap area for a posterior ventrolateral plate on the anterior ventrolateral plate. In the anterior part of the latter there is an oblique groove for the ventral transverse pit-line ( pltrv , Text-fig. 6c). By its broad anterior ventrolateral plate, this form clearly differs from all other acanthothoracids described to date in which this plate is very narrow. However, there is a number of still undescribed forms (e.g. from Siberia and Saudi Arabia) with a similar, broad anterior ventrolateral plate (D. Goujet, pers. comm. 1994). A small acanthothoracid is present in the Cuifengshan Group of Yunnan (Zhu Min, pers. comm. 1994) which TONG-DZUY THANH ET AL.: DEVONIAN VERTEBRATES 183 Vietnam, a, Acanthothoraci gen. et sp. indet. 1, BT 167, right anterolateral and spinal plates in lateral view, camera lucida drawing of an elastomere cast of a specimen preserved as an impression, b-c, Acanthothoraci gen. et sp. indet. 2; b, BT 168, left anterolateral and anterior ventrolateral plates preserved essentially as an impression of the internal surface, with some patches of exoskeleton and external ornamentation, camera lucida drawing; c, BT 165, right anterior ventrolateral plate and spinal plate in ventral view, camera-lucida drawing of an elastomere cast of the specimen preserved as an impression. Abbreviations: AL , anterolateral plate; AVL , anterior ventrolateral plate; pbrl, postbranchial lamina of the anterolateral plate; pltrv, transverse ventral pit-line; SP , spinal plate. TEXT- FIG. 7. Youngolepis praecursor Zhang and Yu, BT 169, Khao Loc Formation, Tong Vai, Ha Giang Province, Vietnam. Camera-lucida drawing of the right lower jaw in lateral view. Abbrevi- ations: art , glenoid articular fossa; mdc, pores of the mandibular sensory-line canal; plid , hori- zontal part of infradentary pit-line ; plid2, vertical pit-line of infradentary 2; vmdp , ventral man- dibular pits. vmdp seems to be identical to this second form from Tong Vai. All the acanthothoracids known to date are Late Lochkovian to Early Emsian in age. Class osteichthyes Huxley, 1880 Subclass sarcopterygii Romer, 1955 Infraclass dipnomorpha Ahlberg, 1991 Genus youngolepis Zhang and Yu, 1981 Youngolepis praecursor Zhang and Yu, 1981 Plate 3, fig. 6; Text-figure 7 Material. A single lower jaw of the right side (BT 169). Locality and horizon. Exposure 1 (Text-fig. 1) of the Tong Vai valley. Description. A small right lower jaw of a cosmine-covered sarcopterygian is similar to that of Youngolepis praecursor , described by Chang (1991), and shows the characteristic ventral series of large sensory pits (vmdp. Text-fig. 7). The pores of the mandibular canal are relatively large (mdc. Text-fig. 7), and the horizontal and vertical pit-lines (plid, plid2. Text-fig. 7) are well marked. The articular area is poorly preserved (art. Text-fig. 184 PALAEONTOLOGY, VOLUME 38 7). In addition, there are some cosmine-covered dermal bone fragments with very large and closely-set pores, which may belong to a different taxon. CONCLUSIONS The vertebrate fauna from Tong Vai accords with the ‘ Polybranchiaspis liaojaoshanensis - Dongfangaspis qujingensis palaeocommunity’ as defined by S. T. Wang (1991) from the base of the Xishancun Formation of the Cuifengshan Group of Qujing, Yunnan. However, P. liaojaoshanensis is known to extend into the overlying Xitun Formation, where it occurs in association with Youngolepis praecursor (Chang 1982). We would thus be inclined towards correlating the fish horizon in Tong Vai with the Xitun Formation of the Cuifengshan Group of Yunnan which is referred to the Late Lianhuashanian - Early Nagaolingian. Although fragments with a Polybranchiaspis- like ornamentation occur also in the more southerly situated Vietnamese localities of Trang Xa and Dong Mo, the material referred to by Tong-Dzuy Thanh and Janvier (1990) as ‘ Polybranchiaspis sp.’ from Dong Mo probably belongs to a different genus. Its ornamentation of small, isometric and rounded tubercles, and the lack of basal recesses are rather suggestive of Bannhuanaspis , yet its size is much smaller than that of the latter. Two forms of acanthothoracid placoderms have been described herein, one of which is unquestionably new. The occurrence of this taxon is consistent with the Pragian age of this locality. Acknowledgements. This survey has been financially supported by project K.T. 04 of the Vietnam Program of Fundamental Research in Natural Sciences. It also is part of the IGCP 306 and 328. This research has been made while one of the authors (T.D.T.) was Invited Professor at the Museum National d’Historie Naturelle, Paris. We are grateful to Professor H. Lardeux and Dr F. Paris (Rennes) for information on the dacryoconarids and scolecodonts, and to Drs D. Goujet (Paris) and Zhu Min (Beijing) for information on the acanthothoracid. REFERENCES ahlberg, p. E. 1991. A re-examination of sarcopterygian interrelationships, with special reference to the Porolepiformes. Zoological Journal of the Linnean Society, 103, 241-287. belles-isles, m. 1985. 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Lower Devonian vertebrate paleocommunities from South China. 487-497. In chang mee-mann, zhang guo-rui and Liu yu-hai (eds). Early Vertebrates and Related Problems of Evolutionary Biology. Science Press, Beijing, 514 pp. yang shih-pou, p’an kiang and hou hung-fei 1981. The Devonian System in China. Geological Magazine , 117, 113-138. zhang mee-mann and yu xaobo 1981. A new crossopterygian, Youngolepis praecursor , gen. et sp. nov., from Lower Devonian of E. Yunnan, China. Scientia Sinica , 24, 89-97. TONG-DZUY THANH TA HOA PHUONG Department of Geology Hanoi University 90, Nguyen Trai str. Dong Da, Hanoi, Vietnam PHILIPPE JANVIER U.R.A. 12 du C.N.R.S. Laboratoire de Paleontologie 8, rue Buffon 75005 Paris, France DOAN NHAT TRUONG Typescript received 13 April 1994 Institute of Geology and Mineral Resources Revised typescript received 8 September 1994 Dong Da, Hanoi, Vietnam THE EARLY CRETACEOUS BRACH IOSAU RID DINOSAURS ORNITHOPS/S AND EUCAMEROTUS FROM THE ISLE OF WIGHT, ENGLAND by WILLIAM T. BLOWS Abstract. The lectotype of Ornithopsis is usually placed within the Brachiosauridae, but is unlike any other material that has been referred to the genus. This referred material is also brachiosaurid but is regarded as belonging to the genus Eucamerotus which was originally established without a type species. Eucamerotus foxi sp. nov. is erected for this material, and a holotype and five paratypes are designated. Eucamerotus is placed within the Brachiosauridae. Several genera of sauropod dinosaurs, previously established from the Lower Cretaceous Wealden formation of the Isle of Wight, are nomina vana as they are based on inadequate type material. All described Wealden sauropod material other than dorsal vertebrae should be described as Sauropoda Incertae Sedis or Brachiosauridae Incertae Sedis. Several Lower Cretaceous sauropod genera were established by Owen, Seeley, Hulke and others, mostly based on inadequate material. Cetiosaurus brevis Owen, 1842 was founded on some vertebrae from Sussex with other vertebrae also referred to it. These referred specimens were made the type of Cetiosaurus conybeari by Melville (1849). A large humerus from Sussex was used by Mantell (1850) to establish the name Pelorosaurus conybeari. Ornithopsis hulkei Seeley, 1870 was based on two dorsal centra, one from Sussex, the other from the Isle of Wight, both of which were subsequently renamed by Owen (1875): the Sussex specimen as Bothriospondylus elongatus and the Isle of Wight specimen as Bothriospondylus magnus. Hulke (1870, 1871) described a dorsal neural arch from the Isle of Wight as Eucamerotus without giving it a species name. Chondrosteosaurus gigas Owen, 1876 and C. magnus Owen, 1876 were established for Isle of Wight vertebrae, cervical and dorsal respectively. Owen (1876) also proposed the synonymy of Chondrosteosaurus magnus with Bothriospondylus magnus. Lydekker proposed the presence of two American genera in the Weald, a new species of Pleurocoelus (P. valdensis Lydekker, 1889), based on vertebrae, and Morosaurus ( Camarasaurus ) (Lydekker, 1892), based on foot bones. The name Ornithopsis hulkei has been much used for sauropod material, both Lower Cretaceous and Upper Jurassic, despite the type specimen being an isolated dorsal centrum, which offers little for comparison with other vertebrate specimens. Ornithopsis would be considered as a nomen vanum but for the fact that dorsal vertebrae are ‘very diagnostic among the sauropods’ (Berman and McIntosh 1978, p. 33), and the name remains widely used in dinosaur literature for Wealden sauropods. A brief systematic review and discussion of the species are included here. Abbreviations. BMNH, Natural History Museum, London; MIWG, Museum of Isle of Wight Geology, Sandown, Isle of Wight. SYSTEMATIC PALAEONTOLOGY Class reptilia Linnaeus, 1758 Order saurischia Seeley, 1888 Suborder sauropodomorpha Huene, 1932 Infraorder sauropoda Marsh, 1878 Family brachiosauridae Riggs, 1904 Diagnosis. Following McIntosh (1990a, 19906) and Riggs (1904): large sauropods with forelimbs longer than hind limbs; vertebrae with deep, complex pleurocoels; strong opisthocoely | Palaeontology, Vol. 38, Part 1, 1995, pp. 187-197, 1 pl.| ©The Palaeontological Association 188 PALAEONTOLOGY, VOLUME 38 throughout the dorsal series; short simple massive neural spines throughout, tallest over the shoulder region. Genus ornithopsis Seeley, 1870 Type species. O. hu/kei Seeley, 1870 Ornithopsis hulkei Seeley, 1870 Text-figure 1a-b 1870 Ornithopsis hulkei Seeley, p. 279. 1875 Bothriospondylus magnus Owen, p. 24. pis. 8-9. 1879 Ornithopsis Seeley; Hulke, p. 754. 1882 Ornithopsis Seeley; Hulke, p. 375. Lectotype. BMNH 28632. posterior dorsal vertebra, chosen from syntypes of Seeley 1870, from Brook, Isle of Wight, England. Figured in Text-figure 1a-b. Type horizon. Wealden Marls (Wessex Formation) Lower Cretaceous (Barremian). Diagnosis. Medium-sized brachiosaurid sauropod; posterior dorsal vertebrae are opisthocoelian with tall narrow centra; pleurocoels extend over the posterior two-thirds of the centrum near the base of the neural arch; the centrum has a basal ridge; parapophyses occur high on the neural arch. Remarks. BMNH 28632 is the lectotype of Ornithopsis hulkei (Text fig. 1a-b) and was originally proposed as the syntype together with a vertebra from Sussex (BMNH 2239). There is no justification for linking these two vertebrae together as the syntypes, and Lydekker (1888) noted Seeley’s approval for making the Isle of Wight specimen the type of Ornithopsis hulkei. The other specimen is here regarded as Sauropoda Incertae Sedis and Owen’s binomen, Bothriospondylus elongatus , is a nomen vanum restricted to the type specimen. BMNH 28632 is very different to all other specimens referred to Ornithopsis hulkei. On this basis, the binomen can only be retained for this specimen, until such time as new vertebrae referable to Ornithopsis hulkei are found in association with other bones. Since BMNH 28632 is restricted to a centrum only, precise family affinities cannot be established, but the following features are suggestive of a brachiosaurid origin. The centrum is tall and narrow and has a prominently ridged base. The deep pleurocoel is sub-triangular to round, occupying the posterior two-thirds of the centrum close to the neural arch. This is distinct from the other dorsal vertebrae currently referred to O. hulkei , where the pleurocoels are more anterior or extend nearly the length of the centrum, and the base is flat. The opisthocoelous nature of the centrum is well developed with a prominent anterior ball, and the parapophyses appear to have been high on the neural arch beyond that portion of the vertebra preserved. The combination of a high parapophysis position with strong opisthocoely suggests that this is a dorsal centrum from the caudal end of the sequence. Strong opisthocoely occurs only in the first four anterior dorsals in diplodocids where the parapophysis is sited on the centrum (dorsals 1-3 in Diplodocus and Apatosaurus excelsus), the centra becoming more amphiplatyan towards the posterior of the series. Middle and posterior dorsals of brachiosaurids, camarasaurids and titanosaurids have strong opisthocoely. Posterior camarasaurid centra appear short in length relative to height, whilst brachiosaurid centra are more elongate and become progressively more so anteriorly. The increased length of BMNH 28632 relative to height is suggestive of a brachiosaurid origin. The neural and lateral processes are missing, and thus the specimen lacks most of the parts which bear the features cited by McIntosh (1990a) as titanosaurid, except for the pleurocoel which is regular, deep and distinct in the specimen. BLOWS: CRETACEOUS BRACHIOSAURID DINOSAURS 189 text-fig. 1 . a-b, Ornithopsis hulkei, lectotype, BMNH 28632, dorsal vertebral centrum. A, anterior view; b, left lateral view, c, Eucamerotus foxi sp. nov., holotype, BMNH R2522, neural arch in anterior view. Both from the Lower Cretaceous Wessex Formation of Brook, Isle of Wight. All x 0-33. not moderate and irregular as in titanosaurids. The internal bone Structure incorporates large, coarse cavitations, a brachiosaurid feature, unlike the fine cancellous bone structure of cetiosaurids and other sauropods (J. McIntosh, pers. comm.). 190 PALAEONTOLOGY, VOLUME 38 Genus eucamerotus Hulke, 1871 Type species. Eucamerotus foxi sp. nov. Eucamerotus foxi sp. nov. Plate 1, figures 1-6; Text-figures lc, 2, 5 Derivation of name. After William Fox who collected most of the paratypes. 1871 Eucamerotus Hulke, p. 36. Holotype. BMNH R2522, vertebral neural arch. Text-figure lc. Type horizon and locality. Wealden Marls (Wessex Formation), Lower Cretaceous (Barremian) of Brook, Isle of Wight, England. Range. Wealden Marls (Wessex Formation) Lower Cretaceous. Paratypes. BMNH R89, two dorsal vertebrae; BMNH R90, two dorsal vertebrae; BMNH R2524, juvenile dorsal vertebrae. Referred specimens. BMNH R91, three dorsal vertebrae; BMNH R2523 (in part), three dorsal vertebrae; BMNH R406, anterior of dorsal centrum; BMNH R708, dorsal centrum; BMNH R94 (in part), dorsal vertebral pieces; MIWG 5314, juvenile dorsal centrum; MIWG 5125, anterior dorsal centrum; M1WG (BP001), new and undescribed partial skeleton. Diagnosis. Medium-sized sauropod; dorsal vertebrae with broad, rounded centra, flattened bases, strongly opisthocoelian; deep lateral pleurocoels mostly placed anteriorly and becoming shallower posteriorly; shallow depth of bone below pleurocoel; tall neural arch with large anterior and posterior supra-neural concavities; strongly ridged neural and lateral spines; broad termination on the neural spine. Remarks. The holotype (BMNH R2522, Text-fig. lc) differs from the lectotype of Ornithopsis and cannot be referred to it (as has been the usual practice). The two genera are therefore not synonymous. All the material previously referred to Ornithopsis can be referred either to Eucamerotus (the dorsal vertebrae listed here) or to Sauropoda Incertae Sedis. No species was founded for Eucamerotus by Hulke, and E. foxi sp. nov. is erected here. Five paratypes, mostly from the Fox collection are also designated. Article 11(c) section (i) of the International Code of Zoological Nomenclature (ICZN 1985) states: 'A work published before 1931 and containing uninominal genus-group names without associated nominal species is accepted as consistent with the Principle of Binominal Nomenclature in the absence of evidence to the contrary’. ICZN Article 12(a) states: 'To be available every new scientific name published before 1931 must satisfy the EXPLANATION OF PLATE 1 Figs 1-6. Eucamerotus foxi sp. nov., paratypes, all are single dorsal vertebrae. 1, anterior view. 2, left lateral view. 3, left lateral view. 4, anterior view. 5, anterior view. 6, left lateral view. All from the Lower Cretaceous Wessex Formation of the Isle of Wight. 1^4 (BMNH R89 in part) are x014; 5 and 6 (BMNH R90 in part) are xOT6. PLATE 1 BLOWS, Eucamerotus foxi 192 PALAEONTOLOGY, VOLUME 38 provisions of Article 1 1 and must have been accompanied by a description or a definition of the taxon that it denotes, or by an indication.’ The ‘indication’ is referred to in ICZN Article 12(b) (7): ‘the proposal of a new genus-group name or of a new species-group name in association with an illustration of the taxon being named... even if contained in a work... that is not consistently binominal’. Four of the new paratypes of E. foxi (BMNH R89 and R90) may be part of a single skeleton, perhaps including four cervical vertebrae (BMNH R87, R87a, R173) described by Hulke (1880), although Fox gave no indication of any association (Blows 1983). These cervical vertebrae are regarded as Sauropoda Incertae Sedis. BMNH R89 (PI. 1, figs 1-4) comprises two dorsal vertebrae, one of which was described and illustrated by Hulke (1880). They are tall with long lateral pleurocoels divided into two or three separate depths, with the deepest cavities being anterior. Large deep supra-neural concavities exist above the neural canals within the neural arch, and the bases of the centra are broad and flat, with less bone below the pleurocoel compared with Omithopsis. BMNH R90 (PI. 1, figs 5-6; Text-fig. 5a) comprises similar, less complete vertebrae than R89, having lower and longer centra. A juvenile centrum (BMNH R2524, Text-fig. 2) described by Hulke (1879) is also included with the paratypes. text-fig. 2. Eucamerotus foxi sp. nov., paratype, BMNH R2524, juvenile dorsal vertebra, a, left lateral view; b, anterior view. From the Lower Cretaceous Wessex Formation of the Isle of Wight, x 0-5. It is similar to the adult forms, being smaller with pleurocoels proportionately larger and deeper, and occupying a larger surface area of the lateral centrum than in the adult. The opisthocoelian nature of the centrum is less well developed than in the adult. The brachiosaurid dorsal vertebral characteristics described by Riggs (1904) and Bonaparte (1986) are: more than ten vertebrae with simple, non-bifurcated neural spines which increase in length from sacrum to mid-dorsal region; large, elongated centra; axially elongated neural arch and base of spine. To this, McIntosh (1990m 19906) has not added familial dorsal vertebral characters, but noted that Brachiosaurus shows the highest neural arches and spines over the shoulders and the lowest over the sacrum. This corresponds with limb length. The pleurocoels are deep and clearly defined within a strongly opisthocoelous centrum. In Eucamerotus, the dorsals correspond with those features indicated for a single vertebra. The neural arches and spines are tall (especially in R89) which suggests a possible anterior presacral position. If this is correct, the absence of neural spine bifurcation precludes a camarasaurid and diplodocid origin, and the lack of posterior slope BLOWS: CRETACEOUS B R ACH IOS A U R I D DINOSAURS 193 to the neural spine excludes them from a titanosaurid origin. The top of the neural spine ex- pands laterally and has a gently rounded crest, when viewed anteriorly, which is very similar to Brachiosaurus. A newly discovered partial skeleton, currently being prepared at Sandown Museum (M1WG BP001) can be referred to Eucamerotus foxi on the basis of the dorsal vertebral morphology, which is identical to that in the paratypes established here. This represents a future opportunity to extend the description of this genus to skeletal elements other than the dorsal vertebrae. BRACHIOSAURIDAE INCERTAE SEDIS Parts of a pelvis and sacrum of a large brachiosaurid sauropod from the cliff at Luccombe Chine, Isle of Wight, were briefly described by Swinton (1946) and Stroh (1949). The sacrum (BMNH R 127 13) comprises four vertebrae (Text-fig. 3), and since most sauropods have five or more, this text-fig. 3. Sauropod sacrum, BMNH R 1 27 1 3, dorsal view, associated with the pelvic bones of Text-fig. 4. From the Cretaceous of Luccombe Chine, Isle of Wight, x 0T4. suggests that some vertebrae may be lost in this specimen. Four lateral sacral ribs extend from both sides and fuse distally at the ilio-sacral joint, but some of this joint has been artificially replaced. The associated pelvis consists of both ilia and both pubes. The two ilia are nearly complete (Text- fig. 4a) and are about 750 mm long and 630 mm deep. They are concave medially and slightly 194 PALAEONTOLOGY, VOLUME 38 convex laterally, with a ridge extending down centrally to the upper margin of the acetabulum. The iliac crest is high as in other brachiosaurid genera. The pubes are long, narrow and flat (Text-fig. 4b-c). Fox found a right ischium and pubis which together were described by Hulke (1882) as the text-fig. 4. a, Sauropod right ilium, BMNH R12713, in lateral view; B, associated right pubis in medial view; c, associated left pubis in lateral view. From the Cretaceous of Luccombe Chine, Isle of Wight. All xOT. type specimen of 1 Ornithopsis eucamerotus ' (BMNH R97). The pubis is slightly shorter than the Luccombe Chine specimen and is broader with a distinct rounded termination. The ischium, illustrated by Hulke articulated to the pubis, now consists of the proximal half only. I am unable to prove that this pubis and ischium are part of the same pelvis. Although Hulke gave a good description, he did not indicate if they were discovered together, and Fox left no evidence of their association in situ. The bones appear to be different in preservation and I consider them to be of separate origin. The addition of a second right ischium to the BMNH R97 assemblage confuses the picture further, and Lydekker (1888) catalogued one ischium as R97a. The name Ornithopsis eucamerotus , for which this is the type, is no longer valid, and the specimen is regarded as Brachiosauridae Incertae Sedis. A complete left femur (MIWG 6484; Text-fig. 5a) has a long slender shaft that narrows towards the distal epiphysis. The head is inclined obliquely upwards on broad trochanters and merges imperceptibly with the shaft rather than flattening at right angles to the shaft as it does in diplodocids. The fourth trochanter is placed about two-thirds up the length of the bone. It is possible that this femur may be part of the new partial skeleton (MIWG BP001, S. Hutt, pers. comm.). The head of a large right humerus (MIWG 5211; Text-fig. 5b) resembles those of brachiosaurids. It has a well preserved rounded articular end surface with a pronounced deltoid crest. BLOWS: CRETACEOUS B R ACH I OS AU RI D DINOSAURS 195 text-fig. 5. A, Eucamerotus foxi sp. nov. paratype dorsal vertebra, BMNH R90 in part, left lateral view, x 014. b-c, Brachiosaurid sauropod; b, left femur, MIWG 6484, in posterior view, x 0 07; c, proximal portion of a humerus, MIWG 521 1, in anterior view, x 0-83. All from the Lower Cretaceous of the Isle of Wight. Taxonomic status of some British sauropods Jurassic material attributed to the genus Ornithopsis. Delair (1959) indicated that sauropod remains from the Jurassic of Dorset were Ornithopsis hut gave no supporting evidence for this. However, since the lectotype of Ornithopsis is a single dorsal centrum of Lower Cretaceous age and no Jurassic specimens are bones homologous with this lectotype, direct comparison and therefore referral is not possible. The name Ornithopsis is therefore confined at present to the Lower Cretaceous and all the Jurassic specimens listed by Delair (1959, pp. 81 -83) are regarded as Brachiosauridae Incertae Sedis (McIntosh 1990c/). These are: 'Ornithopsis humerocristatus ’ Hulke, 1874 based on a humerus from the Kimmeridge Clay of Weymouth, Dorset (BMNH 44635); ' Ornithopsis manselV Lydekker, 1888 based on a humerus from the Kimmeridge Clay of Dorset (BMNH 41626); and ' Ornithopsis? leedsi' Hulke, 1887 based on a proximal portion of a pubis from the Kimmeridgian of Weymouth, Dorset (BMNH 49165). 'Ornithopsis sp.\ based on a tooth from the Portland Stone of the Isle of Portland, Dorset (BMNH R5833), is regarded as Sauropoda Incertae Sedis. The status of Pelorosaurus conybeari Mantell , 1850. Ornithopsis and Eucamerotus have been synonymized with the mainland genus Pelorosaurus by several authors (e.g. Romer 1966; Olshevsky 1978). McIntosh (1990c/ and pers. comm.) tentatively accepted the synonymy of all the English Lower Cretaceous brachiosaurs under Pelorosaurus conybeari , which he stated to be close to Brachiosaurus in most respects. However, the type of Pelorosaurus is a humerus which cannot be compared with dorsal vertebrae, or most of the other bones referred to the Brachiosauridae, and therefore the genera should be regarded as separate. Pelorosaurus is from the Tilgate Stone (Grinstead Clay) which is Valanginian and thus earlier than the Wealden Marls (Barremian) of the Isle of Wight. Between these two horizons, a hiatus occurs in the dinosaur faunas (Hautenvian) as 196 PALAEONTOLOGY, VOLUME 38 noted for the nodosaurs by Blows (1987). Pelorosaurus conybeari is probably best regarded as a nomen vanum as the type specimen is undiagnostic. CONCLUSIONS 1 . The binomen Ornithopsis hulkei can only be upheld for a single dorsal centrum, the lectotype (BMNH 28632) which is placed within the Brachiosauridae. Ornithopsis and Eucamerotus are therefore not synonymous. 2. All other specimens labelled as Ornithopsis are either ‘Sauropoda Incertae Serbs' or are referable to the genus Eucamerotus. Pelorosaurus conybeari cannot safely be synonymized with Isle of Wight specimens. 3. Eucamerotus is regarded as brachiosaurid, with E. foxi sp. nov. established. Acknowledgements. 1 am most grateful to Angela Milner and Sandra Chapman (Natural History Museum, London) and Steven Hutt (Museum of Isle of Wight Geology) for their help with the specimens in their care, to Andrew Milner (Birkbeck College, University of London) for his advice, and to John McIntosh for his comments on sauropods. Photographs are by courtesy of the Photographic Unit of the Natural History Museum, London. REFERENCES berman, d. s. and mcintosh, j. 1978. Skull and relationships of the Upper Jurassic sauropod Apatosaurus (Reptilia, Saurischia). Bulletin of the Carnegie Museum of Natural History, no. 8, 1-35. blows, w. r. 1983. William Fox (1813- 1881), a neglected dinosaur collector of the Isle of Wight. Archives of Natural History , 1 1, 299-313. ^ 1987. The armoured dinosaur Polacanthus foxi from the Lower Cretaceous of the Isle of Wight. Palaeontology, 30, 557-580. bonaparte, j. 1986. The early radiation and phylogenetic relationships of the Jurassic sauropod dinosaurs, based on vertebral anatomy. 247-258. In padian k. (ed.). The beginning of the age of dinosaurs. Cambridge University Press, 378 pp. delair, j. 1959. Mesozoic reptiles of Dorset. Part 2. Proceedings of the Dorset Natural History and Archaeological Society, 80, 52-90. huene, f. von. 1932. Die fossile Reptil-Ordnung Saurischia, ihre Entwicklung und Geschichte. Monographien zur Geologie und Palaeontologie 1, viii + 1-361. hulke, ). 1870. Note on a new and undescribed Wealden vertebra. Quarterly Journal of the Geological Society, London, 26, 318-324. — 1871. Appendix to a 'Note on a new and undescribed Wealden vertebra’. Quarterly Journal of the Geological Society, London, 28, 36-37. — 1874. Note on a very large saurian limb-bone adapted for progression upon land, from the Kimmeridge clay of Weymouth, Dorset. Quarterly Journal of the Geological Society, London, 30, 16-17. — 1879. Note (3rd) on Eucamerotus (Hulke), Ornithopsis (Seeley). Quarterly Journal of the Geological Society, London , 35, 752-762. — 1880. Supplementary note on the vertebra of Ornithopsis (Seeley) = Eucamerotus (Hulke). Quarterly Journal of the Geological Society, London , 36, 31-34. 1882. Note on the os pubis and ischium of Ornithopsis eucamerotus. Quarterly Journal of the Geological Society, London, 38, 372-376. 1887. Note on some dinosaurian remains in the collection of A. Leeds Esq., of Eyebury, Northampton- shire. Part I Ornithopsis leedsii. Quarterly Journal of the Geological Society, London, 42, 695-699. linnaeus, c. 1758. Systema Naturae. 10th ed. vol. 1. Salvi, Stockholm, 824 pp. lydekker, R. 1888. Catalogue of the Fossil Reptilia and Amphibia in the British Museum. Part /. Containing the orders Ornithosauria, Crocodilia, Dinosauria, Squamata , Rhynchocephalia and Pterosauria. British Museum, London, xxviii + 309 pp. 1889. Note on some points in nomenclature of fossil reptiles and amphibians with preliminary notices of two new species. Geological Magazine , (3), 6, 325-326. 1892. Note on two dinosaurian foot bones from the Wealden. Quarterly Journal of the Geological Society, London , 47, 375-376. BLOWS: CRETACEOUS B R ACH IOS AU RI D DINOSAURS 197 mantell, G. 1850. On the Pelorosaurus ; an undescribed gigantic terrestrial reptile, whose remains are associated with those of the Iguanodon and other saurians in the strata of the Tilgate Forest, in Sussex. Philosophical Transactions of the Royal Society , London , 140. 379-390. marsh, o. C. 1878. Principal characters of American Jurassic dinosaurs. Part 1. American Journal of Science, 3,16,411-416. mcintosh, j. 1990a. Sauropoda. 345-401. In weishampel, d. d., dodson, p. and osmolska, h. (eds). The Dinosauria. University of California Press, Berkeley, California, 733 pp. - 19906. Species determination in sauropod dinosaurs with tentative suggestions for their classification. 53-69. In carpenter, K. and CURRIE, p. (eds). Dinosaur systematics : approaches and perspectives. Cambridge University Press, 318 pp. melville, A. 1849. Notes on the vertebral column of the Iguanodon. Philosophical Transactions of the Royal Society , London , 139, 285-300. Olshevsky, G. 1978. The Archosaurian Taxa (excluding the Crocodilia). Mesozoic Meanderings 1, 1-50. owen, R. 1842. Report on British fossil reptiles. Part II. Report of the British Association of the Advancement of Science, XI, 60-204 ( 1841 ). 1875. Monograph of the Mesozoic Reptilia. Part 2 - Bothriospondylus magnus. Palaeontograpliical Society Monograph , 29, 15-26. 1876. Monograph on the fossil Reptilia of the Wealden and Purbeck formations. Supplement 7. Palaeontograpliical Society Monograph , 30, 1-7. ride, w. d. l., sabrosky, c. w., bernardi, G. and melville, r. v. 1985. International code of zoological nomenclature , 3rd edition. University of California Press, Berkeley, California, 338 pp. riggs, e 1904. Structure and Relationships of opisthocoelian dinosaurs. Part 2: the Brachiosauridae. Field Columbian Museum Publication 94, Geological Series , 2, 229-248. romer, a. s. 1966. Vertebrate paleontology (3rd edition). University of Chicago Press, 468 pp. seeley, h. g. 1870. On Ornithopsis , a gigantic animal of the Pterodactyl kind from the Wealden. Annals and Magazine of Natural History, (4), 5, 279-283. 1888. On the classification of the fossil animals commonly named Dinosauria. Proceedings of the Royal Society, London, 43, 165-171. stroh, F. 1949. An Isle of Wight Dinosaur. Proceedings of the Isle of Wight Natural History and Archaeological Association, 4, 93-94. swinton, w. 1946. An Isle of Wight Dinosaur. Illustrated London News, 209, 278. WILLIAM T. BLOWS 39 Bow Arrow Lane Dartford, Kent, DA2 6PG UK Typescript received 19 October 1993 Revised typescript received 8 August 1994 A NEW DIAPSID REPTILE FROM THE UPPERMOST CARBONIFEROUS (STEPHAN I AN) OF KANSAS by Michael deBRAGA and Robert r. reisz Abstract. Diapsids represent one of the most diverse lineages within Amniota, yet, until recently, their Carboniferous record was restricted to one taxon from a single locality near Garnett, Kansas. Accordingly, diapsids were thought not to have undergone the degree of evolutionary radiation which has been attributed to other Carboniferous amniotes. The description of Spinoaequalis schultzei gen. et sp. nov. from Upper Carboniferous deposits at Hamilton Quarry, Kansas, indicates that it is closely related to araeoscelidians and provides the first evidence for the diversification of diapsids within the Carboniferous. In addition, Spinoaequalis possesses a suite of autapomorphies, most notably to the tail, which display evidence for the earliest known aquatic specialization among amniotes. Diapsid a is one of the most successful groups of amniotes (Carroll 1988) and includes three of the four orders of extant reptiles (crocodiles, lizards, and snakes), dinosaurs including birds, flying reptiles, many aquatic taxa, and other, lesser known, extinct groups. Although diapsids are represented by a long, rich fossil record, little is known of their early history. Araeoscelidia, universally recognized as containing some of the earliest recognized members within Diapsida (Reisz 1977, 1981; Benton 1985; Carroll 1988; Gauthier et at. 1988; Evans 1988; Laurin 1991) is represented by two well known genera Petrolacosaurus and Araeoscelis , and two poorly known forms Zarcasaurus Brinkman et al ., 1984 and Kadaliosaurus Credner, 1889. These taxa are regarded as being representative of the Bauplan from which advanced diapsids evolved (Reisz 1981 ; Carroll 1988). In addition, due in part to the homogenous morphology of the known members of this clade, it is considered an interesting side branch in diapsid evolution, but one that did not undergo any significant morphological differentiation during its tenure in the Carboniferous. Consequently, increased diapsid diversity is generally thought to coincide only with the appearance of the specialized eosuchians Claudiosaurus and Coelurosauravus and neodiapsids in the Upper Permian (Laurin 1991). Reisz (1988) briefly introduced two new diapsids from the Upper Carboniferous Hamilton Quarry of Kansas. He suggested that one of these diapsids may be closely related to araeosceloids (University of Kansas Vertebrate Palaeontology collection KUVP 12484), remarking that the limbs possessed similar propodial/epipodial ratios. He chose, however, not to name or classify the specimen formally, but remarked that the unusual caudal anatomy of this amniote was suggestive of aquatic affinities. Further preparation and detailed inspection of its anatomy has permitted a nearly complete skeletal reconstruction (Text-fig. 1). Furthermore, a brief phylogenetic analysis provides strong evidence that this small reptile is indeed a diapsid and the sister taxon to Araeosceloidea. A detailed comparison with later, better known aquatic reptiles (Russell 1967; Currie 1981a; Frey 1982; deBraga and Carroll 1993) has been undertaken to assess its anatomical potential for aquatic propulsion (Hildebrand 1982). (Palaeontology, Vol. 38, Part 1, 1995, pp. 199-212.| © The Palaeontological Association 200 PALAEONTOLOGY, VOLUME 38 text-fig. 1. Reconstruction of Spinoaequalis schultzei gen. et sp. nov. in lateral view; Hamilton Quarry, Greenwood County, Kansas; Virgilian Series (Stephanian of Europe), Upper Pennsylvanian. Shaded area represents missing data. SYSTEMATIC PALAEONTOLOGY diapsida Osborn, 1903 ARAEOSCELIDIA Williston, 1913 Emended diagnosis. Diapsid reptiles exhibiting long limbs with propodial/epipodial ratios 1:1; anterior margin of scapula slanted posteriorly; and femoral shaft exceeding width of humeral shaft by 50 per cent. Genus spinoaequalis gen. nov. Spinoaequalis schultzei sp. nov. Text-figures 1-5 Derivation of name. From the Latin spina (spine) and aequalis (symmetry) referring to the equal length of caudal neural and haemal spines; specific designation in honour of Dr Hans-Peter Schultze, in recognition of his work on Palaeozoic vertebrates. Holotype. KUVP 12484, a nearly complete, articulated, immature individual with a poorly preserved skull, missing the distal portion of the tail. The specimen was collected in three pieces: one containing the snout region, a second containing the rest of the skull and most of the body, and a third piece which contains the hindlimbs, pelvic region, and the preserved portion of the tail. Type Horizon and Locality. Calhoun Shale, Shawnee Group, Virgilian Series (Stephanian of Europe), Upper Pennsylvanian; Hamilton Quarry near Hamilton, Greenwood County, Kansas. Diagnosis. A small diapsid reptile distinguished by the following autapomorphies: ventral process of squamosal narrow; trunk ribs holocephalic; caudal neural spines distal to eleventh caudal vertebra elongate, at least 50 per cent, taller than those of proximal caudals ; haemal spines are equal in length to the caudal neural spines of same vertebrae; haemal spines increase in length posteriorly; haemal spines with slight distal expansion; caudal centra with a length to height ratio approaching 1:1; caudal neural arches saddle-shaped; transverse processes absent from caudal vertebrae; interclavicle long approaching the length of eight dorsal vertebrae; and acetabulum sub-circular in outline. Description. The specimen was collected originally as three separate sections, and as a result, it cannot be illustrated as a single figure. Therefore, each block is figured separately (Text-figs 2-4). The smallest piece (Text-fig. 2) contains paired premaxillae, a poorly preserved lacrimal, fragments of what are interpreted as the deBRAGA AND REISZ: CARBONIFEROUS DIAPSID 201 text-fig. 2. Spinoaequalis schnitzel gen. et sp. nov.; KUVP 1 2484 ; Hamilton Quarry, Greenwood County, Kansas; Virgilian series (Stephanian of Europe), Upper Pennsylvanian; anterior portion of snout. 5 mm nasals, and the left maxilla. Of the two larger pieces, one (Text-fig. 3) has suffered damage over much of the exposed surface (corresponding to the specimen's dorsal surface) and has, therefore, been embedded in bioplastic and prepared from its ventral side. Most of the palate, the right maxilla in lateral view, and the medial half of the posterior portion of the left maxilla, the left prefrontal, the paired frontals in ventral view, and a portion of the right parietal are all preserved in this piece. In addition, the block contains what is left of the cheek region and portions of both lower jaws as well as most of the remainder of the skeleton. The second large piece (Text-fig. 4) which contains the remains of the pelvis, a complete left hindlimb and foot, the right foot, and the preserved region of the tail was prepared from the left side and presents the opposite view from that of the other large piece containing most of the skeleton. The premaxilla presents the typical diapsid configuration, as the dorsal processes of both bones, as preserved, are quite slender (Text-fig. 2). This agrees with the configuration in both Petrolacosaurus and Araeoscelis as well as in eosuchians (personal observation) and probably represents a diapsid synapomorphy. Captorhinids, Protorothyris and Paleothyris possess a comparably broad premaxillary dorsal process which occupies nearly the entire dorsal surface of the snout tip (Carroll 1969; Clark and Carroll 1973; Heaton 1979). The tooth-bearing portion of the premaxilla has portions of three teeth preserved, of which the first is a simple, slender peg. Five teeth are described in Petrolacosaurus (Reisz 1981), Araeoscelis (Reisz et al. 1984), and Paleothyris (Carroll 1969). The reduced number in Spinoaequalis may be an autapomorphy of this taxon, but the state of preservation of the tooth-bearing region of the premaxilla is not sufficient to draw a definite conclusion. The maxilla (Text-figs 2, 5) is similar to the configuration in Paleothyris and the araeosceloids Petrolacosaurus and Araeoscelis. There is a canmiform region, but the caniniform teeth are not much larger than the first premaxillary tooth. The teeth are very slender and are quite similar to those in Petrolacosaurus. The plate-like frontals (Text-fig. 5) have a large orbital margin, and are constricted above the orbits. This latter condition is present in araeosceloid and eosuchian diapsids and represents a synapomorphy of these taxa (Laurin and Reisz 1995). Much of the posterior half of the cheek (Text-fig. 5) is preserved and the posteroventral border of the lower temporal fenestra is discernible. The configuration differs somewhat from that seen in Petrolacosaurus in that the post-temporal bar is composed of a slender ventral process of the squamosal and a shorter dorsal process of the quadratojugal. It appears that the lower temporal fenestra is located farther posteriorly, or is relatively larger in Spinoaequalis than in Petrolacosaurus. However, the posteroventral margin of the lower temporal fenestra has never been established confidently in Petrolacosaurus (Reisz 1981, text-fig. 2). A sliver of bone, visible directly behind the squamosal, may represent the quadrate. However, the preservation of this region of the skull is poor, and this identification is uncertain. The palate is only partially exposed. The left pterygoid is visible in ventral aspect and is essentially similar to that of araeosceloids except that the transverse flange is not directed anterolaterally and hence retains the primitive transverse orientation (Text-fig. 5). No other palatal elements are visible except for a small portion of the ectopterygoid. The posterior border of the suborbital fenestra can be detected along the anterolateral edge of the ectopterygoid. 202 PALAEONTOLOGY, VOLUME 38 text-fig. 3. Spinoaequalis schultzei gen. et sp. nov.; KUVP 12484; Hamilton Quarry, Greenwood County, Kansas; Virgilian Series (Stephanian of Europe), Upper Pennsylvanian; ventral aspect of skeleton minus caudal region, x 1 . The braincase and occiput are only incompletely preserved. The exoccipitals are preserved, however, and can be seen as isolated elements. The ventral and lateral borders for the foramen magnum can be seen clearly on the left exoccipital. The posterior margin of the parasphenoid lying behind the overlying posterior half of the lower jaw resembles that of the araeosceloid Petrolacosaurus in being concave along its posteriomedial margin. This derived condition may suggest an autapomorphy for Araeoscelidia or perhaps a more inclusive diapsid synapomorphy. This concavity of the parasphenoid exposes the basioccipital to a greater degree than that which is seen in Paleothyris (see Carroll 1969, text-fig. 4) or other captorhinomorphs (Clark and Carroll 1973). In these taxa a posteriorly directed flange of the parasphenoid overlies the basioccipital ventrally. A small bone, partially covered by the basioccipital, may represent the opisthotic (Text-fig. 5). The stapes is a small, robust element (Text-fig. 5) that does not differ in any significant way from the stapes of other early amniotes. The perforating foramen is present and the large footplate suggests a supportive rather than an auditory role for this element in Spinoaequalis. The mandibles are partially preserved, with the nearly complete left jaw ramus exposed medially and the posterior half of the right jaw ramus exposed in lateral view. The generally slender configuration of the lower jaw is quite similar to that found in Petrolacosaurus. This slender configuration is certainly the primitive condition for Araeoscelidia, and differs from the much more robust jaws found in Araeoscelis (Reisz et a/. 1984). Twenty-two presacral vertebrae are visible in Spinoaequalis (Text-fig. 3). There is room for an additional four vertebrae within the column making the probable count twenty-six. Petrolacosaurus is reconstructed as having twenty-six presacrals (Reisz 1981), but Araeoscelis has a long presacral series of twenty-nine vertebrae (Reisz et al. 1984). Most of the presacral series in Spinoaequalis is exposed only in ventral aspect. Although the bases of the arches can be seen in some of the mid-dorsals and on the axis, little detail can be observed. deBRAGA AND REISZ: CARBONIFEROUS DIAPSID 203 text-fig. 4. Spinoaequalis schultzei gen. sp. nov.; KUVP 12484; Hamilton Quarry, Greenwood County, Kansas; Virgilian Series (Stephanian of Europe), Upper Pennsylvanian; hindlimb and caudal region, x 1-3. The atlantal neural arch (Text-figs 3, 5) is preserved but can be seen only in partial internal aspect. Except for the neural spine, the axis is well preserved. The axial centrum is keeled ventrally, but the keel is not as strongly pronounced as in araeosceloids. In addition, unlike all other known araeoscelidians, the cervical centra of Spinoaequalis are not appreciably longer than those of the dorsal series. Two cervical ribs are preserved and are associated with the axis and third cervical vertebra. Unfortunately these rib heads are too poorly preserved to determine whether they are dichocephalic or holocephalic. Articular surfaces for the trunk ribs appear to be composed of a single facet and are located directly below the anterior zygapophysis on the respective neural arch. Holocephalous trunk rib heads would represent an autapomorphy of Spinoaequalis. Intercentra are visible throughout the presacral series as in most early amniote groups. The sacral series is not preserved and the first eight caudals are very poorly preserved (Text-fig. 4). Beyond this region, twenty-six well exposed caudals are present. The remainder of the tail was lost during excavation. In strong contrast to the condition seen in araeosceloids and most other amniotes, where the caudal neural spines get progressively shorter and eventually virtually disappear, along the length of the tail (Reisz 1981, text- fig. 1), the caudal neural spines of Spinoaequalis (Text-figs 1, 4) increase in height posteriorly: the spines increase dramatically in height from the tenth caudal (second vertebrae of the last twenty-six) to about the fifteenth and then remain tall, increasing slightly to the twenty-eighth caudal, beyond which there is no noticeable increase in neural spine height for the remainder of the preserved portion of the tail. In addition, in other Permo-Carboniferous amniotes, the haemal spines are generally quite long at the base of the tail, and decrease rapidly in length posteriorly. In most cases the decrease in length is such that distinct haemal spines are absent by the middle of the caudal series. The opposite occurs in Spinoaequalis. where the haemal spines are shortest at the base of the tail, and then steadily increase in length posteriorly, remaining long throughout the preserved portion of the tail and matching the height of the neural spines. The haemal spines are slightly expanded distally, but this expansion is only very weakly developed, and does not in any way approach the condition seen in the eosuchian Hovasaurus (Currie 1981n). In most other amniotes, including Petrolacosaurus , the haemal spines actually taper distally. The caudal vertebrae also exhibit well developed neural arches with very tall zygapophyses, together formed into a saddle-shaped structure (Text-fig. 4). This unusual appearance is probably the result of the dorsal expansion of the zygapophyseal articulating facets. 204 PALAEONTOLOGY, VOLUME 38 text-fig. 5. Spinoaequalis schultzei gen. et sp. nov.; KUVP 12484; Hamilton Quarry, Greenwood County, Kansas; Virgilian Series (Stephanian of Europe), Upper Pennsylvanian. Magnification of skull region from Text-figure 3. Transverse processes are absent in Spinoaequalis throughout the preserved portion of the tail (ninth to thirty- fourth vertebrae). The combination of rudimentary transverse processes along with tall spines (described above) results in a tail the transverse width of which does not exceed 25 per cent, of its total height. The caudal centra are unspecialized, but, in combination with the well developed neural arches, result in the combined height of the arch and centrum approaching their antero-posterior length, a condition unknown in any other Carboniferous amniote. The pectoral components of the appendicular skeleton of Spinoaequalis are well preserved (Text-figs 1, 3) and, in most respects, similar to those of araeosceloids. The interclavicle resembles that of Petrolacosawus except that it is relatively longer. Its length occupies seven and one half dorsal vertebrae and is 25 per cent, longer than the humerus. In araeosceloids, such as Petrolacosawus and Araeoscelis, the interclavicle is equal to the length of only five and one half dorsal vertebrae and is equal to the humerus in length. The elongate interclavicle may be the result of the juvenile nature of the specimen, for, as demonstrated by Currie (198 In), interclavicular length is negatively allometric relative to dorsal vertebral length. The clavicles are also preserved and appear unremarkable in comparison with those of other early tetrapods. The scapulocoracoid is ossified as two separate elements. On the left side of the specimen (Text-fig. 3), the anterior-most element supports the glenoid surface along its postero-distal margin. Although the ossification of this region is poor, a large, well developed supraglenoid buttress is visible. This process is similar to that present in araeosceloids and partly conceals the coracoid foramen which lies directly below. The overall size of the scapula (height) is less than that of an araeosceloid of equivalent size. This may be related to its juvenile nature or it may represent an autapomorphy of this taxon. The reconstruction (Text-fig. 1) has been drawn with the scapula possessing typical araeosceloid proportions. Very little else of consequence can be identified, deBRAGA AND REISZ: CARBONIFEROUS DIAPSID 205 although the anterior margin of the right scapulocoracoid appears gently convex, so that in a reconstructed individual (Text-fig. 1), this margin would appear to be orientated posteriorly. This configuration is apparent in all araeosceloids (Reisz 1981 ; Reisz et al. 1984) and differs from the tall straight anterior scapular margin present in other Palaeozoic amniotes (Carroll 1969). The forelimb (Text-fig. 3) is distinguished by its elongate and slender configuration. The distal ends of the limb elements are not preserved and neither are any of the carpal ossifications. An entepicondylar foramen is not visible but a groove located along the postero-distal margin of the humerus presumably represents the proximal limits of this structure. Given the low degree of ossification in other parts of this skeleton, it is likely that the limbs are equally underdeveloped and, therefore, lack ossified ends and their associated structures. The manus is only preserved on the left side and is incomplete, except for the third and fourth digits which have a typically primitive phalangeal count of four and five respectively. The pelvic girdle has only the right ilium and ischium preserved (Text-fig. 4). The elements are unremarkable and hence differ little from the typical early amniote configuration. The ilium has a strongly developed posteriorly directed iliac blade and contributes to most of the acetabular surface. The ischium forms the remainder of the acetabulum. Unlike Petrolacosaurus and other Palaeozoic amniotes, such as Paleothyris, the acetabulum is not anteroposteriorly long but nearly circular. This circular configuration was described by Laurin (1991) as an eosuchian synapomorphy. In Spinoaequalis , it may simply represent the lack of complete ossification or it may represent a unique condition that may reflect some modification in the motion of the hindlimb. The hindlimbs are virtually complete, with the right limb best preserved. The femur and crus are nearly equal in length and as such are typical of araeosceloids. The femoral shaft is much more robust (nearly 50 per cent, thicker) than the humeral shaft. This condition is also present in araeosceloids and the eosuchian Apsisaurus (Laurin 1991). A robust femur is absent in Paleothyris and captorhinids and it may, therefore, represent a diapsid synapomorphy. As in the forelimb, the hindlimb is incompletely ossified. The articulating ends of the limb bones are not preserved and most of the tarsus is missing, with the exception of two small circular structures, best interpreted as the astragalus and calcaneum. The pes is complete and possesses the typically primitive count of 2, 3, 4, 5, 4. As in araeosceloids and unlike other Palaeozoic amniotes, the first metatarsal is much less than half the length of the fourth metatarsal (Text-fig. 3). DISCUSSION Phylogenetic position Phylogenetic analysis of Spinoaequalis indicates that it is a basal diapsid reptile closely related to the oldest known diapsid, Petrolacosaurus kansensis. This phylogenetic interpretation is based on data evaluated below. A total of nine taxa including two outgroups were used in this analysis. Out-group selection is based on the well established sister-group relationship between captorhinids and Paleothyris to Diapsida (Heaton and Reisz 1986; Laurin 1991; Laurin and Reisz 1995). Anatomical data for the out-groups was taken from direct observation and from Carroll (1969) and Heaton (1979). The in-group includes the two best known araeosceloids Petrolacosaurus (Reisz 1981) and Araeoscelis (Reisz et al. 1984), the eosuchians Apsisaurus (Laurin 1991 ) and Hovasaurus (Currie 1981a), and the younginiformes Youngina (Gow 1975; Carroll 1981 ; Currie 19816) and Acerosodontosaurus (Currie 1979). Fifty characters (Appendices 1 and 2) are used in the present analysis, most of which are taken from Laurin (1991) and Laurin and Reisz (1995). However, some of the characters (character numbers below refer to those in Appendices 1 and 2) have been reinterpreted (nos 33, 42) and a few are original (nos 1, 13, 38, 44, 45, 46, 47, 49). The analysis was performed on a Macintosh Quadra 800 computer using the branch-and-bound algorithm of PAUP 3.1.1, which finds the most parsimonious trees (Swofford 1993). All characters were left unordered and subjected to deltran optimization, which tends to minimize synapomorphies at any given node. Only one most parsimonious tree (Text-fig. 6) was found requiring seventy steps to resolve and with a consistency index of 0.742 excluding uninformative characters. The cladistic analysis supports the monophyly of Diapsida and the nested sister-group relationship between Spinoaequalis and Araeosceloidea to Eosuchia (Younginiformes), as most recently defined by Laurin (1991) and 206 PALAEONTOLOGY, VOLUME 38 text-fig. 6. Cladogram of basal diapsid inter- relationships. Ambiguous characters are denoted by an asterisk, reversals by a minus sign, and in the case of a multi-state character, the derived state is placed m parentheses. Nodes assigned a letter in the figure are followed here by the character numbers referred to in Appendix I : Node A (Diapsida) 1, 5, 7, 12, — 1 6*( 1 ), 17, 24, 37 and 41; Node B (Araeoscelidia) 27, 33 and 38*; Node C (Eosuchia) 13, 32 and 39; Node D (Araeosceloidea) 15, 18*, 19, 20, 21*. 22*, 28*, 36* and 40*; and Node E ( Spinoaequalis schultzei) I 1 . 23, 25, 35, 44, 45, 46, 47, 48, 49 and 50. Laurin and Reisz (1995). In addition, the sister-group relationship between Spinoaequalis and Araeosceloidea, coupled with their shared derived appendicular anatomy, allows for the re- establishment of the higher taxon Araeoscelidia (Williston 1913) to accommodate these Palaeozoic diapsid taxa. For brevity we will not discuss all of the character states diagnosing the various nodes, but, as a result of the addition of Spinoaequalis , will consider only those changes that have revised the diagnosis or resolved critical issues of ambiguity for Diapsida and Araeosceloidea. Given the highly specialized anatomy of Spinoaequalis , a more detailed discussion of the specific autapomorphies diagnosing this taxon will be considered in the section on lifestyle interpretation. Diapsida is universally recognized as a monophyletic group but some specific issues concerning character optimization have been problematic. Reisz et al. (1984) determined that the presence of a lower temporal fenestra was ambiguous for Diapsida and could have evolved twice. This interpretation was based on the absence of a lower temporal fenestra in Araeoscelis. However, the presence of a lower temporal fenestra in Spinoaequalis confirms, for the first time, the derived character as an unambiguous synapomorphy for Diapsida with a reversal in Araeoscelis. Araeosceloidea, as most recently defined by Laurin (1991), is diagnosed by eight autapomorphies (numbers preceding character refer to character number in Appendix 1): 18 -dorsal and sacral neural arches shallowly excavated; 19 -cervical centra with sharp ventrally placed keel; 20- cervical centra elongate; 21 - mammillary processes present on dorsal neural spines; 22 - accessory processes on cervical ribs present; 28 - enlarged coracoid process for triceps musculature; 33- propodial/epipodial ratios 1:1, 36 - paired, large pubic tubercles present. One additional unambiguous autapomorphy has been more recently recorded by Laurin and Reisz (1995): 15 - transverse flange of pterygoid orientated anterolaterally. Therefore, until the present study, a total of nine autapomorphies diagnosed the clade. Of the nine autapomorphies only one (no. 5 above) was ambiguous. The present analysis supports the monophyly of Araeosceloidea but revises the diagnosis by excluding one character (no. 33) and creating ambiguity for five of the remaining eight characters: nos 18, 21, 22, 28, and 36. This ambiguity arises due to the incomplete preservation of Spinoaequalis which precludes character state determination for the five characters. Therefore, from the original literature, only three unambiguous characters (nos 15, 19, and 20) remain to diagnose Araeosceloidea. One additional character (no. 40) is added as a result of this present analysis, but it is ambiguous. The higher level taxon Araeoscelidia, as resurrected here, is now diagnosed by three characters, only one (no. 38) being ambiguous: 27 - scapular blade slanted posteriorly; 33- propodial/epipodial ratios 1:1; and 38 - femoral shaft width exceeds width of humeral shaft by 50 per cent. The ambiguity for character no. 38 stems from its presence in the derived state in the eosuchian Apsisaurus. The character may have arisen independently in araeoscelidians and deBRAGA AND REISZ: CARBONIFEROUS DIAPSID 207 Apsisaurus or it may be a diapsid synapomorphy with a reversal in Neodiapsida. Of the three characters, nos 27 and 38 are new to this study and no. 33 is a former araeosceloid synapomorphy. The confident identification of Spinoaequalis as an araeoscelidian has obviously affected the identification, if not the composition, of diapsids and araeoscelidians. In addition, the presence of Spinoaequalis along with an additional as yet undescribed diapsid from the same locality (Reisz 1988), suggests that diapsids were more diverse in the Pennsylvanian than was previously believed. These finds alter the prevailing view that diapsids diversified only around the Permo-Triassic boundary. Instead, diapsid evolutionary radiation may have been well under way during the Carboniferous, very soon after the appearance of its first recognized member. Lifestyle interpretation The Hamilton quarry of south-eastern Kansas represents a palaeovalley where rapid sediment deposition occurred in a marine setting (Feldman et al. 1993). The fauna is dominated by aquatic vertebrates, including hundreds of superbly preserved small acanthodian fish. Only a handful of fully terrestrial amniote specimens have been found, and most of them are fragmentary and disarticulated, suggesting that their presence is the result of postmortem displacement (Feldman et al. 1993). In strong contrast, the delicately constructed skeleton of Spinoaequalis has been preserved in articulation. The unfinished articulating surfaces of the long bones, the lack of tarsal and carpal ossification, and the exploded nature of the cranium attest to the immaturity and delicacy of this specimen, suggesting that this individual was not subjected to postmortem transport, but may have been a member of this community. Therefore, the possibility lhat Spinoaequalis represents an aquatic, or at the very least a semi-aquatic, amniote must be considered. The juvenile nature of the specimen makes evaluation of certain parts of the skeleton, for example some of the appendicular components, difficult. However, there is extensive evidence for aquatic affinities in the tail : 1 , caudal neural and haemal spines increase in length posteriorly; 2, distal expansion of haemal spines, presumably to strengthen and resist tensile forces applied by powerful lateral flexors of tail; 3, loss of transverse processes throughout most of caudal series; 4, saddle-shaped neural arches with tall zygapophyses to restrict dorso-ventral flexion of tail and hence improve its sculling efficiency; and 5, vertebral bodies (centrum and neural arch) anteropostenorly compressed, resulting in a length to height ratio approaching 1:1. Most of the features described above are common to aquatic diapsids as documented in the available literature (Russell 1967; Currie 1981a; Carroll 1988; Carroll and deBraga 1992; deBraga and Carroll 1993) and will be briefly discussed below. The unusual configuration of the neural and haemal spines has been alluded to above, but the significance of this arrangement is that, among tetrapods, only aquatic or semi-aquatic organisms possess the characteristic increase in both neural and haemal spine height from base to at least mid- caudal length (deBraga and Carroll 1993). In addition, distal expansion of the haemal spines is also common to taxa that have been interpreted as having an aquatic or semi-aquatic lifestyle including, in addition to the amniote Hovasaurus , the anamniote Archeria (Holmes 1989). The haemal spine expansion in Spinoaequalis , although not as strongly developed as in Hovasaurus (Currie 1981a), certainly exhibits an incipient condition that further supports the suggestion that the tail was modified to enable an aquatic existence. The absence of transverse processes beyond the most proximal portion of the tail (usually around the tenth caudal vertebrae) is well documented for aquatic taxa such as mosasaurs (deBraga and Carroll 1993) and Hovasaurus (Currie 1981a). Transverse processes are also absent in Spinoaequalis , whereas they remain well developed in non-aquatic amniotes throughout most of the caudal series. The loss of transverse processes is probably the result of the need to compress the tail so that it might function more effectively as a sculling organ. The unusual saddle-shaped neural arches result from the elaboration of tall zygapophyses. Presumably, this zygapophyseal configuration would tend to resist flexion along the dorso-ventral axis of the tail, thereby improving its effectiveness as a sculling organ. In aquatic taxa, tall, well- developed zygapophyses are generally present only on the anterior-most caudals, where much of the muscular stress would be imparted during lateral flexion of the tail (Russell 1967; Carroll and 208 PALAEONTOLOGY, VOLUME 38 deBraga 1992; deBraga and Carroll 1993). In aquatic reptiles, such as Hovasaurus (Currie 1981a) and mosasaurs, the absence of well developed zygapophyses beyond the most proximal region of the tail coincides with the presence of anteroposteriorly-expanded neural spine bases. These accessory articulations serve to resist vertebral dislocation in the absence of functional zygapophyses. The absence, in Spinoaequalis , of accessory articulations may explain the need to maintain well-developed zygapophyses beyond the most proximal region of the tail. As in crocodiles (Frey 1982), it is possible that modifications to the caudal musculature may have also served to stabilize the tail. The absence of functional zygapophyses may also serve to reduce the transverse width of the tail in many aquatic taxa. Aigialosaurs and mosasaurs lose all functional zygapophyses beyond the pygal series (Russell 1967; Carroll and deBraga 1992; deBraga and Carroll 1993). The retention of zygapophyses in Spinoaequalis may present a paradox initially, but the configuration of the zygapophyses (transversely narrow) and the absence of transverse processes does not interfere with lateral compression of the tail. As mentioned above, the loss of transverse processes in Spinoaequalis results in a tail that is only 25 per cent, as wide as it is tall. These ratios are similar to those of other aquatic taxa (personal observation) and differ from the configuration in non-aquatic amniotes where the tail is much broader, with the width approaching 50 per cent, of its height. The last caudal modification present in Spinoaequalis is the antero-posterior compression of the caudal centra. The result is a vertebral body which is as tall as it is long. This differs from the pattern in most Palaeozoic amniotes (except in aquatic taxa) where the antero-posterior length of the caudal vertebrae, excluding spines, is always greater than its height (deBraga and Carroll 1993). There is very little doubt that the tail of Spinoaequalis possesses all of the necessary refinements required of an aquatic or semi-aquatic animal. However, it is surprising that, unlike most other aquatic amniotes, Spinoaequalis does not appear to have any significant modifications to the limb girdles and retains typically terrestrial long, slender limbs. In Hovasaurus (Currie 1981a) and other aquatic taxa (Russell 1967; Carroll and deBraga 1992) the scapula has a low aspect. This modification is interpreted as an aid in lowering the centre of gravity in an aquatic animal. This is required so that stability in the water can be maintained. Slight reduction in scapular height has been identified in the lizard Aigialosaurus (Carroll and deBraga 1992), although it does not possess any other typically aquatic appendicular characteristics. The poor ossification of the scapular blade in Spinoaequalis precludes confirmation of whether scapular reduction is an aquatic characteristic or simply an indicator of immaturity. Some aquatic diapsids do have long limbs, most notably the hindlimbs of Hovasaurus (Currie 1981a). However, the limbs of Hovasaurus are modified in that the manus, and to an even greater extent the pes, possess digits that are nearly of equal length. This is apparent when comparing digits III— V of Hovasaurus with the same digits in Petrolacosaurus , Spinoaequalis , or most other Palaeozoic amniotes. In Hovasaurus digit III is 80 per cent, of the length of digit IV. This ratio is only slightly greater than that present in Petrolacosaurus and Spinoaequalis. (75 per cent.). However, the ratio between the fifth digit and the fourth is quite noticeably different when comparing Hovasaurus and the latter taxa. In Hovasaurus , as in many other aquatic taxa, the hands and feet are modified into paddles and, accordingly, the digits are subequal in length. The fifth digit of the pes in Hovasaurus has increased in length to such an extent that it exceeds the length of the third digit and approaches (exceeding 80 per cent.) the total length of the fourth (Currie 1981a). In Spinoaequalis , the fifth digit retains the characteristic terrestrial ratio where it is always shorter than the third digit and only slightly greater than one-half the length of the fourth digit. The evidence presented here seems to pose a contradiction. The tail of Spinoaequalis certainly exhibits typically aquatic features and yet most features of the limbs suggest a fully terrestrial lifestyle. This apparent conflict has been noted also in the Cretaceous lizard Aigialosaurus (Carroll and deBraga 1992). This taxon possesses a typically terrestrial morphology with only slight modifications to the tail, most notably compression of the vertebral centra. These modifications are even less striking than those present in Spinoaequalis (the neural and haemal spines are not greatly elongated in Aigialosaurus ), yet show a progressive pattern of modification which is only completely deBRAGA AND REISZ: CARBONIFEROUS DIAPS1D 209 manifested in their fully aquatic relatives the mosasaurs. The modifications present in Spinoaequalis, although not convincingly representative of a fully aquatic animal, are certainly incipient for that lifestyle and offer a rare glimpse of a ‘transitory’ organism. CONCLUSIONS The evidence presented above demonstrates that from both phylogenetic and biological points of view, diapsids were diversifying during the Palaeozoic. Spinoaequalis clearly represents an initial attempt at occupying an aquatic habitus not expressed by any other known Carboniferous amniote. It is noteworthy to consider that for a very long time aquatic amniotes are represented only by diapsid reptiles. Aquatic turtles do not make their appearance until the Mesozoic and synapsids (whales) do not invade the seas until the Cenozoic. It is likely that some aspect of both the anatomy and the physiology of diapsids imparts to them a selective advantage in invading the aquatic medium. Seymour (1982) demonstrated the energetically efficient means of aquatic locomotion among living diapsid reptiles. The typical sinusoidal motion present in diapsids is advantageous for aquatic locomotion. Diapsids were not only the first amniotes apparently to return to the water, they have continued to do so repeatedly and in greater number. Acknowledgements. We wish to thank Dr Hans-Peter Schultze for the loan of the specimens and Ms Diane Scott for the preparation of the material. We thank M. Laurin for reviewing the manuscript and S. P. Modesto for many helpful and insightful comments in its preparation. This research was funded partly by grants from NSERC (Natural Sciences and Engineering Research Council of Canada), FCAR (Fonds pour la Formation de Chercheurs et l’Aide a la Recherche), and the University of Toronto. REFERENCES benton, m. j. 1985. Classification and phylogeny of the diapsid reptiles. 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MICHAEL deBRAGA ROBERT R. REISZ Department of Zoology University of Toronto 3359 Mississauga Road Mississauga, Ontario L5L-1C6, Canada Typescript received 1 August 1994 Revised typescript received 3 October 1994 ABBREVIATIONS USED IN THE TEXT-FIGURES Ana atlantal neural arch Na nasal Ang angular Opi opisthotic Art articular Psph parasphenoid Axe axial centrum Part prearticular Bo basioccipital Pm premaxilla Cor coronoid Ptg pterygoid D dentary Q quadrate Ect ectopterygoid Qj quadratojugal Exo exoccipital Sa surangular F frontal Spl splenial Lac lacrimal St stapes Max maxilla Sq squamosal deBRAGA AND REISZ: CARBONIFEROUS DIAPSID 21 1 APPENDIX 1 Description of characters used in the phylogenetic analysis. Characters are ordered anatomically. A zero in parentheses denotes the primitive condition whereas a number one or two in parentheses represents the derived state. 1. Dorsal process of premaxilla broad (0) or narrow (1), resulting in dorsal exposure of external nares. 2. Lacrimal large forming posterior border of external nares (0), or reduced and excluded from narial margin (1). 3. Anterodorsal process of maxilla absent (0) or present ( 1 ), reaching nasal and dorsal limit of external nares. 4. Caniniform teeth present (0) or absent (1). 5. Lateral margins of frontals straight resulting in a parallelogram shape (0) or lateral margins constricted above orbit (1) creating an hour-glass shape. 6. Dorso-lateral margins of parietal not excavated (0) or excavated (1) for adductor musculature. 7. Upper temporal fenestra absent (0) or present (1). 8. Posterior process of postorbital short, not reaching posterior limit of upper temporal fenestra (0), or long (1), extending beyond posterior border of fenestra. 9. Occipital flange of squamosal present (0) or absent (1). 10. Quadrate not exposed in lateral aspect behind squamosal (0) or exposed (1). 11. Ventral process of squamosal broad with the distal width approaching total height (0) or slender with width much less than total height (1). 12. Lower temporal fenestra absent (0) or present (1). 13. Posterior process of jugal short and relatively broad (0) not reaching beyond mid-point along ventral margin of lower temporal fenestra or long and slender (1) approaching posterior limit of lower temporal fenestra. 14. Paroccipital process not reaching cheek (0) or well ossified and reaching suspensorium (1). 15. Transverse flange of pterygoid orientated transversely or postero-laterally (0) or oriented antero-laterally (1). 16. Ectopterygoid present and large (0), present but small (1) and restricted to lateral margins of palate, or absent (2). 17. Suborbital fenestra absent (0) or present (1). 18. Neural arches or posterior dorsal and sacral vertebrae not excavated (0) along lateral margins or shallowly excavated (1). 19. Ventral surface of cervical and anterior dorsal centra without sharp keel (0) or strongly keeled (1). 20. Cervical vertebrae and remainder of presacral column subequal (0) or cervical vertebrae elongate (1). 21. Neural spines of dorsal vertebrae without dorsolaterally projecting (mammillary) processes (0) or mammillary processes present ( 1 ). 22. Anterior margin of cervical ribs without accessory processes (0) or accessory processes present (1). 23. Trunk rib heads dichocephalic (0) or holocephalic (I). 24. Sternum not mineralized (0) or mineralized (1). 25. Interclavicle equal to not more than the length of six dorsal vertebrae (0) or interclavicle length equal to eight dorsal vertebrae ( 1 ). 26. Interclavicle head diamond shaped (0) or T-shaped (1). 27. Anterior margin of scapula straight (0) or slanted posteriorly (1). 28. Coracoid process for triceps musculature small (0) or large (1). 29. Humeral ends robust exceeding one third of total humeral length (0) or humerus gracile (1) with ends less than one third the total length 30. Entepicondyle of humerus weakly developed (0) or large and strongly developed (1). 31. Radial shaft straight (0) or twisted (1) along its long axis. 32. Olecranon process on ulna present (0) or absent (1). 33. Propodial/epipodial ratios less than one (0) or equal to one (1). 34. Iliac blade with well-developed postero-distal process (0) or expanded into fan-shaped structure dorsally (1). 35. Acetabulum elongate or oval in configuration (0) or circular (1). 36. Pubic tubercles small (0) or large (1). 37. Adductor crest on femoral shaft present (0) or absent (1). 38. Lemoral shaft equal to humeral shaft in diameter (0), exceeding humeral shaft diameter by 50 per cent. ( 1 ), or humeral shaft diameter exceeds that of femur by 50 per cent. (2). 212 PALAEONTOLOGY, VOLUME 38 39. Femur equal to humerus in length (0) or femur at least 10 per cent, longer than humerus (1). 40. Tibia without distinct ridge (0) for articulation with astragalus or tibia with distinct ridge that fits into astragalar groove (1). 41. Metatarsal I at least 50 per cent, the length of metatarsal IV (0) or less than 50 per cent, the length (1) of metatarsal IV. 42. Manus and pes short and broad (0) or long and slender (1). 43. Metapodials do not overlap proximally (0) or do overlap (1). 44. Neural spines of proximal caudal vertebrae equal or taller than those of distal portion (0) or proximal caudal vertebrae shortest and increasing in height posteriorly (1). 45. Haemal spines longer than neural spines of same caudal vertebrae (0) or neural and haemal spines of equal length (1). 46. Haemal spines tallest at base of tail and decreasing in height posteriorly (0) or haemal spines shortest at base of tail increasing in length posteriorly (1). 47. Haemal spines not expanded distally (0), slightly expanded distally (1), or greatly expanded distally (2). 48. Caudal vertebrae (neural arches and centra) longer than tall (0) or length and height subequal (1). 49. Caudal zygapophyses flat and not expanded dorsally (0), zygapophyses tall (1), or functional zygapophyses absent (2). 50. Transverse processes present throughout most of caudal series (0) or absent on distal caudals (1). APPENDIX 2 Data matrix for taxa examined in present analysis. Numbers above taxon names refer to character state numbers from Appendix 1 . A question mark represents missing data. Taxon Captorhinidae Paleothyris Spinoaequalis Petrolacosaurus Araeoscelis Apsisaurus A cerosodon tosaurus Youngina Hovasaurus 111111111 1222222 1234567890123456789012345 0000000700000002000000000 000000070000000000000000? 100010777? 1 17701 17007? 1? 1 1000101000010? 11111111070 10001010000001 11111111010 ??????? 7000 1 177 1 101 10707? 7 1 1 1 1? 1 1 111 1 17? 1 10000017? 1111111111111001 100000170 ???? 1111111 110777000001 10 Taxon Captorhinidae Paleothyris Spinoaequalis Petrolacosaurus Araeoscelis Apsisaurus A cerosodon tosaurus Youngina Hovasaurus 2222333333333344444444445 6789012345678901234567890 0000100000000000000000000 00010000000000001 10777000 0171000101711071111111111 01 1 100010011101 1 1 10000000 01110001001111111 10000000 000100107701 1 1??????????? ???? 1 1 101 1010777? 1??????? 10001 1 101 101017? 170000000 1000101000012171 111112121 THE SKULL OL THE HERBIVOROUS SYNAPSID EDAPHOSAURUS BOANERGES FROM THE LOWER PERMIAN OF TEXAS by S. P. MODESTO Abstract. The cranial anatomy of the Lower Permian synapsid Edaphosaurus boanerges is described, based upon well-preserved material from the Geraldine Bonebed (Wichita Group: Nocona Formation) of north- central Texas. Two autapomorphies for this species are identified: (1) 120-150 teeth are present on each palatal tooth plate; and (2) the mandibular symphysis is deeply excavated dorsally. Phylogenetic analysis of the interrelationships of Edaphosaurus species supports the hypotheses that the Lower Permian Texan species E. boanerges , E. cruciger, and E. pogonias are a monophyletic group, and E. boanerges is excluded from a clade formed by E. cruciger and E. pogonias. The suite of cranial specializations that characterizes Edaphosaurus is interpreted as an adaptation complex towards terrestrial herbivory. Isodonty, the presence of cutting edges on the marginal teeth, the oblique orientation of the cutting edges, and the shouldering of the marginal teeth, indicate that the anterior marginal teeth of E. boanerges served to crop bite-sized portions from tough, terrestrial plants. The food was then triturated by the palatal and mandibular tooth plates; minor grinding was provided also by the procumbent posterior teeth of the maxilla and dentary. The morphology of the jaw suspension indicates that the mandible was capable of fore-and-aft translation; the orientation of tooth plate occlusal surfaces and palatal tooth wear in E. boanerges indicate that propalinal movement was a major component of the grinding phase during oral food processing. The dual organization of the feeding system in Edaphosaurus is the earliest known example of its kind among amniotes. The Permo-Carboniferous is arguably one of the most interesting times in amniote evolutionary history, for it was during this time that the first large terrestrial herbivorous and carnivorous vertebrates appeared. The edaphosaurid synapsid genus Edaphosaurus was one of the most abundant, widespread and long-lived of the large herbivores. Edaphosaurus is currently recognized as the oldest known genus of herbivorous amniote (Modesto and Reisz 1992). Recent studies have identified two small faunivorous taxa, Ianthasaurus and Glaucosaurus (Reisz and Berman 1986; Modesto 1994), as basal edaphosaurids. Accordingly, the presence of both faunivorous and herbivorous taxa within Edaphosauridae makes the family an indispensable component of investigations into the origins of terrestrial vertebrate herbivory (Modesto 1992). Although Edaphosaurus has been known for well over one hundred years, its presence at many edaphosaurid localities is indicated only by fragments of the distinctive neural spines. Most species assigned to Edaphosaurus are represented by one or two poorly preserved skeletons, and the occasional tooth plate or isolated appendicular elements. Accordingly, our knowledge of the cranial anatomy of Edaphosaurus is imperfect. Most of what is known is based mainly upon descriptions of a single flattened and incomplete skull, the holotype of Edaphosaurus pogonias (Case 1906; Broom 1910; Watson 1916; Romer and Price 1940). Romer and Price (1940) were the last workers to describe this specimen. Although their description of the skull is now known to feature several major errors (Brinkman and Eberth 1983), recent studies (e.g. Olson 1986; Reisz 1986; Carroll 1988) continued to refer to it. Interestingly, exceptionally preserved cranial materials attributed to E. boanerges have been available since the publication of Romer and Price’s (1940) Review of the Pelycosauria. Between | Palaeontology, Vol. 38, Part I, 1995, 213-239.] ©The Palaeontological Association 214 PALAEONTOLOGY, VOLUME 38 1934 and 1941, an unprecedented amount of edaphosaurid material was recovered from the Geraldine Bonebed in Archer County, Texas (Wichita Group: Nocona Formation) by Harvard and Amherst College field parties. The remains of at least fourteen skeletons of this species were collected, including several complete, articulated skulls (Sander 1987). Accordingly, the material from Geraldine has made E. boanerges the best known member of the genus. However, that label does not extend to the cranial morphology, since the original description of E. boanerges (Romer and Price 1940) was based upon materials collected by Romer during the 1934 excavation, which apparently produced complete jaws but only a few disarticulated cranial elements. Romer and Price's (1940) reconstruction of the skull of E. boanerges appears to be a reworking of their reconstruction of the skull of E. pogonias, since most of the sutures are represented by dashed lines. The skulls collected during the 1939 and 1941 excavations were partially prepared, but only to serve as the basis for exhibition models. More recently, these specimens were used in a review of early synapsid phylogeny (Brinkman and Eberth 1983). The rich assemblage of Geraldine materials provides an opportunity to describe thoroughly the cranial osteology of an edaphosaurid. The exceptional preservation of the tooth-bearing elements of the Geraldine skulls also permits an investigation into the adaptation to herbivory that has long been attributed to Edaphosaurus. This hypothesis was prompted by the presence of the large denticulate plates on the palate and the lingual surface of the mandible, and the presence of a large, barrel-shaped body. Most edaphosaurid marginal dentitions that were available to early workers were not well preserved, and accordingly did not figure in their hypotheses concerning diet. The well preserved Geraldine materials shed additional light on edaphosaurid herbivory. This description and restudy of the skull of Edaphosaurus boanerges is essential in the light of recent systematic studies of early amniotes, for much remains to be clarified concerning the relationships of primitive synapsids. The goals of this work are to provide a detailed description of the skull of Edaphosaurus boanerges , to determine its probable feeding mechanism, to strengthen the hypothesis of herbivory attributed to this genus using the new cranial data, and to provide a robust phylogeny for Edaphosaurus. Institutional abbreviations. AMNH, American Museum of Natural History, New York; MCZ, Museum of Comparative Zoology, Harvard University; ROM, Royal Ontario Museum, Toronto. SYSTEMATIC PALAEONTOLOGY synapsida Osborn, 1903 eupely cosauri a Kemp, 1982 Family edaphosauridae Cope, 1882 Genus edaphosaurus Cope, 1882 Type species. Edaphosaurus pogonias Cope, 1882 Diagnosis. Edaphosaurids (see Modesto and Reisz 1990 for familial diagnosis) with small skulls, approximately equal in length to five dorsal centra; posterior process of the postorbital short, does not extend posterior to the level of the parietal foramen; nasal is approximately three-quarters the length of the frontal; frontal anterior process reduced in antero-posterior length to one-third frontal sagittal length; posterior cheek deeply emarginated; tooth plates are developed on the palate and the inner aspect of the mandible; palatal tooth plates are formed by the palatine, ectopterygoid, and pterygoid; mandibular tooth plates are formed by anterior coronoid, posterior coronoid, and prearticular; marginal teeth are isodont, slightly swollen distally, and feature fine serrated tips that curve slightly backwards; cutting edges of the cheek teeth are inclined obliquely with respect to the axis of the tooth row. Maxillary teeth become increasingly laterally directed posteriorly, while the MODESTO: PERMIAN SYNAPSID 215 text-fig. 1. Edaphosaurus boanerges Romer and Price 1940. Outline guide to skull reconstructions in Text- figures 2-4. a, skull and left mandible in left lateral view; b, right mandible in medial view; c, skull in dorsal view; d, skull and left mandible in ventral view; e, skull in occipital view. Scale bar represents 20 mm. opposing dentary teeth become increasingly medially directed; neural spines of the sacral and anterior caudal vertebrae are tall and pointed, with longitudinal ridges running along their lateral surfaces; multiple lateral tubercles, when present, are usually arranged horizontally on the neural spines. Edaphosaurus boanerges Romer and Price, 1940 Text-figures 1-18 1916 Edaphosaurus sp., Williston, p. 233, fig. 81. 1940 Edaphosaurus boanerges , Romer and Price, p. 48, fig. 6a; p. 66, fig. 8; p. 79, fig. 12f; p. 86, fig. 15c-d; p. 391, fig. 66. Diagnosis. A medium-sized Edaphosaurus characterized by the presence of 120-150 teeth on each palatal tooth plate and a jaw symphysis that is deeply excavated dorsally; distinguished from other edaphosaurids by the following suite of advanced and primitive characters: frontal lateral lappet slender; anterior presacral neural spines slender; and lateral tubercles slender. Horizon and Locality. Nocona Formation (formerly Admiral Formation; see Hentz 1988 for stratigraphical review for north-central Texas), Wichita Group, Lower Permian. Study specimens are from the Geraldine Bonebed, approximately 13 km northwest of Archer City, Archer County, Texas. Holotype. MCZ 1531, a pair of mandibles. According to Romer and Price (1940), this number originally contained 'the remains of about six individuals’ from Geraldine, with the type jaws forming part of a mounted 216 PALAEONTOLOGY, VOLUME 38 MCZ specimen. In the early 1980s all specimens except the type jaws were reassigned to MCZ numbers 4309-4324. Study material. MCZ 1680, a partial skeleton with an obliquely compressed skull; MCZ 1762, a partial skeleton with fragmentary skull and mandibles; MCZ 1764, a fragmentary skull; MCZ 4309, a partial skull with mandibles (formerly part of MCZ 1531); ROM 37760, a fragmentary left maxilla. This is not an exhaustive list of Edaphosaurus boanerges specimens reposited at the MCZ, ROM, or elsewhere, and includes only those specimens examined here. Description. The Geraldine specimens permit a confident restoration of the skull of Edaphosaurus boanerges (Text-figs 1-4). The reconstruction is based mainly upon MCZ 1762, with additional information taken from text-fig. 2. Edaphosaurus boanerges Romer and Price 1940. Restoration of skull and left mandible in left lateral view, and right mandible in medial view. Scale bar represents 10 mm. MCZ 1680, MCZ 1764, and MCZ 4309. The mandible is reconstructed mainly from MCZ 4309, with additional data taken from MCZ 1680 and MCZ 1762. Several features distinguish this genus from other Permo-Carboniferous synapsids. Most significantly, the cheek margin is greatly emarginated, the slender subtemporal bar is displaced dorsally, and the temporal fenestra is enlarged antero-posteriorly. The MODESTO: PERMIAN SYNAPSID 217 text-fig. 3. Edaphosaurus boanerges Romer and Price 1940. Restoration of skull and left mandible in dorsal and palatal views. Scale bar represents 10 mm. text-fig. 4. Edaphosaurus boanerges Romer and Price 1940. Restoration of skull in occipital view. Scale bar represents 10 mm. supraorbital shelf is very deep transversely and conceals the orbits in dorsal view. The posterior maxillary teeth become increasingly laterally directed posteriorly along the marginal tooth row. Skull. The dorsal process of the premaxilla (Text-fig 5), obliquely elongate in cross section, overlies a broad anterior shelf of the nasal. The vomerine process is not preserved well enough for description. The premaxilla PALAEONTOLOGY, VOLUME 38 text-fig. 5. Edaphosaurus boanerges Romer and Price 1940; MCZ 1680; Geraldine Bonebed, Lower Permian; Archer Co., Texas. Skull roof and right mandible in right lateral view, and left angular in medial view. Scale bar represents 10 mm. accommodates five teeth, but none is preserved well enough to determine their length. However, the cross- sectional area of the premaxillary tooth stumps of MCZ 4309 are similar to those of the maxillary dentition, which suggests that the premaxillary teeth probably differed little in size from those of the maxilla. The septomaxilla (Text-fig. 5) extends the full height of the narial opening, and the medial shelf is large enough to have easily made contact with the nasal septum at the midline. The presence of a posterolateral process on the septomaxilla, seen in sphenacodontids, cannot be determined. The maxilla (Text-figs 5—7) is a slender rod of bone accommodating 18-21 teeth. All previous descriptions of the marginal dentition of Edaphosaurus restored the teeth vertically, as in most other early tetrapods. The well preserved Geraldine materials reveal that the alveolar ridges of the maxillae and dentaries are twisted, such that their posterior teeth become directed laterally and medially, respectively. The lateral edge of the maxillary alveolar ridge becomes disproportionately thinner posteriorly than the medial edge, and the ventral surface of the alveolar portion exhibits a progressive lateral flexure, approximately 13°-16° at the sixteenth tooth position, and roughly 35°-MO° at the eighteenth and nineteenth tooth positions. Accordingly, the angle of tooth implantation changes, and the posterior maxillary teeth become increasingly laterally directed. In lateral aspect, the ventral margin of the maxilla is arched weakly, and the lateral edge forms a distinct lip over the tenth MODESTO: PERMIAN SYNAPSID 219 text-fig. 6. Edaphosaurus boanerges Romer and Price 1940; MCZ 1762; Geraldine Bonebed, Lower Permian; Archer Co., Texas, a, left lateral and b, right lateral views of skull. Scale bar represents 10 mm. through fifteenth teeth. The implantation of the teeth (Text-fig. 9) is protothecodont. Each tooth bears a perceptible shoulder, beyond which it attenuates to a sharp tip. The tips are compressed slightly transversely and curve slightly posteriorly. Posterior cutting edges are aligned slightly posterolaterally, whereas anterior cutting edges are inclined anteromedially. Many teeth feature extremely fine serrations along their cutting edges, and these are emphasized by short, oblique grooves running inwards from the edge; those teeth lacking serrations presumably lost them from heavy use. Approximately every third tooth in the maxillae of MCZ 1 762 is at the same level of development, and there are few natural gaps in the marginal dentition, suggesting that tooth replacement was relatively rapid. Wear is present on several anterior teeth in MCZ 1762, occurring as a planing-off of the lingual surface of the shoulder; the posterior teeth are too damaged to determine true tooth-to-tooth wear. However, examination of ROM 37760 reveals that many of the procumbent posterior teeth display similar wear on their lingual surfaces. In lateral aspect, the lacrimal (Text-figs 5-6. 10) underlies the dorsal flange of the maxilla anteriorly, but as the lacrimal becomes progressively thicker posteriorly, it comes to overlie the maxilla totally. The medial wall of the lacrimal duct is thicker than the lateral wall, perhaps to strengthen contact with the ventral process of the prefrontal medially. The lacrimal is greatly thickened along the orbital margin and has a well-developed contact with the ventral process of the prefrontal Anteriorly, the nasal (Text-figs 5-7) has a strongly scarred shelf for the reception of the premaxilla, and the internasal suture is bevelled and irregular, presumably to strengthen the snout against forces generated during feeding. The ventral process of the prefrontal (Text-figs 5-7) is transversely thick and is attached solidly to the medial surface of the lacrimal. The transverse width of the ventral process decreases ventrally in direct proportion to a progressive increase in the width of the lacrimal, forming a stout buttress of constant width between the skull roof and palate (Text-fig. 10). The ventral process continues dorsally as a ridge on the ventral surface of the posterodorsal process. Romer and Price (1940) reconstructed the frontal with a large lateral lappet. However, the lateral lappet of the frontal (Text-figs 5-8) is markedly slender, with a lateral exposure about one-quarter that of the 220 PALAEONTOLOGY, VOLUME 38 text-fig. 7. Edaphosaurus boanerges Romer and Price 1940; MCZ 1762; Geraldine Bonebed, Lower Permian; Archer Co., Texas, a, palatal and b, dorsal views of skull. Scale bar represents 10 mm. postfrontal. Posteriorly, the frontal overlies, and has a moderately to deeply serrate suture with, the parietal; a ventral ridge extends anteriorly from this suture to contact and merge with the ventral ridge and ventral process system of the prefrontal. A notable feature of the parietal (Text-figs 6-8) is its concave lateral edge. Contrary to previous interpretations, the lateral edge of the parietal was free and formed the dorsal margin of the temporal fenestra. The medial half of the ventral surface of the bone is dominated by two well-developed parasagittal ridges. The lateral ridge is continuous with the ventral ridge of the frontal, and presumably marks the former contact of the orbital-plate cartilage, whereas the medial ridge arises immediately anterior to the parietal foramen, extends to the posterior edge of the parietal, and overlies an anterodorsal pilaster-like process of the postparietal. Posteriorly, the parietal has a small occipital shelf that contacts the postparietal and the tabular. The lateral edges of the postparietal (Text-fig. 1 1) of MCZ 1 762 are imperfectly preserved, making it difficult to establish the precise nature of the contact with the tabular and the parietal. However, scars present on the posterior margin of the parietal suggest that the postparietal overlies the occipital flange of the parietal. A pair of pilaster-like projections arise from a point slightly lateral to the centre of the anterior surface and end dorsally as broad-based supports for the medial ventral rugosities of the parietals. These processes lie snugly within the crenels of the dorsal process of the supraoccipital. A small, median process extends anterodorsally from the postparietal to interpose itself between the posterior ends of the parietals; this is inferred by a small, triangular gap which lies sagitally between the ends of the articulated parietals. An anterodorsal process is found also on the postparietal of Edaphosaurus pogonias (AMNH 4009). MODESTO: PERMIAN SYNAPSID 221 text-fig. 8. Edaphosaurus boanerges Rcmer and Price 1940; Geraldine Bonebed, Lower Permian; Archer Co., Texas. Skull table of MCZ 1762 in ventral view. Scale bar represents 10 mm. text-fig. 9. Edaphosaurus boanerges Romer and Price 1940; Geraldine Bonebed, Lower Permian; Archer Co., Texas. Maxillary teeth of MCZ 1762. a, occlusal and b, lingual views of 6th and 7th right maxillary teeth; c, lingual view of the tip of unankylosed maxillary tooth, showing serrations. Scale bars represent 1 mm. The supratemporal (Text-figs 6-8) is a narrow, gently arched bone with little lateral exposure. The supratemporal of Edaphosaurus boanerges differs little from that of E. pogonias. The supratemporal of the latter species was reconstructed by Romer and Price (1940) as a large element, but re-examination of the holotype reveals that it, too, is a slender, predominantly occipital element. The relatively thick dorsal edge of the tabular (Text-figs 6-8) occupies a broad embayment in the posterior edge of the parietal. Though the ventromedial edge of the tabular is not preserved, the preserved parts of the bone rapidly thin inwards from the dorsal edge, suggesting that the ventromedial edge was quite thin. Sutural surfaces on the occipital surfaces of the paroccipital process and lateral process of the supraoccipital mark its ventromedial limits. PALAEONTOLOGY. VOLUME 38 222 text-fig. 10. Edaphosaurus boanerges Romer and Price 1940; Geraldine Bonebed, Lower Permian; Archer Co., Texas. Left antorbital region of MCZ 1762 in posterior view. Hachure indicates broken surface. Scale bar represents 10 mm. text-fig. 1 1 . Edaphosaurus boanerges Romer and Price 1940; Geraldine Bonebed, Lower Permian; Archer Co., Texas. Postparietal of MCZ 1762. a, dorsal and b, posterior views. Scale bar represents 5 mm. The postfrontal (Text-figs 5-8) consists of a small but thick posterior process that gives rise to a wedge- shaped anterior flange that forms the posterior half of the supraorbital hood. The sutural surface for the postorbital is twisted: internally and medially the posterior process of the postfrontal overlies the base of the postorbital posterior process, whereas laterally it underlies the postorbital. The postorbital (Text-figs 6-8) is a slender, sigmoidal bone. The posterodorsal process does not extend posteriorly beyond the pineal foramen, and it is completely overlain by the parietal. In spite of the fragmentary nature of the available squamosals, it is very unlikely that the postorbital contacted the squamosal. The posterodorsal process does not possess an area that may be interpreted as a sutural surface for the squamosal, nor does the parietal immediately posterior to the postorbital bear any markings for the reception of the squamosal. The jugal (Text-figs 6-7) is remarkably slender in lateral view, and is laterally compressed for most of its length except for the slightly swollen anterior third. A short protuberance extends medially from the anterior jugal process to contact the palate. The sutural surface for the squamosal is extensive and marked by strong ridges and furrows. MODESTO: PERMIAN SYNAPSID 223 text-fig. 12. Edaphosaurus boanerges Romer and Price 1940; Geraldine Bonebed. Lower Permian; Archer Co., Texas. Palatoquadrate ossifications and associated elements of MCZ 1762. a, medial and b, lateral views. Scale bar represents 10 mm. text-fig. 13. Edaphosaurus bo- anerges Romer and Price 1940; Geraldine Bonebed, Lower Per- mian; Archer Co., Texas. Left squamosal of MCZ 1680. a, lateral and b, medial views. Scale bar represents 10mm. The ventral process of the squamosal (Text-figs 6, 12-13) is well developed. An occipital flange extends medially from the ventral process of the squamosal, and serves as a broad base for the supratemporal and, to a lesser extent, the tabular. A thickened, irregular prominence on the medial edge of the squamosal marks the area receiving the tip of the paroccipital process. The anterior process displays either a slight anteroventral curvature, as in MCZ 1762, or extends forward without arching, as in MCZ 1680. Despite the absence of well preserved specimens, Romer and Price (1940) described the quadratojugal as extending anteriorly under the postorbital bar. However, the quadratojugal (Text-fig. 12) is antero-posteriorly short and covered laterally by the squamosal, resembling closely those of sphenacodonts. 224 PALAEONTOLOGY, VOLUME 38 text-fig. 14. Edaphosaurus boanerges Romer and Price 1940; Geraldine Bonebed, Lower Permian; Archer Co., Texas. Left epipterygoid of MCZ 1 764. a, lateral and b, medial views. Scale bar represents 10 mm. The palate departs from the typical primitive synapsid condition in the possession of a pair of large tooth plates, formed by the palatine, ectopterygoid, and pterygoid. These plates are tilted ventrolaterally, are faintly concave in order to meet more firmly the gently convex tooth plates of the mandible, and accommodate about 120-150 teeth each. The internal nares (Text-fig 3) are more elongate than suggested by Romer and Price (1940), but they are neither as long, nor as transversely constricted, as in carnivorous eupelycosaurs. The median longitudinal depression between the tooth plates is deep and compressed transversely, and the post- plate region is significantly more abbreviated than in other genera. The ventrolateral surface of the vomer (Text-fig. 7) is slightly concave and covered by a shagreen of tiny teeth, which is replaced anteriorly by a smooth surface ingrained by shallow striae. The largest vomerine teeth reach a maximum diameter equal to approximately one-half that of an average-sized plate tooth. The palatine’s (Text-figs 6-7) contribution to the tooth plate is a thick, diamond-shaped structure which bears approximately thirty-two conical teeth. The majority of the teeth are approximately one-half as long and two-thirds the diameter of the maxillary dentition. They are roughly uniform in diameter and are densely packed. Smaller teeth, some approaching the size of the vomerine teeth, occupy the lateral and anterior fringes of the tooth-bearing area. All well-preserved palatal teeth display some degree of wear, which generally takes the form of a planing-off of the tips of the teeth. However, the tips of most teeth appear to have been planed off by previous preparators, making it difficult to identify true tooth wear. A diagonally-orientated orbitonasal ridge arises on the dorsal surface near the lateral edge of the palatine, forms the medial wall of the lateral orbitonasal foramen, and runs anteromedially to the medial orbitonasal foramen. Laterally, the orbitonasal ridge has a small contact with the lacrimal and the ventral process of the prefrontal. The ectopterygoid (Text-figs 5, 7) is a small element that is almost completely covered ventrally by about fifteen teeth. Laterally, the ectopterygoid has a small contact with the jugal. The pterygoid (Text-figs 5, 7, 12) is the largest and most complex palatal element. The low dorsal lamina of the pterygoid is scarred medially with numerous longitudinal ridges and grooves, presumably required to withstand the forces generated by the jaw adductor musculature. The ventral surface of the palatal ramus is covered completely by teeth except for the edges bordering the interpterygoid vacuity and the jugal. The tooth plate faces slightly rostrally as well as anterolaterally, and lies well below the level of the cheek in lateral aspect. Nearly 100 teeth are present, and these are set deeply into the alveolus of the tooth plate. The thin quadrate ramus of the pterygoid is similar to those of sphenacodontids, but differs strongly from other eupelycosaurs in the elaboration of the region associated with the epipterygoid. The ramus rises directly upwards from the dental plate and wraps around the basicranial process of the epipterygoid. A broad, prominent channel of unknown function issues from the scrolled flange enclosing the basicranial process and ends abruptly on the dorsal surface of the palatal plate. The basal portion of the epipterygoid (Text-figs 12, 14) overlies the quadrate ramus of the pterygoid in lateral view. The basicranial process extends medially from the basal portion and ends in a tall, screw-shaped recess for the basipterygoid process of the basiparasphenoid. The ventral half of the recess faces slightly posteriorly as well as medially, whereas the dorsal half faces anteromedially. The basicranial process is held firmly within the anterior fold of the quadrate ramus of the pterygoid. The dorsal columella is a slender, transversely compressed finger of bone that arches posteriorly. The dorsal and posterior margins of the vertical plate of the quadrate are thickened and flare slightly laterally (Text-fig. 12). The posterior margin has a strong contact with the squamosal and a smaller sutural surface for MODESTO: PERMIAN SYNAPSID 225 text-fig. 15. Edaphosaurus boanerges Romer and Price 1940; Geraldine Bonebed, Lower Permian; Archer Co., Texas. Braincase of MCZ 1762. a, left lateral, b, right lateral, c, dorsal, d, ventral, and e, occipital views. Scale bar represents 10 mm. the quadratojugal. A shallow, rounded depression posteromedial to the quadrate foramen probably received the distal end of a cartilaginous extension of the stapes. The two condyles are aligned parasagittally, are separated by a deep notch, and share a single articulating surface. The braincase (Text-fig. 15) resembles in most respects that of sphenacodontids, but differs in the morphology of the paroccipital processes and the organization of the region formerly surrounding the pituitary body. As in most early synapsids, there is a marked tendency towards fusion of the elements : the parasphenoid and the basisphenoid are united, the supraoccipital is fused to the opisthotics and the prootics, and the basioccipital and exoccipitals are fused. Because the basisphenoid and its dermal cover, the parasphenoid, are indistinguishably fused, the term basiparasphenoid is used here when referring to this complex. The cultriform process is poorly known, but 226 PALAEONTOLOGY, VOLUME 38 text-fig. 16. Edaphosaurus boanerges Romer and Price 1940; Geraldine Bonebed, Lower Permian; Archer Co., Texas. Sphenethmoid of MCZ 1764. a, posterior and b, right lateral views. Scale bar represents 10mm. what is preserved indicates that it projected forward from the anterior end of the bone as a narrow trough. The bifaceted basipterygoid processes extend anterolaterally from the complex. Each has a prominent hourglass- shaped articulating surface, with a dorsal facet directed posterolaterally, and a marginally larger ventral facet orientated anterolaterally. Immediately posterior to the dorsal basipterygoid demi-facets, the lateral walls of the basiparasphenoid of MCZ 1 762 have been pushed inwards revealing the underlying vidian canals. Crushing makes it difficult to determine the suture with the prootics. Ventrally, the basal tubera contacted the ventral margins of the prootics and the stapedial footplates. The longitudinal trough of the sphenethmoid (Text-fig. 16) is open dorsally; the dorsal edges of the trough feature distinct lips that project medially, but these do not appear to have been interconnected by cartilage, as their edges are smoothly finished. The well preserved posterior edge is strongly sigmoidal, as in other forms in which this bone is known. Unfortunately, the anterior portion of the element is missing, and it is impossible to determine how far anteriorly the bone extended. The prootics (Text-fig. 15) form the relatively gracile dorsum sella. The dorsum sella is poorly preserved in MCZ 1762, but what is present suggests that it resembles a thin, posteriorly-arching wall, which differs significantly from the thick, plate-like structures of other early synapsids. As in sphenacodontids (Romer and Price 1940), the prootic forms the anterolateral wall of the otic capsule, but the free dorsal border is smooth, rounded, and is considerably longer than those described for sphenacodontids (Romer and Price 1940; Eberth 1985). Each opisthotic (Text-fig. 15) contacts the basiparasphenoid on either side of a deep, ventral emargination representing the lateral margin of the ventral opening of the otic capsule. A ventral flange extends ventrally, abuts the basioccipital tubercle, and marks the posterior edge of the fenestra ovalis. The paroccipital process extends slightly ventrally as well as posterolaterally, and terminates with a blunt, downturned tip. A pronounced ridge at the base of the process on the anteroventral edge abutted the anterior edge of the stapedial dorsal process, and immediately posterior to the ridge lies an elongate scarred area for the reception of the dorsal process of the stapes. Dorsally, the supraoccipital (Text-fig. 1 5) lies just below the upper edge of the postparietal, and its unfinished dorsal edge is crenellated for the accommodation of the pilaster-like processes of the latter. Light scarring on the lateral processes marks the sutural surface for the tabular. The dorsal tips of the exoccipitals constrict slightly the dorsal part of the foramen magnum. The dorsal edge of the shallow notochordal pit on the occipital condyle probably marks the ventral extent of the exoccipitals, and a pronounced median ridge along the floor of the braincase of MCZ 1762, exaggerated by crushing, marks the line of contact between the fused exoccipitals. The basioccipital forms most of the semicircular occipital condyle. The articulating surface of the condyle is separated from its neck by narrow ridges, and a medial ridge, more strongly developed than that seen in sphenacodontids, arises from the ventral lip of the condyle and merges anteriorly with the body of the basioccipital. Paired basioccipital tubera, arched strongly ventrally in parasagittal section, extend laterally to contact the ventral flanges of the opisthotics. The stapes (Text-fig. 12) is similar to that of sphenacodontids (Romer and Price 1940; Eberth 1985). The dorsal process widens above the footplate, and has a strongly convex lateral margin, which is slightly thinner than the medial edge. The quadrate process is blade-like rather than rod-like as described by Romer and Price (1940). It ends in unfinished bone, and was probably tipped with cartilage. The stapedial foramen is large MODESTO: PERMIAN SYNAPSID 227 relative to the size of the footplate, as two small, thin sheets couple the body to the footplate. The footplate is oval in medial view, with the long diameter aligned parallel to the axis of the stapedial foramen. Mandible. Relative to its length, the mandible of Edaphosaurus (Text-figs 2-3) is much deeper than those of other eupelycosaurian genera. The symphysis can be subdivided into a large, anterodorsal pad and a smaller, posteroventral pad. A large denticulate plate occupies the central third of the lingual surface, and accommodates approximately sixty teeth that are indistinguishable from those of the palatal plates. The tooth plate does not extend as far forward as restored by Romer and Price (1940). The alveolar ridge of the dentary is twisted posteriorly, causing the posteriormost marginal teeth to become medially directed. Except for the vertically aligned angular keel, the jaw leans laterally. text-fig. 17. Edaphosaurus boanerges Romer and Price 1940; Geraldine Bonebed, Lower Permian; Archer Co., Texas. Left mandible of MCZ 4309. a, medial and b, lateral views. Scale bar represents 10 mm. The dentary (Text-fig. 17) occupies the anterior 70 per cent, of the mandible in lateral view. It forms most of the anterior symphyseal pad, but makes no contribution to the smaller posterior pad. The anterior pad is incised deeply by an anterior extension of the meckelian canal. Posteriorly, the dentary contacts the angular and surangular with a serrate, overlapping suture, and forms the lateral portion of the angular coronoid eminence. The dentary accommodates about 23 tall, isodont teeth, which, except for their slightly smaller size, resemble those of the upper marginal dentition. The alveolar ridge of the dentary is twisted inwards posteriorly, such that the most posterior marginal teeth lean lingually. Unfortunately, the surfaces of most teeth are damaged, but the orientation of wear present on the labial surfaces of the recumbent teeth suggests that they contacted the upper dentition. 228 PALAEONTOLOGY, VOLUME 38 Anteriorly, the splenial (Text-fig. 17) extends downwards and medially as a prominent symphyseal flange, which contacts its fellow at the midline. The anterior half of the symphyseal flange of the splenial is exceedingly thin, such that a pocket lies dorsally between the anterior and posterior symphyseal pads. This condition differs from that seen in Edaphosawus pogonias (AMNH 4009) and Dimetrodon , in which the symphyseal area consists of a single large pad. Although the symphyseal flange of the splenial does extend farther ventrally than in other eupelycosaur taxa, it is not as extensive as reconstructed by Romer and Price (1940), as they have apparently restored the mandible vertically. The mandible displays, instead, a strong lateral lean, which foreshortens the lateral exposure of the splenial. Posteriorly, the splenial becomes twisted almost 90° beneath the medially expanded tooth plate, and its posterior edge forms the anterior margin of the caudally-directed inframeckelian foramen. The anterior coronoid (Text-fig. 17) is moderately arched dorsally and accommodates approximately sixteen teeth. Most of the bone overlies the posterior end of the splenial, but anteriorly and posteriorly it has smaller contacts with the dentary and prearticular, respectively. The posterior coronoid (Text-fig. 17) is a typically triradiate structure. The ventral half supports a dense field of about forty isodont, peg-like teeth. The tooth field is approximately four tooth bases wide, but the teeth are not arranged in true rows as in some multiple- tooth rowed captorhimds, as they are irregularly positioned. In ventromedial view, the tooth field is dorsally arched. The tips of several teeth bear oblique facets, which may represent true tooth wear. The superior half of the posterodorsal process is etched deeply by a system of vermiculate grooves, and its dorsal rim bears deep pits and a strong spur, for the insertion of the jaw adductor musculature. The prearticular (Text-fig. 17) forms most of the floor of the adductor fossa. Its anterior third is expanded medially and accommodates nine teeth. The prearticular overlies a long medial shelf of the angular, but posteriorly this contact becomes attenuated and eventually disappears as the prearticular becomes more closely associated with the articular, where the prearticular becomes exceedingly thin and twisted, and sheathes the ventral face of the pterygoideus process of the articular. The dorsal margin of the surangular (Text-fig. 17) is moderately arched laterally. It is notably thickened dorsally, but becomes thinner ventrally. Anteriorly, the surangular is sandwiched between the posterodorsal processes of the posterior coronoid and dentary, and the dorsal margin bordering the posterior coronoid is deeply scarred, demonstrating that the M. adductor mandibulae externus extended at least this far posteriorly onto the surangular. The angular (Text-figs 5, 17) is the second largest bone in the mandible. A medially-projecting shelf buttresses the prearticular and forms the ventral margin of the inframeckelian foramen. Ventrally, a deep, vertical keel extends downwards from the body of the angular, and becomes thinner in cross-section distally. The edge of the keel is smoothly finished anteriorly, but the posterior third is thickened and slightly crenulated, which suggests that the edge of the keel may have served as the site of insertion for musculature of uncertain origin. The posterior third of the keel is arched slightly laterally, possibly to allow the pterygoideus musculature to insert on the ventral surface of the pterygoideus process. The articulating surface for the condyle of the quadrate dominates the dorsal surface of the articular (Text- figs 5, 17-18) and is approximately 50 per cent, longer in antero-posterior dimension than the articulating A text-fig. 18. Edaphosawus hoanerges Romer and Price 1940; Geraldine Bonebed, Lower Permian; Archer Co., Texas. Right articular of MCZ 1762. a, medial and b, ventrolateral views. Hachure indicates broken surface. Scale bar represents 10 mm. B pra/ss MODESTO: PERMIAN SYNAPSID 229 surface of the opposing quadrate. The inward-tilting surface consists of two main elliptical areas divided by an antero-posteriorly directed ridge which fits into a notch in the quadrate. The ridge continues anteriorly and swells into a large, anterior boss. The anterior process of the articular extends forwards along the floor of the adductor fossa between the surangular and prearticular and narrows anteriorly, ending in unfinished bone that presumably continued forwards as cartilage. A robust retroarticular process projects backwards and bears numerous fine ridges and furrows for attachment of the M. depressor mandibulae. In contrast to the reconstruction of the mandible by Romer and Price (1940), the pterygoideus process of the articular projects posteriorly as well as ventromedially. Its posterodorsal surface is marked by pits and grooves, which suggests that the pterygoideus musculature may have inserted at least this far posterodorsally on the process. A longitudinal groove, presumably the chorda tympani canal, traverses the sutural surface for the prearticular (Text-fig. 18). DISCUSSION Phylogenetic relationships The family Edaphosauridae occupies a prominent phylogenetic position among early synapsids as the sister group to Sphenacodontia (sensu Reisz et al. 1992), the Permo-Carboniferous clade which eventually gave rise to mammals. The relationships of Edaphosauridae to other basal synapsid groups is given in Text-figure 19a. B / lanthasaurus / / Glaucosaurus novomexicanus \//E. boanerges b£wE. cruciger X'E. pogonias Cynodontia text-fig. 19. Phylogenetic trees discussed in the text. A, cladogram showing the phylogenetic position of Edaphosauridae among Palaeozoic Synapsida. Adapted from Rowe (1988), Laurin and Reisz ( 1990), and Reisz et al. (1992). b, cladogram illustrating a hypothesis of edaphosaund interrelationships. See text for synapomorphies diagnosing nodes A-C. Edaphosauridae is comprised currently of three genera and nine species from the Permo- Carboniferous of North America and Europe (Reisz 1986; Modesto 1994). Seven edaphosaurid species are assigned to the genus Edaphosaurus. However, the assignment of two European species to the genus has been questioned because of the fragmentary nature of their respective holotypes (Reisz and Berman 1986; Modesto and Reisz 1990). Although based upon only fifteen morphological characters, a tentative phylogeny for edaphosaurids presented by Modesto and Reisz (1992) corroborated previous hypotheses concerning interrelationships among the better known species of Edaphosaurus (Romer and Price 1940; Reisz and Berman 1986). The Geraldine E. boanerges cranial material described here allows for the reinterpretation of the cranial anatomy of other members of the genus. Accordingly, this permits a phylogenetic analysis of Edaphosaurus more comprehensive than heretofore possible. The following edaphosaurid taxa, including Edaphosaurus boanerges , form the ingroup: E. novomexicanus , from the Permo-Carboniferous of New Mexico, redescribed recently by Modesto and Reisz (1992); the two largest edaphosaurids, E. cruciger and E. pogonias , from the Lower Sphenacodontia Therapsida Caseasauria Varanopseidae Ophiacodontidae EDAPHOSAURIDAE Haptodus Sphenacodontidae Tetraceratops Biarmosuchia Dinocephalia Gorgonopsia Dicynodontia Therocephalia 230 PALAEONTOLOGY, VOLUME 38 Permian of Texas, known adequately from early descriptions (Case 1907; Romer and Price 1940) with both cranial and postcranial material examined by the author. In addition to the cranial information presented in this paper, the postcranial osteology of E. boanerges is known from a description by Romer and Price (1940). Due to their fragmentary nature, three taxa are omitted from the analysis: Edaphosaurus colohistion , from the Lower Permian Pittsburgh Formation of West Virginia, excluded as it is known only from a single series of presacral vertebrae and dorsal ribs (Berman 1979); similarly, two small European taxa assigned to the genus (Reisz 1986) are omitted. The following taxa serve as outgroups: Ianthasaurus liardestii , from the Upper Pennsylvanian of Kansas (Reisz and Berman 1986; Modesto and Reisz 1990), and Glaucosaurus megalops , from the Lower Permian of Texas and identified recently as an edaphosaurid (Modesto 1994), represent the small, presumably carnivorous, members of the family; Haptodus garnettensis (Laurin 1993) and the varanopseid Mycterosaurus (Berman and Reisz 1982) serve as more distant outgroups. Thirty-six characters were used in the analysis. These are described in Appendix 1 . Many of these are from the literature (Romer and Price 1940; Brinkman and Eberth 1983; Modesto and Reisz 1992), although a few are new. The analysis was run on a Macintosh Quadra 800 computer using the branch-and-bound algorithm of paup 3.1, which is guaranteed to find the most parsimonious trees. Character states were optimized using the delayed transformation (deltran) algorithm and run unordered. The most parsimonious tree (Text-fig. 19b) requires 38 steps and has a consistency index of 0 973. Synapomorphies are grouped below under the nodes and/or the taxonomic units that they diagnose. Numbers appearing in square brackets refer to character descriptions listed in Appendix 1 ; multiple character states, indicated as 1 or 2, are encased in parentheses. A negative sign indicates a reversal, and asterisks denote ambiguous characters, which may define more inclusive nodes. Node A. The following synapomorphies diagnose Edaphosaurus'. 1. marginal teeth slightly bulbous [1]; 2. alveolar ridges twisted [7]; 3. supraorbital margin expanded laterally [10]; 4. parietal lateral margin deeply concave [11*]; 5. quadrate condylar portion saddle-shaped [14*]; 6. jaw suspension offset ventrally [15*]; 7. skull short [16*]; 8. postorbital and antorbital regions subequal [17*]; 9. tooth plates present [19]; 10. cervical centra short [23*]; 11. neural arches not excavated [-28*]; 12. dorsal vertebrae with elongate transverse processes [29*]; 13. sacral and caudal neural spines with rugose tips [30*]; 14. sacral and caudal neural spines with longitudinal ridges [31*]; 15. caudal neural spine tips expanded sagitally [32*]; 16. caudal neural spines tall and pointed [33*]; 17. dorsal ribs strongly curved [34*]; 18. dorsal rib tubercula greatly reduced [35*]. Node B. These apomorphies diagnose the clade of Texan edaphosaurids, E. boanerges , E. cruciger , and E. pogonias: 1. marginal teeth with cutting edges [2*]; 2. frontal lateral lappet slender [9]; 3. postorbital does not contact squamosal [12*]; 4. mandible short and deep [20*]; 5. splenial lateral exposure enlarged [22*]; 4. ilium with well-developed anterodorsal process [36(2)*]. Node C. These apomorphies diagnose the clade of E. cruciger and E. pogonias : 1. dentary antero- posterior length equal to or less than two-thirds of mandibular length [21]; 2. swollen-tipped lateral tubercles present [26(2)]; 3. club-shaped anterior presacral neural spines [27], Eighteen apomorphies diagnose the genus Edaphosaurus. Three of these are newly identified Edaphosaurus synapomorphies: the twisting of the alveolar ridges [7]; the saddle-shaped quadrate condyle [14]; and the absence of lateral excavations on the neural arches [28], However, five of the six apomorphies diagnosing the clade of Texan edaphosaurs are ambiguous since they cannot be determined in E. novomexicanus , and therefore may represent additional synapomorphies of the genus. Similarly, many of the apomorphies diagnosing Edaphosaurus are ambiguous, due to the total absence of postcrania of Glaucosaurus megalops. It is possible that analysis of new material attributable to this little edaphosaurid may unite it more strongly to Edaphosaurus. The presence of serrations on the marginal teeth, the oblique arrangement of the cutting edges of the marginal teeth, the presence of a medial process on the jugal, the anterior folding of the quadrate flange of MODESTO: PERMIAN SYNAPSID 231 the pterygoid, and the presence of a posterior infra-meckelian foramen, all present in E. boanerges , but not currently determinable in other members of the genus, may represent further synapomorphies of Edaphosaurus. In the course of compiling the data matrix, two characters used formerly to diagnose this genus were found to be of limited use. The first, reduced marginal dentition (Reisz 1986; Reisz and Berman 1986), is difficult to assess, since eupelycosaurian tooth counts cannot be separated into discrete categories for the purposes of character-state coding. In any event, Glaucosaurus megalops possesses fewer marginal teeth than Edaphosaurus. The second problematical character, the presence of an ectepicondylar foramen (Romer and Price, 1940; Reisz 1986), can be determined only in E. boanerges and E. pogonias. Edaphosaurus boanerges , E. cruciger , and E. pogonias form a clade, with the latter two species being more closely related to each other than either is to E. boanerges. Romer and Price (1940) suggested tentatively that these species may have formed a species phylum, since E. cruciger appears to replace E. boanerges , and E. pogonias in turn appears to replace E. cruciger in regular succession in the Wichita and Clear Fork deposits; the sequence would be among the earliest of examples of anagenesis in Amniota. However, the Texan edaphosaurids demonstrably do not form a species phylum, as each possesses at least a single autapomorphy. Edaphosaurus pogonias is distinguished among Permo-Carboniferous synapsids in possessing two spade-like dorsal processes on the ilium. Its sister taxon E. cruciger is distinguished by one autapomorphy, the anterior margins of the clavicular plate and the clavicular stalk describe a distinct angle in anteroventral view (personal observation of AMNH 4060); the same edges on the clavicles of the other species of Edaphosaurus form a continuous, concave margin. Edaphosaurus boanerges possesses two autapomorphies : ( 1 ) the palatal tooth plates of this species possess 20-50 per cent, more teeth than those of other Edaphosaurus species for which tooth-plate tooth counts can be determined; and (2) the jaw symphysis is deeply excavated dorsally. However, these autapomorphies are currently ambiguous, because these characters are indeterminable in the single skull assigned to E. cruciger. Diet and feeding system The superb quality of the E. boanerges cranial material warrants a re-examination of the adaptation to herbivory that has long been attributed to Edaphosaurus. Although the genus possesses many features that are shared with other early herbivores, Williston (1914) had misgivings that Edaphosaurus was herbivorous, and later postulated a diet of (unspecified) invertebrates (Williston 1916). Case (1918) believed that the morphological evidence available at the time was equivocal, and considered Edaphosaurus to have been either exclusively molluscivorous or exclusively herbivorous. Both hypotheses were prompted by the presence of tooth plates on the palate and the inner aspect of the mandible. Romer and Price (1940) concurred with Case's (1918) second hypothesis, remarking that fossils of freshwater molluscs are absent from the terrestrial deposits that have produced Edaphosaurus specimens, and added that a large, barrel-shaped rib cage is found only in herbivorous reptiles. However, the adaptation to herbivory in Edaphosaurus has been questioned recently (Munk and Sues 1993), and it is therefore necessary to review the evidence supporting the hypothesis of herbivory in this genus. In addition to the presence of the tooth plate dental batteries and the barrel-shaped body, there are several other, non-dental features mentioned briefly by Romer and Price (1940) and subsequent authors (Olson 1986; Reisz 1986) that lend support to the herbivory hypothesis, largely because they are found also in other herbivorous forms and are not present in carnivorous taxa. These include small skull size, isodonty, reduced marginal tooth number, the abbreviated antorbital region, enlarged temporal fenestrae, the ventral offsetting of the jaw suspension, and antorbital buttressing. The last two features suggest clearly that the preferred food was tougher and more resistant than that utilized by other eupelycosaurian taxa of similar skull size. With the exception of isodonty, the morphology of the marginal tooth series of Edaphosaurus has been ignored completely when the hypothesis of herbivory is considered. Although dental 232 PALAEONTOLOGY, VOLUME 38 morphology is the foremost indicator of probable diet in fossil tetrapods, the evidence for edaphosaurid herbivory provided by tooth plate morphology has overshadowed that of the marginal dentition. This is unusual, given that well preserved maxillary teeth from the Briar Creek Bonebed were figured and described briefly by Williston (1916). However, the marginal teeth of Edaphosaurus were described by Romer and Price (1940) as slightly bulbous pegs, and hence were considered unremarkable. The Geraldine material reveals that marginal teeth of Edaphosaurus have several features that are consistent with a diet of terrestrial plant foliage. Notably, cutting edges are present on the marginal teeth, and they are inclined obliquely with respect to the long axis of the tooth row. Although this feature is found in some carnivorous reptiles (Molnar and Farlow 1990) as well as in many herbivorous ones, the marginal teeth of Edaphosaurus widen slightly before tapering to form distinctive shoulders, a trait that is never observed in the teeth of carnivorous types (Galton 1986). Furthermore, the cutting edges of unworn teeth bear fine, oblique serrations that are emphasized by grooves on the lingual surfaces of the teeth. The oblique orientation of the grooves suggests that the serrations here are strikingly similar to those found in other herbivorous reptiles, which are directed more-or-less apically, rather than those of carnivorous reptiles, which are invariably perpendicular to the cutting edge of the teeth (Galton 1986). Interestingly, many of the mature teeth in Edaphosaurus have lost their serrations, which suggests that the preferred food was highly abrasive and possibly siliceous. The general morphology of the tooth plates is relatively well known (Romer and Price 1940; Modesto and Reisz 1992), and the hypothesis that the plates served to crush food has not been disputed. Romer and Price (1940) observed that the articular facet of the articular was longer antero-posteriorly than that of the quadrate, and suggested that propaliny was probably present. However, they did not elaborate on the subject. The cranial materials described here suggest that propalinal movement of the mandible was a necessary component to the grinding action of the tooth plates. Further evidence for propalinal movement of the jaws comes from additional morphology of the jaw suspension, the orientation of the tooth plates with respect to the jaw suspension, and palatal tooth wear. The strongest evidence for fore-and-aft jaw movement is suggested by the nature of the contact between the quadrate and the articular. The condylar portion of the former is modified from the bicondylar type characteristic of other eupelycosaurs: instead of two parasagittally-aligned, elongate condyles, there is a single, broad, saddle-shaped articulating surface. The trough of the quadrate condyle sat in tongue-and-groove fashion over the antero- posterior ridge that bisects the opposing articulating facet on the articular. As noted by Romer and Price (1940), the articular was clearly capable of anlero-posterior translation relative to the quadrate since its articulating facet is approximately 50 per cent, longer antero-posteriorly than that of the quadrate; the overall antero-posterior range of movement appears to have been no more than about 8 mm, or approximately 7 per cent, of the antero-posterior length of the mandible. The long axes of the palatal and mandibular tooth plates are roughly parallel to the plane of articulation between the articular and the quadrate in medial view (Text-figs 2, 17), whereas those of the marginal tooth rows are set at an angle to the axis of translation. This suggests that propaliny was associated with the requirement for an efficient grinding mechanism, and evidence from palatal tooth wear supports this postulate. The tips of most well-preserved tooth plate teeth display oblique bevelling of their lateral and medial surfaces; bevelling of the anterior or posterior surfaces of tooth plate teeth, which would be expected to be equally common if plate occlusion was strictly orthal, is less frequent. An SEM study of tooth plate teeth referable to E. hoanerges (Olson et al. 1991) suggests strongly that the wear was induced by propalinal tooth plate movement. Propalinal jaw action may also have been responsible for the wear seen on the lingual surfaces of the marginal teeth. The bevelling present on the ventral surfaces of the recumbent, posterior maxillary teeth must have resulted from the opposing dentary teeth sliding antero-posteriorly beneath them; it is unlikely that such uniform wear was incurred during orthal occlusion. Since the above-mentioned morphological evidence is identifiable in cranial material of all members of the genus (where preserved), propaliny can be considered an adaptation uniting the species of Edaphosaurus. MODESTO: PERMIAN SYNAPSID 233 The jaw musculature must have been arranged appropriately in Edaphosaurus in order to effect fore-and-aft movement of the mandibles. The temporal fenestra is antero-posteriorly expanded, suggesting that posterior fibres of the jaw adductor muscles were inclined at roughly 45° relative to the long axis of the mandible, and therefore may have served to draw the mandible posteriorly. The anterior pterygoideus muscle, originating from the dorsal surface of the large palatal tooth plate, probably served to pull the mandible anteriorly. A similar arrangement is hypothesized to power propalinal jaw movement in dicynodonts (Crompton and Hotton 1967; King et al. 1989). Interestingly, propalinal jaw movement may have been assisted by a posteriorly-directed muscle attaching to the vertical keel of the angular. The posterior third of the keel is thickened and crenulated, suggesting that it may have served for muscular attachment. The strong evidence for propalinal jaw movement, and its requirement for suitably orientated muscles to power the propalinal jaw stroke, suggests that this may have been the case. Such a peculiar muscular arrangement was suggested also for dinocephalian therapsids, although the hypothetical muscle was considered to assist only in abducting the mandible (Kemp 1982). Lastly, the peculiar arrangement of the marginal tooth rows, due to the twisting of the alveolar ridges of the maxilla and dentary in all species of Edaphosaurus , is an unusual development among Palaeozoic tetrapods; there are no extant analogues that may suggest a reason for such a remarkable condition. What is noteworthy is that the orientation of the marginal teeth alters immediately anterior to the tooth plates, which implies that only the marginal teeth anterior to the tooth plates could function effectively to crop small pieces from food items; the recumbent marginal teeth adjacent to the plates could not take part in cropping actions, as their tips would not be able to slide past their fellows in the opposing dentition. These recumbent maxillary and dentary teeth may have added respectively their lingual and labial surfaces to the total area of the neighbouring tooth plates, as the lingual surfaces of well preserved procumbent marginal teeth display wear suggestive of such contact. However, since the long axes of the marginal tooth rows are positioned at an angle to the axis of propalinal movement, the posterior marginal teeth would only have been able to occlude at the end of the forward translation of the mandible during propalinal jaw movement, as the upper and lower tooth rows would have been drawn apart when the mandible moved posteriorly. Their contribution to the grinding phase of food processing, however, would have been minor compared to that of the tooth plate dentition. Nevertheless, the division in function between the anterior and posterior regions of the marginal tooth rows in this early amniote genus is quite remarkable. Marginal tooth morphology, tooth plate organization, the evidence for propaliny, and the suite of non-dental features which are shared with known herbivorous reptiles form a character complex that strongly supports the hypothesis of herbivory in Edaphosaurus. The feeding system of this genus appears to be the most specialized of the early Permo-Carboniferous synapsids. Food processing appears to have been comprised of two distinct steps: ( 1 ) the anterior marginal dentition served to section bite-sized pieces from terrestrial plants; and (2) the tooth plates served to pulverize the food via propalinal jaw action. Grinding presumably prepared the food for fermentative digestion. Among other Palaeozoic tetrapods, compelling evidence for propalinal jaw action has been presented only for dicynodonts, which appear much later in the Upper Permian (King et al. 1989). Edaphosaurus , therefore, is the oldest amniote known to have been capable of fore-and-aft translation of the mandible. Perhaps more importantly, Edaphosaurus is further distinguished as the oldest known amniote to exhibit a dual-purpose, two-step feeding system. Such partitioning of function in the oral region is not seen elsewhere in amniotes until cynodont therapsids appear at the close of the Permian (Kemp 1982). Acknowledgements. I am greatly indebted to Dr Farish Jenkins and Mr Charles Schaff (Museum of Comparative Zoology), Dr Eugene Gaffney (American Museum of Natural History), and Dr Hans-Dieter Sues and Mr Kevin Seymour (Royal Ontario Museum) for both the loan of the specimens and their assistance during my visits to their institutions. Dr John Bolt (Chicago Field Museum) kindly arranged the loan of 234 PALAEONTOLOGY. VOLUME 38 additional specimens. Thanks must go also to Drs Darryl Gwynne, Roger Hansell, Christopher McGowan, and Mr Michael deBraga for reviewing earlier drafts. Ms Diane Scott provided technical assistance. A hearty handshake goes to Dr Robert R. Reisz, at whose suggestion this study was undertaken, for unflagging encouragement and enthusiasm, and for critically reading the manuscript. REFERENCES berman, d. s 1979. Edaphosawus (Reptilia, Pelycosauria) from the Lower Permian of northeastern United States, with description of a new species. Annals of the Carnegie Museum , 48, 185-202. — and reisz, r. r. 1982. Restudy of Mycterosaurus longiceps (Reptilia, Pelycosauria) from the Lower Permian of Texas. Annals of the Carnegie Museum , 51, 423-453. brinkman, d. b. and eberth, d. a. 1983. The interrelationships of pelycosaurs. Breviora, 473, 1-35. broom, r. 1910. A comparison of the Permian reptiles of North America with those of South Africa. Bulletin of the American Museum of Natural History , 28, 197-234. carroll, r. l. 1988. Vertebrate paleontology and evolution. W. H. Freeman and Co., New York, 698 pp. case, e. c. 1906. On the skull of Edaphosaurus pogonias Cope. Bulletin of the American Museum of Natural History , 22. 19-26. — 1907. Revision of the Pelycosauria of North America. Carnegie Institution of Washington, Publication, 55, 1-176. — 1918. A mounted skeleton of Edaphosaurus cruciger Cope, in the geological collection of the University of Michigan. Occasional Papers of the Museum of Zoology, University of Michigan, 62, 1-8. cope, e. d. 1882. Third Contribution to the history of the Vertebrata of the Permian Formation of Texas. Proceedings of the American Philosophical Society, 20, 447-461. Crompton, a. w. and hotton III, n. 1967. Functional morphology of the masticatory apparatus of two dicynodonts (Reptilia, Therapsida). Postilla, 109, 1-51. eberth, d. a. 1985. The skull of Sphenacodon ferocior , and comparisons with other sphenacodontines (Reptilia, Pelycosauria). Circular of the New Mexico Bureau of Mines and Mineral Resources, 190, 1-39. galton, p. m. 1986. Herbivorous adaptations of Late Triassic and Early Jurassic dinosaurs. 203-221. In k. padian (ed ). The beginning of the age of dinosaurs. Cambridge University Press, Cambridge, 378 pp. hentz, T. F. 1988. Lithostratigraphy and paleoenvironments of upper Paleozoic red beds, North-Central Texas: Bowie (new) and Wichita (revised) Groups. University of Texas, Austin, Bureau of Economic Geology Report of Investigations, 17, 1-55. kemp, t. s. 1982. Mammal-like reptiles and the origin of mammals. Academic Press, London, 363 pp. king, g. m., oelofsen, b. w. and rubidge, b. s. 1989. The evolution of the dicynodont feeding system. Zoological Journal of the Linnean Society , 96, 185-211 laurin, m. 1993. Anatomy and relationships of Haptodus garnettensis, a Pennsylvanian synapsid from Kansas. Journal of Vertebrate Paleontology , 13, 200-229. — and reisz, R. r. 1990. Tetraceratops is the oldest known therapsid. Nature , 345, 249-250. modesto, s. p. 1992. Did herbivory foster early amniote diversification? Journal of Vertebrate Paleontology, Abstracts, 1 1, 49A. 1994. The Lower Permian synapsid Glaucosaurus from Texas. Palaeontology, 37, 51-60. — and reisz, R. r. 1990. A new skeleton of Ianthasaurus hardestii, a primitive edaphosaur (Synapsida: Pelycosauria) from the Upper Pennsylvanian of Kansas. Canadian Journal of Earth Sciences, 27, 834—844. 1992. Restudy of Permo-Carboniferous synapsid Edaphosaurus novomexicanus Williston and Case, the oldest known herbivorous amniote. Canadian Journal of Earth Sciences, 29, 2653-2662. molnar, r. e. and farlow, j. o. 1990. Carnosaur paleobiology. 210-224. In weishampel, d. b., dodson, p. and osmolska, H. (eds). The Dinosauria. University of California Press, Berkeley, 773 pp. munk, m. and sues, h.-d. 1993. Gut contents of Parasaurus (Pareiasauria) and Protorosaurus (Archosauro- morpha) from the Kupferschiefer (Upper Permian) of Hessen, Germany. Paldontologische Zeitschrift, 67, 169-176. olson, E. c. 1986. Relationships and ecology of the early therapsids and their predecessors. 47-60. In hotton HI, N., mclean, p. D., roth, J. J. and roth, E. c. (eds). The ecology and biology of mammal-like reptiles. Smithsonian Institution Press, Washington, 326 pp. — hotton III, n. and beerbower, j. r. 1991. Wear of tetrapod teeth as indication of Lower Permian herbivory. Journal of Vertebrate Paleontology Abstracts, 11, 49A. osborn, h. f. 1903. On the primary division of the Reptilia into two subclasses, Synapsida and Diapsida. Science, 17, 275-276. MODESTO: PERMIAN SYNAPSID 235 reisz, r. r. 1986. Pelycosauria. In wellnhofer, f. (ed.). Handbuch der Paldoherpetologie, Teil 17A. Gustav Fischer Verlag, Stuttgart, 102 pp. — and berman, D. s. 1986. lanthasaurus hardestii n. sp., a primitive edaphosaur (Reptilia, Pelycosauria) from the Upper Pennsylvanian Rock Lake Shale near Garnett, Kansas. Canadian Journal of Earth Sciences , 23, 77-91. — and scott, d. 1992. The cranial anatomy of Secodontosaurus, an unusual mammal-like reptile (Synapsida: Sphenacodontidae) from the early Permian of Texas. Zoological Journal of the Linnean Society, 104, 127-184. romer, a. s. and price, l. i. 1940. Review of the Pelycosauria. Geological Society of America, Special Paper, 28, 1-538. rowe, T. 1988. Definition, diagnosis, and origin of Mammalia. Journal of Vertebrate Paleontology, 8, 241-264. sander, p. M. 1987. Taphonomy of the Lower Permian Geraldine Bonebed in Archer County, Texas. Pcdaeo geography , Palaeoclimatology, Palaeoecology , 61, 221-236. watson, D. m. s. 1916. Reconstructions of the skulls of three pelycosaurs in the American Museum of Natural History. Bulletin of the American Museum of Natural History, 35, 637-648. williston, s. w. 1914. The osteology of some American Permian vertebrates. I. Contributions from Walker Museum, 1, 107-162. — 1916. Synopsis of the American Permo-Carboniferous Tetrapoda. Contributions from Walker Museum, 1, 193-236. S. P. MODESTO Department of Zoology, Erindale College Typescript received 3 May 1994 University of Toronto, Mississauga Revised typescript received 26 September 1994 Ontario, Canada L5L 1C6 ABBREVIATIONS USED IN THE TEXT-FIGURES ac anterior coronoid Pf postfrontal an angular Pi palatine ana atlantal neural arch po postorbital ar articular pop paroccipital process ar/ss sutural surface for articular pra prearticular bcr basicranial recess pra/ss sutural surface for prearticular bo basioccipital prf prefrontal bpt basipterygoid process prm premaxilla bps basiparasphenoid pro prootic cu cultriform process Pt pterygoid d dentary q quadrate ds dorsum sella qfl quadrate flange of pterygoid ec ectopterygoid qj quadratojugal eo exoccipital s stapes ep epipterygoid sa surangular f frontal sa/ss sutural surface for surangular fo fenestra ovalis srn septomaxilla icf internal carotid foramen so supraoccipital j jugal sp splenial 1 lacrimal sq squamosal Ipso lateral process of supraoccipital St supratemporal m maxilla t tabular mj medial process of jugal t/ss sutural surface for tabular n nasal v vomer op opisthotic vp prf ventral process of prefrontal P parietal vf op ventral flange of opisthotic pc posterior coronoid 236 PALAEONTOLOGY, VOLUME 38 APPENDIX 1 Description of characters used in the analysis. Characters are listed in order of their location on the skull, the mandible, and the postcranial skeleton. 1. Marginal teeth: taper gradually (0) or are slightly bulbous (1). The marginal teeth of all Edaphosaurus species are slightly swollen distally. The teeth of the outgroup taxa taper gradually to their distal tips, and represent the plesiomorphic condition. 2. Marginal teeth : cutting edges are absent (0) or present ( 1 ) on mesial and distal surfaces. The marginal teeth of the Texan species of Edaphosaurus feature cutting edges on their mesial and distal surfaces. This character is indeterminable in E. novomexicanus. No cutting edges are present on the teeth of the outgroup taxa. 3. Premaxillary dentition: larger than (0) or equal to or smaller than (1) the maxillary teeth in basal cross- section. On the basis of basal cross-sectional diameter, the premaxillary teeth are roughly equal to the maxillary teeth in size in both Glaucosaurus and Edaphosaurus. Because premaxillary teeth are unknown in Ianthasaurus , this character may diagnose Edaphosauridae. The presence of premaxillary teeth larger than maxillary teeth (except caniniforms) is primitive for eupelycosaurs. 4. Caniniform region: present (0) or absent (1). Neither Glaucosaurus nor Edaphosaurus possesses a caniniform region. Accordingly, the presence of a caniniform region is the primitive condition. 5. Caniniform tooth: absent (0) or present (1). There is no caniniform tooth in either Glaucosaurus or Edaphosaurus. The presence of a caniniform represents the primitive condition for edaphosaurids. 6. Maxilla: long, extends past orbit (0) or short, does not extend beyond posterior orbital margin (1). The derived condition diagnoses here the clade of Edaphosauridae plus Sphenacodontia. The long maxilla of Glaucosaurus is a reversal (Modesto 1994). 7. Maxillary and dentary alveolar ridges: straight (0) or twisted (1). The alveolar ridges of the maxillae and dentaries of all members of Edaphosaurus are twisted such that the orientation of the marginal dentition becomes laterally directed as one progresses posteriorly. The marginal teeth of the outgroup taxa are vertically directed, representing the primitive condition. 8. Prefrontal : ventral process tongue-like (0) or expanded medially ( 1 ). In Glaucosaurus and Edaphosaurus the ventral process of the prefrontal is greatly expanded medially, forming most of the antorbital buttress that characterizes both taxa. The presence of a prefrontal ventral process that is transversely slender is plesiomorphic. 9. Frontal: lateral lappet broad, antero-posterior width no less than one-quarter frontal sagittal length (0) or narrow, antero-posterior width no less than one-ninth frontal sagittal length (1). The lateral lappet of the frontal is remarkably slender in the Texan edaphosaurids, displaying an antero-posterior width approximately one-ninth the sagittal length of the frontal. The lateral lappet of Haptodus has an antero- posterior width roughly one-fifth the length of the frontal, whereas the same figure for the edaphosaurids Edaphosaurus novomexicanus and Ianthasaurus is approximately one-quarter. Although varanopseids are not considered to possess a lateral lappet (Brinkman and Eberth 1983), the frontal of Mycterosaurus has a broad contribution to the orbital rim. This character cannot be determined in Glaucosaurus. 10. Supraorbital margin : weakly developed, interorbital width less than frontal sagittal length (0) or expanded laterally, interorbital width 50 per cent, greater than frontal sagittal length (1). The supraorbital margin of Edaphosaurus is a broad shelf formed by the prefrontal, frontal, and postfrontal. The transverse breadth of the supraorbital margin is roughly 75 per cent, of the antero-posterior length of the frontal, and, accordingly, the orbits are concealed in dorsal view. The supraorbital margins are weakly developed or absent in the other genera, their transverse breadth lying between 26 per cent, and 46 per cent, of the sagittal length of the frontal, and the orbits are clearly visible in dorsal view. 1 1. Parietal: lateral margin roughly straight or convex (0) or deeply concave (1) in dorsal aspect. The lateral edge of the parietal is deeply embayed in dorsal aspect in all species of Edaphosaurus. In Ianthasaurus , Haptodus , and Mycterosaurus the lateral margin of the parietal is straight to markedly convex, interpreted here as a plesiomorphy. 12. Postorbital: contacts (0) or separate from (1) squamosal. The postorbital posterodorsal process in E. boanerges , E. cruciger and E. pogonias is short and does not contact the squamosal. Since the state of this character cannot be determined in either E. novomexicanus or Glaucosaurus , it may diagnose a more inclusive node with Edaphosauridae. The outgroup taxa are plesiomorphic in that the postorbital contacts the squamosal. MODESTO: PERMIAN SYNAPSID 237 13. Quadratojugal : large and forms ventral margin of posterior cheek (0) or small and covered laterally by squamosal ( 1 ). The derived state diagnoses the clade of Edaphosauridae plus Sphenacodontia (sensu Reisz et al. 1992). This character cannot be determined in Glaucosaurus. 14. Quadrate: condyles distinct, separate (0) or confluent, forming a saddle-shaped articulating facet (1). The articulating surface of the quadrate is a single, broad articulating surface that is yoke-shaped in posterior aspect in all Edaphosaurus species. Two elongate, rounded ridges present as condyles represents the primitive condition. 15. Jaw suspension: at level of (0) or offset ventrally from (1) maxillary tooth row. In all species of Edaphosaurus the jaw suspension is positioned far below the level of the upper tooth row. This is easily demonstrated as a ratio between the distance the jaw suspension lies ventral to the longitudinal axis of the upper marginal tooth row and the length of the cheek (taken along the longitudinal axis of the upper tooth row). In Edaphosaurus this figure is approximately 29 per cent. The jaw suspensions of the other genera are primitive in that they lie slightly below the longitudinal axes of their respective upper tooth rows, with a jaw suspension depth falling between 3 per cent, and 12 per cent, of the length of the cheek. 16. Skull: long, eight dorsal centra or more in length (0), or short, five dorsal centra or less in length (1 ). The skulls of all Edaphosaurus species are relatively short, being less than five dorsal centra in length. The skulls of lanthasaurus and the outgroup taxa are at least eight dorsal centra in length ; relatively long skulls are therefore primitive. 17. Postorbital region: shorter than (0) or equal to or longer than (1) antorbital region. In all species of Edaphosaurus , the antero-posterior length of the postorbital region of the skull is equal to, or even marginally greater than, the antorbital length. The postorbital regions of lanthasaurus , Haptodus, and Mycterosaurus are less than half the length of their respective antorbital regions. A postorbital region that is shorter than antorbital length is a plesiomorphy of eupelycosaurs. 18. Pterygoid: transverse flange present (0) or absent (1). A transverse flange is absent from the pterygoid in Glaucosaurus and Edaphosaurus. Because the palate is unknown for lanthasaurus , this character may diagnose Edaphosauridae. The presence of a transverse pterygoid flange is plesiomorphic for eupelycosaurs. 19. Tooth plates: absent (0) or present (1). Edaphosaurus novomexicanus possesses palatal tooth plates that undoubtedly contacted similar plates on the mandibles. Palatal and mandibular tooth plates are present in E. boanerges , E. cruciger , and E. pogonias. The palatal plate is formed by the palatine, ectopterygoid and the pterygoid, whereas the mandibular tooth plate is formed by the anterior and posterior coronoids, and the prearticular. Tooth plates are not present in the outgroup taxa; the absence of tooth plates is the primitive condition for eupelycosaurs. 20. Mandible: dorso-ventral height one-quarter or less (0) or one-third or greater (1) total length. The mandibles of the three Texan edaphosaurs are relatively deep, with a height no less than one-third the total length of the mandible. In contrast, those of lanthasaurus , Mycterosaurus and Haptodus are relatively slender, with a height equal to or less than one-quarter the total length of the mandible. Since the posterior ends of both the skull and the mandible are absent in Glaucosaurus , the character state cannot be determined for this taxon. The mandible is unknown in E. novomexicanus. 21. Dentary: comprises 70 per cent, or more (0) or 66 per cent, or less (1) of the mandibular antero-posterior length. The dentaries of Edaphosaurus cruciger and E. pogonias are 66 per cent, and 63 per cent, of the total length of the mandible, respectively. The dentary of E. boanerges is about 70 per cent, of the length of the mandible, and this figure in Haptodus and Mycterosaurus is roughly 80 per cent. The mandibles of lanthasaurus and Glaucosaurus are inadequately known, but resemble more closely those of carnivorous eupelycosaurs. The presence of a dentary that is more than two-thirds the length of the mandible represents the primitive condition for Edaphosaurus. 22. Splenial: lateral exposure one-fifth or less (0) or one-third or more (1) the height of the anterior end of the mandible. The splenial is deep and occupies the lower one-third of the anterior end of the mandible in lateral view in those species of Edaphosaurus for which mandibular material is available. In contrast, the splenial has only a slender, antero-posteriorly elongate lateral exposure in the outgroup taxa. 23. Cervical centra: equal to or longer than (0) or shorter than (1) mid-dorsal centra. The cervical centra are notably shorter than those of the dorsal centra in Edaphosaurus. In contrast, the cervical vertebrae are slightly longer antero-posteriorly than the dorsal vertebrae in lanthasaurus (Reisz and Berman 1986). The cervicals and dorsal are approximately equal in length in Haptodus and Mycterosaurus. The character state for this and the following characters cannot be determined in Glaucosaurus. 24. Presacral neural spines : short (0), or long, more than five times the height of the centrum ( 1 ). The presacral neural spines are greatly elongated in all edaphosaurid taxa for which postcrania is available. In the 238 PALAEONTOLOGY, VOLUME 38 outgroup taxa, neural spines are always less than five times the height of the centrum. Other Permo- Carboniferous synapsids feature greatly elongate neural spines, but these have evolved independently (Reisz et al. 1992). 25. Presacral neural spines : laterally compressed (0) or subcircular ( 1 ) in distal cross section. Except for a short basal portion which is expanded slightly antero-posteriorly, the presacral neural spines of Ianthasaurus and Edaphosaurus are subcircular in distal cross-section. The presence of blade-like neural spines is primitive for eupelycosaurian synapsids. 26. Presacral neural spines: lateral tubercles absent (0), present and moderately developed (1), present and gall-like (2). The elongate neural spines of the presacral vertebrae of Ianthasaurus and Edaphosaurus feature laterally-directed processes. Swollen, gall-like tips are present on many of the tubercles of both E. cruciger and E. pogonias. The lateral surfaces of the presacral neural spines of the outgroup taxa are devoid of processes, and represent the plesiomorphic condition. 27. Presacral neural spines: anterior spines are slender (0) or club-shaped (1). The distal ends of the neural spines of the anterior presacral vertebrae of E. cruciger and E. pogonias are slightly thickened laterally and expanded antero-posteriorly to twice the basal diameter of the subcircular portion of the spine. The expansion is so great that the spines resemble pegged clubs. Romer and Price ( 1 940) report a definite, albeit slight, sagittal expansion of the cervical spines of E. boanerges, but clearly not to the extent seen in the other Texan species. 28. Neural arches: excavated (0) or not excavated (1). The neural arches of all Edaphosaurus species do not display the shallow excavations present in those of Ianthasaurus , Haptodus, or Mycterosaurus. The presence of excavations on neural arches is plesiomorphic for eupelycosaurs. 29. Dorsal vertebrae: transverse processes moderately developed (0) or elongate (1). The transverse processes of the presacral vertebrae of Edaphosaurus are elongate. The transverse processes of the outgroup taxa are relatively short transversely, and represent the primitive condition for eupelycosaurs. 30. Sacral and caudal vertebrae: neural spine tips smoothly finished (0) or rugose (1). The distal tips of the sacral and caudal neural spines in Edaphosaurus are roughened with crenulated edges. The tips of the sacral and caudal neural spines in Ianthasaurus , Haptodus , and Mycterosaurus are plesiomorphic in that they are smoothly finished. 31. Sacral and caudal vertebrae: neural spines smooth-sided (0) or with longitudinal ridges (1). The lateral surfaces of the sacral and caudal neural spines of Edaphosaurus feature rough, longitudinal ridges. The lateral surfaces of the caudal neural spines of Ianthasaurus, Haptodus, and Mycterosaurus are plesiomorphic in that they are smoothly finished. 32. Caudal vertebrae: neural spines are rectangular in lateral aspect (0) or expanded sagittally (1). The distal ends of the caudal neural spines of Edaphosaurus are expanded antero-posteriorly. The caudal neural spine tips of Ianthasaurus, Haptodus, and Mycterosaurus are plesiomorphic in that they are squared in lateral aspect. 33. Caudal vertebrae : neural spines are short and squared (0) or tall and pointed ( 1 ) in lateral aspect. The distal tips of the caudal neural spines of all Edaphosaurus species are tall (at least twice the height of the neural arch proper) and taper to pointed tips. The neural spines of Ianthasaurus, Haptodus, and Mycterosaurus are plesiomorphic in that distally they are squared in lateral aspect, and are never taller than their respective pedicels. 34. Dorsal ribs: curved proximally only (0) or curved throughout length (1). The dorsal ribs of all species of Edaphosaurus are strongly curved throughout their length. Only the proximal regions of the dorsal ribs of Ianthasaurus, Haptodus, and Mycterosaurus are strongly curved ; the distal parts of the ribs are only slightly bowed. 35. Dorsal ribs: tubercula well developed, flange-like (0) or reduced to low tuberosities (1). The tubercular heads of the dorsal ribs of all species of Edaphosaurus are present only as small rugosities. The tubercular heads of the dorsal ribs of Ianthasaurus, Haptodus, and Mycterosaurus are normally developed as prominent projections of bone, representing the primitive condition for eupelycosaurs. 36. Ilium: anterodorsal process smaller than posterodorsal process and convex in lateral view (0) or equal to posterodorsal process in size and triangular in lateral view (1). The ilia of the Texan edaphosaurids have triangular, spade-like anterodorsal processes that equal the posterodorsal processes in size. The iliac anterodorsal processes of Ianthasaurus, Haptodus, and Mycterosaurus are low and convex in lateral aspect, and never approach the size of the posterodorsal processes. MODESTO: PERMIAN SYNAPSID 239 APPENDIX 2 Distribution of the character states among the eight taxa examined in the analysis. The numbers in the top column (1-36) refer to the characters described in Appendix 1. A question mark indicates that the character state could not be determined because of missing data. Character number Taxon Mycterosaurus Haptodus Ianthasaurus Glaucosaurus E. novomexicanus E. boanerges E. cruciger E. pogonias Character FS48 number Taxon Mycterosaurus Haptodus Ianthasaurus Glaucosaurus E. novomexicanus E. boanerges E. cruciger E. pogonias 12 3 4 5 6 0 0 0 0 0 0 0 0 0 0 0 1 0 0 7 0 0 1 0 0 1110 17 7 111 111111 117 111 1 1 I 1 I 1 1 2 2 2 2 2 9 0 12 3 4 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 7 0 1 0 7 7 0 7 ? 1 7 7 7 11 110 111 111111 111111 1 1 1 7 8 9 0 12 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 17 0 7 ? 1 1 0 1 1 7 111111 I 1 1 I 1 1 1 I 1 I 1 1 2 2 2 2 2 3 5 6 7 8 9 0 0 0 0 0 0 0 0 0 0 0 0 0 I 10 0 0 0 ?????? 110 111 110 111 12 1111 12 1111 I 1 1 I 1 I 3 4 5 6 7 8 0 0 0 0 0 0 I 0 0 0 0 0 17 0 0 0 ? 7 7 7 7 7 1 111111 I 1 1 I 1 1 111111 111111 3 3 3 3 3 3 12 3 4 5 6 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 ?????? 11111? 111111 1 I 1 1 I 1 111111 NOTES FOR AUTHORS The journal Palaeontology is devoted to the publication of papers on all aspects of palaeontology. 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Published by Longman in collaboration with the Palaeontological Association, xiii +241 pp. Price £13-95. Available in the USA from Halsted Press at U.S. $24-95. © The Palaeontological Association, 1995 Palaeontology VOLUME 38 -PART 1 CONTENTS The origin of algal-bivalve photo-symbiosis TERUFUMI OHNO, TETZUYA KATOH CUld TERUFUMI YAMASU 1 The Tethyan bivalve Roudairia from the Upper Cretaceous of California M. X. KIRBY and L. R. SAUL 23 A new plourdosteid arthrodire from the Upper Devonian Gogo Formation of Western Australia JOHN A. LONG 39 Decapods in ammonite shells: examples of inquilinism from the Jurassic of England and Germany R. FRAAYE and M. JAGER 63 Discontinuity in the Plio-Pleistocene Eurasian water vole lineage D. NERAUDEAU, L. VIRIOT, J. CHALINE, B. LAURIN and T. VAN KOLFSCHOTEN 77 Composition and distribution of the inoceramid bivalve genus Anopaea J. A. CRAME and S. R. A. KELLY 87 Decay and fossilization of non-mineralized tissue in coleoid cephalopods AMANDA J. KEAR, DEREK E. G. BRIGGS and DESMOND T. DONOVAN 105 A new palaeontological technique describing temporal shape variation in Miocene bivalves TRACY A. GLASSBURN 133 The ultrastructure of spores of Cooksonia pertoni D. EDWARDS, K. L. DAVIES, J. B. RICHARDSON and L. AXE 153 Lower Devonian biostratigraphy and vertebrates of the Tong Vai valley, Vietnam TONG-DZUY THANH, P. JANVIER, TA HOA PHUONG and DOAN NHAT TRUONG 169 The Early Cretaceous brachiosaurid dinosaurs Ornithopsis and Eucamerotus from the Isle of Wight, England WILLIAM T. BLOWS 187 A new diapsid reptile from the uppermost Carboniferous (Stephanian) of Kansas MICHAEL deBRAGA and ROBERT R. REISZ 199 The skull of the herbivorous synapsid Edaphosaurus boanerges from the Lower Permian of Texas S. P. MODESTO 213 Printed in Great Britain at the University Press, Cambridge ISSN 0031-0239 VOLUME 38 • PART 2 • JULY 1995 Published by The Palaeontological Association • London Price £45-00 THE PALAEONTOLOGICAL ASSOCIATION (Registered Charity No. 276369) The Association was founded in 1957 to promote research in palaeontology and its allied sciences. COUNCIL 1995-1996 President : Dr R. A. Fortey, Department of Palaeontology, Natural History Museum, Cromwell Rd., London SW7 5DB Vice-Presidents'. Dr J. A. Crame, British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 OET Dr J. E. Dalingwater, School of Biological Sciences, Williamson Building, The University, Manchester Ml 3 9PL Treasurer: Dr T. J. Palmer, Institute of Earth Studies, University of Wales, Aberystwyth, Dyfed SY23 3DB Membership Treasurer: Dr M. J. Barker, Department of Geology, University of Portsmouth, Burnaby Road, Portsmouth POl 3QL Institutional Membership Treasurer : Dr J. E. Francis, Department of Earth Sciences, The University, Leeds LS2 9JJ Secretary: Dr M. P. Smith, School of Earth Sciences, University of Birmingham, Birmingham B15 2TT Newsletter Reporter: Dr S. Rigby, Department of Geology, University Road, Leicester LEI 7RH (co-opted) Marketing Manager: Dr L. Cherns, Department of Geology, University of Wales College of Cardiff CF1 3YE Publicity Officer: Dr P. A. Allison, P.R.I.S., The University, P.O. Box 227, Whiteknights, Reading RG6 2AB Newsletter Editor: Dr R. B. Rickards, Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ Editors Dr P. D. Lane, Department of Geology, University of Keele, Keele, Staffordshire ST5 5BG Dr P. Doyle, School of Earth Sciences, University of Greenwich, Brewhouse Lane, London El 9NU Dr A. R. Milner, Department of Biology, Birkbeck College, Malet Street, London WC1E 7HX Dr C. J. Cleal, Department of Botany, National Museum of Wales, Cardiff CF1 3NP Dr R. M. Owens, Department of Geology, National Museum of Wales, Cardiff CF1 3NP Dr B. M. Cox, British Geological Survey, Keyworth, Nottingham NG12 5GG Other Members: Dr A. King, English Nature, Northminster House, Peterborough PEI 1UA Dr C. V. Milsom, School of Biological and Earth Sciences, Liverpool John Moores University, Liverpool L3 3AF Dr M. Purnell, Department of Geology, University of Leicester, University Road, Leicester LEI 7RH Overseas Representatives Argentina: Dr M. O. Mancenido, Division Paleozoologia invertebrados, Facultad de Ciencias Naturales y Museo, Paseo del Bosque, 1900 La Plata. Australia: Dr K. J. McNamara, Western Australian Museum, Francis Street, Perth, Western Australia 6000. Canada: Professor S. H. Williams, Department of Earth Sciences, Memorial University, St John’s, Newfoundland A1B 3X5. China: Dr Chang Mee-mann, Institute of Vertebrate Palaeontology and Palaeoanthropology, Academia Sinica, P.O. Box 643, Beijing. Dr Rong Jia-yu, Nanjing Institute of Geology and Palaeontology, Chi-Ming-Ssu, Nanjing. France: Dr J.-L. Henry, Institut de Geologie, Universite de Rennes, Campus de Beaulieu, Avenue du General Leclerc, 35042 Rennes Cedex. Iberia: Professor F. Alvarez, Departamento de Geologia, Universidad de Oviedo, C /. Jesus Arias de Velasco, s/n. 33005 Oviedo, Spain. Japan : Dr I. Hayami, University Museum, University of Tokyo, Hongo 7-3-1, Tokyo. New Zealand: Dr R. A. Cooper, New Zealand Geological Survey, P.O. Box 30368, Lower Hutt. Scandinavia: Dr R. Bromley, Fredskowej 4, 2840 Holte, Denmark. USA: Professor A. J. Rowell, Department of Geology, University of Kansas, Lawrence, Kansas 66044. Professor N. M. Savage, Department of Geology, University of Oregon, Eugene, Oregon 97403. Professor M. A. Wilson, Department of Geology, College of Wooster, Wooster, Ohio 44961. Germany: Professor F. T. 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LATE CAMBRIAN AGNOSTOI D TRILOB ARGENTINA by JOHN H. SHERGOLD, OSVALDO BORDONARO and ELADIO LINAN Abstract. Late Cambrian agnostoid trilobites are described from an in situ locality near the base of the El Relincho Formation in Mendoza Province, northwestern Argentina, and from allochthonous blocks in the younger, Ordovician, Empozada and Los Sombreros Formations of Mendoza and neighbouring San Juan Provinces. The faunas of the olistolites fall into three age groups in terms of North American Late Cambrian biochronology: one Trempealeauan and two late Dresbachian assemblages are represented. Species occurring are compared with appropriate taxa from the USA, Canada and Australia. Species of Lotcignostus previously described by Rusconi are reassessed on the basis of replicas of the types and the present material. Precordilleran Argentina is a N-S elongated belt about 500 km in length situated between the Pampeanas Ranges to the east and the Cordillera de los Andes to the west. The region contains a fairly complete sequence of Cambrian rocks which have the most abundant and closely investigated trilobite biofacies in South America. These are distributed in two sedimentary environments: carbonate shelf to the east and continental slope to the west (Text-figs 1 -2). Cambrian trilobite biofacies follow this distribution: the endemic species inhabited the restricted carbonate shelf whilst the cosmopolitan species are found in the mixed talus facies interdigitating with the open shelf. STRATIGRAPHY The stratigraphy of the Cambrian carbonate shelf facies is well known though the work of Baldis and Bordonaro (1985) who studied a continuous sequence from the Lower Cambrian to Lower Ordovician. Currently, the stratigraphy of Cambrian slope facies is not well known because of abrupt facies changes, chaotic sedimentation and relatively poor palaeontological recovery. Text- figure 2 shows a stratigraphical synthesis of the Precordilleran Cambrian rocks. More data can be found in Bordonaro (1992). Late Cambrian agnostoid trilobites from the Precordillera of Mendoza Province were studied principally by Rusconi (1948, 1950a, 19506, 1951a, 19516, 1952, 1953, 1954, 1955a, 19556, 1955c), but many of his determinations are grossly erroneous. Partly as a result of inadequate illustration, much of his work is difficult to interpret. However, the material is extant and revision is possible, so that misleading biostratigraphical conclusions drawn from it may be corrected. Revised generic assignments have been made by Shergold (1977) and Shergold et al. (1990). The objective of the present paper is the description of new material from the classic Mendoza locality and from new localities discovered in Mendoza and San Juan. The agnostoids here described are from the Los Sombreros Formation (San Juan Province), Empozada Formation (Mendoza Province), and El Relincho Formation (Mendoza Province). The Los Sombreros Formation is a sequence of almost one thousand metres thickness cropping out on the eastern flank of the Tontal Range in the western Precordillera of San Juan. It is composed of a talus association of shale and thinly bedded limestone with olistolites, olistostromes, calcareous breccias and channelled conglomerates. The age is not known precisely, but it was probably deposited during the Ordovician, since it is common to find calcareous olistolites containing [Palaeontology, Vol. 38, Part 2, 1995, pp. 241-257, 3 pis] © The Palaeontological Association 242 PALAEONTOLOGY, VOLUME 38 text-fig. 1. Geographical and geological setting of the Cambrian rocks of Precordilleran Argentina. Material studied here is from localities OA, Ojos de Agua; LS, Los Sombreros; CP, Cerro Pelado; EM, Empozada. allochthonous Middle and Late Cambrian trilobites, and also autochthonous Early and Middle Ordovician graptolites in dark green shales (Cuerda et al. 1983). The Empozada Formation is about 300 m thick and crops out in the San Isidro area to the west of Mendoza city. It is composed mainly of black shales with abundant calcareous olistolites, breccias and sandstones. It contains allochthonous Late Cambrian trilobites which occur in dispersed calcareous blocks within the lower half of the unit. The age of deposition of the Empozada Formation is at least mid-Ordovician as indicated by the presence of the graptolites Nemagraptus gracilis (see Cuerda 1979) and Glossograptus hincksi. The El Relincho Formation is a unit composed mainly of limestone and black shale exposed in Cerro Pelado to the west of Mendoza city. The age of the base of this formation is Late Cambrian SHERGOLD ET AL.: AGNOSTOID TRILOBITES 243 EPOCH POLYMERIC TRILOBITE BIOZONES PRE&6ftbiLLERA LITHOLOGY Limestone Marl 1 1 Sandstone Dolomite Llmollte Conglomerate Oolitic Limestone Shale 1-*- “ Breccia text-fig. 2. Cambrian stratigraphy of Precordilleran Argentina. In the slope facies of the Los Sombreros Formation, beds containing the names of representative trilobite genera indicate allochthonous blocks. The asterisked names show the biostratigraphical position of the fossils studied against a basically North American timescale. 244 PALAEONTOLOGY, VOLUME 38 because conodonts belonging to the Proconodontus tenuiserratus Zone have been found (Heredia 1990). The top of the formation is not yet dated. SYSTEMATIC PALAEONTOLOGY All material used in this study is identified as the Bordonaro Collection and is deposited in the collections of the Departamento de Paleontologiga Invertebrados, Universidad Nacional de San Juan (PIUNSJ), Argentina. Descriptive terminology follows Harrington et al. (1959), with additional terms from Opik (1967), Shergold (1977), and Shergold et al. (1990). Order agnostida Salter, 1 864a Superfamily agnostoidea M’Coy 1849 Family agnostidae, M’Coy, 1849 Subfamily agnostinae, M’Coy, 1849 Genus lotagnostus Whitehouse, 1936 Subgenus lotagnostus Whitehouse, 1936 Type species. Agnostus trisectus Salter, 18646, p. 10, by original designation of Whitehouse, 1936, p. 101. Lotagnostus ( Lotagnostus ) peladensis (Rusconi, 1951a) Plate 1, figures 1-9 v 195 1 Homagnostus peladensis Rusconi, 1951a, p. 2, text-fig. 1. vl951 IHomagnostus manantialensis Rusconi, 1951a, p. 2, text-fig. 2. vl951 Triplagnostus pedrensis Rusconi, 19516, pi. 7, text-fig. 7. Material. Many dozens of cephala and pygidia preserved as calcite exoskeletons, external and internal moulds; studied paradigm PIUNSJ 651-662. explanation of plate 1 Figs 1-9. Lotagnostus ( Lotagnostus ) peladensis (Rusconi, 1951a). 1, PIUNSJ 651 ; cephalon with exoskeleton mostly preserved; locality CP74, El Relincho Formation, Cerro Pelado, Mendoza; x 8. 2, PIUNSJ 652; laterally compressed cephalon, mostly effaced, showing weak scrobiculation; same locality; x 8. 3, PIUNSJ 653; sagittally compressed cephalon, mostly exfoliated; same locality; x 10. 4, PIUNSJ 654; laterally compressed, mostly exfoliated cephalon, same locality; x 8. 5, PIUNSJ 662; mostly exfoliated cephalon; olistolite LC9, Empozada Formation, San Isidro, west of Mendoza; x 8. 6, PIUNSJ 656; pygidium preserved with thin exoskeletal vestige; locality CP74, El Relincho Formation, Cerro Pelado, Mendoza; x 6. 7, PIUNSJ 657; latex replica of sagitally slightly compressed pygidium; same locality; x 6. 8, PIUNSJ 658; pygidium with exoskeleton preserved, same locality; x 6. 9, PIUNSJ 661 ; pygidium, largely exfoliated with laterally constricted acrolobe; olistolite LC9, Empozada Formation, San Isidro, west of Mendoza; x 10. Figs 10-1 1 . Lotagnostus (Lotagnostus) attenuatus (Rusconi, 1955a). 10, MNH Mendoza 18208B; silicone replica of mostly exfoliated, weakly scrobiculate syntype cephalon; 300 m west of San Isidro, Mendoza; x 8. 1 1, MNH Mendoza 18208A; silicone replica of exfoliated pygidium showing tripartite posterior lobe and faintly constricted, scrobiculate acrolobe; same locality; x 8. Fig. 12. Lotagnostus ( Lotagnostus ) trisectus (Salter, 1864). MNH Mendoza 9973; silicone replica of exfoliated strongly scrobiculate cephalon, the original material of Goniagnostus verrucosus Rusconi, 19516; Cerro Pelado, west of Casa de Piedra, Depto de las Heras, Mendoza; x 10. Figs 13-15. Glyptagnostus reticulatus (Angelin, 1851) sensu lato. All material from olistolite LST3, Los Sombreros Formation, Tontal Range, San Juan. 13, PIUNSJ 700; latex replica of sagittally compressed, exfoliated cephalon; x 12. 14, PIUNSJ 699; incomplete, exfoliated cephalon; x 8. 15, PIUNSJ 701; obliquely compressed, exfoliated pygidium; x 16. PLATE 1 SHERGOLD et a /., Lotagnostus, Glyptagnostus 246 PALAEONTOLOGY, VOLUME 38 Occurrence. Olistolite LC9, Empozada Formation, San Isidro, Mendoza, and locality CP74, at the base of the El Relincho Formation, Cerro Pelado, Mendoza. Description. Cephalon en grande tenue with non-deliquiafe border furrows; acrolobe unconstricted, often very faintly scrobiculate; median preglabellar furrow well-defined; glabella trilobed, with long (sag.) ogival anterior lobe; anterior glabellar furrow well-defined, curved adaxiallyjiackwards ; anterolateral lobes well-defined, separated by a forward extension of the posterior lobe, constrained posteriorly by prominent lateral furrows at which the glabella is laterally constricted; posterior furrows weakly defined, not transglabellar; posterior lobe elevated, parallel-sided, with angular culmination; axial node placed in anterior half immediately behind the glabellar constriction; basal lobes large, long (exsag.), undivided. Pygidium en grande tenue, quadrangular, with non-deliquiate border furrows; gently constricted, non-scrobiculate acrolobe; axis trilobed, only gently constricted at second lobe; anterior two lobes tricomposite, first axial furrow discontinuous, separated medially by large axial node extending forwards over the two anterior lobes; posterior edges of muscle scar impressions are faintly visible on the second axial lobes of some specimens (PI. 1, figs 6-7); posterior lobe lanceolate, ending in rounded point and terminal node; minute posterolateral spines situated at level of rear of axis. Remarks. This species most closely resembles Lotagnostus ( Lotagnostus ) hedini (Troedsson, 1937) because it is essentially non-scrobiculate while remaining en grande tenue. It cannot be synonymized with that species, however, because the anterolateral glabellar lobes are separated by an extension of the median body of the posterior lobe; the basal lobes are longer (exsag.), and in the pygidium the first axial furrow is medially discontinuous. In this last characteristic, L. (L.) peladensis resembles L. (L.) americanus (Billings, 1860), L. ( L .) asiaticus Troedsson, 1937 and L. ( L .) punctatus Lu, 1964. The synonymy suggested above is based on evaluation of silicone replicas obtained from the Rusconi collection by A. R. Palmer and replicated for Shergold in 1972. Other species of Lotagnostus are represented in Rusconi’s collections but they differ from the specimens noted above in being more highly scrobiculate. For example, specimens attributed tQ. Goniagnostus atenuatus [sz'c] Rusconi (1955c, p. 28, pi. 2, figs 13-14; herein PI. 1, figs 10-11), which also has a tripartite posterior axial pygidial lobe, G. rotundatus Rusconi (19516, p. 6, texQfig. 6) and G. verrucosus Rusconi (19516, p. 5, text-fig. 5, illustrated as a pygidium; herein PI. lffig. 12) which are based on heavily scrobiculate cephala. These specimens so closely resemble L. (L.) trisectus (Salter, 18646) that Shergold et al. (1990, fig. 9.1a) used the cephalon of verrucosus to illustrate the species trisectus, thus effectively synonymizing these species (see also Manca 1992, fig. 2). Age. L. (L.) peladensis is associated in olistolite LC9 with the olenid trilobite Mendoparabolina pirquinensis Rusconi, 1951a which seems to be a species of Bienvillia Clark, 1924 very close to B. corax (Billings, 1865). This is known elsewhere from boulders in the Levis Formation of Quebec (Billings 1865; Rasetti 1944) and Shallow Bay Formation (Cow Flead Group) of western Newfoundland (Rasetti 1954; Fortey et al. 1982; Ludvigsen et al. 1989), and the Gorge Formation of Vermont. In western Newfoundland, B. corax is associated with Lotagnostus ( Lotagnostus ) hedini and is representative of the Keithia schucherti Fauna, of Sunwaptan age, correlated with the Saukiella serotina Subzone of the Saukia Zone in continental USA (e.g. Oklahoma) (see Ludvigsen et al. 1989). Judging from the morphological similarity of the taxa in LC9, a similar age may be assumed. Genus oncagnostus Whitehouse, 1936 Subgenus oncagnostus Whitehouse, 1936 Type species. Agnostus hoi Sun, 1924, p. 28; by original designation of Whitehouse 1936, p. 84. Oncagnostus ( Oncagnostus ) sp. Plate 3, figures 13-15 Material. The internal and external moulds of a single cephalon, and the external mould of a pygidium, PIUNSJ 678-679. Occurrence. Olistolite Em Ol, Empozada Formation, San Isidro, Mendoza. SHERGOLD ET A L.\ AGNOSTOID TRILOBITES 247 Description. Cephalon en grande tenue, with narrow (sag.) borders and deliquiate border furrows, and weakly scrobiculate, unconstricted acrolobe divided sagittally by median preglabellar furrow; glabella proportionately short (sag.), elevated, with weakly ogival anterior lobe differentiated from posteroglabella by strong, continuous, anterior transglabellar furrow; posteroglabella with prominent lateral notches behind anterolateral lobes and adjacent to front of basal lobes as in some species of Innitagnostns ; condition of glabellar culmination unknown; axial glabellar node at mid-length of posteroglabella; basal lobes more extensive transversely than exsagittally ; short posterolateral spines. Pygidium en grande tenue, with non-deliquiate border furrows and unconstricted, non-scrobiculate acrolobe, lacking a median post-axial furrow; relatively long (sag.) axis, laterally inflated, constricted where the first segmental furrow intersects the axial furrow; first furrow interrupted medially, defining anterolateral ellipsoidal lobules; second axial furrow interrupted medially by prominent, elongate axial node which extends on to front part of posterior lobe; posterior lobe longer (sag.) than anterior two lobes combined, laterally inflated, posteriorly broadly rounded, bearing nodular lines, but poorly defined terminal node; posterolateral spines prominent, retrally sited across the rear of the pygidial axis. Remarks. Oncagnostus ( Oncagnostus ) was revived by Shergold et al. (1990) to include four species previously classified within the closely related Agnostus ( Homagnostus ). The pygidia of the subgenera are similar in that they both develop anterolateral lobules on the pygidial axis and accordingly do not have a continuous transaxial anterior furrow. In general, however, species of Oncagnostus have deliquiate border furrows in both cephalon and pygidium, have an often long (sag.) and inflated pygidial axis which is broadly rounded posteriorly, and a relatively broader (tr.) glabella. They often lack a median preglabellar furrow, but not in the presently described species, and they frequently have retral posterolateral pygidial spines lying level (tr.) with the posterior end of the pygidial axis. The pygidium of our species resembles Homagnostus comptus Palmer (1962, pi. 1, fig. 13), from Nevada, H. tumidosus Hall and Whitfield sensu Palmer (1968, pi. 7, fig. 8) from Alaska, Homagnostus sp. 2 sensu Shergold (1982, pi. 5, fig. 12), from western Queensland, and, to some extent, specimens from southern Alberta referred to Homagnostus obesus (Belt) by Westrop (1986, pi. 1, figs 1-3). The cephalon is also not unlike that assigned by Palmer (1962, pi. 1, fig. 12) to H. comptus , but the North American specimen lacks a median preglabellar furrow. Most similar is the specimen that Opik (1963, pi. 2, fig. 12) referred to Innitagnostns [ Agnostus ] inexpectans (Kobayashi) which is comparably en grande tenue, weakly scrobiculate and has an identical glabellar format, including the centrally situated axial glabellar node. Species of Innitagnostns seemingly are characterized by an axial node located farther towards the anterior of the posteroglabella, and frequently the anterior glabellar lobe is cleft slightly by the median preglabellar furrow. However, this is not always the case, and the possibility of the Argentinian specimen described here representing Innitagnostns rather than Oncagnostus cannot be dismissed. More material is required to confirm the present determination. Age. The species mentioned above are from the late Dresbachian of the USA and equivalent Idamean Stage of Australia. The Nevadan and Australian species occur within the Glyptagnostus reticulatus Range Zone, but the Alaskan species is associated with Acmarhachis acuta (Kobayashi), and is probably representative of the Dunderbergia Zone of the Great Basin. The Albertan specimens are slightly younger, occurring in the Irvingella major Subzone of the Elvinia Zone. Genus trilobagnostus Harrington, 1938 Type species. Agnostus innocens Clark, 1923, p. 122; by original designation of Harrington, 1938, p. 148. TrilobagnostusI sp. Plate 2, figures 1-9 Material. Thirteen cephala and seven pygidia preserved as calcite exoskeletons, PIUNSJ 663-677. Occurrence. Olistolite Em 02, Empozada Formation, San Isidro, Mendoza. 248 PALAEONTOLOGY, VOLUME 38 Description. Subrectangular cephalon, strongly convex, narrow, non-deliquiate border furrow; unconstricted acrolobe, non-scrobiculate; lacking median preglabellar furrow; glabella essentially bilobed, short, with subsphaerical frontal lobe; anterior glabellar furrow well defined and weakly curved backward; posterior lobe convex, unfurrowed, with broadly rounded culmination; axial node subcentral; small basal lobes. Pygidium subrectangular, degree of deliquiation of border furrow depending on preservation, internal moulds being deliquiate but external moulds being non-deliquiate; narrow borders; unconstricted, non- scrobiculate acrolobe, lacking median post-axial furrow; moderately long axis (sag.), tapering rearwards, posteriorly rounded; anterolateral lobes well defined, as in Oncagnostus ( Oncagnostus ) delimited by furrows that are curved forward, not transaxial; second furrow interrupted medially by prominent axial node lapping on to the front of the posterior lobe which narrows rearwards, failing to extend to the posterior border furrow; insignificant terminal node; stout, incurved posterolateral spines retrally sited to the rear of the termination of the axis. Remarks. Material from Em 02 is compared with the type species of Trilobagnostus which has recently been refigured as Micragnostus innocens (Clark, 1923) by Ludvigsen et al. (1989, p. 12, pi. 1, fig. 25). These authors remark on the length of the pygidial axis and the nature of its anterolateral furrows, and illustrate a similar border furrow and retral posterolateral spines to those described here. Also very similar are the specimens from Jilin Province, China, which Qian (1986, p. 263, pi. 67, figs 1-7) placed in Geragnostus ( Micragnostus ) cf. subobesus (Kobayashi, 1936), but these are likely to be slightly younger. Shergold et al. (1990) noted the apparent similarity of Trilobagnostus to the subgenera of Oncagnostus as conceived by them ( Oncagnostus , Kymagnostus and Strictagnostus) and suggested that it could form a fourth subgenus. There is also great similarity to species of Eurudagnostus , especially E. brevispinus Lermontova (1951, pi. 2, figs 5-6, non fig. 7) and Rudagnostus , which is reflected in the synonymies proposed by Shergold et al., i.e. Eurudagnostus [= Oncagnostus ] and Rudagnostus [= Trilobagnostus ]. However, all the taxa involved require thorough revision and reassessment beyond the scope of this paper. Our present uncertainty is expressed in the question mark and open nomenclature. Age. The type specimen of Trilobagnostus innocens (Clark) is associated with a species of Lotagnostus of the hedini group. Thus a Late Cambrian, Saukia Zone, age is probable for it. By inference, Trilobagnostus ? sp. may have a similar age, possibly the same as Lotagnostus ( Lotagnostus ) peladensis (Rusconi). Subfamily glyptagnostinae Whitehouse, 1936 Genus glyptagnqstus Whitehouse, 1936 Type species. Glyptagnostus toreuma Whitehouse, 1936, p. 101 [ = Agnostus reticulatus Angelin, 1851, p. 8]. EXPLANATION OF PLATE 2 Figs I -9. Trilobagnostusl sp. All material from olistolite Em 02, Empozada Formation, San Isidro, west of Mendoza. 1, PIUNSJ 663; cephalic exoskeleton; x 14. 2, PIUNSJ 664; cephalic exoskeleton; x 14. 3, PIUNSJ 665; cephalon with most of exoskeleton preserved; x 10. 4, PIUNSJ 666; latex replica of cephalic exoskeleton; x 12. 5, PIUNSJ 667; latex replica of cephalic exoskeleton; x 14. 6, PIUNSJ 668; latex replica of cephalic exoskeleton; x 12. 7, PIUNSJ 674; latex replica of pygidial internal mould; x 14. 8, PIUNSJ 675; pygidium with exoskeleton largely preserved; x 14. 9, PIUNSJ 676; partly exfoliated pygidium; x 12. Figs 10-14. Acmarhachis sp. cf. A. acuta (Kobayashi, 1938, sensu Rasetti, 1961). All material from olistolite OA2, Los Sombreros Formation, San Juan. 10, PIUNSJ 694a; partly exfoliated cephalon; x 24. 11, PIUNSJ 695; partly exfoliated cephalon; x 16. 12, PIUNSJ 696; largely exfoliated pygidium; x 12. 13, PIUNSJ 697 ; partly exfoliated pygidium; x 20. 14, PIUNSJ 698; incomplete pygidial exoskeleton; x 16. Fig. 15. Neoagnostus ( Neoagnostus ) sp., PIUNSJ 703; internal mould of small pygidium; locality CP74, El Relincho Formation, Cerro Pelado, Mendoza ; x 20. PLATE 2 SHERGOLD et al. , agnostoid trilobites 250 PALAEONTOLOGY, VOLUME 38 Glyptcignostus reticulatus (Angelin, 1851) sensu lato Plate 1, figures 13-15 Material. Three cephala and two pygidia preserved as external moulds, P1UNSJ 699-702. Occurrence. Olistolite T3, Los Sombreros Formation, Sierra del Tontal, San Juan. Remarks. Although very poorly preserved, this material has the typical characteristics of Glyptagnostus reticulatus (Angelin), and, eventually, when more material is available it may be possible to refer it to the subspecies reticulatus reticulatus. The material illustrated here is the first record of this cosmopolitan species in South America. Essentially comparable material occurs in Australia (Shergold 1982) and the Ellsworth Mountains of West Antarctica (Shergold and Webers 1992). Age. All material is representative of the Glyptagnostus reticulatus Zone, recognized worldwide (see references in Shergold 1982). Subfamily incertae sedis Genus acmarhachis Resser, 1938 Type species. Acmarhachis typicalis Resser, 1938, p. 47, by original designation. Acmarhachis cf. A. acuta (Kobayashi, 1938) sensu Rasetti, 1961 Plate 2, figures 10-14 cf. 1961 Acmarhachis acuta (Kobayashi); Rasetti, p. 109, pi. 23, figs 1-8 (see Pratt, 1992, p. 39 for synonymies). Material. Thirteen cephala and nine pygidia preserved as external moulds and exoskeletons; studied paradigm PIUNSJ 694-698. Occurrence. Olistostrome level OA2, Los Sombreros Formation, Sierra del Tontal, San Juan. Description. Cephalic border narrow, gently convex; border furrow subdeliquiate, narrow and deep; acrolobe smooth, unconstricted, lacking median preglabellar furrow, although some specimens have an incipient furrow in front of the glabella. Glabella long and narrow, with elongate, semicircular anterior lobe; anterior glabellar furrow deep, gently arched forwards; anterolateral furrow shallow and chevronate; the posterior lobe is tumid with elevated culmination, laterally constricted where the chevronate anterolateral furrow intersects the axial furrow; axial glabellar node subcentral on the posterior lobe. Pygidium subrectangular, border narrow and uniform, with diminutive, advanced posterolateral spines; border furrow subdeliquiate, shallow; acrolobe unconstricted ; axis long and posteriorly ogival ; second axial segment subpentagonal and laterally constricted, with a large, prominent axial node; the posterior lobe is lanceolate, its tapered posterior end bearing a terminal node which touches the border furrow. In very small specimens, the posterior lobe is more rounded. Remarks. Acmarhachis was reappraised by Pratt (1992, p. 38), who considered it to represent a pseudagnostine genus. However, for reasons earlier explained (Shergold 1982; Shergold et ah 1990), we prefer to retain Acmarhachis within the Agnostidae. Pratt also listed previously described species, grouping most into the American species A. typicalis and A. acuta. Among the species that he documented, the Argentinian material most closely resembles the former in terms of the diagnostic characteristics of the first segment of the pygidial axis, being laterally undivided. In North America, A. typicalis has been described from the North West Territories of Canada (Kobayashi 1938; Pratt 1992), Nevada (Palmer 1962), and Alabama (Resser 1938), where it has an early Dresbachian, Crepicephalus Zone, age. However, in terms of furrowing, axial proportions and shape, the Argentinian species clearly most resembles that from Maryland, described by Rasetti ( 1961 ) as Acmarhachis acutus (Kobayashi, 1938), of late Dresbachian, Dunderbergia Zone, age. The SHERGOLD ET AL.\ AGNOSTOID TRILOBITES 251 Argentinian species differs from the youngest species so far documented, A. hybrida (Shergold, 1980, p. 20, pi. 11. figs 1-6), from western Queensland, in the position of the axial glabellar node. This lies farther forward in the Australian species, which is further distinguished by the presence of a faint median preglabellar furrow. Age. Acmarhachis acuta (Kobayashi) reportedly has a long range from late in the Middle Cambrian through to the early part of the Late Cambrian in North America, Siberia, Kazakhstan, south-central China and northern and southeastern Australia. The Argentinian species appears most likely to date from the later part of this range. Family diplagnostidae Whitehouse, 1936 emend. Opik, 1967 Subfamily pseudagnostinae Whitehouse, 1936 Genus pseudagnostus Jaekel, 1909 Subgenus pseudagnostus Jaekel, 1909 Type species. Agnostus cyclopyge Tullberg, 1880, p. 26, by original designation of Jaekel 1909, p. 400. Pseudagnostus ( Pseudagnostus ) idalis idalis Opik, 1967 Plate 3, figures 1-6 1982 Pseudagnostus ( Pseudagnostus ) idalis idalis Opik, 1967; Shergold, p. 26, pi. 2, figs 1-13 [with synonymy]. Material. Six cephala and two pygidia, preserved as calcitic internal moulds and exoskeletons, PIUNSJ 680-685. Occurrence. Olistolite Em 01, Empozada Formation, San Isidro, Mendoza. Description. Cephalon en grande tenue, strongly deliquiate, with unconstricted acrolobe; preglabellar median furrow deeply incised, widening forward; spectaculate, anterior glabellar furrow being gently curved backward. Pygidium en grande tenue, strongly deliquiate, with gently constricted acrolobe, plethoid and ampullate deuterolobe; retral posterolateral spines sited a little forward of a transverse line drawn across the rear of the deuterolobe. Age. According to Shergold (1982), this taxon characterizes the Late Cambrian, Idamean, zones of Glyptagnostus reticulatus, Proceratopyge cryptica and Stigmatoa diloma in the Georgina Basin, western Queensland, Australia. Pseudagnostus ( Pseudagnostus ) idalis Opik, 1967 sensu lato Plate 3, figures 7-12 Material. Eight cephala and twelve pygidia preserved as external moulds and exoskeletons, PIUNSJ 686-693. Occurrence. Olistostrome level OA2, Los Sombreros Formation, Sierra del Tontal, San Juan. Remarks. The Pseudagnostidae from the Los Sombreros Formation have morphologies referable to Pseudagnostus (P.) idalis Opik sensu kito according to the classification of Shergold (1977). In general, the exoskeleton shows a higher degree of effacement than Ps. (Ps.) idalis idalis as described above. However, it cannot be assigned to any known subspecies because of differences in preservation. This taxon differs from Ps. (Ps.) idalis s. /. of Shergold (1982, pi. 2, figs 14-15) because its cephalon has substantially less deliquiate border furrows and better defined anterolateral glabellar lobes. Pygidia may be essentially similar, but their varying modes of preservation prevent detailed comparison. Preservation also prevents adequate comparison with Ps. (Ps.) idalis denisonensis Jago (1987, p. 210, pi. 24, figs 4—12) from southwestern Tasmania, and Pseudagnostus spp. described by Jell et al. (1991, p. 463, figs 4-5) from western Tasmania, although the former shares with the Argentinian taxon a similar, subcentrally positioned, axial glabellar node. Also 252 PALAEONTOLOGY, VOLUME 38 similar, on some specimens of Ps. (Ps.) idalis s.l., is the sagittally elongated deuterolobe, which may have a central depression. Such features, however, may be related to preservation. Both of the Tasmanian occurrences are slightly younger than the Idamean as defined by Shergold (1982, 1989, 1993). Specimens with similar morphologies from western Zhejiang Province, China, described by Lu and Lin (1989, p. 232, pi. 14, figs 1^1), are also assigned to Pseudagnostus (Ps.) idalis Opik. These occur in the Proceratopyge fenghwangensis Zone, which correlates with the late Idamean of Australia. Genus neoagnostus Kobayashi, 1955 Subgenus neoagnostus Kobayashi, 1955 Type species. Neoagnostus aspidoides Kobayashi, 1955, p. 473, by original designation. Neoagnostus ( Neoagnostus ) sp. Material. A single small pygidium measuring (Lp2) 1-9 mm, PIUNSJ 703. Occurrence. Locality CP74, autochthonous El Relincho Formation, Cerro Pelado, Mendoza Province. Description. Pygidium with comparatively wide (tr, sag.) borders, non-deliquiate border furrows and minute posterolateral spines; rounded and laterally unconstricted acrolobe; axis with effaced anterior transaxial furrow, axial node situated across (sag.) second lobe, defined only posteriorly; effaced accessory furrows; deuterolobe short (sag.), barely defined but with terminal axial node indicated. Remarks. The combination of extremely small posterolateral spines, subcircular acrolobe and short (sag.) deuterolobe permit comparison with previously described material from China, Australia and North America (Vermont). Neoagnostus (N.) longicollis (Kobayashi, 1966) sensu Zhou and Zhang (1985, p. 68, e.g. pi. 27, fig. 7), from northern Shanxi and southern Jilin, is essentially similar except that it possesses a third pair of axial lobules. N. (N.) araneavelatus (Shaw, 1951, especially pi. 24, fig. 15) from Vermont, and N. (V.) orbiculatus (Shergold, 1975, particularly pi. 12, fig. 10) from western Queensland, Australia, have more circular acrolobes. N. (N.) quasibi/obus (Shergold, 1975, see pi. 12, figs 5-7), also from western Queensland, has the most similar acrolobe morphology, but seems to have more prominent posterolateral spines. All of these species have virtually effaced anteroaxes and imperceptible deuterolobes. All similarly occur in the latest Cambrian: Fengshanian, Mictosaukia orientalis Assemblage Zone in Shanxi and Changia Assemblage Zone of Jilin in China; Payntonian, Neoagnostus ( N .) quasibi/obus / Sltergoldia nomas Assemblage Zone in western Queensland; and their equivalents in Vermont. EXPLANATION OF PLATE 3 Figs 1-6. Pseudagnostus ( Pseudagnostus ) idalis idalis Opik, 1967. All material from olistolite Em Ol , Empozada Formation, San Isidro, west of Mendoza. 1, PIUNSJ 680; internal mould of cephalon; x 10. 2, PIUNSJ 681 ; latex replica of mostly exfoliated cephalon; x 10. 3, PIUNSJ 682; latex replica of cephalic internal mould; x 10. 4, PIUNSJ 683b; latex replica of cephalic internal mould; x 10. 5, PIUNSJ 685; latex replica of largely exfoliated pygidium; x 12. 6, PIUNSJ 684; internal mould of pygidium; x 10. Figs 7-12. Pseudagnostus ( Pseudagnostus ) sp. cf. P. idalis Opik, 1967 sensu lato. All material from olistolite OA2, Los Sombreros Formation, San Juan. 7, PIUNSJ 686; mostly exfoliated cephalon; x 16. 8, PIUNSJ 687; small cephalic internal mould; x 20. 9, PIUNSJ 688; mostly exfoliated cephalon; x 16. 10, PIUNSJ 689; early holaspid pygidium showing initial development of deuterolobe; x 24. 11, PIUNSJ 690; internal mould of early holaspid pygidium with fully developed deuterolobe; x 16. 12, PIUNSJ 691 ; internal mould of late holaspid pygidium; x 16. Figs 13-15. Oncagnostus ( Oncagnostus ) sp. All material from olistolite Em Ol, Empozada Formation, San Isidro, west of Mendoza. 13, PIUNSJ 678b; latex replica of partly exfoliated, weakly scrobiculate cephalon; x 16. 14, PIUNSJ 678a; counterpart of fig. 13, cephalic exoskeleton; x 16. 15, PIUNSJ 679; latex replica of exfoliated pygidium; x 14. PLATE 3 SHERGOLD et ai, Pseudagnostus, Oncagnostus 254 PALAEONTOLOGY, VOLUME 38 SUMMARY Late Cambrian agnostoids have been obtained from the autochthonous El Relincho Formation, and from five olistolites in the Empozada and Los Sombreros Formations (Text-fig. 3). Agnostoids MENDOZA SAN JUAN unit Order of Occurrence of Olistolites Agnostoids Autochthonous Unit Agnostoids Unit Order of Occurrence of Olistolites Agnostoids Em 02 < s: cc o Em 01 LC9 ► ? Trllobagnostus sp Pseudagnostus . Idalls Idalis Oncagnostus (0.) sp. Lotagnostus (L.) peladensis LST3 _ Glyptagnostus ’ retlculatus < r cc o CP7^ Lotagnostus (L.) peladensis Neoagnostus (N.) sp. 0A2 Pseudagnostus idalls ’ Acmarnachls cr. acuta B MENDOZA SAN JUAN Unit Blo- chronology of Olistolites Agnostoids Autochthonous Unit Agnostoids Unit Blo- chronology of Olistolites Agnostoids < o < i'u O a s: LC9 Em 02 Em 0 I Lotagnostus (L.) peladensis ► ? Trllobagnostus sp Pseudagnostus Idalls Idalls Oncagnostus (0.) sp. < T. cr o o X (_> CP74_^ Lotagnostus JL.) peladensis ” Neoagnostus (N.) sp. z o i— < r cr o o cc 0A2 LST3 Pseudagnostus Idalls ’ Acmarhacbls cl. acuta _ Glyptagnostus retlculatus text-fig. 3. a, Stratigraphical distribution of the olistolites in the Empozada and Los Sombreros Formations; b, their inferred biochronological order. Note that the fauna recorded from the El Relincho Formation at Cerro Pelado is autochthonous, and also the youngest of the faunas described. SHERGOLD ET A L. \ AGNOSTOID TRILOBITES 255 identified from them include: CP74, Lotagnostus ( Lotagnostus ) peladensis (Rusconi), Neocignostus (Neoagnostus) sp.; LC9, Lotagnostus ( Lotagnostus ) peladensis (Rusconi); Em 02, Trilobagnostusl sp.; Em Ol, Oncagnostus (Oncagnostus) sp., Pseudagnostus (Ps.) idalis idalis Opik; OA2, Acmarhachis cf. 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Varias especies de trilobitas del Cambrico de Canota. Revista del Museo de Historia Natural de Mendoza, 6, 5-17. 1953. Nuevos trilobitas cambricos de la Quebrada de la Cruz. Boletln Paleontologico de Buenos Aires, 27, 8 pp. - 1954. Trilobitas cambricos de la Quebradita Oblicua, Sud Cerro Aspero. Revista del Museo de Historia Natural de Mendoza, 7, 3-60, 4 pis. - 1955a. Mas fosiles cambricos y ordovicios de San Isidro, Mendoza. Boletln Paleontologico de Buenos Aires, 31, 4 pp. - 1955b. Nota previa sobre organismos ordovicios y cambricos de San Isidro, Mendoza. Boletln Paleontologico de Buenos Aires, 32, 4 pp. SHERGOLD ET A L. \ AGNOSTOID TRILOBITES 257 1955c. Fosiles cambricos y ordovicios al Oeste de San Isidro, Mendoza. Revista del Museo de Historia Natural de Mendoza , 8, 3-64, 5 pis. salter, j. w. 1 864c/. A monograph of the British trilobites from the Cambrian, Silurian, and Devonian formations. Part 1. Monograph of the Palaeontographical Society , 16 (67), 1 80, pis 1-6. 18646. 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Uppermost Cambrian and lowest Ordovician trilobites of North and Northeast China. 63-163, pis 1-29. In nanjing institute of geology and palaeontology, academia sinica (compiler). Stratigraphy and palaeontology of systemic boundaries in China. Cambrian-0 rdovician Boundary 2. Anhui Science and Technology Publishing House, Beijing, 412 pp. JOHN H. SHERGOLD Australian Geological Survey Organisation Post Office Box 378 Canberra, ACT 2601, Australia OSVALDO BORDONARO CRICYT, cas. correo 131 5500-Mendoza, Argentina ELADIO LINAN Paleontologia, Facultad de Ciencias Universidad de Zaragoza 50009 Zaragoza, Spain Typescript received 16 October 1993 Revised typescript received 21 March 1994 TELEPHINID TRILOBITES FROM THE ORDOVICIAN OF SWEDEN by PER AHLBERG Abstract. Twelve telephinid trilobite species, all assigned to the genus Telephina , from the Middle and Upper Ordovician of Sweden are described or discussed. In Sweden, the genus appears in equivalents of the uppermost Didymograptus murchisoni Biozone and ranges into the late Ashgill or Harjuan ( Jerrestadian Stage), where only one species, T. wegelini , is present. The others are restricted largely to strata belonging to the Hustedograptus teretiusculus and Nemagraptus gracilis biozones. In Baltoscandia, telephinid trilobites are commonest in fine- grained rocks west of the Central Baltoscandian Confacies Belt, and they seem to have occupied relatively peripheral sites on the continental plate of Baltica. The Telephintdae Marek, 1952 includes small- to medium-sized, micropygous trilobites with large eyes and short (tr.) pleurae. They are characteristic elements of many Ordovician faunas, and range upwards into the pre-Hirnantian Ashgill. It is generally agreed that they were adapted to a pelagic mode of life (e.g. Fortey 1975, 1981, 1985). The earliest reference to telephinid trilobites from the Ordovician of Sweden is by Angelin (1854), who described Telephina wegelini from the Upper Ordovician of the Siljan district in Dalarna, central Sweden. Subsequently, additional material of this species was described from the Upper Ordovician Fjacka Shale at various localities in this area (Linnarsson 1871, p. 350; Tornquist 1884, p. 89). During the latter half of the nineteenth century, telephinids were also reported from the island of Oland, southern Sweden, and Jamtland, central Sweden (Linnarsson 1872; Tullberg 1882; Moberg 1890; Wiman 1893; Flolm 1897). Later Hadding (191 3 C o 03 ■D os Ashgill Dicellograptus complanatus Amorphognathus ordovicicus X a> CL Pleurograptus CL => — linearis o o Dicranograptus clingani Amorphognathus superbus CO c CO 3 CO O Diplograptus multidens Amorphognathus tvaerensis > C Nemagraptus gracilis CO o > o o Q) "O Pygodus anserinus o CO 0) "O "O C Hustedograptus teretiuseulus Pygodus serra > c CO —1 Didymograptus murchisoni Eoplacognathus suecicus ~ c ~ c o ;= t- . I 1 1 text-fig. 2. Approximate ranges of telephinid trilobites in the Middle and Upper Ordovician of Sweden. Many specimens in older collections are only vaguely localized with respect to the stratigraphy, and for most species the ranges shown are tentative. Stratigraphy slightly modified after Jaanusson (1982n, fig. 2). grained limestones or mudstones. The appearance of telephinids in the Middle Ordovician of Vastergotland seems to be related to brief eastward shifts of the general facies of the Oslo Region (Jaanusson 1964, p. 53; 1973, p. 21; 1982h, p. 168). Within the Central Baltoscandian Confacies Belt, rare specimens of Telephina are also known from drill cores in western Latvia (Mannil 1963), and the Pskov district of western Russia. No telephinids are known from the North Estonian and Lithuanian confacies belts. In North America, Telephina species have been recorded only from the Appalachian orogenic belt. The oldest forms are from the Llanvirn of the northern part (western Newfoundland and southern Quebec). In the southern and central Appalachians of the USA, Telephina is widely distributed in beds equivalent to the Hnstedograptus teretiuseulus and Nemagraptus gracilis biozones. Analysis of the distribution of shelly faunas and conodonts in this area has revealed a differentiation into three Middle Ordovician confacies belts (Jaanusson and Bergstrom 1980). Ulrich (1930, p. 47) noted that ‘ in the Appalachian Valley remains of Telephus are confined to areas in the eastern half of the valley’, that is, to the Blount Confacies Belt of Jaanusson and Bergstrom (1980), and this is confirmed by the available evidence (V. Jaanusson, pers. comm. June 1993). The faunas of the Blount Belt are closely similar to those of northeastern Ireland and the Girvan district of southwestern Scotland (Jaanusson and Bergstrom 1980, p. 102). The latter area has also yielded telephinids, such as Telephina girvanensis (Reed, 1935) and T. subsecuta (Reed, 1944). These species were redescribed by Tripp (1976). In Baltoscandia, the closest equivalent to the Blount Belt is the Central Baltoscandian Confacies Belt, but the Blount Belt also includes analogues of the Oslo belts and the Scanian Confacies Belt (Jaanusson and Bergstrom 1980, p. 100). 262 PALAEONTOLOGY, VOLUME 38 In conclusion, most species of Telephina appear to be restricted to sequences situated fairly peripherally on the continental plates, at least in Baltica and in Laurentia. The lack of Telephina on the Siberian Platform supports this view. SYSTEMATIC PALAEONTOLOGY The terminology used herein in general follows that of Harrington et al. in Moore (1959), except that the terms rachis and dorsal furrow are preferred to axis and axial furrow. The glabella is taken to exclude the occipital ring and furrow. The palpebral area of the fixigena is between the palpebral furrow and the dorsal furrow. Illustrated and cited specimens are deposited in the type collections of the Geological Survey of Sweden, Uppsala (SGU), the Department of Historical Geology and Palaeontology, University of Lund (LO or LR), the Palaeontological Museum, Oslo (PMO), the Palaeontological Museum, University of Uppsala (PMU), and the Swedish Museum of Natural History, Stockholm (RM). All specimens were painted with matt black opaque and then lightly coated with a sublimate of ammonium chloride prior to being photographed. Dorsal views are shown unless stated otherwise in the captions. Measurements were made with a micrometer eyepiece fitted in a binocular microscope. All dimensions were measured as straight-line distances. The accuracy of all measurements is to 0 05 mm. Estimated values and transverse measurements arrived at by doubling the width from the sagittal line are indicated with a question mark. The following symbols are used for measured parameters: Lc, length (sag.) of cephalon (excl. occipital spine and anterior pair of spines); G, length (sag.) of glabella; Lo, length (sag.) of occipital spine; Wc, maximum width (tr.) of cranidium; Wg, maximum width (tr.) of glabella; Wf, maximum width (tr.) of fixigena (inch palpebral lobe). Family telephinidae Marek, 1952 Diagnosis. See Fortey 1975, p. 94. Remarks. The concept of the family Telephinidae was discussed comprehensively by Fortey (1975), and his definition and discussion cover all important aspects. Genus telephina Marek, 1952 Type species. Telephus fractus Barrande, 1852 (p. 890, pi. 18, figs 30-34), from the Kraluv Dvur Formation (Ashgill) at Kraluv Dvur, Bohemia; by original designation. EXPLANATION OF PLATE 1 Figs 1-13. Telephina bicuspis (Angelin, 1854). All specimens except 1-2 and 13 are from the lower Anderso Shale ( Hustedograptus teretiusculus Biozone) on the northwestern shore of Anderson, Jamtland (locality 1 of Hadding 1912, pi. 7a, 1913fi, fig. 12). 1-2, neotype, RM Ar 37315; dorsal and anterodorsal views; Oslo, Norway; original of Thorslund (1935, pi. 2, figs 1-2); x 8. 3-4, LO 2566t; cranidium in dorsal and anterior views; original of Hadding (1913a, pi. 1, fig. 4); coll. A. Hadding 1912; x 7. 5-6, LO 2544t; cranidium in dorsal and anterior views; original of Hadding (1913a, pi. 1, fig. I a-d)\ coll. A. Hadding 1912; x 6. 7, LO 2565t; cranidium; original of Hadding (1913a, pi. 1, fig. 3 a-b); coll. A. Hadding 1912; x 7-5. 8, SGU 8637; cranidium; coll. P. Thorslund 1949; x 7. 9, LO 6701 1 ; incomplete librigena; coll. A. Hadding 1912; x 5. 10, LO 2564t; cranidium; original of Hadding (1913a, pi. 1, fig. 2); coll. A. Hadding 1912; x 7-5. 11, LO 2546t; incomplete thoracic tergite; original of Hadding (1913a, pi. 1, fig. 6); coll. A. Hadding 1912; x 7. 12, LO 2547t; incomplete pygidium, latex cast from external mould; original of Hadding (1913a, pi. 1, fig. 7); coll. A. Hadding 1912; x 13. 13, SGU 6687; incomplete librigena in ventral view; O. Ottsjon, Follinge area, Jamtland; original of Thorslund (1935, pi. 2, fig. 6); coll. P. Thorslund 1934; x 5. PLATE I AHLBERG, Telephina bicuspis 264 PALAEONTOLOGY, VOLUME 38 Diagnosis. Telephinid trilobites with wide (tr.) glabella, tapering forward and broadly rounded to truncate in front. Cranidial anterior border narrow (tr.), distally turned downward to form a pair of spines; width of anterior border (between lateral extremities of spines) less than half the width (tr.) of occipital ring. Posterior border short (tr.). Librigenae with very large crescentic eyes and generally long genal spines. In addition to genal spines, one or two pairs of marginal librigenal spines may be present. Pygidial rachis with two rings, that may bear paired spines or tubercles, and short (sag.) terminal piece. Dorsal surface generally tuberculate, especially on glabella and occipital ring, and commonly with a pattern of fine, raised lines on the external exoskeletal surface. Glabella with three or four pairs of smooth muscle attachment areas. Remarks. The earliest representatives of Telephina appear near the base of the Llanvirn. The genus underwent prolific radiation during the Middle Ordovician and ranges upwards into the pre- Hirnantian Ashgill. The origin of the genus was discussed by Fortey (1975), who showed that it was probably derived from a species of the early Ordovician genus Oopsites Fortey, 1975. Species attributed to Telephina appear to have a distinctive arrangement of the glabellar muscle attachment areas. The posterior pair is generally prominent, transversely elongate, and situated immediately in front of the outer ends of the occipital furrow. The second area is larger, composite, and situated generally at about half the length of the glabella. The anterior sets are generally indistinct, small, and situated fairly close to the dorsal furrows. The inner, posterior part of the fixigena is commonly smooth, kidney-shaped, and slightly vaulted, and this area may also be a muscle attachment area (cf. Whittington 1965, p. 369; Fortey 1975, p. 100). Nikolaisen (1963) proposed the subgenus Telephina ( Telephops ), with T. granulata (Angelin, 1854) as type species, for those species with a pair of spines or horns on the glabella. In most other characters, the type species of this subgenus is like the type and other species of Telephina ( Telephina ), and I am inclined to the view that the presence or absence of glabellar spines is not of subgeneric significance, because in many evolving trilobite lineages spines can be ephemeral characters. A metalibrigenal spine appears to be present in most species referable to Telephina ( Telephops ). A corresponding spine may, however, also be present in species attributed to Telephina ( Telephina ). Thus, I follow Tripp (1976, p. 376) and regard Telephina ( Telephops ) as a synonym of Telephina ( Telephina ). Telephina bicuspis (Angelin, 1854) Plate 1, figures 1-13; Plate 2, figures 1-12 *1854 Telephus bicuspis Angelin, p. 91, pi. 41, figs 22 and 22 a. v.1882 Telephus sp.; Tullberg, p. 233. v.1890 Telephus bicuspis Ang, ; Moberg, p. 16. v.1897 Telephus bicuspis Ang.; Holm, p. 463 [partim], v. 1913a Telephus bicuspis Ang.; Hadding, pp. 33-35, pi. 1, figs 1-7. v. 19136 Telephus bicuspis Ang.; Hadding, pp. 75-76, pi. 8, figs 1-4 [copies of Hadding’s (1913a, pi. 1, figs la-c, 56-7) original figures]. v.1930 Telephus haddingi Ulrich, pp. 12-13, pi. 1 , figs 1 1-18 [copies of Hadding’s (1913a, pi. 1, figs 2-7) original figures]. v.1930 Telephus jamtlandicus Ulrich, p. 13, pi. I, figs 8-10 [copies of Hadding's (1913a, pi. 1, fig. 1 a-d) original figures], .1930 Telephus bicuspis Angelin; Ulrich, p. 12, pi. 2, figs 20-21 [copies of Angelin’s (1854) original figures], v.1935 Telephus bicuspis Ang.; Thorslund, pp. 20-21, 60, pi. 2, figs 1-6. v.1954 Telephus bicuspis Angelin; Kobayashi, pi. 6, fig. la-c [drawings of Hadding’s (1913a, pi. I, figs 1, 5-7) specimens], .1963 Telephina (Telephina) bicuspis (Angelin, 1854); Nikolaisen, pp. 364-367, pi. 1, figs 1? and 2-10. .1963 Telephina (Telephina) furnesensis Nikolaisen, pp. 367-368, pi. 1, fig. 1 1 .1963 Telephina (Telephina) aff. furnesensis Nikolaisen, p. 360, fig. 4. AHLBERG: TELEPHINID TRILOB1TES 265 .1963 Telephina ( Telephina ) norvegica Nikolaisen, pp. 373-375, pi. 3, figs 1-2. 1975 Telephina bicuspis Hadding; Fortey, p. 95. Neotype. A nearly complete cranidium (RM Ar37315; PI. 1, figs 1-2), figured and selected by Thorslund (1935, pi. 2, figs 1-2). The specimen is from Oslo, Norway, and it may be Angelin’s (1854) original (cf. Holm 1897, p. 463; Thorslund 1935, p. 21; Nikolaisen 1963, p. 365). The horizon is not precisely known, but it comes probably from the Engervik Member of the Elnes Formation (Ogygiocaris Shale or 4aa.s of earlier usage). Additional material. About one hundred cranidia, four eyes, three librigenae, one thoracic tergite, and one pygidium from Jamtland, and fifteen cranidia from Oland. Emended diagnosis. Cranidium wide (length/width ratio TO: 1-6-1-8). Glabella and occipital ring distinctly tuberculate. Anterior end of glabella broadly rounded to truncate with a slight backward curvature medially. Fixigenae wide (tr.) and subtriangular. Palpebral area with narrow, raised rim along postero-lateral margin. Anterior border relatively wide (width between lateral extremities of spines 04— 05 times that of occipital ring). Pygidium wide with broadly rounded posterior margin. Description. Length of cranidium (sag.; excl. occipital spine) 055 to 065 times the width, and widest along a transverse line passing through the anterior half of the glabella. Glabella highly convex (tr.), tapering forward, broadly rounded to truncate anteriorly (or curved slightly backwards medially), and generally 080-0-85 times as long (sag.) as its maximum width. Anterior part of glabella steeply down-sloping to preglabellar furrow, which is tucked beneath the frontal convexity of the glabella. Occipital furrow deep, widest medially, and curved forward abaxially. Occipital ring with moderately long, posteriorly directed spine, and a prominent tubercle antero-medially. Fixigenae wide (tr.) and subtriangular. Palpebral area convex, strongly down-sloping laterally and antero-laterally, and with a narrow, raised rim or ridge postero-laterally. This rim extends parallel to the posterior part of the palpebral furrow. Palpebral lobe anteriorly slightly wider than posteriorly, depressed below the level of the palpebral area and separated from it by a well-defined palpebral furrow. Facial suture running forwards and outwards at about 30° to sagittal line from posterior border furrow, then curving strongly around lateral extremity of palpebral lobe to run inwards and slightly forwards. Anterior border distally turned downward to form a pair of spines, which is generally seen in dorsal view. Width (tr.) of anterior border (between lateral extremities of spines) 0-4 to 05 times that of occipital ring. table 1. Dimensions (in mm) of cranidia of Telephina bicuspis. Lc G Lo Wc Wg Wf LO 6703t 200 1 60 100? 3-20 1-55 0-95 RM Ar 37315 3-30 2-35 — 5-55 2-80 1-45 LO 2565t 410 300 — 7-15 3-90 215 LO 2564t 4-35 315 3-30? 7-35? 3-75 2-15 SGU 8641 4-50 3 30 — 7-30 3-75 2-15 LO 2566t 4-80 3-55 — 8-65? 4-45 2-55 SGU 8657 5-35 400 — 8-70 4-75 2-50 SGU 8658 6-20 4-45 — 11-25 5-55 3-35 SGU 8659 6 65? 4-70 — 10-65 5-60 2-85 LO 2544t 7-30 5-50 — — — 3-00 SGU 8642 800 5-75 — 13-25 6-60 3-60 Librigena with approximately semi-elliptical outer margin, and with long, slender and gently curved genal spine. Extraocular cheeks narrow, widest (tr.) at genal spine. Eye bounded on outer side by a deep furrow, outside which is a convex border. Thoracic tergite with pointed pleura. Rachial ring nearly twice as wide (tr.) as the pleura, and with a posteriorly directed spine at posterior margin. Pleural furrows transverse and widest (exsag.) adaxially. Articulating furrow deep and curved backwards medially. 266 PALAEONTOLOGY, VOLUME 38 Pygidium semicircular to subtriangular in outline and about 1-6 times wider (tr.) than long (sag.; inch articulating half-ring). Rachis highly convex (tr.), tapering backwards, and truncate to bluntly rounded posteriorly. Articulating furrow wide (sag.) and deepest laterally. Two rachial rings well defined by a wide and deep ring furrow. Rachial rings bear a prominent pair of tubercles or spines at mid-line. Terminal piece short (sag.) and steeply downsloping to short (sag.) postrachial field. Pleural region with narrow (tr.) horizontal area adaxially, steeply downsloping and concave laterally. Pleural furrows absent. Border very narrow. The external exoskeletal sculpture consists of relatively widely spaced tubercles on the glabella and on the occipital ring, and a reticulate pattern of raised lines anteriorly and laterally on the palpebral area. Furthermore, well-preserved specimens show a pattern of fine, raised lines on the palpebral lobe and on the glabella. Four pairs of smooth muscle attachment areas are present on the glabella. The posteror pair is transversely elongate and situated immediately in front of the outer ends of the occipital furrow. A second area is considerably larger, composite, diagonally directed, and situated at about half-way along the length of the glabella. The two anterior sets are small and situated close to the dorsal furrows. A smooth, kidney-shaped, and vaulted area is present adaxially on the posterior part of the fixigena, and it may also represent a muscle attachment area. Remarks. In the wide, arched anterior border and the wide fixigenae, Telephina bicuspis closely resembles the early Ordovician genus Oopsites Fortey, 1975 (cf. Fortey 1975, p. 95). On the other hand, the short (tr.) posterior border, the presence of an occipital spine and spines or prominent tubercles on the pygidial rachial rings, and the arrangement of the muscle insertion areas, suggest that it is best classified as a species of Telephina. There is considerable variation exhibited by the material. Much of this variation, such as the expression of the tubercles, is due to varying degrees of flattening and to the mode of preservation. The width of the fixigenae and the shape of the glabella can, however, be shown to vary intraspecifically. The fixigena is 050 to 0-65 times as wide as the maximum width of the glabella. In dorsal view, the anterior end of the glabella ranges from broadly rounded to truncate with a slight backward curvature medially. In general, the front of the glabella is broadly rounded in juvenile specimens, whereas it tends to be truncate in mature ones. Small specimens also have a pair of shallow lateral depressions on the glabella that disappear during ontogeny, and they are generally effaced in cranidia longer (sag.) than 3 5 mm (cf. Nikolaisen 1963, p. 366). Well-preserved specimens exhibit cephalic muscle insertion areas (PI. 2, figs 9, 11-12); their arrangement is similar to that of T. americana (Billings, 1865) (see Whittington 1965, p. 369, pi. 37, figs 5 and 18). T. furnesensis Nikolaisen, 1963 and T. norvegica Nikolaisen, 1963, both from the middle Elnes Formation in the Mjosa area of Norway, agree in all essential features with T. bicuspis as described herein. Therefore, I regard them as subjective junior synonyms of T. bicuspis. Occurrence. In Scandinavia, this species is known from the middle Elnes Formation (4aaj_2 and 4aa3 of earlier usage; Owen et ctl. 1990) in the Oslo Region (Nikolaisen 1963, p. 366; Wandas 1984, p. 217), the lower Anderso Shale (Uhakuan Stage) in Jamtland, and the Folkeslunda Limestone (Lasnamaegian Stage) on Oland. EXPLANATION OF PLATE 2 Figs 1-12. Telephina bicuspis (Angelin, 1854). Lower Anderso Shale, section in Raftan rivulet, Follinge area, Jamtland (1, 5-6), lower Anderso Shale on the northwestern shore of Anderson, Jamtland (2-4), and the Folkeslunda Limestone of Oland (7-12). 1, SGU 6684; cranidium; original of Thorslund (1935, pi. 2, fig. 3); coll. P. Thorslund 1934; x 7. 2, LO 6702t; cranidium, latex cast from external mould; coll. A. Hadding 1912; x 7. 3, LO 6703t; small cranidium; coll. A. Hadding 1912; x 7-5. 4, LO 6704t; cranidium; x 7-5. 5-6, SGU 8638; cranidium in dorsal and anterior views; coll. P. Thorslund 1937; x 6. 7, SGU 8639; cranidium; Lerkaka, central Oland; coll. G. C. von Schmalensee 1881; x 6. 8, SGU 8640; cranidium; Slagerstad, southern Oland; coll. J. C. Moberg 1887; x 6. 9, RM Ar 23864; cranidium; Slagerstad, southern Oland; coll. J. G. Andersson 1892; x 5. 10, SGU 8641; cranidium; Lerkaka, central Oland; coll. G. C. von Schmalensee 1881; x6-5. 11-12, SGU 8642; cranidium in dorsal and anterior views; Slagerstad, southern Oland; coll. J. C. Moberg 1887; x 5-5. PLATE 2 AHLBERG, Telephina bicuspis 268 PALAEONTOLOGY, VOLUME 38 text-fig. 3. Telephina intermedia (Thorslund, 1935). Lower Anderso Shale; Hustedograptus teretiusculus Biozone; Raftan rivulet, Follinge area, Jamtland; coll. P. Thorslund 1934. a, holotype, an incomplete cranidium; original of Thorslund (1935, pi. 2, fig. 7) and Nikolaisen (1963, pi . 2, fig. 1 ); SGU 6688. b, nearly complete librigena; original of Thorslund (1935, pi. 2, fig. 8); SGU 6689. Both x7-5. In Jamtland, it is widely distributed in the lower Anderso Shale (Hustedograptus teretiusculus Biozone) and it has been collected from a large number of localities. These include, among others: (1)0. Ottsjon and a stream section of the Raftan rivulet in the Follinge area (sections described by Thorslund 1935, pp. 6-9); (2) Anderson in the central Storsjon area (locality 1 of Hadding 1912, pi. 7a; 19136, fig. 12); (3) the northern shore of Norderon in the central Storsjon area (see Thorslund and Jaanusson 1960, fig. 22); (4) Mellersta Uton in the central Storsjon area; (5) east of Ovre Malang, about 1 1 km SE of Sunne; (6) a road section (temporary exposure) at Borgen. 2-3 km NW of Oviken; and (7) a stream section 600 m NW of Abbasen, about 4 km NNW of Oviken. On Oland, the species is known from the Folkeslunda Limestone ('Centaurus limestone’; Moberg 1890) at: (1) Skarlov, south of Hulterstad, southern Oland; (2) Slagerstad, south of Stenasa, southern Oland; (3) Brunneby (drainage ditch east of the main road), north of Stenasa, southern Oland; (4) Lerkaka, north of Runsten, central Oland; and (5) from a loose boulder at Stora Mossen, NNW of Boda, northern Oland. A nearly complete cephalon of T. bicuspis is known from the lowermost Uhaku Stage in the Engure drill core (depth: 966 00 m) of western Latvia. Telephina ulrichi (Thorslund, 1935) Plate 3, figures 1-2 v*1935 Telephus ulrichi Thorslund, pp. 21-22, 60-61, pi. 2, figs 9-10. Holotype. An internal mould of a nearly complete cranidium (SGU 6691 ; PI. 3, fig. 1), illustrated by Thorslund (1935, pi. 2, fig. 10), from the lower Anderso (‘Ogygiocaris’) Shale, Hustedograptus teretiusculus Biozone, associated with Botrioides efflorescens (Hadding, 19136), O. Ottsjon, Follinge area, Jamtland (see Thorslund 1935, p. 6 for locality data). Additional material. A largely exfoliated cranidium (SGU 6690; PI. 3, fig. 2), illustrated by Thorslund (1935, pi. 2, fig. 9). Dimensions of holotype (mm). Lc = 3-85; G = 2-75; Lo = 3 00; Wc = 5-00; Wg = 2-85; Wf = 1-35. Diagnosis. See Thorslund (1935, pp. 21-22 and 60-61). Remarks. Telephina ulrichi is closely comparable with T. bicuspis but differs in having a proportionately narrower and longer glabella, and narrower (tr.) fixigenae. Although the width of AHLBERG: TELEPHINID TRILOBITES 269 table 2. Dimensions (in mm) of cranidia of Telephina mobergi. Lc G Lo Wc Wg Wf LR 1 1-95 1-35 3-25 1-70 115 SGU 8643 2-60 1-85 1 35 4-90? 2-75 1 40 LO 2569t 3-20 2-25 — 510 3-05 1-45 LO 6705t 3-40 2-35 — 5-70? 3-50 1 50 SGU 8645 415 2-80 — 8-35 4-85 2-35 LO 2549t 5-40 3-85 — — 5 15 — LO 2568T 610 4-20 — 10-50? 6-75 2-80 the fixigenae is a variable feature in most species of Telephina , their width in T. ulrichi seems to fall outside the range of variation seen in T. biscuspis , and I regard them as two separate species. The glabella of T. ulrichi is subequal in length and width, whereas it is considerably wider than long in T. bicuspis. The occipital ring of T. ulrichi is comparatively long (sag.) with a long occipital spine. Tubercles are faintly indicated on the occipital ring and along the sagittal line of the glabella. Occurrence. In addition to the type locality, known from the lower Anderso Shale in a section in the Raftan rivulet, Follinge area, Jamtland (see Thorslund 1935, p. 7 for a locality description). Telephina intermedia (Thorslund, 1935) Text-figure 3 v* 1935 Telephus intermedins Thorslund, pp. 22 and 61, pi. 2, figs 7-8. 1963 Telephina ( Telephina ) intermedia (Thorslund, 1935); Nikolaisen, pp. 369-370, pi. 2, figs 1-5. Holotype. An incomplete cranidium (SGU 6688 ; Text-fig. 3a), illustrated by Thorslund (1935, pi. 2, fig. 7) and Nikolaisen (1963, pi. 2, fig. 1), lower Anderso (‘Ogygiocaris’) Shale, Hustedograptus teretiusculus Biozone, section in Raftan rivulet, Follinge area, Jamtland (see Thorslund 1935, p. 7 for locality data). Additional material. An incomplete librigena (SGU 6689; Text-fig. 3b), illustrated by Thorslund (1935, pi. 2, fig. 8). Dimensions of holotype (mm). Lc = 510; G = 365; Wg = 4-70; Wf = F70?. Diagnosis. See Thorslund (1935, pp. 22 and 61). Remarks. In the outline and proportions of the individual parts of the cranidium, Telephina intermedia bears a strong similarity to T. bicuspis. The only difference observed is that T. intermedia has a pair of distinct depressions on the glabella. It is doubtful whether this is of specific significance, because such depressions are present in juvenile specimens of T. bicuspis , and may also be faintly indicated in adult specimens. Hence, T. intermedia may eventually prove to be a junior subjective synonym of T. bicuspis. For the time being, however, I treat it as a distinct species. Occurrence. Outside the type locality, this species has been described from the middle-upper Elnes Formation in the Oslo Region of Norway (Nikolaisen 1963, p. 369). Telephina mobergi (Hadding, 1913«) Plate 3, figures 3-14 v*1913a Telephus mobergi Hadding, pp. 37-38, pi. 2, figs 12-17. 270 PALAEONTOLOGY, VOLUME 38 v. 19 1 36 Telephus mobergi Hadding; Hadding, p. 76, pi. 8, figs 6-8 [copies of Hadding’s (1913a) original figures]. v.1917 Telephus mobergi Hdg; Isberg, pp. 593-596, pi. 6, figs 1-3. v.1930 Telephus mobergi Hadding; Ulrich, pp. 14-15, pi. 2, figs 1-9 [copies of Hadding’s (1913a) original figures]. .1963 Telephina ( Telephina ) mobergi (Hadding, 1913); Nikolaisen, pp. 371-373, pi. 2, figs 6-12. Lectotvpe. An incomplete cranidium (LO 2568T ; PI. 3, fig. 7) figured by Hadding (1913a, pi. 2, fig. 13), selected and refigured by Nikolaisen (1963, pi. 2, fig. 6), lowermost Anderso (‘Ogygiocaris’) Shale, lower Hustedograptus teretiusculus Biozone, Anderson, Jamtland (locality 1 of Hadding 1912, pi. 7a, 19136, fig. 12). Additional material. Thirty-three cranidia, seven librigenae, ten fragmentary eyes, and five thoracic tergites. The specimens are preserved in a dark grey limestone or calcareous siltstone, and in general they are slightly compressed. Emended diagnosis. Cranidium subrectangular in outline and wide (length/width ratio TO: T6-2-0). Glabella strongly tapered forward, slightly pear-shaped in dorsal view, and with a pair of distinct, longitudinally elongated depressions. Glabella smooth. Anterior part of palpebral lobe wide, and directed along a nearly transverse line passing just in front of the glabella. Description. Cranidium subrectangular in outline, about three-fifths as long as it is wide, and widest along a transverse line passing through the anterior part of the glabella. Glabella moderately convex, strongly tapered forward, broadly rounded anteriorly, slightly pear-shaped in dorsal view, and 0-6-0-8 times as long (sag.) as its maximum width (Table 2). Slightly posterior to the mid-length of glabella there is a pair of distinct, longitudinally elongated depesssions. Occipital furrow moderately deep and wide, curved forward abaxially. Occipital ring bears a moderately long, slender spine, posteriorly directed and with circular cross section. Fixigenae subtriangular and wide (tr.). Palpebral area convex and strongly downsloping anteriorly and laterally. It is widest (tr.) anteriorly, gradually narrowing backwards. Palpebral lobe widest anteriorly and directed forward and slightly outward from the posterior border furrow, then curved abruptly inward along a transverse line passing just in front of the glabella. Librigena fairly wide with semicircular outer margin and very long spine, directed laterally. Extraocular cheeks and border widest at librigenal spine. Border convex (tr.). Thoracic tergites with short (tr.), pointed pleurae. Pleural furrows transverse and widest (exsag.) adaxially. Rachial ring nearly twice as wide (tr.) as the pleura, and with a posteriorly directed spine at posterior margin. Surface sculpture poorly known but appears to be smooth except for granules on the occipital ring and the thoracic rachial rings. In addition, a reticulate pattern of raised lines is present laterally and antero-laterally EXPLANATION OF PLATE 3 Figs 1-2. Telephina ulrichi (Thorslund, 1935); lower Anderso Shale; Hustedograptus teretiusculus Biozone; Jamtland; coll. P. Thorslund 1934. 1, holotype, SGU 6691; a nearly complete cranidium; original of Thorslund (1935, pi. 2, fig. 10); 6. Ottsjon, Follinge area; 2, SGU 6690; cranidium, internal mould; original of Thorslund (1935, pi. 2, fig. 9); Raftan rivulet, Follinge area. Both x7. Figs 3-14. Telephina mobergi (Hadding, 1913a); lowermost Anderso Shale; lower Hustedograptus teretiusculus Biozone; northwestern shore of Anderson, Jamtland (3-5, 7-8, 11-14; coll. A. Hadding 1912), and Fagerdal, Jamtland (6, 9-10; coll. P. Thorslund and R. Skoglund 1961). 3, LO 2569t; cranidium; original of Hadding (1913a, pi. 2, fig. 14); x 8. 4, LO 6705t; cranidium; x 8. 5, LO 6706t; cranidium; x 8. 6, SGU 8643; cranidium; x 9. 7, lectotype, LO 2568T; an incomplete cranidium; original of Hadding (1913a, pi. 2, fig. 13) and Nikolaisen (1963, pi. 2, fig. 6); x 6. 8, LO 6707t; cranidium; x 8. 9, SGU 8644; cranidium; x7. 10, SGU 8645; cranidium; x 7. 11, LO 2570t; incomplete librigena; original of Hadding (1913a, pi. 2, fig. 16), Isberg (1917, pi. 6, figs 2-3), and Nikolaisen (1963, pi. 2, fig. 8); x 6. 12, same librigena, latex cast from external mould; x 6. 13, LO 2550t; incomplete thoracic tergite; original of Hadding (1913a, pi. 2, fig. 17); x 8. 14, LO 6708t; incomplete thoracic tergite; x8. PLATE 3 AHLBERG, Telephina 272 PALAEONTOLOGY, VOLUME 38 on the palpebral area, and transversely arranged terrace lines occur on the doublure of the occipital ring. Rare specimens exhibit a pattern of fine raised lines on the external exoskeletal surface and transversely elongate muscle attachment areas immediately in front of the outer part of the occipital furrow. Pygidium not known. Remarks. Telephina mobergi most closely resembles T. sulcata Nikolaisen, 1963, from the basal Elnes Formation (Helskjer Member; Owen et al. 1990, p. 17) in the Mjosa area, Norway, but T. sulcata has a considerably less tapered and nearly subrectangular glabella, and shorter (exsag.) lateral glabellar depressions (furrows). T. bipunctata (Ulrich, 1930), from the Botetourt Formation (Caradoc; Baltoniodus gerdae Subzone; S. M. Bergstrom, pers. comm. 1992) of the southern Appalachians (Virginia), also invites comparison. In the proportions of the individual parts of the cranidium it is closely comparable with T. mobergi , but has deeper and more distinct lateral glabellar depressions, a strongly curved genal spine, and the external surface has a distinct pattern of raised lines and a more conspicuous muscle attachment area immediately in front of the occipital furrow. It must be emphasized, however, that the majority of the specimens ascribed to T. mobergi are largely exfoliated and the surface sculpture is poorly known. Isberg (1917) described damaged and irregularly regenerated lenses in the eyes of T. mobergi. Occurrence. In Sweden this species is known with certainty only from the type stratum and type locality, and from the lower Anderso Shale at Fagerdal (temporary exposure in the northern part of the village), about 8 km north of Hammerdal, Jamtland. Outside Sweden, the species has been described from the upper Elnes Formation (formerly Ogygiocaris Shale or 4aa3) in the Oslo Region of Norway (Nikolaisen 1963, p. 371). Telephina wegelini (Angelin, 1854) Plate 4, figures 1-9 * 1854 v.1884 v. 1913a v. 1925 .1930 v.1930 71963 non 1971 ? 1979 71980 Telephus wegelini Angelin, p. 91, pi. 41, fig. 23. Telepltus fractus Barr.; Tornquist, pp. 89-90 [remarks]. Telephus wegelini Ang. ; Hadding, pp. 40-41, pi. 2, figs 18-19. Telephus wegelini Angelin; Warburg, pp. 90-92, pi. 1, figs 16-18. Telephus wegelini Angelin; Ulrich, pp. 13-14, pi. 2, figs 10-12 [copies of Angelin's (1854, pi. 41, fig. 23) and Hadding's (1913a, pi. 2, figs 18-19) original figures]. Telephus linnarssoni Ulrich, pp. 15-17, pi. 2, figs 15-17 [copies of Warburg's (1925, pi. 1, figs 16-18) original figures]. Telephina ( Telephina ) wegelini (Angelin, 1854); Nikolaisen, pp. 383-384. Telephina cf. linnarssoni (Ulrich); Dean, pp. 46-48, pi. 22, figs 1-2, 1 1. Telephina sp. ; Bruton and Owen, fig. 6. Telephina sp.; Owen and Bruton, p. 11, pi. 1, fig. 9. Type data. The holotype by monotypy (Angelin 1854, pi. 41, fig. 23) cannot be traced, and is considered lost. A nearly complete but flattened cranidium (LO 2571T; PI. 4, fig. 5), figured by Hadding (1913a, pi. 2, fig. 18), is here selected as neotype. It was collected by S. L. Tornquist from the Fjacka Shale (formerly black Tretaspis or Trinucleus shale; lower Ashgill) at Vikarbyn in the Siljan district, Dalarna (see Tornquist 1883, p. 58 for locality data). Material. Fourteen cranidia from the Fjacka Shale, and one cranidium from the Boda Fimestone. Remarks. Only cranidia of this species are known, and they show considerable variation due to varying degrees of flattening. For instance, the anterior border is clearly visible in dorsal view in strongly flattened specimens (PI. 4, fig. 7), whereas it is tucked beneath the frontal lobe of the glabella in specimens retaining more of their original convexity (PI. 4, fig. 8). To the detailed description given by Warburg (1925, p. 90) it can be added that the occipital spine is long with a circular cross section (PI. 4, fig. 2), and the posterior part of the palpebral area has AHLBERG: TELEPHINID TRILOBITES 273 a distinct, kidney-shaped muscle insertion area. Furthermore, there is a narrow, raised ridge or rim along the postero-lateral margin of the palpebral area. table 3. Dimensions (in mm) of cranidia of Telephina wegelini. An asterisk indicates that the specimen is strongly flattened. Lc G Lo Wc Wg Wf LO 6709t 3-40 2-65 — 5-25 2-80 1-50 LR 2* 3 40? 2-65? — 5-95 3-50 1-30 SGU 8646* 415 3-15 — 6-50 4-35 1-35 LO 67 1 Ot* 4-35 3-20 — 5-75 3-75 1-30 SGU 4106 4-55 3-35 — 7-00? 4-20 1 50 LO 2571T 4-60 3-70 240 6-60 4-25 1-80 LO 2572t* 4-70 3-70 2-75 7-25 4-70 1 -80 Warburg’s (1925) description of T. wegelini is based on a fairly well-preserved cranidium (SGU 4106; PI. 4, figs 8-9) from the Boda Limestone in the Siljan district. It differs in some minor respects from the neotype and other specimens from the Fjacka Shale, and Ulrich (1930, p. 15) assigned it to a new species, T. linnarssoni. This specimen is, however, uncompressed, and the differences pointed out by Ulrich (1930) can largely be attributed to the flattening of the specimens from the Fjacka Shale. Hence, I concur with Nikolaisen (1963, p. 383) and regard T. linnarssoni as a junior subjective synonym of T. wegelini. A fragmentary cranidium from the Chair of Kildare Limestone (Ashgill) of eastern Ireland was described by Dean (1971, p. 46) as T. cf. linnarssoni (Ulrich). The poor preservation makes evaluation difficult, but it differs from T. wegelini in having a proportionately wider (tr.) glabella, which is strongly tapered forwards and less broadly rounded in front. T. wegelini is closely comparable with the type species, T.fracta from the Ashgill of Bohemia, and the two species are distinguishable only on the basis of minor characters. I have examined the type specimen of T.fracta (see Horny and Bastl 1970, pi. 4, fig. 1 1), and it differs from T. wegelini mainly in that the anterior part of the palpebral lobe is narrower, and the palpebral area lacks a raised rim along the postero-lateral margin. Moreover, there is no indication of muscle insertion areas on the palpebral areas, but this may be due to the mode of preservation. Occurrence. Upper Ordovician (Harjuan Series) in the Siljan district, Dalarna. One specimen (SGU 4106; PI. 4, figs 8-9) is from the Boda Limestone at Boda ; the remaining ones are from the Fjacka Shale (Pleurograptus linearis Biozone) at Vikarbyn, Amtjarn, Enan, and Skattungbyn. In addition, specimens questionably assigned to the species are known from the upper Solvang Formation (lowermost Ashgill) in the Oslo Region of Norway (Nikolaisen 1963, p. 383; Owen and Bruton 1980, p. 11). Telephina granulat a (Angelin, 1854) Plate 4, figures 13-14; Plate 5, figures 1—11; Plate 6, figures 1-3 *1854 Telephus granulatus Angelin, p. 91, pi. 41, fig. 21 v.1875 Bohemillaip. ) denticulata Linnarsson, pp. 495-497, pi. 22, figs 4-5. .1897 Aeglina denticulata (Linrs.); Holm, p. 461. v.1897 Telephus bicuspis Ang.; Holm, p. 463 [partim], v. 191 3a Telephus granulatus Ang.; Hadding, pp. 35-37, pi. 1, figs 8-10. v. 19136 Telephus granulatus Ang.; Hadding, p. 76, pi. 8, figs 9-10 [copies of Hadding’s (1913a, pi. 1, figs 8, 10) original figures], v.1930 Telephus granulatus Angelin; Ulrich, p. 11, pi. 1, figs 19-23 [copies of Hadding’s (1913a, pi. 1, figs 8-10) original figures]. 274 PALAEONTOLOGY, VOLUME 38 v.1936 Telephus granulatus Ang. ; Asklund, pp. 9-10, pi, 2, figs 1-7. non 1963 Telephina ( Telephops ) granulata (Angelin, 1854); Nikolaisen, pp. 386-387, text-fig. 5, pi. 4, fig. 13. v.1963 Telephina (Telephops) bos Nikolaisen, pp. 389-391, pi. 4, figs 4-9. v. 1982b Telephina sp.; Jaanusson, p. 177. Type data. The specimen figured by Angelin (1854, locality given as ‘Norvegiae’) cannot be located and is considered lost. No other possible syntypes can be traced, and as neotype I select a cranidium (PMO 72698; PI. 5, fig. 1) from the Vollen Formation (formerly Ampyx Limestone or 4a/(; Owen et al. 1990) on the western side of Bygdoy in Oslo, Norway. It was illustrated by Nikolaisen (1963, pi. 4, fig. 8), who assigned it to a new species, T. bos. Angelin's illustration (1854, pi. 41 , fig. 21 ) is of a tuberculate cranidium with fairly narrow (tr.) fixigenae and a pair of spines (broken) at the anterior end of the glabella. For a long time, however, the concept of T. granulata has been based on Hadding's (1913a) fairly detailed description, which is based on material from Jamtland. It would have been preferable to choose one of Hadding’s (1913a) specimens as neotype, but this is not possible because Angelin’s missing specimen was from Norway (precise locality not known). T. bos Nikolaisen, 1963 from Norway agrees in all essential features with T. granulata sensu Hadding, 1913a, and I regard them as conspecific. To retain stability, a neotype was therefore chosen among specimens described as T. bos by Nikolaisen (1963). In this context, it is worth noting that the specimens described as T. granulata by Nikolaisen (1963, p. 386) differ in some respects from T. granulata sensu Hadding, 1913a, and seem to represent a different species. Material. Fourteen nearly complete cranidia, six fragmentary cranidia, four librigenae, two incomplete thoracic tergites, and two pygidia (SGU 3954 and 6721). The specimens are generally preserved as internal moulds. Description. Length of cranidium (sag. ; excl. occipital spine) about 0-7 times the width. Glabella highly convex (tr.), widest adjacent to or slightly in front of the occipital furrow, tapering forward (more rapidly in the anterior part), broadly rounded anteriorly, and generally about 09 times as long (sag.) as its maximum width. Preglabellar furrow tucked beneath the frontal convexity of the glabella. A pair of horns or spines is present at the top of the frontal slope of the glabella. These spines are situated far apart from each other and project obliquely forward, outward, and upward from the antero-lateral parts of the glabella. Occipital ring with a moderately long and slender spine, posteriorly directed and with circular cross section. Palpebral area EXPLANATION OF PLATE 4 Figs 1-9. Telephina wegelini (Angelin, 1854). All specimens except 8-9 are from the Fjacka Shale ( Pleurograptus linearis Biozone) at Amtjarn (1-3; coll. C. Wiman 1906), Enan (4), and Vikarbyn (5-7; coll. S. L. Tornquist) in the Siljan district, Dalarna. 1, PMU D2148; flattened cranidium; x 8. 2, PMU D2146; flattened cranidium with complete occipital spine; x 6. 3, PMU D2147; flattened cranidium; x 6. 4, SGU 8646; flattened cranidium; x 6. 5, neotype, LO 2571T; a nearly complete cranidium; original of Hadding (1913a, pi. 2, fig. 18); x 6. 6, LO 6709t; flattened cranidium; latex cast from external mould; x 8. 7, LO 67 1 Ot ; flattened cranidium; x 8. 8-9, SGU 4106; cranidium in dorsal and anterior views; original of Warburg (1925, pi. 1, figs 16-18); Boda Limestone at Boda, Siljan district, Dalarna; coll. G. Linnarsson; x 6-5. Figs 10-11. Telephina sp. B. SGU 8647; cranidium in left lateral and dorsal views; Anderso Shale, Mellersta Uton, central Storsjon area, Jamtland; x 6. Fig. 12. Telephina sp. A. LO 2548t; flattened cranidium; original of Hadding (1913a, pi. 2, fig. 24); Lower Dicellograptus Shale, Kyrkbaken rivulet in Rostanga, Scania; x 8. Figs 13-14. Telephina granulata (Angelin, 1854); upper Anderso Shale (Nemagraptus gracilis Biozone), Anderson, central Storsjon area, Jamtland. 13, SGU 8648; cranidium; locality 2 of Hadding (1912, pi. 7a; 19136, fig. 12); coll. P. Thorslund 1956; x8. 14, LO 2567t; cranidium with glabellar muscle attachment areas; original of Hadding (1913a, pi. 1 , fig. 9); locality 5 of Hadding (1912, pi. 7a; 19136, fig. 12); coll. A. Hadding 1912; x 7. PLATE 4 AHLBERG, Telephina 276 PALAEONTOLOGY, VOLUME 38 crescentic and moderately wide (tr.). Palpebral lobe slightly wider anteriorly than posteriorly. Width (tr.) of anterior border (between lateral extremities of spines) about one-third that of occipital ring. Librigena with approximately semi-elliptical outer margin and extremely long genal spine, which is directed laterally to postero-laterally. Extraocular cheeks narrow and occupied mainly by a convex border, which is strongly downsloping laterally. A distinct, postero-laterally directed metalibrigenal spine is present. Extraocular cheeks widest (tr.) at genal spine. Visual surface bounded on outer side by a deep furrow. Thoracic rachial rings highly convex (tr.) and with a posteriorly directed spine at posterior margin. Pleurae not known. Pygidium subtriangular in outline and slightly wider than long (length/width ratio about 10: T3). Rachis highly convex (tr.), tapering backwards, and occupying slightly more than half of the maximum pygidial width at its anterior end. Terminal piece small, poorly defined, and fused with the posterior rachial ring. Rachial rings bear a pair of spines or prominent tubercles very close together at mid-line. Posterior end of rachis truncate and sloping down almost vertically to the short (sag.) post-rachial field. Pleural region narrow, steeply downsloping laterally, and with a narrow, convex border. Anterior margin of pleural region a narrow, raised rim. Antero-lateral corners of pygidium pointed or with a short spine. Pleural furrows not apparent. Surface sculpture consists of fairly widely spaced tubercles on the glabella, the occipital ring and the thoracic rachial rings. In addition, transversely arranged terrace lines are present on the ventral surface of the occipital ring, and the external exoskeletal surface of the pygidial pleural region exhibits fine, raised lines arranged in a Bertillon pattern. At least two pairs of smooth muscle attachment areas appear to be present on the glabella. The posterior pair is transversely elongate and situated immediately in front of the outer parts of the occipital furrow. The anterior pair is larger, composite, diagonally directed, and situated at about half-way along the length of the glabella. Remarks. The material of T. granulata displays considerable morphological variation. Much of this variability is due to variation in the width and shape of the fixigenae, and in the curvature of the palpebral lobe. Modest variation in the shape of the glabella and in the position of the glabellar spines can also be observed. The holotype of T. bos Nikolaisen, 1963 (PMO 72701) differs from T. granulata in having wider fixigenae and a proportionately wider and shorter glabella. It may well be sagittally compressed, however, and is considered a junior synonym (see above). The specimens described by Nikolaisen (1963, p. 386) as T. granulata are from the upper Elnes Formation (probably Hustedograptus teretiusculus Biozone) in the Oslo Region, Norway. The small cranidium figured in Nikolaisen’s text-fig. 5 differs from T. granulata as described herein in having wider (tr.) fixigenae and the glabellar spines close together in a fairly posterior position. In the position of the glabellar spines, it approaches T. biseriata (Asklund, 1936), but the wide fixigenae (closely resembling those of T. bicuspis ) indicate that it cannot be assigned to that species. The narrow palpebral lobe and the extremely long and stout occipital spine distinguishes the cranidium figured in Nikolaisen's pi. 4, fig. 13 from those of T. granulata. In addition, it has the glabellar spines fairly close together, and the palpebral lobe is more evenly curved than in most specimens referred to T. granulata. Hence, I conclude that the specimens described as T. granulata by Nikolaisen (1963) do not belong to that species. T. bicornis (Ulrich, 1930), from the Effna Limestone (Caradoc; Prioniodus variabilis Subzone; S. M. Bergstrom, pers. comm. 1992) of the southern Appalachians (Virginia), is very similar to T. granulata. However, I hesitate to regard them as conspecific because there appear to be slight differences. For instance, the fixigenae are consistently somewhat wider (tr.) and the tubercles are larger and more conspicuous in T. bicornis , which in addition, has the short metalibrigenal spine situated much closer to the genal spine. Ulrich (1930, p. 25) emphasized that the glabellar spines are in a more posterior position in T. bicornis , but this is a variable feature (compare the cranidia figured by Ulrich 1930, pi. 4, figs 6 and 8). A fragmentary cranidium from the Brickworks Quarry Shales Member, Knockerk Formation (Caradoc), of eastern Ireland was illustrated and described by Brenchley et al. (1967, p. 302, pi. 7, figs 7-8) as T. cf. bos Nikolaisen. It is closely comparable with T. granulata , but differs in having slightly wider (tr.) fixigenae and a less broadly rounded glabellar front. In these respects the Irish specimen is more like T. bicornis , and it probably represents that species (cf. Romano 1980, p. 68). AHLBERG: TELEPHINID TRILOBITES 277 table 4. Dimensions (in mm) of cranidia of Telephina granulata. Lc G Lo Wc Wg Wf LO 2567t 3-95? 2-95 — 5-45? 3-20 1 30 SGU 8648 4-25 3 10 — 6-15? 3-55 1 50 SGU 8651 4-90 3-75 — 6-70? 3-90 1-60 SGU 8660 500? 3-90 — 6-85 4 15 1-65 PMO 72698 5-35 4-00 — 7-10? 4-00 1 65 LO 67 1 2t 5-95 4-45 — 7-75 4-85 1-85 SGU 6427 7-00 5-25 — 9-50 5-80 2-00 Additional material from the Brickworks Quarry Shales was described by Romano and Owen (1993), who reassigned the Irish form to T. cf. biconus. Occurrence. In Jamtland, this species has been collected from limestones in the Nemagraptus gracilis Biozone on Anderson (localities 2 and 5 of Hadding 1912, pi. 7a; 19136, fig. 12), on the southwestern shore of Bynaset, Froson, at Hara about 9 km south of Sunne (see Thorslund 1937, p. 1 1 for locality data), at Digernas about 4 km north-east of Sunne, and at Ytterhallen in the Hallen area (loose boulder). In Vastergotland, T. granulata is known from an argillaceous limestone in the lowermost part of the upper Dalby Limestone in the Gullhogen quarry on the southeastern slope of northern Billingen (see Jaanusson 19826, p. 176 and Holmer 1989, p. 6 for locality data and stratigraphy). In terms of the graptolite biozonation, the Vastergotland specimens were recovered from strata corresponding with the uppermost Nemagraptus gracilis Biozone or, more probably, the lowermost Diplograptus multidens Biozone. A nearly complete cephalon is known from the Kukruse Stage in the Blidene drill core (depth 910 85 m) in western Latvia, and a cephalon tentatively assigned to the species has been recorded from the uppermost Uhaku Stage in the Lopatovo-8 drill core (depth 456-30 m) in the Pskov district of western Russia. Telephina aff. granulata (Angelin, 1854) Plate 6, figures 4-8 v.1919 Telephus granulatus Ang.; Funkquist, p. 39, pi. 2, fig. 9. v.1951 Telephus granulatus Ang.; Nilsson, pp. 684, 688. Material. One nearly complete cranidium (LO 67 1 4t) and two incomplete cranidia (LO 2966t and 67 1 3t). Dimensions (mm). Lc G Lo Wc Wg Wf LO 67 1 4t 5-65 4 15 — 7-50? 4-35 2 00 Remarks. The cranidia are very like those of T. granulata but differ in having a slightly longer glabella, which is truncate in front. In addition, the spines on the glabella are in a slightly posterior position and closer to the mid-line than in T. granulata , especially in the specimen figured on Plate 6, figures 7-8. Occurrence. Killerod Formation (‘ bronni beds’; equivalent to part of the upper Hustedograptus teretiusculus Biozone according to Bergstrom 1973, p. 15) at Killerdd in south-east Scania (locality 2 of Regnell 1960, fig. 4; section described by Nilsson 1951, p. 683). It is also known from a loose boulder at Rodmolla in the Tosterup area, south-east Scania (cf. Funkquist 1919, p. 42). Telephina biseriata (Asklund, 1936) Plate 6, figures 9-13 v*1936 Telephus biseriatus Asklund, pp. 1 1-12, pi. 1, figs 9-1 1. 278 PALAEONTOLOGY, VOLUME 38 Type data. The holotype by monotypy is a nearly complete cranidium (SGU 6714; PI. 6, fig. 9), illustrated by Asklund (1936, pi. 1, figs 9-11). It was collected by G. Linnarsson in 1871 from a shore section on northwestern Anderson in the central Storsjon area. Jamtland. Its stratigraphical position is not known precisely, but it was probably collected from a dark grey limestone in the middle-upper part of the Hustedograptus teretiusculus Biozone (middle Anderso Shale). Material. In addition to the holotype, six cranidia, one incomplete pygidium, and fragments of the eyes. The majority of the specimens are preserved as internal moulds in a dark grey limestone and seem to retain their original convexity. Description. Glabella subequal in length (sag.) and maximum width or slightly wider than long. A pair of horns or spines, situated very close together, is present at 0-6-0 7 of the glabellar length from its posterior end. Occipital spine probably present but not preserved. Anterior border narrow (sag.) with the spines situated very close together (width between lateral extremities of spines one-quarter to one-third that of occipital ring). Thorax and extraocular librigenae not known (Table 5). Surface sculpture consists of fairly widely spaced tubercles on the glabella and the occipital ring, and terrace lines occur on the ventral surface of occipital ring. The tubercles are most prominent along the mid-line of the glabella. The fixigenae and the pygidium appear to be smooth, except for indistinct 'wrinkles’ anterolaterally on the palpebral area. Remarks. This species is distinctive and differs from T. granulata in that the glabellar spines are situated very close together in a posterior position. It is worth noting, however, that the position of the spines is a variable feature. In the holotype (PI. 6, fig. 9), for instance, they are in an extremely posterior position, whereas they are more anteriorly placed in the cranidium figured on Plate 6, figures 11-12. The expression of the tubercles varies in strength, but this can be attributed probably to the mode of preservation. The glabella is generally subequal in length and maximum width, and comparatively longer than in T. granulata. The pygidium is slightly wider than long and very similar to that of T. granulata. Occurrence. Middle Anderso Shale (middle-upper Hustedograptus teretiusculus Biozone) on the northwestern and northern shore of Anderson (cf. Thorslund 1937, p. 10), the northern shore of Norderon (see Thorslund and Jaanusson 1960, fig. 22), and 0-5 km E of Lovtorpet on Froson in the central Storsjon area, Jamtland. In addition, a few cranidia are known from coeval strata at Onsvedsbacken south of Sunne, Jamtland (see Hadding 1912 for locality data). The majority of the specimens are from a dark grey, bedded limestone generally referred to as the Biseriata Limestone (' Telephina biseriata beds’ of Thorslund and Jaanusson 1960). Conodonts recovered from this limestone are indicative of the Eoplacognathus lindstroemi Sub-biozone and the lower EXPLANATION OF PLATE 5 Figs 1-11. Telephina granulata (Angelin, 1854). All specimens except 1 are from the upper Anderso Shale (Nemagraptus gracilis Biozone), central Storsjon area, Jamtland. 1, neotype, PMO 72698; a nearly complete cranidium; original of Nikolaisen (1963, pi. 4, fig. 8); Vollen Formation, western side of Bygdoy in Oslo, Norway; coll. F. Nikolaisen 1958; x 5-5. 2-4, SGU 6427; cranidium in dorsal, anterior, and left lateral views ; original of Hadding ( 1 9 1 3«, pi. 1 , fig. 8a-c) ; Hara south of Sunne ; coll. G. C. von Schmalensee 1 884 ; x 6. 5, RM Ar 9897a; cranidium with glabellar spines; original of Asklund (1936, pi. 2, fig. 2); Ytterhallen, Hallen area (loose boulder); coll. G. C. von Schmalensee; x 6. 6, SGU 8649; cranidium with glabellar muscle attachment areas; Hara south of Sunne; coll. G. C. von Schmalensee 1884; x 7. 7, SGU 8650; cranidium; Hara south of Sunne; coll. G. C. von Schmalensee 1884; x 7. 8, SGU 8651; cranidium; Hara south of Sunne; coll. P. Thorslund 1936; x7-5. 9, SGU 6721; nearly complete pygidium; original of Asklund (1936, pi. 2, fig. 7); Bynaset, Froson; x 9. 10, RM Ar 9899; nearly complete librigena; original of Asklund (1936, pi. 2, fig. 4); Ytterhallen, Hallen area (loose boulder); coll. G. C. von Schmalensee 1885; x 2-5. 1 1, RM Ar 9897b; incomplete librigena in ventral view; Ytterhallen, Hallen area (loose boulder); coll. G. C. von Schmalensee; x 6. PLATE 5 AHLBERG, Telephina granulate i 280 PALAEONTOLOGY, VOLUME 38 Pygodus anserinus Biozone (Bergstrom el al. 1974, table 10), and, in terms of the graptolite biozonation, the Biseriata Limestone seems to represent the middle-upper part of the H. teretiusculus Biozone. Telephina aff. biseriata (Asklund, 1936) Plate 6, figure 14 Material. An incomplete cranidium (SGU 8656), largely exfoliated, collected by P. Thorslund in 1937. Dimensions (mm). G = 4-20; Wg = 5 00; Wf = 1-60. Remarks. The cranidium resembles that of T. biseriata in having the glabellar spines situated close together, but they are in a more anterior position (at about 0-9 of the glabellar length from its posterior end). In addition, it has a proportionately wider glabella (length/width ratio 1 : 1-2) and considerably narrower (tr.) fixigenae with the facial suture curved more evenly around the lateral extremity of the palpebral lobe. It seems to represent a new, undescribed species, but with the limited material at hand it is left under open nomenclature. The glabellar surface sculpture consists of fairly widely spaced tubercles, except for two pairs of large, smooth muscle attachment areas. The posterior pair is transversely elongate and situated immediately in front of the outer parts of the occipital furrow. The anterior pair is larger and situated about half way along the glabella. Occurrence. Dark grey limestone in the middle Anderso Shale (probably upper Hustedograptus teretiusculus Biozone) on the northwestern shore of Anderson, Jamtland (locality 1 of Hadding 1912, pi. 7a; 19136, fig. 12). Telephina sp. A Plate 4, figure 12 v. 19 13a Telephus sp.; Hadding, p. 42, pi. 2, fig. 24. v. 19 136 Telephus sp.; Hadding, p. 76, pi. 8, fig. 5 [copy of Hadding’s (1913a, pi. 2, fig. 24) original figure]. v.1930 Telephus species undetermined; Ulrich, pi. 1, fig. 2 [copy of Hadding’s (1913a, pi. 2, fig. 24) original figure]. Material. An internal mould of a flattened cranidium (LO 2548t), collected by A. Hadding in 1911. Dimensions (mm). Lc = 340?; G = 2-50; Lo = 2-25?; Wc = 5-25; Wg = 3 00; Wf = 1-35. EXPLANATION OF PLATE 6 Figs 1-3. Telephina granulata (Angelin, 1854). 1, SGU 8652; incomplete librigena; upper Anderso Shale (Nemagraptus gracilis Biozone) at Hara south of Sunne, Jamtland; coll. P. Thorslund 1936; x6. 2-3, cranidia; upper Dalby Limestone, Gullhogen quarry, Billingen, Vastergotland; coll. J. Johansson. 2, LO 671 It. 3, LO 6712t. Both x 6. Figs 4-8. Telephina aff. granulata (Angelin, 1854). Killerod Formation at Rodmolla, Tosterup area (4; coll. K. A. Gronwall) and at Killerod (5-8; coll. R. Nilsson 1943), south-east Scania. 4, LO 2966t; fragmentary cranidium; original of Funkquist (1919, pi. 2, fig. 9). 5-6, LO 67 1 3t ; incomplete cranidium in dorsal and anterior views. 7-8, LO 67 1 4t ; nearly complete cranidium in dorsal and anterior views. All x 6. Figs 9-13. Telephina biseriata (Asklund, 1936). Middle Anderso Shale (middle-upper Hustedograptus teretiusculus Biozone) on Anderson (9, 11-12) and Norderon (10), central Storsjon area, and at Onsvedsbacken (13) south of Sunne, Jamtland. 9, holotype, SGU 6714; a nearly complete cranidium; original of Asklund (1936, pi 1, figs 9-11); x 8. 10, SGU 8653; incomplete pygidium; coll. P. Thorslund 1950; x 9-5. 1 1-12, SGU 8654; nearly complete cranidium in dorsal and anterior views; coll. P. Thorslund 1950; x7-5. 13, SGU 8655; cranidium; coll. P. Thorslund 1950; x 7. Fig. 14. Telephina aff. biseriata (Asklund. 1936). SGU 8656; Middle Anderso Shale, northwestern shore of Anderson, Jamtland (locality I of Hadding 1912, pi. 7a, 19136, fig. 12); x 6. PLATE 6 AHLBERG, Telephina 282 PALAEONTOLOGY, VOLUME 38 table 5. Dimensions (in mm) of cranidia of Telephina biseriata. Lc G Lo Wc Wg Wf SGU 6714 3-55 2-65 4-35 2-55 1 20 SGU 8655 4-45 3-40 — 600? 3-55 1-30? SGU 8654 5-20 3-70 — 6-70 400 L65 Remarks. The specimen is strongly flattened and imperfectly preserved. A comparison with named taxa is therefore difficult. The overall shape of the cranidium and the glabella is similar to that of T. bicuspis and it may belong to that species. It differs, however, in having a stouter occipital spine, narrower (tr.) fixigenae, and less strongly curved palpebral lobes. The posterior part of the palpebral area is fairly wide (tr.), and in this respect it is similar to flattened specimens of T. wegelini. Occurrence. Lower Dicellograptus Shale (probably middle part of the Hustedograptus teretiusculus Biozone) at the Kyrkbacken rivulet in Rostanga, Scania, southern Sweden (locality Illb of Moberg 1910, p. 114, pi. 3; section III: 3 of Hadding 19136, p. 19). Telephina sp. B Plate 4, figures 10-11 Material. An internal mould of a nearly complete cranidium (SGU 8647), collected by G. Linnarsson in 1871. Dimensions (mm). Lc = 7-60; G = 500; Wc = 1000?; Wg = 5 85; Wf = 2-25?. Remarks. The cranidium slopes down steeply anteriorly and differs from those of most other species of Telephina in having a strongly convex glabella and extremely convex palpebral areas, which are steeply downsloping laterally. The fixigenae are narrow (tr.) with a crescentic and ridge-like palpebral area. The dorsal and palpebral furrows are wide and deeply incised. The glabella is tapered forwards and steeply downsloping anteriorly. The glabellar frontal lobe is truncate and distinctly arched backwards medially. The occipital furrow is very wide (sag.) and deep. Tubercles are present on the glabella and the occipital ring. A broadly similar form from the Engervik Member of the Elnes Formation at Huk in Oslo, Norway, was described and figured by Nikolaisen (1963, p. 384, pi. 3, figs 15-16) as Telephina sp. no. 2. Occurrence. Anderso Shale (probably lower part; Hustedograptus teretiusculus Biozone) on Mellersta Uton in the central Storsjon area, Jamtland. Telephina sp. C (not figured) v.1948 Telephus sp.; Thorslund, p. 362, pi. 11, fig. 10. v.1964 Telephina sp.; Jaanusson, p. 17. Material. A flattened and poorly preserved cranidium (PMU Vg 37), about L3 mm long (sag.; excl. occipital spine). Remarks. The poor preservation makes evaluation difficult, but the specimen shows the following: the glabella is tapered forward, rounded in front, and subequal in length and maximum width; the occipital ring is fairly long (sag.) with a stout and broad-based occipital spine, and the fixigenae are wide (tr.). AHLBERG: TELEPHINID TRILOBITES 283 Occurrence. Lower Dalby Limestone in the Kullatorp drill core, Kinnekulle, Vastergotland (depth 86-50-86 52 m). In terms of the graptolite biozonation, it was probably recovered from strata corresponding to the Nemagraptus gracilis Biozone (e.g. Jaanusson 1964, table 1, 1982c;, fig. 4). Acknowledgements. Dr Euan N. K. Clarkson, Edinburgh, Dr Richard A. Fortey, London, and Professor Valdar Jaanusson, Stockholm critically read the drafts of the manuscript and suggested valuable improvements. Dr Linda Hints, Tallinn, kindly provided me with material from drill cores in the East Baltic. 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PER AHLBERG Department of Historical Geology Typescript received 26 November 1993 and Palaeontology, Solvegatan 13 Revised typescript received 27 April 1994 S-223 62 Lund, Sweden THE RESPIRATORY ORGANS OF EURYPTERI DS by PHILLIP L. MANNING and JASON A. DUNLOP Abstract. Cuticle fragments from the upper Silurian (Pndoli Series) of south Shropshire, England, are described and interpreted as the respiratory organs of eurypterids. These fragments, combined with whole body evidence, suggest a dual respiratory system: lamellate book-gills, homologous with those of modern xiphosurans and arachnid book lungs, and an additional Kiemenplatten on the true sternite, the roof the branchial chamber. Kiemenplatten is used in preference to gill-tract, because it is a more ‘neutral’ term, without functional implications. Eurypterids may have been partially terrestrial: the Kiemenplatten is interpreted as an accessory aerial respiratory organ, most closely analogous to the branchial ‘lungs' of certain terrestrial crabs. Cuticular projections from the Kiemenplatten are interpreted as having held a layer of water to keep the structure moist during excursions onto land. A new reconstruction of the eurypterid respiratory system is presented. Eurypterid respiratory organs were first described by Laurie (1893) from a specimen of Slimonia as ‘branchial lamellae,’ and were interpreted as being located on the dorsal surface of the abdominal plates (Blatfiisse). The Blatfiisse consist of five pairs of plate-like appendages (Clarke and Ruedemann 1912, pi. 26, fig. 2; Waterston 1975, fig. 4a) which are ventral to the true sternites (ventral body wall) of the opisthosoma, and they enclose a series of five pairs of branchial chambers (Waterston 1975) between themselves and the true sternites. It is these branchial chambers which contain the respiratory organs, which were described subsequently from Baltoeurypterus as five pairs of oval respiratory areas termed ‘Kiemenplatten’ (Holm 1898); these are areas of raised, conical ‘spinules’ covered in microscopic cuticular projections, arranged hexagonally as ‘rosettes’ (Holm 1898; Wills 1965). They were later re-interpreted as being on the ventral surface of the true sternite (the roof of the branchial chamber), not on the Baltfiisse (Moore 1941), and were subsequently renamed ‘gill tracts’ (Wills 1965). Their position within the branchial chamber of Tarsopterella was reconstructed in detail by Waterston (1975). Some eurypterids may have been capable of terrestrial activity (Stormer 1976; Rolfe 1980) and the Kiemenplatten (gill tracts) have been interpreted variously as having aquatic and/or aerial respiratory functions (Stormer 1976; Rolfe 1980; Selden 1985), comparable with isopod pseudotracheae (Stormer 1976). A possible osmoregulatory function was suggested by Waterston (1979) and by Selden (1985), and plastron respiration by Rolfe (1980), with the microscopic cuticular projections acting like plastron hairs. Palaeophysiological calculations suggested that the respiratory surface area (RSA) alone of the gill tract was inadequate to supply a eurypterid’s energy requirements (Selden 1985). From this, it was inferred that the gill tract acted primarily as an accessory aerial ‘lung’, and that eurypterids possessed additional true gills which had yet to be found (Selden 1985). Taugourdeau (1967) figured gill tract material from the Sahara in micropalaeontological preparations, but did not recognize its significance. During an investigation into the earliest demonstrably terrestrial biota, from the late Silurian of Ludford Lane (Jeram el al. 1990), a number of unusual fragments of arthropod cuticle were recovered. These authors figured gill tract material and interpreted it as the posterior end of an unknown arthropod. New discoveries of these cuticle fragments are described here, and interpreted as representing fragments of the respiratory organs of eurypterids. IPalaeontology, Vol. 38, Part 2, 1995, pp. 287-297, 2 pls| © The Palaeontological Association 288 PALAEONTOLOGY, VOLUME 38 GEOLOGICAL SETTING The fossils came from the Platyschisma Shale Member of the Downton Castle Sandstone Formation, above the Ludlow Bone Bed at its type locality in Ludford Lane, Ludlow, Shropshire (SO 51 16 7413), and are of late Silurian (Pn'dolf Epoch) age (see Bassett et al. 1982 for details). This sequence is interpreted as a nearshore deposit (Smith and Ainsworth 1989), and work by one of us (PLM, unpublished) and by Maquaker (1994) suggests that the Ludlow Bone Bed represents a deepening event, with the overlying Platyschisma Shale Member being deposits reworked in a shallowing sequence. The best preserved material was collected from organic-rich horizons within the Platyschisma Shale Member, capping reworked, storm-generated deposits, which are characterized by hummocky cross-stratification. These organic-rich horizons are probably the result of the argillaceous and organic elements of the sediment load settling out after a severe storm. The high quality of preservation of these delicate arthropod fragments may be related to the small grain size of the sediments. Schmitz (1992) recognized within the Ludlow Bone Bed a high concentration of iridium (049 ppb) compared with background (0 040 ppb), which he suggested was precipitated from sea water. Although he did not exclude a relation of the anomaly initially with an asteroid impact event, there is little evidence (such as tektites and shocked quartz) for this at the time of deposition of the Ludlow Bone Bed, and Antia (1979) suggested a volcanic origin for some of its constituents. The evidence for such an origin for part of the bone bed is supported by the high percentage of quartz grains which have highly patchy extinction patterns and contain abundant inclusions (Schmitz 1992). We suggest that the high concentrations of iridium (Schmitz 1992) relate directly to the sedimentary environments prevailing at the time of deposition (Manning 1993; Maquaker 1994). The deepening event, which resulted in sediment by-pass and the subsequent build-up of vertebrate sands, would also allow a concentration of iridium to accumulate, precipitated from the sea water. The uncertain report of the crustacean Ceratiocaris sp. from this sequence (Bassett et al. 1982, fig. 6, p. 13) could not be substantiated in this present study. The eurypterids which have been recognized from it by the senior author are as follows: Pterygotus sp; Pterygotus ( Pterygotus ) denticulatus; Eurypterus sp; Eurypterus cephalaspis; Hughmilleria sp; Hughmilleria banksi; Nanahughmilleria sp; Parahughmilleria sp; Erretopterus ( Truncatiramus ) gigas gigas and Stylonurus sp. The respiratory material described here is too fragmentary to ascribe to any of these taxa. MATERIALS AND METHODS Fragments of arthropod and plant cuticle were recovered by hydrofluoric acid (60 per cent.) maceration of samples of sediment following the method of Shear et al. (1987). The resulting EXPLANATION OF PLATE 1 Figs 1-6. Scanning electron micrographs of cuticular material which represents fragments of eurypterid Kiemenplatten; Upper Silurian (Pn'dolf), Ludford Lane, Shropshire. 1, LL1 119.1 ; group of seven spinules in assumed life orientation, showing the basic conical shape, terminal spine, surface sculpture and size variation; x 170. 2, LL1 1 19.2; pair of spinules, showing the shape, sculpture and the smooth inner surface where the cuticle is folded over (at the top left); x 350. 3, LL1 119.2; detail of cuticular projections ornamenting the spinules, showing the polygonal arrangement extending out from the surface; x 790. 4, LL 1121; detail of the cuticular projections, here more densely packed and no longer polygonally oriented ; x 1200. 5, LL1 1 17; detail of a single regular "rosette" of projections from the surface of the Kiemenplatten, showing their approximately circular cross-sectional area; x 4500. 6, LL1 1 17; detail of Kiemenplatten near the base of the spinules, where the cuticular projections have merged into smooth cuticle and which shows a single pore of approximately 1-0 //m in diameter; x 5000. PLATE 1 MANNING and DUNLOP, Eurypterid Kiemenplatten 290 PALAEONTOLOGY, VOLUME 38 residues were picked for cuticle under both transmitted and incident light. Eurypterid cuticle represents the most common arthropod fragments and was identified by its distinctive morphology and ornamentation (Tollerton 1989; Manning 1993). Material interpreted as eurypterid respiratory organs was dried, mounted on aluminium stubs and gold-coated. It was examined using a Jeol 2020 scanning electron microscope (SEM). All figured material is held in the Department of Geology, Manchester Museum, University of Manchester, numbers LL1 1 1 7-LL1 123. A specimen of a eurypterid, Rhenopterusl sp. (Hunterian Museum, Glasgow, no. A23113), believed to show respiratory structures (Selden 1985, p. 223, who referred to it by its Hunterian Museum loan number, G807), was studied under incident light. Preserved specimens of the extant xiphosuran Limulus polyphemus were examined for comparative purposes. RESULTS Kiemenplatten ( gill tract) The material includes highly ornamented, conical, cuticular structures (PI. 1, figs 1-2). These are sometimes found isolated, sometimes grouped, and occasionally attached to larger sheets of cuticle. These cones have a total length of 0-5-2 0 mm and have a basal width of 50-200 //m. The tips of the cones are drawn out into long, tapering spines, typically between 30-150 /mi long, which have no surface sculpture (PI. 1, figs 1-2). The rest of each cone has a dense sculpture of microscopic cuticular projections which stand proud of the surface by approximately 10-15 //m (PI. 1, figs 3^4). These projections are 2-3 pm wide and give the impression of originally having been cylindrical, and perhaps hollow, but having subsequently become compressed (PI. 1, fig. 4). However, the internal surface of the Kiemenplatten, where visible (PI. 1, fig. 2), does not show corresponding pores leading into these cuticular projections, suggesting that they may be composed of solid cuticle. When compared with the material figured by Holm (1898) and Wills (1965) it is clear that these conical structures represent eurypterid Kiemenplatten. The latter term is used in preference to gill tract as discussed below. The term spinule was introduced by Wills (1965) for the cones (conical structures) covering the surface of the Kiemenplatten. When examined in detail, the polygonal arrangement of the cuticular projections noted by the previous authors is apparent (PI. 1, fig. 3) including the ‘rosettes’ (PI. 1, fig. 5) of Wills (1965), which have a diameter of approximately 20 pm, with the cuticular projections spaced approximately 2 /mi apart. However, these projections are less regular and more densely distributed closer to the tip of the spinule, where they lose the ‘rosette’ arrangement (PI. 1, fig. 4). Pores were found sparsely distributed in the cuticle between these projections, especially close to the base of the spinules where the projections are less dense (PI. 1, fig. 6). These pores have smooth margins, which suggests that they are not artefacts, and have a consistent diameter of between 0-5-10 /tm. EXPLANATION OF PLATE 2 Figs 1-5. Scanning electron micrographs of lamellate cuticular material interpreted as fragments of eurypterid book-gills, from Ludford Lane, Shropshire. 1, LL 1118; parts of eighteen lamellae attached to a large fragment of cuticle, which may represent the dorsal surface of the Blatfuss; x 115. 2, LL 1118; detail of lamella from figure 1 showing the thickened supporting bar with the ribbed surfaces of the lamella hanging from and continuous with it ; x 490. 3, LL1 1 18; detail of lamellae from figure 1 showing them overlapping like the lamellae of modern Limulus book gills; x 230. 4, LL1 123; fragment of a single lamella, showing a wider, ribbed surface; x 230. 5, LL1 122; fragment of a single lamella, showing a broken edge revealing the cross sectional shape of the supporting bar and the two sheets of the lamellae hanging from it, and the smooth inner surface of the lamellae; x 230. PLATE 2 MANNING and DUNLOP, Eurypterid book-gills 292 PALAEONTOLOGY, VOLUME 38 Lamellate gills Other fragments recovered consist of small thickened cuticular bars (PL 2, figs 1-5) up to 7 mm long and approximately 20 //m wide. These bars are ovate in cross section, but with a concave interior surface and support two sheets of thin cuticle (PI. 2, fig. 5). These cuticle sheets are estimated to have been 20 /an apart, and less than 0-5 /an thick where there is no surface sculpture. The cuticle sheets are fragmentary, at most 3 mm wide but usually much narrower. The two sheets suggest that they once formed an enclosed structure with a smooth interior surface and an exterior surface ornamented with a series of solid, cuticular ‘ribs’ lying perpendicular to the supporting bar (PI. 2, figs 1-3). These ribs are approximately 2-3 /an wide, with a spacing of 2-5 /an and stand proud of the surface by approximately 5 pm. There are cross-bars, approximately 0T-0-5 pm wide, between the cuticular ribs (PI. 2, figs 1-5) which do not appear to be artefacts. The spacing of these cross-bars is irregular and they occur more commonly towards the thickened cuticular bars. These supporting bars and their cuticle sheets are usually found isolated, but occasionally up to eighteen overlapping sheets, connected to fragmentary sheets of cuticle (PI. 2, fig. 1), are found. These structures are interpreted as fragments of the marginal edges of lamellate gills, using the book-gills of Lunulas as a comparison. Longer fragments show that the supporting bars were curved, suggesting that the whole structure may have been semicircular in life, as are the gill lamellae of Limulus. text-fig. 1 . Phosphatized eurypterid in ventral view. Rhenopterusl sp.. Lower Carboniferous, Montagne Noire region, France; HM A231 13; x 1-5. Specimen interpreted as showing book-gills (arrowed) in life position, consisting of stacked, overlapping lamellae within a branchial chamber. Whole body evidence An undescribed specimen of Rhenopterusl sp. (Text-fig. 1) is interpreted as showing a single, open branchial chamber which contains at least seven phosphatized, overlapping, lamellate structures. These structures are interpreted as the gills of a single branchial chamber approximately in life position. This specimen provides strong supportive evidence for the presence of lamellate gills in MANNING AND DUNLOP: EURYPTERID RESPIRATORY ORGANS 293 eurypterids and further suggests that the individual lamellae have an approximately semicircular shape and also that they attach obliquely, close to the midline of the body as in Limulus. DISCUSSION Interpretation of the Kiemenplatten ( gill tract) We are confident that these dissociated fragments of Kiemenplatten belong to eurypterids because their structure matches the material described and figured by Holm (1898) and Wills (1965) from whole body specimens. Also, some fragments show the margins of the Kiemenplatten where it merges with sternite cuticle which matches recognizable fragments of eurypterid cuticle (see Manning 1993 for a discussion of cuticle form and structure). Kiemenplatten material is reasonably common in macerates containing large quantities of eurypterid fragments, and has not been demonstrated to occur in any other arthropod group. Material superficially similar to the spinules described here, but lacking obvious cuticular projections arranged in ‘rosettes’, has been described as scorpion gill tract from the Upper Carboniferous (Kjellesvig-Waering 1986). This interpretation is probably incorrect because these structures originate from the scorpion abdominal plate, not from the true sternite (A. Jeram, pers. comm.). The fragments recovered during this study can be regarded as being part of a larger, oval area of Kiemenplatten, as noted by previous authors (e.g. Holm 1898). In fragments attached to sternite cuticle the spinules tend to be small, suggesting that the Kiemenplatten is most developed in its centre. The fragmentary nature of this material does not allow the size of the whole Kiemenplatten area to be determined. The Kiemenplatten bears all the hallmarks of a respiratory structure with its increased surface area formed by the spinules (PI. 1, figs 1-2). If the projections from the spinules (PI. 1, figs 3-5) were hollow, this would also increase the respiratory surface area (RSA). It seems likely that the cuticle of the spinules was backed by a blood sinus and provided a surface for gas exchange. There seems no reason to doubt that the Kiemenplatten could have functioned as an accessory ‘gill’ in water, but what is more interesting is the suggestion that it is a structure which evolved primarily for respiration in air. The structure of the Kiemenplatten suggests that the downward-hanging spinules (PI. 1, figs 1-2) would not have collapsed in air, leading to a reduction in RSA, in the same way as a lamellate gill. The presence of downward projecting Kiemenplatten spinules could also have maintained a cavity above the lamellae by preventing them from being compressed against the roof of the branchial chamber (A. Jeram, pers. comm.). The suggested primary respiratory function of the highly vascularized regions of the eurypterid sternite, is contradicted by the use of the term gill tract (Wills 1965). Because of its functional implications the term gill tract is rejected and the term Kiemenplatten (Holm 1898) is preferred here as a more ‘neutral’ term. The overall morphology of the eurypterids shows that they were clearly primarily aquatic animals (Selden 1985). However, by closing the Blatfiisse during excursions onto land they could have reduced water loss over the gills, in the same way that a narrow book-lung spiracle prevents water loss in arachnids, while relying on gas exchange with air over the gill tract. Since air has a higher partial pressure of oxygen than water, the RSA of the Kiemenplatten may not have needed to be as great as that of the lamellate gills in order to support metabolically the animal in air. The respiratory evidence therefore suggests that at least some eurypterids could have ventured onto land, but the degree to which these animals could have been terrestrial can only be answered in a fuller account of Kiemenplatten palaeophysiology and corroborative evidence from eurypterid palaeoecology. The small pores described in the Kiemenplatten (PI. 1, fig. 6) could be interpreted as spiracles leading into some sort of tracheal system (as the figures of Stormer 1976 appear to suggest), but no such tracheae backing them were observed in any of the specimens. An alternative hypothesis is that they were backed by osmoregulatory cells, although this is mere conjecture at this stage. The spines at the tips of the spinules (PI. 1, figs 1-2) could possibly have been a protective device against haematophagous parasites. 294 PALAEONTOLOGY, VOLUME 38 text-fig. 2. Interpretative reconstruction of two branchial chambers of a generalized eurypterid. The lamellate book-gills (Lg) originate from the dorsal surface of the Blatfiisse (B) and occupy most of the branchial chamber. Blood entered a Blatfuss from a hypothetical blood sinus (Si) and from here entered the lamellae, probably by tidal flow. The Kiemenplatten (K) is a well vascularized oval area of the sternite (S), comprising a series of spinules (Ks) and located above the lamellae within the branchial chamber. Kiemenplatten have also been found in association with eurypterid fragments in macerates from older horizons at Monterrey, Virginia (Silurian, Llandovery) and younger ones at Hudwick Dingle, Shropshire (Devonian, Lochkovian) and Gilboa, New York (Devonian, Givetian) (unpublished observations). Initial examination of this material suggests some minor, but potentially significant differences, from the material described here. Interpretation of the lamellate gills We are confident that these lamellate structures belong to eurypterids and are not the gills of xiphosurans or crustaceans since, like the Kiemenplatten, the lamellae are occasionally found attached to recognizable eurypterid cuticle (Manning 1993). Xiphosurans and non-ostracode crustaceans were not found in the Ludford sequence either as recognizable fragments in macerates, macrospecimens or trace fossils. Also, the lamellae are reasonably common in macerates containing large amounts of eurypterid fragments. Scorpion cuticle fragments have been recorded, and these lamellae could represent the gills of aquatic forms; however scorpion cuticle was rare, rarer even than the lamellate structures within the macerates. Comb-like structures have been described as the pectinated appendages of the eurypterid Cyrtoctenus (Stormer and Waterston 1968). These were subsequently interpreted as modified spines of the distal limb podomeres with a sweep-feeding function (Waterston et al. 1985). Detailed examination of the lamellate structures found in this present study has shown that they display two ribbed surfaces, not individual filaments attached to a supporting bar as in Cyrtoctenus. Based on these characters we are confident that the lamellate structures from Ludford Corner are not appendicular sweep-feeding devices. The eurypterid book-gills resemble those of Limulus in having a marginal thickening (PI. 2, figs 1-5), but differ from those of living xiphosurans in having the ribs on the surface of the lamellae (PI. 2, figs 1-4). These ribs may have strengthened and supported the lamellae, but the fragmentary MANNING AND DUNLOP: EURYPTER1D RESPIRATORY ORGANS 295 evidence does not show if the whole lamella was ribbed or only the margins, which have therefore been preferentially preserved. All the fragments of lamellae found in this study were ribbed, regardless of size. The ribs are not obviously homologous, or functionally analogous, with the struts separating the air spaces between the lamellae of arachnid book lungs (e.g. Reisinger et al. 1990), so that the lamellae would probably have collapsed in air. However, it is worth noting that certain extant terrestrial crabs, e.g. Cardisoma and Geograspus (Mill 1972; Farelly and Greenaway 1992), have reduced lamellate gills with thickened and stiffened lamellae which help support the structure in air and allow effective ventilation and draining of the gills when the crab comes onto land. The total number of lamellae comprising any particular eurypterid gill found in this study, and the shape and variation in shape of the entire lamellae, cannot be determined for this fragmentary material. The Rhenopterusl specimen (Text-fig. 1) and comparisons with Limulus suggests that the lamellae were quite large, occupying most of the space in the branchial chamber. The dorsal surface of the eurypterid Blatfiisse has not been described satisfactorily (Selden 1985). We speculate that, as in Limulus , where the gills attach to the gill operculum, the dorsal surface of the homologous eurypterid Blatfiisse is the attachment site of their lamellae. The large fragments of cuticle attached to some specimens (PI. 2, fig. 1) may represent part of this dorsal surface. The Blatfiisse appear to have served the dual purpose of attachment area and protection for the lamellate gill. If the animal did come onto land, the lamellate gills would probably have collapsed onto the dorsal surface of the Blatfiisse without the support of water. A collapsed gill would probably have been ineffective for aerial respiration and this could explain the need to evolve an accessory aerial respiratory organ in a partially terrestrial animal. Reconstruction of the eurypterid respiratory system While Kiemenplatten and lamellate gills have not been recorded from a single specimen to date, we have no evidence that the two structures belong to two different taxa. On this basis the eurypterid respiratory system is reconstructed as possibly comprising two elements (Text-fig. 2), as suggested by Selden (1985): lamellate book-gills and the accessory Kiemenplatten. The multiple lamellae of the book-gills were probably attached to the dorsal surface of the Blatfiisse and were presumably the principal means of aquatic respiration. By analogy with Limulus , the Blatfiisse and their gills would have connected to a blood sinus towards the midline of the animal and there would have been a tidal flow of haemolymph in and out of the lamellae. The Kiemenplatten hung above the gills within the branchial chamber and was probably also backed by a blood sinus, gas exchange occurring with the haemolymph in this sinus. The ‘ branchial lung' model of Kiemenplatten function The eurypterid Kiemenplatten has no counterpart in any other chelicerate group and thus represents a previously unknown respiratory system in arthropods. The pseudotracheal model for the Kiemenplatten proposed by Stormer (1976) appears inappropriate. Isopod pseudotracheae are invaginated cutaneous tubules lying within the blood sinus of an appendage (Snodgrass 1952), whereas the eurypterid Kiemenplatten is interpreted as a vascularized region of evaginations of the body wall (PI. 1, figs 1-2). The plastron model of Kiemenplatten function (Rolfe 1980) was rejected by Selden (1985) because the cuticular projections were claimed to be too widely spaced to hold a meniscus. This study suggests that cuticular projections on the Kiemenplatten (PI. 1, figs 3-5) are over twice as long and wide as typical hydrofuge plastron hairs. There is no evidence that the Kiemenplatten projections were water repellent or that they had linkages between the tops of the projections (PI. 1, figs 4-5) to provide an incompressible air space as in a plastron (Mill 1972). More significantly, a plastron is a secondarily aquatic-adapted respiratory mechanism originally of terrestrial arthropod lineages, whereas eurypterids are suggested as having been primarily aquatic animals attempting terrestrialization (Selden 1985). The closest arthropod analogues to eurypterid Kiemenplatten are the cutaneous brachial lungs of certain terrestrial crabs, e.g. Ocypode and Pseudo thelpusa (Mill 1972; Little 1990), formed from 296 PALAEONTOLOGY, VOLUME 38 highly vascularized regions of the branchial chamber wall (i.e. not the gills, as in Cardisoma ) and which act as osmoregulatory and aerial respiratory organs. However, it is worth comparing the apparent strengthening structures both on eurypterid and crab gill lamellae, which may suggest that the eurypterid lamellae had some terrestrial adaptations. Terrestrial crabs must still keep their gills or branchial lungs moist (Mill 1972), presumably to avoid desiccation. The cuticular projections on the eurypterid Kiemenplatten may have served principally to trap a fine meniscus of water, in order to keep the area moist, a requirement of all respiratory surfaces (Hill and Wyse 1989), and functioning longer on land. This is similar to a plastron, except that, rather than trapping air as the animal enters water, and then holding a meniscus of water away from a tract as in the hydrofuge hairs of a plastron, these projections may have held a meniscus of water next to the Kiemenplatten. It is worth noting that, when removed from water and dried on SEM stubs, the fragments of Kiemenplatten took longer to dry than comparable cuticular fragments. It is interesting to observe that recent crabs attempt terrestrialization in two ways: adapting their gills directly into lamellate 'lungs’ (Mill 1972; Little 1990; Farrelly and Greenaway 1992), as has occurred with the arachnid book-lungs (Selden and Jeram 1989); and, alternatively by vascularization of the branchial chamber wall (Mill 1972; Little 1990), which is apparently analogous to the eurypterid Kiemenplatten. Different eurypterid taxa may similarly have used different strategies for aerial respiration, i.e. Kiemenplatten or strengthened book-gills, but we have no evidence for this dual adaptation at present, and we favour the model proposed in Text-figure 2. Eurypterids, however, appear ultimately to have failed to colonize land and this may be the result, in part, of their reliance on the Kiemenplatten, whereas the successful terrestrial chelicerates transformed their lamellate book-gills directly into lamellate book-lungs. Acknowledgements. We thank Dr P. A. Selden for his encouragement and advice, Drs W. A. Shear, A. J. Jeram and S. Braddy for helpful discussions, Dr W. D. I. Rolfe for the loan of the Rhenopterus ? specimen, Mr R. Hartley for drawing Text-figure 2 and Mr D. F. A. Nicholson and English Nature for permission to collect from Ludford Corner. JAD acknowledges a NERC studentship to conduct research into early terrestrial ecosystems. REFERENCES antia, d. d. j. 1979. Bone-beds: a review of their classification, occurrence, genesis, diagenesis, geochemistry, palaeoecology, weathering, and microbiotas. Mercian Geologist , 7, 93-174. bassett, M. G., lawson, J. d. and white, d. e. 1982. The Downton Series as the fourth Series of the Silurian System. Lethaia, 15, 1-24. Clarke, j. m. and ruedemann, r. 1912. The Eurypterida of New York. Memoir of the New York State Museum , 14, (2 vols), 1-439, pis 1-88. farrelly, c. a. and Greenaway, p. 1992. Morphology and ultrastructure of the gills of the terrestrial crabs, Crustacea, Gecarcinidae and Grapsidae: adaptations for air-breathing. Zoomorphology , 112, 39-49. hill, R. w. and wyse, g. a. 1989. Animal physiology. 2nd Edition. Harper and Row, New York, 656 pp. holm, G. 1898. Uber die Organisation des Eurypterus fischeri Eichw. Memoirs of the Academy of Science , St. Petersburg , 8, 1-57. jeram, a. j., selden, p. a. and edwards, d. 1990. Land animals in the Silurian: arachnids and myriapods from Shropshire, England. Science , 250, 658-661. kjellesvig-waering, E. n. 1986. A restudy of the Fossil Scorpionida of the world. Palaeontographica Americana , 55, 1-287. laurie, m. 1893. The anatomy and relations of the Eurypteridae. Transactions of the Royal Society of Edinburgh , Earth Sciences , 37, 509-528. little, c. 1990. The terrestrial invasion: an ecophysiological approach to the origins of land animals. Cambridge Studies in Ecology, Cambridge tJniversity Press, Cambridge, 304 pp. manning, p. l. 1993. Palaeoecology of the eurypterids of the Upper Silurian of the Welsh Borderland. Unpublished M.Sc. thesis. University of Manchester. maquaker, j. h. s. 1994. Palaeoenvironmental significance of bone-beds in organic-rich mudstone successions: an example from the Upper Triassic of South West Britain. Zoological Journal of the Linnean Society, London , 112, 285-308. MANNING AND DUNLOP: EUR YPTER1D RESPIRATORY ORGANS 297 mill, p. J. 1972. Respiration in the invertebrates. Macmillan Press, London, 212 pp. moore, p. f. 1941. On gill like structures in the Eurypteridae. Geological Magazine , 78, 62-70. reisinger, p. w. m., focke, p. and linzen, b. 1990. Lung morphology of the tarantula, Eurypelma californicum Ausserer, 1871 (Aranae: Theraphosidae). Bulletin of the British Arachnologica! Society, 8, 165-170. rolfe, w. d. i. 1980. Early invertebrate faunas. 1 17-157. In panchen, a. l. (ed.). The terrestrial environment and the origin of land vertebrates. Academic Press, London and New York, 633 pp. selden, p. a. 1985. Eurypterid respiration. 209-226. In challoner, w. g. and lawson, j. d. (eds). Evolution and environment in the Late Silurian and Early Devonian. Philosophical Transactions of the Royal Society of London , Series B, 309, 342 pp. — and jeram, a. j. 1989. Palaeophysiology of terrestrialisation in the Chelicerata. Transactions of the Royal Society of Edinburgh , Earth Sciences , 80. 303-310. shear, w. a., selden, p. a., rolfe, w. d. i., bonamo, p. m. and Grierson, j. d. 1987. New terrestrial arachnids from the Devonian of Gilboa, New York (Arachnida, Trigonotarbida). American Museum Novitates, 2901, 1-74. schmitz, b. 1992. An iridium anomaly in the Ludlow Bone Bed from the Upper Silurian, England. Geological Magazine, 129, 359-362. smith, r. d. a. and Ainsworth, r. b. 1989. Hummocky cross-stratification in the Downton of the Welsh Borderland. Journal of the Geological Society, London, 146, 897-900. snodgrass, R. e. 1952. Textbook of arthropod anatomy. Cornell University Press, New York, 363 pp. stormer, L. 1976. Arthropods from the Lower Devonian (Lower Emsian) of Alken-an-der-Mosel, Germany. Part 5 : Myriapoda and additional forms, with general remarks and problems regarding invasion of land by arthropods. Senckenbergiana Lethaea, 57, 87-183. — and waterston, c. d. 1968. Cyrtoctenus gen. nov., a large Palaeozoic arthropod with pectinate appendages. Transactions of the Royal Society of Edinburgh, Earth Sciences, 68, 63-104. taugourdeau, p. 1967. Debris microscopiques d’eurypterides du Paleozoi'que saharien. Revue de Micropaleontologie, 10, 119-127. tollerton, v. p. 1989. Morphology, taxonomy and classification of the Order Eurypterida, Burmeister 1843. Journal of Paleontology, 63, 642-657. waterston, c. d. 1975. Gill structure in the Lower Devonian eurypterid Tarsopterella scotica. Fossils and Strata, 4, 241-254. — 1979. Problems of functional morphology and classification in stylonurid eurypterids, Chelicerata, Merostomata, with observations on the Scottish Silurian Stylonuroidea. Transactions of the Royal Society of Edinburgh, Earth Sciences, 70, 251-322. — oelofsen, b. w. and oosthuizen, r. d. f. 1985. Cyrtoctenus witterbergensis sp. nov. Chelicerata: Eurypterida, a large sweep feeder from the Carboniferous of South Africa. Transactions of the Royal Society of Edinburgh , Earth Sciences, 76. 339-358. wills, l. j. 1965. A supplement to Gerhard Holm’s ‘Uber die Organisation des Eurypterus fischeri Eichw.’ with special reference to the organs of sight, respiration and reproduction. Archiv for Zoologi, 18, 93-145. PHILLIP L. MANNING Department of Earth Sciences University of Sheffield Dainton Building, Brookhill Sheffield S3 7HF JASON A. DUNLOP Department of Earth Sciences University of Manchester Manchester M13 9PL Typescript received 28 September 1993 Revised typescript received 27 May 1994 OCCURRENCE OF THE BIVALVE GENUS MANTICULA IN THE EARLY CRETACEOUS OF ANTARCTICA by J. A. CRAME Abstract. A new occurrence of a pergamidiid bivalve genus, which can probably be assigned to Manticula Waterhouse, 1960, is established within the Early Cretaceous (Berriasian) of Antarctica. Such a record is of particular interest as this taxon was only known previously from the Late Triassic of New Zealand and New Caledonia. The Antarctic material is contained within a new species, M. complanata , which is shown to be somewhat smaller and less inflated than the genotypic M. problematica (Zittel). There are indications from the Antarctic species that, at least in juvenile specimens, the hinge region of the left valve is characterized by a prominent saddle-shaped fold (or tooth) and a triangular resilifer. Using features such as these and details of the shell structure, it is possible to establish close links between Manticula and the pergamidiid genus Krumbeckiella on the one hand, and the eurydesmid genus Eurydesma on the other. The eurydesmid- pergamidiid group is essentially a Southern Hemisphere one with high-latitude origins in the Early Permian. Following a phase of expansion through the Triassic, it would appear to have retracted to the single Antarctic occurrence of Manticula in the Early Cretaceous. During the course of systematic geological surveys, a thick sequence of Late Jurassic-Early Cretaceous marine clastic rocks was discovered on Byers Peninsula, western Livingston Island, South Shetland Islands (62° 38' S; 61° 04' W) (Smellie et al. 1980, 1984) (Text-fig. 1 ). This sequence is in places highly fossiliferous, and a variety of ammonite and belemnite types has been used to establish an age-range of at least Kimmeridgian-Valanginian (Smellie et al. 1980). Further field studies have recently been completed and an estimated 1 km thickness of mudstone-dominated lithologies has been combined into the new Byers Group. It is envisaged that these sediments accumulated in a marginal fore-arc setting (Crame et al. 1993). Bivalves form a prominent component of the marine invertebrate macrofaunal assemblage from the lower levels of the Byers Group (principally the President Beaches Formation; Crame et al. 1993). Epifaunal types present include retroceramids, inoceramids, various oxytomids, occasional entoliids and several types of oyster; infaunal and semi-infaunal groups include nuculids, nuculanids, grammatodonlids, trigoniids, astartids and other small heterodonts. An initial study (Crame 1984) identified a number of distinctive elements within this bivalve fauna, with perhaps the most unusual one being a small-medium, mytiliform and almost smooth taxon with superficial similarities to both the Buchiidae and Inoceramidae. Nevertheless, subsequent detailed examination revealed that it clearly could not be assigned to either of these families; it would seem, instead, to be referable to one of the lesser-known pteriomorph groups, the Pergamidiidae Cox, 1969. The smooth, mytiliform Byers Peninsula taxon can probably be referred to the pergamidiid genus Manticula Waterhouse, 1960. Such a determination is of immediate biostratigraphical and biogeographical interest, for Manticula has hitherto been recorded from only the Late Triassic (Carnian-Norian) of New Zealand and New Caledonia; indeed, the stratigraphical range of the entire Pergamidiidae is only Upper Triassic-Lower Jurassic (Cox 1969). As the Byers Peninsula material is dated unequivocally as earliest Cretaceous (Berriasian; Crame et al. 1993), it would (Palaeontology, Vol. 38, Part 2, 1995, pp. 299-312, 3 pis) ©The Palaeontological Association 300 PALAEONTOLOGY, VOLUME 38 text-fig. I . Locality map for Byers Peninsula, western Livingston Island, a. The northern Antarctic Peninsula region, b, Byers Peninsula - showing localities at which Manticula has been collected and the outcrop of the lower part of the Byers Group (shaded). A more detailed geological map is given in Crame et al. (1993, fig. 1 ). CRAME: CRETACEOUS BIVALVE 301 appear that Manticula might be a Lazarus Taxon ( sensu Jablonski 1986), with no known Jurassic representative, and Antarctica serving as a last refuge for this formerly more widespread family. SYSTEMATIC PALAEONTOLOGY Order pterioida Newell, 1965 Suborder pteriina Newell, 1965 Superfamily ambonychioidea Miller, 1877? Family pergamidiidae Cox, 1969 Genus manticula Waterhouse, 1960 Type species. Mytilus problematicus Zittel (1864); by original designation. Diagnosis. Small-medium (and occasionally large) mytiliform bivalves; prominent, pointed beaks; generally smooth but can exhibit low concentric folds and fine radial striae; largest forms may develop bizarre gibbous shape in ?RV ; thickened, striated hinge region bears oblique, ridge-like fold or ‘tooth ’-this feature may become overthickened and obscured in large specimens; thickened shell largely calcific - predominantly crossed-foliated? Storage of Material : All Antarctic specimens (prefixed by P.) are housed in the collections of the British Antarctic Survey, Cambridge, UK. New Zealand specimens from the C. T. Trechmann Collection are housed in the Department of Palaeontology, Natural Elistory Museum, London (NHM); specimens prefixed TM are located in the reference collections of the Institute of Geological and Nuclear Sciences, Lower Hutt, New Zealand. Manticula complanata sp. nov. Plate 1, figures 1-10; Plate 2, figures 1-2; Text-figure 2 Type material. Holotype: P.241.9 (internal mould LV). Paratypes: P.241 .8, 10, 18, P.245. 10-12, P. 1667. 1, 6^9, 11-18, 20, 21, 23-25, P.1653.3, 4, P.1655.9-1 1, P.1661.16, P.1664.21, P.1665.8, 9, 12, 14, 15, P.1666.1-4. P.1668.3-10, P.2193.83-85, 90-95, P.2201.6, 7, 9, 11, 13-15, 17, 18, 20-22, P.2202.19, P.2203.1, P.2153.80-82, P.2233.4-12, 16, 17, 19. All the specimens were obtained from the President Beaches Formation, the principal lithostratigraphical unit within the lower Byers Group, western Byers Peninsula (Text-fig. 1). Occurrence. As for the type material. Associated macrofossils date the President Beaches Formation as Berriasian (Smellie et al. 1980), and there are some indications that at least the lowest 360 m may be assignable to the Early Berriasian (Crame et at. 1993). Derivation of name. Latin ‘ complanata ’, flattened; referring to the non-inflated form of this species. Diagnosis. A small Manticula which does not exhibit any grossly over-inflated valves. Description. A small-medium sized, elongate-rounded and almost smooth bivalve which tapers dorsally into a finely pointed umbo and expands ventrally to become well rounded ; a number of specimens give a superficial impression of bilateral symmetry. This species is equivalve, or very nearly so (see possible minor differences, below), with no statistically significant differences between the mean lengths and widths of the best preserved left and right valves (Student’s Mest, P < 0 001). Measurements taken on some 60 specimens indicate a mean length (L) of 35-73 mm (s.d. = 14-38, range = 12-64 mm), mean width (W) of 25-22 mm (s.d. = 9-37, range = 9^14 mm) and mean W/L of 0-712 (s.d. = 302 PALAEONTOLOGY, VOLUME 38 0 069, range = 048-0-83). There is a spectrum from more or less bilaterally symmetrical specimens (e.g. PI. 1, fig. 2) to obviously obliquely elongated ones (e.g. PI. 1, fig. 7). In the latter there are clear traces of a short, straight posterodorsal hinge, together with a variably-developed radial, posterodorsal furrow. It is just possible that this feature is more deeply impressed in left than right valves (PI. 1, figs 7-10). In a typical specimen, the outline in the posterodorsal region is very slightly more angular than in the corresponding anterodorsal region; the ventral margin is always well rounded. The poorly defined umbonal region terminates in a sharply pointed beak. This feature rises just above the hingeline and varies from slightly prosogyrous to slightly opisthogyrous (PI. 1, figs 1-10). Both left and right valves are weakly inflated, with the maximum degree of inflation occurring in the umbonal and central regions of the valve. In specimens preserved in fine- to medium-grained sandstone, the principal ornament pattern comprises very fine concentric growth lines with superimposed radial growth threads. The latter can be traced from the umbo to the ventral margin, where they may become somewhat erratic in their course (e.g. PI. 1, figs 5, 9). Some specimens preserved in mudstone reveal slightly coarser concentric ornament, which may be described as wrinkles. They also show, especially in the central regions of the valve, more pronounced radial ornament (PI. 1, figs 1-3). A few specimens exhibit a very clearly delimited larval shell (or prodissoconch). On P.2201 . 16 (PI. 2, fig. 1), this takes the form of a smooth, inflated, cap-like structure bordered by an annular sulcus. In its longest dimension it measures approximately 430 //m and towards the outer borders there are traces of a shallow depression which may mark the separation of Prodissoconch I from Prodissoconch II. In any event, it would appear that the former of these two subdivisions must have been comparatively large and this may be taken as evidence of nonplanktotrophic or even brooded larval development (Jablonski and Lutz 1980). The first 1-2 mm growth of the dissoconch proper is characterized by acute, regularly spaced, radial ribs which are crossed by faint concentric riblets (e.g. PI. 2, fig. 1 ). This initial cancellate pattern is stronger than anything seen on the adult shell. Details of the hingeline and immediately adjacent areas are particularly well preserved on three small, juvenile specimens: the internal moulds of two left valves (P.2201.16, P.2233.5; PI. 2, figs 1-2) and the external mould of a right (P.241 .8). All three specimens show the hinge to be a comparatively broad, complex structure whose principal features are picked out by very fine, regular growth lines. In particular, directly beneath the beak (marked by the prodissoconch) these lines pick out a prominent ridge-like fold which is broadly analogous to a tooth. In specimen P.2201 . 16 (PI. 2, fig. 1) this ridge can be seen to slant obliquely forwards and span the whole width of the hinge area. It falls away steeply on both flanks from a comparatively sharp crest, and indications that it is hollow in the centre are confirmed by examination of P.2233.5 (PI. 2, fig. 2). Anterior to the tooth-like ridge, in both left and right valves, the hinge appears to be simple, straight and marked by sub-parallel growth lines (PI. 2, figs 1-2). However, immediately in front of the ‘tooth’ in both specimens, P.241.8 and P.2201 . 16 (PI. 2, fig. 1), there are traces of a shallow, transverse depression which may mark the line of a narrow byssal notch. Immediately posterior to the tooth-like ridge there are traces of a deeply impressed ligament pit. This feature is clearest in specimen P.2201 . 16 (PI. 2, fig. 1), where it has an oblique, triangular outline and can be seen to be firmly recessed into the space directly beneath the umbo. The floor of the pit is covered by fine, sub- horizontal growth lines. In specimen P.2233.5 the form of the ligament pit is less obvious (PI. 2, fig. 2), but in P.241 .8 it is again obliquely triangular. In all three specimens the posterior segment of the hinge seems to be composed of an irregular set of elongate grooves and ridges. These features are perhaps clearest on specimen P.2233.5 (PI. 2, fig. 2). EXPLANATION OF PLATE 1 Figs 1-10. Manticula complanata sp. nov. ; Berriasian; Byers Group; Livingston Island, Antarctica. 1, paratype, P . 1 667 . 6 ; internal mould of a probable right valve. 2, paratype, P . 1 667 . 20 ; internal mould of a right valve. 3, paratype, P . 1 667 .12; internal mould of a right valve. 4, paratype, P . 2203 . I ; internal mould of a left valve. 5, holotype, P.241.9; internal mould of a left valve. 6, paratype, P.2153.80; internal mould of a probable right valve. 7, paratype, P . 1 668 . 3 ; internal mould of an incomplete left valve. 8, paratype, P . 1 668 . 4 ; internal mould of an incomplete right valve. 9, paratype, P.241.8; internal mould of an incomplete probable right valve. 10, paratype, P.2233. 17; internal mould of a left valve. Specimens 1-3 are preserved in mudstone, and 4—10 in fine sandstone. All are x 1. PLATE 1 CRAME, Manticula complanata 304 PALAEONTOLOGY, VOLUME 38 text-fig. 2. Scanning electron micrograph of crossed- foliated shell structure in the hinge region of a probable right valve of Manticula complanata sp. nov. (P.2233.6); x 1560. Only thin ( < 1 mm) remnants of shell material are preserved on any specimen. As far as can be determined, these are nearly always calcitic in nature and crossed-foliated in structure (Text-fig. 2). This type of shell material has been detected in several parts of both left and right valves (including both hinge regions). Although nearly always showing signs of alteration, it can be seen to comprise at least two orders of obliquely orientated lamellae which intersect at a low angle (Text-fig. 2). Occasionally, this foliated layer passes into a fine grained homogeneous zone which may represent an altered inner aragonitic layer. It is noticeable too, how a few mudstone moulds have an irridescent, nacreous sheen. A band of prismatic shell material in the central region of specimen P.2233.6 is taken to represent a myostracal shell layer. Discussion. The material described here bears a striking resemblance to the smallest specimens of Manticula problematica (Zittel), the type species of the genus from the Late Triassic (Carnian- Norian) of New Zealand and New Caledonia (e.g. PI. 3, figs 1-4). There is a considerable degree of overlap in both overall valve outlines and the form of the narrow, pointed beaks; in addition, at least some small specimens of M. problematica possess a radial, posterodorsal depression (e.g. Wilckens 1927, pi. 2, fig. 6). However, some of the prolific New Zealand material exhibits rather straighter anterior margins and there is an impression of a slightly more prominent umbonal region than in the Antarctic species (PI. 3, figs 1-4). The most obvious difference between Manticula complanata sp. nov. and M. problematica is in their respective maximum sizes. Whereas the former reaches no more than 64 mm in length, the latter can be in excess of 110 mm. The larger New Zealand and New Caledonian forms are obviously more inflated, with some specimens exhibiting a dramatic expansion of the ventral margins to produce a bizarre, gibbous shape (PI. 3, figs 5-6). Such specimens were the basis of Trechmann’s (1917) new species, Mytilus mirabilis (= Mytilus trechmanni Waterhouse, 1960), but it is now apparent that there is every gradation between the most flattened forms of Manticula problematica and the grossly inflated M. trechmanni ; the two species have thus been synonymized (Waterhouse 1960). Although it has been claimed that the gibbous form is a feature of the right EXPLANATION OF PLATE 2 Figs 1-3. Scanning electron micrographs of the hinge region of Manticula. 1, P.2201 . 16; beak and central hinge region of a juvenile left valve of M. complanata sp. nov. ; further details of the slanting, tooth-like ridge, triangular ligament pit and cap-like prodissoconch are given in the text ; x 60. 2, P . 2233 . 5 ; beak and central hinge region of a juvenile left valve of M. complanata sp. nov.; slanting, tooth-like ridge and ligament pit partially eroded; x 20. 3, TM 7672; locality GS 14977; rubber peel from an internal mould of a left valve of M. problematica (Zittel); behind a blunt, rounded anterior lobe (right hand side) is a deeply impressed subcentral resilifer; further details given in the text; x 12. PLATE 2 CRAME, Manticula 306 PALAEONTOLOGY, VOLUME 38 valve only (Waterhouse 1960), it would seem that in a number of instances it is genuinely difficult to distinguish left from right (e.g. see Avias 1953, pi. 24, figs 1-3). It is unclear whether two gibbous valves would have been in juxtaposition, or whether one was always paired with a flatter, lid-like valve. It is apparent that the largest New Zealand specimens have greatly thickened shells, with thicknesses of 6-7 mm being recorded in the hinge region (Waterhouse 1960). Much of this is due to very prominent outer calcitic layers in which irregular to branching crossed-foliated structures predominate (Waterhouse 1960; Carter 1990a,fi). The innermost, aragonitic layers apparently have a crossed-lamellar structure. Despite the large number of specimens that have been collected, our knowledge of the hinge area of M. problematic a is still incomplate. There has been a general recognition that it is comparatively broad, striated by growth lines and edentulous, but only very rarely is it preserved in its entirety (Trechmann 1917; Wilckens 1927; Marwick 1953; Waterhouse 1960, 1979). In the specimens described by Waterhouse (1960), the ligament appears to have been mounted in the right valve on a small striated plate (or septum) which overlies an umbonal cavity. This plate has a triangular form and terminates abruptly anteriorly against the thickened margin of the shell (Waterhouse 1960, pi. 20, fig. 3). In the adult left valve, there are again impressions of a comparatively small, triangular ligament area, but the specimen illustrated by Waterhouse (1960, pi. 21, fig. 4) is partially distorted. Examination of further adult specimens of M. problematica from locality GS 14977, Eighty-Eight Valley, Nelson, New Zealand, has confirmed that the crucial central region is rarely preserved in its entirety. This is probably because of its location on a septal plate which overlies a deep umbonal cavity. Nevertheless, several specimens indicate that there has been a considerable degree of thickening in this region in both left and right valves, with distinct traces of an anterior blunt, rounded, tooth-like fold. This is most apparent in specimen TM 7672, where it is situated in front of what is taken to be a deeply impressed elongate-triangular resilifer (PI. 2, fig. 3). There is now some evidence to suggest that, as the hinge region of Manticula develops, it becomes considerably thickened and simplified in form. Certainly in the left valve, it would appear that the anterior, narrow, tooth-like ridge may have become transformed into a much blunter, lobe-like feature (PI. 2, figs 1-3). In addition, it may also be that a sub-central, oblique, triangular resilifer is a consistent feature of the genus. Quite how the two valves would have articulated is not known for certain; were the tooth-like ridges in close juxtaposition or was one set slightly in front of the other? Whereas some specimens might suggest the presence of a resting groove (or socket) directly in front of the tooth, others show no sign of it. As suggested previously by Trechmann (1917, p. 201), it is more likely that this was the position of a shallow byssal sinus (e.g. PI. 2, figs 1-2). The presence of a thickened, striated hinge region bearing a prominent, tooth-like fold undoubtedly links this material to the Pergamidiidae; no other pteriomorph bivalve family possesses such an arrangement (see further discussion, below). Within this taxon there is a particularly close resemblance externally to small forms of Manticula, and this would appear to be the best genus for the new Antarctic specimens. Of course, it could be argued that lack of large, gibbous forms in the Antarctic collections, together with uncertainty about the nature of the hinge in New Zealand specimens, casts some doubt upon this assignment. Nevertheless, it is felt that, at EXPLANATION OF PLATE 3 Figs 1-6. Manticula problematica (Zittel), Carnian-Norian; Eighty-Eight Valley, Nelson, New Zealand. 1, NHM L. 51985; internal mould of a probable left valve. 2, TM 7673; locality GS14977; rubber peel from an external mould of a right valve. 3, TM 7674; same locality as 2; internal mould of an indeterminate valve. 4, NHM L. 41262; internal mould of a probable left valve; figured previously by Trechmann (1917, pi. 20, fig. 8). 5, NHM L.41266, holotype of Mytilus mirabilis Trechmann, 1917 (= Mytilus trechmanni Waterhouse, 1960, a subjective synonym of Manticula problematica', Waterhouse 1960, p. 426). 6, the same specimen as 5, viewed from the anterior; figured previously by Trechmann (1917, pi. 20, fig. 9a). All are x 1. PLATE 3 CRAME, Manticula problematica 308 PALAEONTOLOGY, VOLUME 38 the present state of our knowledge, it is better to place the Antarctic material within Manticula rather than create a new genus. RELATIONSHIPS AND DISTRIBUTION OF MANTICULA In early studies of the genus, opinion varied as to whether Manticula should be classified within the Mytilidae Rafinesque, 1815 or the Myalinidae Freeh, 1891 (Trechmann 1917; Wilckens 1927; Avias 1953; Marwick 1953). Even when more material became available for study, Waterhouse (1960) was unable to differentiate with certainty between these two categories. In the Treatise on invertebrate paleontology , Cox (1969) placed Manticula within the Pergamidiidae, a new family situated close to the Inoceramidae, within the superfamily Pteriacea Gray, 1847. This taxon comprised four genera with a combined stratigraphical range of Upper Triassic-Lower Jurassic. They are distinguished collectively by their weakly ornamented mytiliform and sub-mytiliform shapes, although it should be emphasized that the genus Pergamidia Bittner, 1891 has an atypical anterior ear and some unusual antero-ventral radial ornament (Cox 1969, fig. C44). The sole Lower Jurassic representative, Semuridia Melville, 1956, may be distinguishable by its nacreous inner shell layers (Carter 1990a), but its anatomy is still far from being fully understood. The two most prolific pergamidiid genera, Manticula and Krumbeckiella Ichikawa, 1958, are characterized by thickened, striated hinge regions which bear a distinctive saddle-shaped fold beneath the beak; this is perhaps best described as a tooth (or tooth-like ridge) in juvenile specimens of Manticula and an ‘ear’ in Krumbeckiella (PI. 2, figs 1-3; Text-fig. 3c). The ligament area in both genera is essentially opisthodetic, and contains a variably developed central resilifer. Krumbeckiella is a similar-sized genus to Manticula but can be distinguished externally by its more oblique outline and protruding anterior margin (e.g. Krumbeck 1924, pi. 195, figs 6, 8, 9a); in some extreme forms the outline is almost quadrate (e.g. Krumbeck 1924, pi. 196, figs 6a, 7a). From the inside, the anterior ear can be seen to overhang an anterior depression which takes the form of a small lunule in the right valve and a byssal slit in the left (Text-fig. 3c; Krumbeck 1924, pi. 195, figs 3b, 9b). Such is the deeply impressed nature of the latter feature in some specimens that the anterior ear is clearly visible from the outside (Krumbeck 1924, pi. 195, figs 12b, c). One of the most closely related genera to both Manticula and Krumbeckiella may be the Early Permian austral taxon Eurydesma Morris, 1845. Although considerably larger and thicker-shelled (some forms reach 160 mm in length), it is characterized by a striated hinge region which bears a prominent saddle-shaped fold (or ear; see Waterhouse and Gupta 1982) directly beneath the beak (Text-fig. 3a-b). Such folds are particularly evident in juveniles and smaller species such as Eurydesma plavfordi Dickins and E. cordata Morris (Dickins 1957 ; Runnegar 1970). In large, adult specimens of Eurydesma , the opisthodetic ligament is mounted on a broad platform which occasionally bears traces of a shallow resilifer (e.g. Waterhouse 1980, fig. 6); otherwise, the ligament surface exhibits subparallel growth striae (Text-fig. 3a-b). The shell structure of Eurydesma is still not known for certain, but it would appear that the greatly thickened outer calcitic layers have a predominantly foliated structure, with some minor homogeneous and simple prismatic material (Runnegar 1970, 1979; Carter 1990a, b). In this respect there would appear to be a very close correspondence with Manticula ; a right valve of M. problematica examined by Carter (1990a) was found to be almost identical in shell structure to Eurydesma playfordi. There is probably a direct line of descent from Eurydesma to the genus Glendella Runnegar, 1970, which has so far only been described from the early Middle Permian of Queensland, Australia (Runnegar 1970). Also globular in shape and almost smooth, Glendella possesses a comparatively broad hinge along which an acute fold in the growth lines picks out a structure analogous to the Eurydesma ‘ear’. However, it is apparent that Glendella is strongly inequivalve, with a large, inflated left valve and smaller, flatter right valve. There are some indications that the ligament area of this right valve is carried more on its dorsal surface and it also possesses a narrow, slit-like byssal notch (Runnegar 1970, pi. 18, fig. 4). Although the correspondence is not exact, there are a number of CRAME: CRETACEOUS BIVALVE 309 text-fig. 3. The hinge region of Eurydesma and Krumbeckiella. a-b, Eurydesma cordata Morris, a, NHM PL4043; right valve showing prominent, subcentral tooth slanting obliquely forwards; the crest of the tooth bears a shallow depression which marks the point of articulation with the left valve tooth; prominent byssal notch lies immediately in front of the tooth ; broad ligament area with fine, subparallel growth striae lies behind it; x 1-5. b, NHM 8-12-5; left valve showing broad, subcentral tooth with narrow crest; x 15. c, Krumbeckiella subtimorensis (Krumbeck). Mineralogisch-Geologisch Museum, Delft, No. 12933; left valve, a subcentral, ridge-like fold forms the basis of an anterior ‘ear’ (N.B. the crest is slightly eroded in this specimen); immediately in front of the ‘ear’ there is a narrow but deep byssal notch and immediately behind it a broad, flat ligament area bears traces of a shallowly impressed, triangular pit; the obliquely sloping anterior margin of this pit is clearly seen; x 1-5; figured previously by Krumbeck (1924, pi. 17, fig. 9b). points of similarity between Glendella and Manticula. These include: their inequivalve nature (at least in certain adult forms), possession of a thick crossed-foliated outer shell layer, and similar hinge regions (Runnegar 1977; Waterhouse 1980). Because of features such as its globular, strongly inequivalve form and its primitive ear and notch in the right valve, it has also been suggested that Glendella may be the earliest representative of the widespread monotoidean family, Buchiidae Cox, 1953 (hitherto Triassic-Cretaceous; Waterhouse 1980; Waterhouse and Gupta 1982). It is accepted generally now that Eurydesma should be classified within its own family, the Eurydesmidae Reed, 1932 (e.g. Runnegar 1979). Because of overall similarities to Late Palaeozoic taxa such as Posidoniella Koninck (Ambonychiidae) and Atomodesma Beyrich (Inoceramidae), most authorities have in turn assigned the Eurydesmidae to the superfamily Ambonychioidea Miller, 1877 (Kaufmann and Runnegar 1975; Dickins 1983); this is probably the best category for the Pergamidiidae too (Carter 1990a). Nevertheless, the presence of a distinct right valve byssal notch suggests at least some pectinoid affinities for Eurydesma (Runnegar 1970; Carter 1990a), and whether Glendella is best assigned to the Eurydesmidae or Buchiidae is, perhaps, still a moot point (Runnegar 1979; Waterhouse 1980). Possible phylogenetic links between the pterioid superfamily Ambonchyiodea and the pectinoid Monotoidea need to be investigated further. Waterhouse and 310 PALAEONTOLOGY, VOLUME 38 Gupta (1982), for example, have gone so far as to suggest that the Eurydesmidae, Pergamidiidae and Buchiidae may collectively be distinct enough to comprise a separate superfamily (the Eurydesmatoidea Reed, 1932). Eurydesma is a consistent component of Permian cool-temperate marine invertebrate assemblages throughout Gondwana. It has been recorded from both eastern and Western Australia, India (various localities). South Africa and Argentina (Runnegar 1979, fig. 2). As stated previously, Glendella is known only from the Middle Permian of eastern Australia and Manticula occurs in the Late Triassic (Carnian-Norian) of both New Zealand and New Caledonia. Krumbeckiella is prolific in the Late Triassic (Norian) of Timor in a palaeoenvironmental setting which is judged to have been close to the southern margins of the Tethyan Ocean (Audley-Charles 1988). At this locality it co-occurred with Pergamidia , which is known from Turkey, and possibly other Tethyan Triassic localities too (Cox 1969). Thus it is possible to conclude that the group of taxa represented by Eurydesma , Glendella, Manticula and Krumbeckiella is essentially a southern one with high-latitude, cool-temperate origins in the Early Permian. The group may well have spread subsequently so that by the Late Triassic it came to occupy marginal-Tethyan environments. Indeed, if Pergamidia is a valid further member of the group, it may well have disseminated through the Tethyan realm proper. Thereafter, however, the story would appear to be one of dramatic range retraction, for there may well be no true Jurassic representatives of either the Eurydesmidae or Pergamidiidae. The sole further stratigraphical record is now established for Manticula in the Early Cretaceous of Antarctica. Such an occurrence may well indicate that this genus became a relict in a high-latitude refugium. It may also be that it can be regarded as a Late Triassic (Carnian-Norian)-Early Cretaceous (Berriasian) Lazarus Taxon (Jablonski 1986), with no known Jurassic records. However, it is apparent that Manticula is still known from comparatively few stratigraphical levels in New Zealand and New Caledonia, and application of 95 per cent, confidence intervals to its Triassic range ( sensu Marshall 1990) could see an extension into the Cretaceous. Precise stratigraphical occurrences of Manticula are currently being reinvestigated. Acknowledgements. I am grateful to Dr M. R. A. Thomson, Dr J. S. Crampton and other BAS colleagues for making their collections of Antarctic Manticula specimens available to me. I also thank Dr Crampton for the loan of Manticula problematica specimens from New Zealand and for much useful discussion. Dr N. J. Morris enabled me to borrow certain elements of the C. T. Trechmann Collection housed in the Department of Palaeontology, The Natural History Museum, London, and also provided advice on a number of topics. Chr. Maugenest kindly allowed me to borrow a small collection of Krumbeckiella specimens from the Mineralogisch- Geologisch Museum. Delft University of Technology, The Netherlands. K. S. Robinson assisted with the SEM work and C. J. Gilbert and P. Bucktrout took the photographs. Constructive criticisms of the manuscript by Professor B. Runnegar and Dr H. J. Campbell are gratefully acknowledged. REFERENCES audley-charles, m. G. 1988. Evolution of the southern margin of Tethys (North Australian region) from the early Permian to late Cretaceous. 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CRAME British Antarctic Survey (NERC) High Cross Typescript received 6 October 1993 Madingley Road Revised typescript received 3 June 1994 Cambridge CB3 OET, UK CHIGUTISAURID TEMNOSPOND YLS FROM THE LATE TRIASSIC OF INDIA AND A REVIEW OF THE FAMILY CHIGUTISAURIDAE by DHURJATI P. SENGUPTA Abstract. Two chigutisaurids (Amphibia, Temnospondyli), Compsocerops cosgriffi gen. et sp. nov. and Kuttycephalus triangularis gen. et. sp. nov., from the Late Triassic Maleri Formation, Pranhita-Godavari valley, Deccan, India are described. In the past, the only known chigutisaurids have been two genera from Australia and probably two from South America. Relationships within the family are analysed and two groups are recognized. They possess marked differences in their palate and dentition. The Late Triassic beds of the Pranhita-Godavari valley exhibit a rapid faunal change. Two faunal zones are present in the Maleri Formation. The age of the lower zone is possibly Late Carnian and the upper is Early Norian. Chigutisaurids are present in the upper faunal zone only. Two new taxa of the family Chigutisauridae, a rare group of temnospondyl amphibians, previously known only from South America and Australia, have been recovered from Late Triassic continental red beds of the Maleri Formation of the Pranhita-Godavari valley, Deccan, India (Text-fig. 1). During the last decade or so, the chigutisaurids have attracted the attention of palaeontologists, as they are known to have crossed the Triassic-Jurassic boundary (Warren and Hutchinson 1983). The new taxa from India have been discovered at a juncture when more information is needed to bridge the geographical gap between the South American and the Australian chigutisaurids. Against this background, the new chigutisaurids seem to be of extreme importance. The appearance of the chigutisaurids in India is accompanied by the disappearance of the metoposaurids and some reptilian forms. The present work suggests that this change possibly indicates the Carnian-Norian faunal turnover. The discovery of the new chigutisaurids thus adds valuable knowledge not only about this group but also about the Indian Late Triassic. SYSTEMATIC PALAEONTOLOGY Order temnospondyli Zittel, 1888 Superfamily brachyopoidea Save-Soderbergh, 1935 Family chigutisauridae Rusconi, 1951 Genus compsocerops gen. nov. Derivation of name. From the Greek compso (beautiful), ceros (horn) and ops (face), alluding to an animal with beautiful horns/projections on the skull. Diagnosis. Large chigutisaurid with parabolic skull, anteriorly placed orbits and a pair of tabular horns; pair of projections present on postparietals, squamosals and quadratojugals; lacrimal absent; pineal foramen anteriorly placed; cultriform process of parasphenoid long and narrow; dentigerous area restricted to anterior region of the skull and lower jaw; complete row of teeth on vomer, palatine and ectopterygoid bones; palatal tooth row separated from marginal row by a | Palaeontology, Vol. 38, Part 2, 1995, pp. 313-339.] © The Palaeontological Association 314 PALAEONTOLOGY, VOLUME 38 Faults Attitudes eh Yerrapalli Formation Kamthi Formation □ Dharmaram Formation Maleri Formation text-fig. 1 . Geological map of area between Dharmaram and Maleri, with significant temnospondyl localities. A schematic section along ‘S’ is shown at top right. Inset indicates the location of the area studied. conspicuous groove; dorsal process of clavicle unusually long; pleurocentrum and intercentrum fused in some vertebrae. Compsocerops cosgriffi sp. nov. Text-figures 2-14 Derivation of name. The species is named after the late Dr John W. Cosgriff, who first identified as brachyopoids some jaw fragments collected from the Maleri Formation. Holotype. ISI A 33, an almost complete skull with attached mandibles, in the collection of the Geological Museum of the Indian Statistical Institute (ISI), Calcutta, India. Referred specimens. ISI A 24-27 and ISI A 34-49 Diagnosis. As for the genus. Horizon and age. All the material described here was collected from the upper part of the Maleri Formation. The type skull was collected from a red clay horizon near Rechni village (Text-fig. 1). An Early Norian age has been assigned to the Upper Maleri fauna in the present work. SENGUPTA: TRIASSIC C H I GUTI S AU R I DS 315 Description Nature of preservation and reconstruction. The type skull is nearly complete with most of the sutures and ornamentation of the skull roof intact (Text-fig. 2). The mandibles were attached to the skull (Text-fig. 3). The text-fig. 2. Compsocerops cosgriffi gen. et sp. nov. Holotype skull, ISI A 33, in dorsal view. Scale bar represents 50 mm. For abbreviations for this and all other Text-figures, see list on p. 339. pmx occiput has been flattened. The palate along with the dentition (Text-figs 3-4) is very well preserved in ISI A 34. A complete left mandible and another fragmentary specimen have been studied, in addition to the mandibles with ISI A 33. A number of postcranial elements have been recovered both from clay and sandstone. Characteristic skull roof bones or vertebrae are always found in association. A list of specimens studied is given in Table 1 . Dorsal surface of the skull (Text-fig. 5). The skull is large and parabolic with conspicuous tabular horns and anteriorly placed dorsolateral orbits. The skull roof is 300 mm long and 400 mm wide with the posterior margin about 170 mm from the rear of the skull roof. A projection is present on the postparietal, squamosal and quadratojugal. The skull is relatively deep (Text-fig. 5b). The skull roof bones show the usual chigutisaurid arrangement. The anterior part of the skull is rounded with the premaxilla at the anteriormost tip. The nasal is broad, expanded anteriorly and strongly ornamented. The frontal is almost rectangular. The parietal is large, rectangular, and shorter than the postparietal. Thicknesses of the bones are at a minimum around the pineal foramen which is relatively anteriorly placed almost at the suture between the parietal and the frontal. The posterior region of the skull is wide and stout and appears to have been the active zone of intensive growth. The tabular horn projects posteriorly. The posterior part of the horn remains unsupported from below as the descending (paroccipital) process of the tabular does not extend posteriorly beneath the horn. The otic notch is marked. The subcircular orbit is formed by the prefrontal, jugal, postfrontal and postorbital. These bones have fainter sculpturing compared with the posterior skull roof bones. The external naris is elliptical and faces anterodorsally. The unusually deep lateral line canal around the posterolateral border of the naris causes the rim of the naris to be raised except anteriorly, where it is confluent with the skull roof. The rim is conspicuous. 316 PALAEONTOLOGY, VOLUME 38 text-fig. 3. Compsocerops cosgriffi gen. et sp. nov. a, holotype skull, ISI A 33, in dorsal view, b, skull, ISI A34, in ventral view. Scale bar represents 50 mm. The ornamentation on the skull roof has numerous pits at the centre of each bone and radiating ridges near the edges. Narrow U-shaped grooves between the ridges gradually widen towards the periphery of each bone. In places, these ridges bear small uneven pustules. The grooves are very coarse on the tabular horns, while the ridges are longest at the posterior of the quadra tojugals. Ventral surface of the skull roof (Text-fig. 6). On the ventral face of the tabular, the descending process starts with a thinning fan of bone which divides the ventral side of the unsupported part of the tabular into two deep SENGUPTA: TRIASSIC CHIGUTISAURIDS 317 table 1. List of specimens studied. Material Specimen no. Compsocerops cosgriffi Parts of vertebra ISI A 22 Parts of vertebra ISI A 24 Right ilium ISI A 25 An isolated occipital condyle (left) with part of the basal ISI A 26 plate of the parasphenoid A broken interclavicle ISI A 27 A complete skull with both mandibles attached ISI A 33 A mostly complete skull with one side of the palate intact ISI A 34 Right side of a skull roof ISI A 35 A complete left mandible ISI A 36 Left posterior portion of a skull roof with tabular and ISI A 37 post-parietal only A nearly complete clavicle ISI A 38 Parts of two vertebrae (i) One intercentrum and pleurocentrum fused together ISI A 39 (ii) One intercentrum ISI A 40 Parts of humerus ISI A 41 Parts of neural spines ISI A 43 to 1 ISI A 49 Kuttycephalus triangularis A complete skull with left lower jaw ISI A 50 Skull fragments ISI A 51 ISI A 52 318 PALAEONTOLOGY, VOLUME 38 text-fig. 5. Compsocerops cosgriffi gen. et sp. nov. a, reconstruction of the skull in dorsal view, b, reconstruction of the skull in lateral view. Scale bar represents 50 mm. B elliptical scars of the internal and external tabularis. Beneath the supratemporal, a semicircular ridge of bone may represent the remains of the ascending ramus of the pterygoid. Near the anterior border of the orbit, on the ventral side of the prefrontal, is a small prominence (Text-fig. 6). This type of prominence in this position has not been reported from any other chigutisaurid. It may indicate the presence of a muscular connection between the roof and the more anterior parts of the palate. It is interesting to note that Benthosuchus sushkim has a pair of projections, the ‘ spina lachrymalis ’ (Bystrow and Efremov 1940), on the dorsal side of the palatines. Ventral surface of the palate (Text-fig. 7a). Posteriorly, the palate is essentially a parallel-sided longitudinal vault with a flat roof. The vertical lateral wall of the pterygoid projects posteriorly as far as the occipital condyle with an exceptionally deep development of the pterygoid. Although the suture is not preserved completely, the posterior parts of the vomers appear to include the anterior tongue of the cultriform process of the parasphenoid, slightly posterior to the level of the anterior borders of the interpterygoid vacuities. The anterior margin of the vomers forms the border of the transversely lenticular anterior palatal vacuity. On the ventral surface of the palate, along the anterior margin of this vacuity, at least two irregular ridges of bone are present. The dentigerous area is restricted to the anterior region of the palate leaving a larger posterior portion, with big subtemporal vacuities, which extends anterior to the centre of the interpterygoid vacuities. The parasphenoid has a large subcircular base and a long and narrow cultriform process with a low ridge-like elevation along its ventral margin at the axis of curvature. The exoccipitals suture with the posterior margin of the body of the parasphenoid. More laterally, the quadrate is exposed between the pterygoid ramus and a flat posterior projection of the quadratojugal. The quadrate condyle is positioned well anterior to the occipital condyle. The quadrate-pterygoid suture is present on the outer side of the downturned wall of the pterygoid. SENGUPTA: TRIASSIC CH IGUTIS AU RI DS 319 text-fig. 6. Compsocerops cosgriffi gen. et sp. nov., 1SI A 35. Prefrontal prom- inence in a, ventral view; b, lateral view; c, enlarged. Scale bars represent 50 mm. text-fig. 7. Compsocerops cosgriffi gen. et sp. nov. a, reconstruction of the skull in ventral view; b, reconstruction of the occiput. Scale bar represents 50 mm. p.mx 320 PALAEONTOLOGY, VOLUME 38 text-fig. 8. Compsocerops cosgriffi gen. et sp. nov. ; ISI A 34; the base of the parasphenoid and the braincase and associated features in dorsal view. Scale bar represents 50 mm. cps Dorsal surface of the palate (Text-fig. 8). The cultriform process forms an elongate canal-like depression. This depression gradually flattens on to the basal plate of the parasphenoid as a pair of shallow depressions which fan out symmetrically. They lead to two crescentic canals for the internal carotid arteries within the base of the parasphenoid (Text-fig. 8). On the dorsal surface of the pterygoid, the base of the ascending process of the pterygoid is preserved. Anterior to this, another lateral canal runs towards the carotid canals. However, it cannot be determined whether an ascending column of the pterygoid (Warren and Hutchinson 1983) was present on the medial margin of this process. It appears that the braincase may have been relatively wide, anteriorly expanded and low. Occiput (Text-fig. 7b). The occiput is an inverted U-shaped structure with the skull roof and the palate present as a flat table in the middle and flanged by two large squamosal-quadratojugal troughs. The inverted U is formed by the downturned quadrate rami of the pterygoids. The exoccipitals form the posteriorly directed condyles. They have quite long necks. The columnar part of the ascending process of the exoccipital is flat and inclined, and meets the descending process of the postparietal and the tabular. Ventrally the exoccipital continues up to the pterygoid, forming a plate which is curved inwards. The exoccipital bears a large oval foramen for nerve (x) just at the point where the process of the exoccipital starts ascending. The otic recess is extremely large and so is the otic notch. No stapes is preserved. At the posterior end, where the quadrate ramus of the pterygoid turns ventrally, a marked posterior projection of the pterygoid is present. Pronounced muscle attachment scars are present on the transverse edge of the postparietal and tabular which are very conspicuous in the occipital view. As mentioned above, a large rectangular trough, formed by the squamosal, quadratojugal and quadrate, is present in C. cosgriffi. The trough has its lower part almost infolded, creating a depression at the bottom. This may represent the origin of the depressor mandibuli muscle (Welles and Estes 1969). A circular paraquadrate foramen is present on the quadratojugal. The quadrate is seen in occipital view, separating the quadratojugal and the downturned pterygoid. The dorsal part of the quadrate-pterygoid suture extends laterally onto the squamosal- quadratojugal trough, whereas more ventrally this suture runs down the medial wall of the trough. Mandible (Text-fig. 9a-d). The mandible has the characteristic chigutisaurid shape, as described by Jupp and Warren (1986). In cross-section it is elliptical with a flat top. The dentition is restricted to the anterior half. The ornamentation in the posterior part consists essentially of large elliptical grooves walled by coarse ridges. SENGUPTA: TRIASSIC CHIGUTISAURIDS 321 text-fig. 9. Compsocerops cosgrijfi gen. et. sp. nov., ISI A 36, left mandible in A, ventral view; b, dorsal view c, lingual view; D, labial view. Scale bars represent 50 mm. 322 PALAEONTOLOGY, VOLUME 38 I II III text-fig. 10. Compsocerops cosgriffi gen. et sp. nov. Presacral vertebrae in I, anterior, II, posterior and III, left lateral aspects, a, parts of pseudostereospondyl dorsal vertebra as preserved in ISI A 39. b, composite reconstruction of a dorsal vertebra based on ISI A 43-47 (neural spine) and ISI A 24 (centra), c, axis based on ISI A 22. Scale bar represents 50 mm. Anteriorly, the ornament consists of anastomosing ridges on the splenial and postsplenial. The articular is exposed on the dorsal surface of the postglenoid area as a triangular bone between the surangular and the prearticular. The posteriormost part of the postglenoid area is pointed but without any marked retroarticular process. Lingually, a small foramen, possibly for the chorda tympani , is present in the prearticular. Two openings for the anterior meckelian foramen and a third, opening a little anterior to it, are visible in the splenial. Three coronoids also appear on the lingual surface and a conspicuous coronoid process is present at the posterior coronoid. Dorsally, the dentary has a thin posterior extension. It increases in width anteriorly. The large adductor fossa is pointed near its anterior tip. The articular fossa is bilobed. The symphysis is formed largely by the dentary, with a small ventral inclusion of the anterior splenial. In the upper jaw, two tooth rows, marginal and palatal are embedded in narrow ridges with a narrow groove in between them. This groove is prominent at the ectopterygoid-maxillary junction. In the maxillary row, the teeth are larger anteriorly and are of uniform shape. All the teeth, including the tusks, are curved lingually. The curvature is probably maximal near the tip. Dentition. A single row of teeth is present in the anterior half of the mandible. No symphysial row is preserved. An indication that a large tusk pit is present near the mandibular symphysis is seen in one specimen, but not in another. The teeth are largest midway along each ramus. At the ectopterygoid-palatine contact, the bite may have been most severe with larger teeth located there. Sixty-four teeth are estimated to have been present in the mandible of ISI A 33. SENGUPTA: TRIASSIC CHIGUTISAURIDS 323 Vertebrae (Text-fig. 10a-c). All the vertebral elements collected are presacral, but their exact position is difficult to determine. In at least one element, the pleurocentra are fused with the intercentrum to give a pseudo- stereospondyl appearance (Text-fig. 10c). From anterior to posterior the convexity of the intercentra decreases. The pleurocentra are two symmetrical, small, roughly spindle-shaped, bones. Possibly they met to form the floor of the neural canal. Anteriorly, they are fused with the intercentrum, so that a notochordal canal is formed near the centre of each vertebral unit. The canal is U-shaped, with the long arm in the axis, and becomes circular posteriorly. The pleurocentra also become curved posteriorly and, while joined with crescentic intercentra, they become almost spool-shaped. This type of vertebra is known only from a few vertebral elements of Metoposaurus ouazzoui and, to some extent, in the entire vertebral column of the almasaurids (Dutuit 1976). The former vertebrae resemble those of C. cosgriffi , but the latter look different. The axis is rectangular in shape. It appears that, more posteriorly, the intercentra become heart-shaped. All of them have strong parapophyses. The neural arch is small and blunt. The neural spines are thick, moderately high, and have two symmetrically disposed posterior and anterior zygapophyses. The anterior side of each spine is marked by two thin symmetrical ridges. The neural arches appear to have been intervertebrally placed. text-fig. 1 1. Compsocerops cosgriffi gen. et sp. nov. ISI A 38, right clavicle in a, ventral view; b, dorsal view; c, posterior view. Scale bar represents 50 mm. Appendicular skeleton (Text-figs 11-14). The preserved appendicular elements of Compsocerops resemble their counterparts in Siderops. The clavicle bears an unusually long cleithral process which begins abruptly and becomes narrow dorsally (Text-fig. 11a-c). Posteriorly, the process is deeply grooved for the cleithrum. The groove continues onto the flat plate of the clavicle where it dies out. The incomplete interclavicle has been reconstructed as a diamond-shaped plate (Text-fig. 12). The clavicle and the interclavicle are very similar to those of Siderops. The humerus is also slender and lacks extensive projections. The angle of torsion is almost 90 degrees (Text-fig. 1 3a-d). The distal articulation is rounded and knob-like in the ectepicondylar region. This was probably the area for the insertion of muscles like the trochlea and capitellum. The entepicondylar side is somewhat flattened. Both condyles are sharp and pointed. The ectepicondyle merges with the supinator process. There is also a well developed furrow for the supinator muscle. The proximal articulation is thinner on the deltopectoral side. The deltopectoral crest is relatively blunt. The area of attachment of the pectoralis 324 PALAEONTOLOGY, VOLUME 38 text-fig. 12. Compsocerops cosgriffi gen. et sp. nov. IS1 A 27, interclavicle in ventral view. Scale bar represents 50 mm. text-fig. 13. Compsocerops cosgriffi gen. et sp. nov. Right humerus in a, anterior view; b, dorsal view; c, posterior view; d, ventral view; based on ISI A 41 and A 42. Scale bar represents 50 mm. muscle is very distinct as are the attachments for the deltoid muscle. Attachment for the medial head of the triceps is also very prominent. The ilium is thin and elongate with prominent ridges dorsally on the external surface (Text-fig. 14a- b). Deep furrows are present on both sides of the dorsal edge of the acetabulum. The acetabulum is a comparatively large knob-like structure with a deep fossa. SENGUPTA: TRIASSICCHIGUTISAURIDS 325 text-fig. 14. Compsocerops cosgriffi gen. et sp. nov., ISI A 25, right ilium in a, medial view; b, lateral view. Scale bar represents 50 mm. text-fig. 15. Kuttycephalus triangularis gen. et sp. nov., holotype skull, ISI A 50, in a, ventral view; B, dorsal view. Scale bar represents 50 mm. Genus kuttycephalus gen. nov. Derivation of name. The genus is named after Mr T. S. Kutty of the Geological Studies Unit, Indian Statistical Institute, who discovered most of the material, including the skull. Diagnosis. Chigutisaurid with relatively triangular skull and fine, reticulate ornamentation; pair of projections on the squamosals and quadratojugals together with tabular horns; postparietal 326 PALAEONTOLOGY, VOLUME 38 text-fig. 16. Kuttyceplialus triangularis gen. et sp. nov., holotype skull, ISI A 50, in dorsal view. Scale bar represents 50 mm. projections are absent; dentigerous area of the upper jaw and palate extends to the posterior half of the skull; cultriform process of the parasphenoid broad; anterior tip of the subtemporal vacuity not reaching level of centre of interptergyoid vacuities; numerous small marginal teeth present. Kuttycephalus triangularis sp. nov. Text-figures 15-18 Derivation of name. The specific name highlights the triangular shape of the skull. Holotype. ISI A 50. A complete skull with left lower jaw in the collection of the Geological Museum of the Indian Statistical Institute, Calcutta, India. Referred specimens. ISI A 51, 52. Diagnosis. As for genus. Horizon and Age. A surface find from a clay bed in the upper part of the Maleri Formation, assigned to the Early Norian. SENGUPTA: TRIASSIC CHIGUTISAURIDS 327 Description of the skull (Text-figs 15-18). The nearly complete skull is distorted and had calcareous encrustation on the bone surface. The left mandible is attached to the skull (Text-figs 17-18). Part of the left side of the skull, along with the mandible, is strongly infolded and rides over the palate. The left side of the skull is more complete. text-fig. 17. Kuttycephalus triangularis gen. et sp. nov. Reconstruction of skull It appears that the skull was distorted by forces acting in more than one direction. The skull roof appears to be shorter and narrower than in other chigutisaurids and, in this, it bears resemblance to a rhytidosteid skull. The skull is 145 mm long and nearly 220 mm wide. The reconstructions of the skull roof, palate and occiput are shown in Text-figures 17-18. The skull shows the usual chigutisaurid bone arrangement. The tabular has a stout large unsupported horn typical of the chigutisaurids. The ornament of K. triangularis is composed of fine ridges and wide grooves branching out rapidly in a reticulate pattern. The ridges are markedly thin (less than 0-5 mm in places). The tabular horns and the quadratojugal and squamosal projections look similar to those observed in C. cosgriffi. The parietal foramen is more anterior than in other chigutisaurids except C. cosgriffi. The border of the naris stands out as a conspicuous rim, as in C. cosgriffi. The lacrimal appears to be absent. The postparietal projections are absent. The pterygoid is vaulted as in other chigutisaurids. The vaulting begins more posteriorly than in C. cosgriffi. The cultriform process of the parasphenoid is wider than other chigutisaurids. In ISI A 50 the process is partly folded, the original width having been greater. The anterior tip of the process extends anterior to the interpterygoid vacuities, and becomes spatulate at the anterior end which is enclosed by the vomers. Unlike the situation in C. cosgriffi , the anterior palatal vacuity is a single elliptical depression. The anterior tip of the subtemporal vacuity does not extend forward beyond the central portion of the interpterygoid vacuity. The upper jaw is characterized by numerous, small, uniform marginal teeth which extend posterior to the centre of the interpterygoid vacuity. The palatal tusks and tusk pits are marked. Thus, unlike C. cosgriffi , no tooth row is present on the palatine and ectopterygoid apart from the tusks. The vomer bears a pair of tusks and tusk pits along with three other smaller teeth at the border of the posterior edge of the anterior palatal vacuity. The tusk pits are shallow, large and circular. The palatine and ectopterygoid also bear smaller tusks. The occiput is typically chigutisaurid with deep vaulting of the palate, and the quadratojugal-squamosal flange opens up into a wide trough on two sides. The quadrate ramus of the pterygoid in the angle between 328 PALAEONTOLOGY, VOLUME 38 its horizontal and vertical portion forms a sharp pointed posterior projection as in C. cosgriffi. The ascending ramus of the pterygoid is not very well preserved. The otic recess is large. DISCUSSION The family Chigutisauridae The family Chigutisauridae was erected by Rusconi (1951) to include several short-faced Triassic temnospondyls from Argentina. The first chigutisaurid, Pelorocephalus mendozensis, was described by Cabrera (1944) from the upper part of the Cacheuta Formation. It was initially placed in the Family Brachyopidae by Romer (1947, 1966). However, Welles and Estes (1969) excluded Pelorocephalus from the family Brachyopidae revalidating the distinctiveness of the chigutisaurids. Rusconi (1948) described another chigutisaurid, Chigutisaurus tunuyanensis. Subsequently he also described C. tenax (Rusconi 1949) and C. cacheutensis (Rusconi 1953) as well as a number of other genera and species (see Rusconi 1950, 1951). Bonaparte (1975) recognized another species from the Ischigualasto Formation (Late Triassic) of Argentina and named it P. ischigualastensis. Later, Bonaparte (1978) synonymized all Argentinian chigutisaurids with P. mendozensis. Recently SENGUPTA: TRIASSIC CH I GUTIS A U RI DS 329 Marsicano (1993) has undertaken a revision of the Argentinian chigutisaurids and recognized the presence of more than one taxon. However, the present discussion is based on the assumption that there are two valid genera of Argentinian chigutisaurids, Pelorocephalus and Chigutisaurus. Warren (1981) described a chigutisaurid Keratobrachyops australis from the Arcadia Formation (Early Triassic) of the Rewan Group of Australia. Subsequently Warren and Hutchinson (1983) described another large chigutisaurid, Siderops kehli , from the Evergreen Formation (Early Jurassic) of south-west Queensland, Australia. Chigutisaurids have been considered as active predators and agile swimmers by Cosgriff (1984). DeFauw (1989) considered chigutisaurids as semiaquatic forms. Warren and Hutchinson (1983) defined the chigutisaurids as having a parabolic skull with anteriorly placed orbits, a deeply vaulted palate, a pair of occipital condyles positioned much posterior to the quadrate condyles, a complete inner row of palatal teeth, an ascending column of the ptergyoid and a pair of tabular horns. The lacrimal is absent. Relationships within the Chigutisauridae The following discussion is intended to bring out some salient features of the two new chigutisaurid genera and species erected in the present work. The characters chosen for detailed analysis are those which have been thought to distinguish chigutisaurid genera. Some of them are argued to be derived and shared by different chigutisaurids, while a few characters, treated as significant by Coldiron (1978) and Warren and Hutchinson (1983), are also discussed. Several projections of the skull roof seem to be of particular systematic value and are discussed first. Tabular horn. Chigutisaurids are distinguished from brachyopids by the presence of a tabular horn and a deep otic notch. Brachyopids, plagiosaurids and some members of the Rhytidosteidae lack tabular horns, and usually possess a small horn with a shallow otic notch. Warren and Black (1985) noticed that, in the ’Capitosaurians’, the otic notch is usually deeply incised almost always with a tabular horn. In this group, the tabular horns are always supported from below but in the chigutisaurids they are not similarly supported. The tabular horn is present in almost all chigutisaurids. It is partly preserved in Keratobrachyops (Warren 1981) but not preserved in Siderops (Warren and Hutchinson 1983). The tabular horn and the posterior part of the skull, consisting of the tabular and the postparietal, are similar in the Argentinian and Indian genera in many respects. Their postparietal and tabular form a flat bony plate which projects out from the squamosal. The deep otic embayment is responsible for this. The lateral side of the tabular horn is long and straight running parallel to the midline. The tip of the tabular horn is always pointed in the Argentinian and Indian genera. The posterior margin of the plate, formed by tabular and postparietal, is concave anteriorly. Keratobrachyops also has the latter character. The angle of the horn with the skull margin, the nature of the posterior boundary of tabular and postparietal and also the shape of the otic embayment of Siderops were probably like other chigutisaurids, rather as reconstructed by Warren and Hutchinson (1983). Postparietal projection. As already mentioned, Compsocerops is characterized by a postparietal projection. This is a narrow, symmetrical, elongate ridge with pointed ends, concave towards the midline and extending a little beyond the posterior margin of the skull roof. The functional significance of this projection is not clear. Somewhat irregular dermal projections are also present in the zatrachydids. They also have a raised ridge at the posterior mid-skull (Langston 1953). Acanthostomatops vora.x, considered to be the most primitive zatrachydid, has no postparietal projections. Other members of the family Zatrachydidae have them, and hence the origin of those projections is thought to be within this family (Boy 1989). Keratobrachyops and the Argentinian forms do not have this projection (though Bonaparte’s 1975 reconstruction of Pelorocephalus ischigualastensis depicts a depressed area in the posterior part of the skull at the midline flanged by two raised portions of the postparietal bones). Shishkin (1987) also mentioned that all chigutisaurids have postparietal projections. However, the postparietal horn is absent in Kuttycephalus. Outside 330 PALAEONTOLOGY, VOLUME 38 the Chigutisauridae, postparietal lappets are known in Cochleosaurus (Steen 1938; Rieppel 1980) and have also been reported by Warren (pers. comm.) in Parotosuchus rewanensis (a capitosaurid) and in two rhytidosteids ( Arcadia myriadens; Warren and Black 1985; and in an undescribed juvenile). Rieppel (1980) differentiated Cochleosaurus florensis from C. bohemicus by the size of the postparietal lappets. In the present work the postparietal projection is noted as a derived character in Compsocerops cosgriffi (as the size, shape and position of the horn is different from that present in the zatrachydiids, Cochleosaurus or in other Australian temnospondyls) and is used here as an autapomorphy ( sensu Eldredge and Cracraft 1980) for the genus. Steen (1938, fig. 32) noticed that the postparietal lappets of Cochleosaurus show allometric growth during ontogeny. Compsocerops , however, does not display this. In the present work no taxonomic significance, above generic level, has been assigned to the postparietal projections. Squamosal projection. A squamosal projection is present in Compsocerops , Kuttycephalus , Pelorocephalus and Chigutisaurus. The former two genera have spatulate, blunt projections at the posterior border of the squamosal. In Compsocerops , the projection is more conspicuous than in Kuttycephalus and is present in all individuals where the squamosal is preserved. The squamosal projection in Compsocerops does not show any definite pattern of growth. The squamosal projection has not been observed in any other Triassic temnospondyls. It is not present in zatrachydids. This is basically a chigutisaurid character though not present in Keratobrachyops. It is not preserved in Siderops. Quadratojugal projection. A quadratojugal projection is present in the Indian and Argentinian genera. In Siderops this region is not preserved. Keratobrachyops does not have any quadratojugal projection. The quadratojugal projection is most conspicuous in Chigutisaurus and Compsocerops. At the posteriormost tip of the quadratojugal, a squarish lappet, with coarse ridges, projects out posteriorly in the latter genus from the squamosal-quadratojugal trough. This projection is also visible in Kuttycephalus. Dentition. The basic dentition is similar in all chigutisaurid genera. A row of small marginal teeth and another row of palatal teeth are present in all genera. A similar sized double row of teeth aligned in parallel is present in the maxilla-ectopterygoid of Compsocerops and Siderops. In Pelorocephalus , Keratobrachyops , Kuttycephalus and in the various species of Chigutisaurus , the double row is present but they are not parallel. Nor are the maxillary and ectopterygoid teeth embedded in narrow ridges as they are in Compsocerops and Siderops. This character is used here as an apomorphy linking these two genera. In Siderops and Compsocerops the dentition of the palate and the upper jaw is restricted to the anterior half of the skull. In Pelorocephalus , the dentigerous area of the upper jaw and palate is positioned further anteriorly. In the lower jaw, the teeth are usually larger and curved lingually. Mandible. The features of the mandible of Compsocerops , as discussed earlier, confirm Jupp and Warren's (1986) character assignments for previously known chigutisaurid mandibles. In all chigutisaurids, the adductor fossa is large and deep while the articular fossa is shallow, feebly bilobed and lingually widening. The postglenoid ridge is not very high in any chigutisaurid. The postglenoid area is relatively longer in all chigutisaurids though the ratio of the total mandibular length and the length of the postglenoid area may vary from genus to genus. This ratio is highest in Chigutisaurus tunuyanensis (2-8) and lowest in Siderops kehli (15). In Compsocerops cosgriffi the ratio is T8 and in Keratobrachyops australis it is 1-76. A distinct coronoid process is present in the lower jaw of Compsocerops as well as in Siderops and Keratobrachyops. Following Warren and Hutchinson (1983), this is thought to be a derived character. Cultriform process of the par asphenoid. The width of the cultriform process of the parasphenoid was taken as an important apomorphy by Coldiron (1978) for some temnospondyls. This process is SENGUPTA: TRIASSIC CHIGUTIS A U R I DS 331 generally believed to be narrower in the chigutisaunds. Among the Indian forms, Kuttycephalus has a wide cultriform process similar to that of Keratobr achy ops. Warren and Hutchinson (1983) noted that only Keratobrachyops has the anterior border of the interpterygoid vacuities placed posterior to the anteriormost tip of the cultriform processes among all the chigutisaurids. Kuttycephalus has this character and it also shows the inverted ‘V’-like grooves running parallel to the vomer- parasphenoid suture as in Keratobrachyops. The comparatively narrow cultriform processes of Siderops, Compsocerops and Pelorocephalus are similar on the other hand. The position of the suture between vomer and parasphenoid, as present in Keratobrachyops and Kuttycephalus , is considered in the present work to be a derived character. The wide cultriform process of Kuttycephalus and Keratobrachyops is also used in the phylogenetic reconstruction. Pcdatcd vacuities. Two major palatal vacuities, the subtemporal vacuity and the interpterygoid vacuity, vary both in shape and size among the chigutisaurid genera. The subtemporal vacuity in Keratobrachyops , Chigutisaurus and Kuttycephalus is less than half of the length of the interpterygoid vacuity. Compsocerops , Siderops and Pelorocephalus have subtemporal vacuities with anterior tips extending beyond the centre of the interpterygoid vacuity. This is considered here to be a derived character. Postcranial elements. Postcranial elements are known only in Siderops, Compsocerops and Chigutisaurus. The clavicle-interclavicle complex and the humerus of the first two are very similar. Compsocerops has fused inter- and pleurocentrum to give the vertebrae a pseudostereospondyl appearance. This is unique within the family. The long dorsal process of the clavicle is a derived character, shared by Compsocerops and Siderops. There are some other characters which have either been thought by earlier authors as important for construction of relationships or show some variations. These characters are discussed below. The polarities of some of these characters are uncertain. Parietal-postparietal ratio. Triassic temnospondyls commonly have the postparietal shorter than the parietal. Metoposaurids, brachyopids, rhytidosteids, capitosaurids and plagiosaurids all have shorter postparietals. Warren and Hutchinson (1983) claimed that this condition prevailed in Keratobrachyops and Siderops but not in Pelorocephalus. Compsocerops and Kuttycephalus also have shorter postparietals. There is no clear indication in Warren and Hutchinson’s work whether the postparietal of Pelorocephalus is equal to its parietal or longer. All available drawings and photographs of Chigutisaurus and Pelorocephalus show that the parietal is roughly equal in length to the postparietal. Warren and Hutchinson’s cladogram, however, depends heavily on the parietal-postparietal ratio for splitting the Australian and Argentinian genera. Anterior palatal vacuity. The shape and size of the anterior palatal vacuity vary widely among chigutisaurids. Coldiron (1978) used the bilobed anterior palatal vacuity as an apomorphy. He considered the single lobed anterior palatal vacuity of the brachyopids as a primitive condition or a secondary development for that group. Chigutisaurids also have an unpaired anterior palatal vacuity. The type of Pelorocephalus (Cabrera 1944) shows a feebly bipartite anterior palatal vacuity (see Bonaparte 1978). The presence of two deeper depressions at two ends gives rise to this type of structure which is visible also in Kuttycephalus. The anterior palatal vacuity of Compsocerops is a complicated structure with ridges and grooves running parallel to both anterior and posterior borders of the vacuity. The shape of the vacuity in Compsocerops is also lenticular. Ornamentation. The ornament of Compsocerops and Siderops is strikingly similar. Both have circular pits present at the centre of ossification and elongate ridges radiating away from the centre. There are grooves between two ridges which widen towards the margin of the bones. The ridges anastomose locally. The ridges do not have symmetrical cross sections. Kuttycephalus, in contrast, has finer straight ridges with close reticulations. This type of ornamentation resembles that in 332 PALAEONTOLOGY, VOLUME 38 table 2. Derived characters used to construct the relationships of the chigutisaurid genera (Text-fig. 19); characters 1 to 11 after Warren and Hutchinson (1983). (1) Short, broad, parabolic skull (2) Zones of intensive growth in cheek region only (3) Lacrimal absent (4) Basicranial joint firmly sutured (5) Pterygoid with a deep vertical ventrally-directed plate forming an inverted ‘U ’-shaped palate; quadrate condyles well below the level of the occipital condyles (6) Squamosal-quadratojugal trough lateral to occiput (7) Retroarticular process long (8) Posterior meckelian foramen and angular-prearticular suture on the ventral surface or very low on lingual surface of lower jaw (9) Articular exposed on dorsal surface of the retroarticular process (10) Quadrate condyles anterior to the occipital condyles (11) Ascending column of pterygoid present (12) Complete row of small marginal palatal teeth present (13) Suture between the cultriform process of the parasphenoid and the vomer situated anterior to the anterior borders of the interpterygoid vacuities (14) Paraquadrate foramen on the quadrate-quadratojugal suture (15) The ratio of maximum palatal width to that of the cultriform process of the parasphenoid very low (10-50) (16) Presence of tabular horns and squamosal and quadratojugal projections in the posterior part of the skull (17) Cultriform process of the parasphenoid long, narrow (18) The anterior tip of the subtemporal vacuity positioned anterior to the centre of interpterygoid vacuity (19) A similar-sized double row of teeth embedded on narrow ridges particularly in the ectopterygoid-maxilla (20) Lower jaw with coronoid process (21) Exceptionally long dorsal process of the clavicle (22) Presence of a pair of projections on the postparietals (23) Posteriorly placed pineal foramen Keratobr achy ops (Warren 1981). The ornamentation of Chigutisaurus appears to be similar to the Kuttycephalus-Keratobrachyops type. The ornament of the Argentinian chigutisaurids, however, has not been described adequately. Vomerine pit and shagreen. Only Siderops has a vomerine pit. Chigutisaurus tenax also has a vomerine shagreen (Rusconi 1951). Quadrate condyles. Quadrate condyles placed anterior to and well below the level of the occipital condyles vary within the family. Chigutisaurus and Pelorocephalus illustrate this variation among the Argentinian forms. The latter and Compsocerops have long cylindrical quadrate condyles. In Siderops and, to some extent, in Chigutisaurus , the condyles appears to have a screw-like appearance (see Howie 1970 for details of this character in capitosaurids). In Kuttycephalus the quadrate condyles are not well preserved. Orbits. The orbit of Chigutisaurus is placed slightly dorsally relative to other genera. In Compsocerops the orbit always remains anterior and lateral. Keratobrachyops, has comparatively larger orbits. Occiput. In the occiput, the height of the skull and the angle of the vaulting of the pterygoid vary from genus to genus. These parameters seem to be highly susceptible to deformation because the combination of the heavy squamosal-quadratojugal flanges with the thinner skull table and basal SENGUPTA: TRIASSIC CHIGUTISAURIDS 333 text-fig. 19. Cladogram depicting relationships of chigutisaurids. Characters used are listed in Table 2. plate of the parasphenoid in between, created a situation in which pressure from above or from the sides may have changed the height of the skull. Minor variations in these characters are not suitable for phylogenetic consideration. The vacuities of the occiput also show some variation. The descending plate of the tabular (posterior to the slender process which comes to the exoccipital) descends down on the dorsal surface of the pterygoid, just at the line of its vaulting in Compsocerops. This plate is wide and thin in Compsocerops , Kuttycephalus, Pelorocephalus and Chigutisciwus. The paraquadrate foramen is housed in the quadratojugal, near its suture with the squamosal, in all the chigutisaurids except Keratobrachyops, where the foramen is on the quadrate-quadratojugal suture. From the above discussion, several apomorphies have been noted for different chigutisaurid genera (Table 2). Some are thought to be typical brachyopid characters (Watson 1956; Cosgriff 1969, 1974; Chernin 1977), shared by chigutisaurids (Warren and Hutchinson 1983). Others are exclusively chigutisaurid characters. A cladogram (Text-fig. 19) has been constructed to depict the relationships of the chigutisaurid genera. It is important to note here that some authors prefer to include Siderops in the family Brachyopidae (Carroll 1987; Morales 1990; Shishkin 1990). The tabular horn is not preserved in Siderops which seems to be the root of the confusion. Shishkin (1990), however, mentioned the absence of other chigutisaurid characters in Siderops , such as the axial trough of the skull. Axial troughs are present in the Indian taxa but not yet noted in the Argentinian ones. Similarly, a keel at the ventral surface of the cultriform process of the parasphenoid has been noted by Marsicano (1990) in the type specimen of Pelorocephalus. This feature is not present in any other chigutisaurid genera. Siderops has all the chigutisaurid characters identified in the present work. Moreover, Siderops has a substantial similarity to Compsocerops , and the presence of the tabular, squamosal and quadratojugal projections is predicted in Siderops. Similarly, the presence of a firmly sutured basicranial joint and the ascending column of pterygoid cannot be verified in the Indian genera. The relevant areas are not well preserved. In several characters, such as orbit size and position of the paraquadrate foramen, Keratobrachyops seems to be distinct from other chigutisaurids. In the shape of the skull and in several palatal characteristics, it resembles Kuttycephalus and Chigutisaurus. All three have a wide 334 PALAEONTOLOGY, VOLUME 38 table 3. The Gondwana succession of the Northern Pranhita-Godavari valley (after Kutty and Sengupta 1989). Formation Main lithologies Important fossils Age Deccan traps Late Cretaceous and Early Tertiary Chikiala Highly ferruginous sandstones and conglomerates ? ? = Gangapur Formation Gangapur Coarse gritty sandstones; grey white to pinkish mudstones with interbedded ferruginous sandstones and concretions Gleichenia Pagiophylum Ptilophyllum Elatocladus Early Cretaceous Kota Sandstones, silstones and clays with limestone bands Holostean fish Sauropods Pterosaurs early mammals Early Jurassic Dharmaram Coarse sandstones and red clays Prosauropods (small and large) Sphenosuchid Late Late Triassic Maleri Red clays, fine to medium sandstones and peloidal calcirudites/ calcarenites Chigutisaurids Metoposaurid Rhynchosaurs Phytosaurs Aetosaurs Early Late Triassic Bhimaram Medium to coarse and fine sandstones, calcareous above and ferruginous below; some red clays Labyrinthodont Dicynodont ? Late Middle Triassic Yerrapalli Red and violet clays; sandstones; calcirudites/ calcarenites Stahleckeriid and Kannemeyeriid dicynodonts Capitosaurid Early Middle Triassic Kamthi Ferruginous Dicynodont from basal Late Late Permian to nonfeldspathic or slightly feldspathic sandstones and purplish siltstones beds Early Triassic Infra-Kamthi Sandstone, carbonaceous and red mudstones; limonitic shales Endothiodontid Cistecephalid (from lithozone 3) Late Permian Barakar Feldspathic sandstones, carbonaceous shales and coal Glossopteris flora Late Early Permian Talchir Tillites, greenish shales and sandstones Early Early Permian cultriform process of the parasphenoid (widest in Kutty cephalus\ see character 15, Table 2), with more posteriorly positioned dentition. The parasphenoid-vomer suture in Keratobrachyops and Kuttycephalus is positioned anterior to the interpterygoid vacuities. This character is not observed in Chigutisaurus. The ornament of the skull roof and the proportions of the subtemporal vacuity SENGUPTA: TRIASSIC C H I GUT I S AU R I DS 335 are also similar. The early separation of Keratobrachyops (Early Triassic) thus seems to be significant. On the other hand, Pelorocephalus, Siderops and Compsocerops are more similar. The cladogram clearly depicts the two different types of chigutisaurid palate. The Keratobrachyops , Kuttycephalus and Chigutisaurus palate differs from the Siderops , Pelorocephalus and Compsocerops palate by the posteriorly extended dentigerous area. The latter type has the anterior tip of the subtemporal vacuities positioned anterior to the centre of the interpterygoid vacuities (which makes the palate more capacious) and a long, narrow cultriform process of the parasphenoid. Keratobrachyops , however, has a coronoid process like that of Compsocerops and Siderops , while Kuttycephalus , unlike Keratobrachyops , has posterior projections on the squamosal and quadrato- jugal. Representatives of the two types of chigutisaurids are found together in one horizon in India and in Argentina. These two types possibly had differences in feeding style and occupied separate niches, as the pattern of dentition and the structure of the palate are different. This may explain the co-existence of these two chigutisaurid morphs in the upper parts of the Maleri and in the Cacheuta formations where no other temnospondyl has so far been reported. Vertebrates and the age of the Maleri Formation The Pranhita-Godavari valley of Deccan, India provides a relatively complete succession of Late Triassic continental strata rich in fossil vertebrates (Table 3). The Maleri Formation consists essentially of elongate sandstone ridges and clay valleys. The fossils collected from successive clay valleys have greatly helped the recognition of the faunal change from the base to the top (Text-fig. 1 ). There are two faunal zones present in the Maleri Formation. Kutty and Sengupta (1989) argued that the age of the lower fauna is Late Carnian and the upper fauna. Early Norian. The lower Maleri fauna includes the metoposaurid Metoposaurus maleriensis , the rhynchosaur Paradapedon huxleyi , and the phytosaur Parasuchus hislopi. Two species of dipnoan, Ceratodus hunterianus and C. virapa , are also common. A cynodont, Exaeretodon statisticae , an eosuchian, Malerisaurus robinsonae, and a small coelurosaur, Walkeria maleriensis, are restricted to the lower Maleri fauna. An aetosaur similar to Typotliorax (Huene 1940), a prosauropod and a dicynodont are also believed to be present. In the upper Maleri fauna, the first three elements of the lower fauna are absent. A different species of Ceratodus , C. nageswari Shah and Satsangi, 1970, is present. Two chigutisaurids, Compsocerops cosgriff and Kuttycephalus triangularis, appear in place of the metoposaurids. Among the phytosaurs, instead of Parasuchus hislopi, a long-snouted primitive form and an advanced Rutiodon- like form have been noticed. Dicynodonts and aetosaurs are still present. A comparison of these two faunas indicates that the lower fauna has metoposaurids while the chigutisaurids are restricted to the upper fauna. In North America and Europe, metoposaurids continued up to the Norian (Roychowdhury 1965; Benton 1986; Chatterjee 1986; Long and Padian 1986; Murry 1986; Hunt and Lucas 1990). In Morocco the picture is not clear as no temnospondyls, except almasaurids and metoposaurids, are found there. On the other hand, chigutisaurids are noted in the Gondwanas and are known from the upper part of the Late Triassic Maleri Formation of the Pranhita-Godavari valley, India, the Late Triassic Cacheuta and Ischigualasto Formations of the Mendoza Province, South America (Bonaparte 1982) and the Early Triassic Arcadia Formation (Rewan Group) and Early Jurassic Evergreen Formation of Queensland, Australia. Though the metoposaurids and the chigutisaurids help to distinguish the lower and upper fauna of the Maleri Formation, their stratigraphical ranges do not help to fix the age of boundary between the two faunas. India is the only country where both metoposaurids and chigutisaurids have been found so far. Apart from the appearance of chigutisaurids, two other events also occurred in the interval between the two Maleri faunas. The rhynchosaurs are absent from the upper fauna and their disappearance may indicate the end of the Carnian (Chatterjee 1974; Tucker and Benton 1982; Benton 1983; Hunt and Lucas 1991). The phytosaurs evolved into advanced forms, evidence of which is very conspicuous in the successive clay valleys of Maleri (T. S. Kutty, pers. comm.). 336 PALAEONTOLOGY, VOLUME 38 The demise of the rhynchosaurs at the end of Carnian is also noted in Wyoming, Arizona and Texas and in Argentina and Scotland. The progressive change in the phytosaurs, as noted in Maleri, has been described from several parts of the world. Kutty and Sengupta (1989) noted that the lower Maleri fauna has the primitive Parasuchus (= Paleorhinus , see Chatterjee 1978) while the upper Maleri fauna has a primitive as well as a specialized Rutiodon- like form, and the immediately overlying lower Dharmaram Formation has only the advanced Nicrosaurus. They noted that, on the basis of the phytosaurs, the lower Maleri can be correlated with the lower part of the Dockum and Chinle formations while the upper Maleri can be equated with the middle part of these formations. The Nicrosaurus-bcax'mg lower Dharmaram Formation can similarly be equated with the upper parts of the Dockum and Chinle formations. The fauna of the Petrified Forest National Park, Arizona and in the Chinle Formation has been described by Murry and Long (1989). They considered the Norian Nicrosaurus to be an advanced phytosaur and Rutiodon to be primitive. In the Placerias and Downs quarries of the St John’s area, Arizona, they found Rutiodon and Paleorhinus together with Metoposaurus. Elsewhere, either Metoposaurus , or Anaschisma , or both, are present with Rutiodon and the age of the assemblage has been considered to be Late Carnian. Nicrosaurus and Rutiodon- like forms have not been found to occur together. The faunal assemblages of the Dockum Formation, characterized by Rutiodon , Nicrosaurus and Metoposaurus perfecta, were thought to be of a later age than the Paleorhinus- bearing fauna (Gregory 1972). The fauna found at Otis Chalk, Howard County, in the lower Dockum Formation (see Murry 1989) has similarities with the lower Maleri fauna. It contains both Metoposaurus and Latiscopus (not found in Maleri), and also Paleorhinus, Angiostorhinus, Rhynchosaurus and protorosaurids like Malerisaurus. If the lower Maleri fauna is thought of as Late Carnian, that would corroborate its correlation with the basal part of the Chinle and Dockum formations. So far, no vertebrates have been collected from the lower Maleri inconsistent with that age. The upper Maleri, with advanced phytosaurs, could be Early Norian (Kutty and Sengupta 1989). As noted by Chatterjee (1974), Chatterjee and Roychowdhury (1974) and Kutty and Sengupta (1989), the correlation of the Maleri faunas with those of the German Keuper is not very straightforward. The last-named authors placed the Franchosuchus-bearing Buntemergel in equivalence with the lower Maleri, because Franchosuchus and Parasuchus were considered by Chatterjee (1978) to be synonyms. The Stubensandstein, on the other hand, contains advanced Mystriosuchus, Nicrosaurus and Rutiodon (Chatterjee 1986). Acknowledgements. I thank the following staff of the Indian Statistical Institute, Calcutta : Professor T. K. Roychowdhury for guidance and help; Mr T. S. Kutty for his help; and Dr S. N. Sarkar who kindly allowed me to consult his unpublished map. I am indebted to Dr A. Warren of La Trobe University, Victoria, and Dr A. R. Milner of Birkbeck College, London, for critically appraising the manuscript. I also thank Dr A. L. Panchen of the University of Newcastle-upon-Tyne, Dr T. S. Kemp of the University Museum, Oxford, and Dr J. F. Bonaparte of Museo Argentino de Ciencias Naturales for their constructive suggestions. Mr D. Pradhan and K. BopuRao helped with fossil collection. Finally, I gratefully acknowledge the encouragement and financial assistance received from the authorities of the Indian Statistical Institute. REFERENCES bhnton, m. j. 1983. The Triassic reptile Hyperodapedon from Elgin: functional morphology and relationships. Philosophical Transactions of the Royal Society of London, Series B , 302, 605-720. — 1986. The Late Triassic tetrapod extinction events. 303-320. In padian, k. (ed ). The beginning of the age of dinosaurs : faunal change across the Triassic-Jurassic boundary. Cambridge University Press, 378 pp. bonaparte, j. F. 1975. Sobre la presencia del laberintodonte Pelorocephalus en la Formacion de Ischigualasto y su significado estratigrafico. Adas 1 Congress Argentinoda Paleontologia y Biostratigrafica, Tucuman, 1, 537-544. 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Palaeogeography, Palaeoclimatology, Palaeoecology, 40, 361-379. warren, a. a. 1981. A horned member of the labyrinthdont Superfamily Brachyopoidea from the Early Triassic of Queensland. Alcheringa, 5, 273-288. and black, t. d. 1985. A new rhytidosteid (Amphibia, Labyrinthodontia) from the Early Triassic Arcadia Formation of Queensland, Australia and a consideration of the relationships of Triassic temnospondyls. Journal of Vertebrate Paleontology , 5, 303-327. and hutchinson, m. n. 1983. The last labyrinthodont? A brachyopid (Amphibia, Temnospondyli) from the Early Jurassic Evergreen Formation of Queensland, Australia. Philosophical Transaction of the Royal Society of London, Series B, 303, 1-62. watson, D. M. s. 1956. The brachyopid labyrinthodonts. Bulletin of the British Museum (Natural History), Geology Series, 2, 317-391. welles, s. p. and estes, r. 1969. Hadrokkosaurus bradyi from the Upper Moenkopi Formation of Arizona. University of California Publications in Geological Sciences , 84, 1-56. SENGUPTA: TRIASSIC CH I GUTIS A U R I DS 339 zittel, K. von, 1888. Handbuch der Paldontologie Abteilwig 1. Paldozoologie Band III. Vertebrata (Pisces, Amphibia, Reptilia, AvesJ. R. Oldenbourg, Munich and Leipzig, 900 pp. DHURJATI P. SENGUPTA Geological Studies Unit Indian Statistical Institute Typescript received 28 July 1993 203 Barrackpore Trunk Road Revised typescript received 25 May 1994 Calcutta 700035, India ABBREVIATIONS USED IN THE FIGURES a angular ac acetabulum acr ascending ramus of the pterygoid adf adductor fossa amf anterior meckelian foramen ar articular artf articular fossa acc. eo ascending process of the exoccipital cr coronoid crp coronoid process cps canal on the dorsal side of the cultriform process of the parasphenoid d dentary dsc, sq descending process of the squamosal ect ectoptergyoid eo exoccipital ept epipterygoid f frontal fcht chorda tympanic foramen ic intercentrum icr intercoronoid J jugal Id lateral depression mx maxilla n nasal p parietal pal palatine par prearticular pc pleurocentrum per precoronoid pmf posterior meckelian foramen pmx premaxilla po postorbital pof postfrontal pp postparietal prf prefrontal ps parasphenoid psl postsplenial pt pterygoid ptpr posterior projection of the pterygoid q quadrate qj quadratojugal sa surangular sd semicircular depression on the dorsal surface of the base of the parasphenoid sp splenial sq squamosal st supratemporal t tabular v vomer OSTRACODE AND CONODONT DISTRIBUTION ACROSS THE LU DLOW/PRI DOLl' BOUNDARY OF WALES AND THE WELSH BORDERLAND by C. G. MILLER Abstract. The ostracodes and conodonts of the Silurian Ludlow/Pridoh Series boundary are documented in detail at Ludlow, and described from across Wales and the Welsh Borderland. The Upper Whitcliffe Formation and its lateral equivalents are characterized by the ostracode Calcaribeyrichia torosa and the conodonts Ozarkodina confluens , O. excavala , Panderodus serratus and Coryssognathus dubius. The Downton Castle Sandstone Formation and its lateral equivalents are characterized by the ostracodes Frostiella groenvalliana , Londinia arisaigensis, L. fissurata and Nodibeyrichia verrucosa. Conodont faunal trends across the Welsh Borderland reflect an increasingly turbulent environment towards the top of the Ludlow Series. The sudden ostracode faunal change at the base of the Downton Castle Sandstone at Ludlow (shelf) contrasts with a gradual change at Long Mountain (basin) and parallels shelf-basin palynofacies. Ostracode faunal variations in the Downton Castle Sandstone Formation at Ludlow coincide with minor lithofacies variations. Local variations in ostracode and land plant spore frequency may be related to proximal channels that delivered sediment off an irregularly prograding shoreline. Ostracodes correlate the base of the Downton Castle Sandstone across the Welsh Borderland to localities in east central Wales where bone beds are absent. Combined conodont and ostracode evidence suggests that the base of the Pridoli Series is at the base of the Downton Castle Sandstone Formation in Britain. ‘So brilliantly black are many of the organic fragments, that when discovered, this bed conveyed the impression that it enclosed a triturated heap of black beetles cemented in a rusty ferruginous paste’ (Murchison 1839, p. 198). This is the first description of the bed which was first mentioned by Murchison (1834), later described in detail (Murchison 1852) and named the Ludlow Bone Bed (Murchison 1854). Murchison (1839, p. 198) also noted that, ‘this bone bed is not merely local, since fragments having the same structure, but of greater thickness than any of Ludford. have been found near Richard’s Castle; and there is every reason to believe that it extends through various parts of the Ludlow promontory.’ The Ludlow Bone Bed, which consists essentially of acanthodian remains and thelodont dermal denticles, is the lowest of several bone beds in the Ludlow Bone Bed Member at Ludford Corner, Ludlow (Holland etal. 1963;Antia \979a, 1980). For the purpose of the present study, other bone beds, either higher in the section at Ludlow or at any other locality in the Welsh Borderland, will be referred to simply as a bone bed, thus implying no correlative significance with the Ludlow Bone Bed itself. Murchison never stated that the Ludlow Bone Bed defined the upper limit of the Silurian System. French workers (Dorlodot 1912; Barrois et al. 1918, 1922) mis- translated Murchison (1842, p. 648) and considered the Ludlow Bone Bed as the Siluro-Devonian boundary (White 1950). The Ludlow Bone Bed was then accepted (Stamp 1920, 1923; and subsequent workers) as the base of the Devonian System. The suggestion that the Siluro-Devonian boundary be raised to be coincident with the base of the Monograptus uniformis Zone (Holland 1965), led to abandonment of the Welsh Borderland as a standard for the Siluro-Devonian boundary (McLaren 1977). The Siluro-Devonian boundary is now defined at a level coincident with the base of the M. uniformis Biozone, within Bed 20 at Klonk in the Czech Republic (Chlupac 1972; McLaren 1977). This is stratigraphically higher than the Ludlow Bone Bed. To accommodate the strata between these two stratigraphical markers a fourth and youngest series of the Silurian had (Palaeontology, Vol. 38, Part 2, 1995, pp. 341-384, 3 pls| © The Palaeontological Association 342 PALAEONTOLOGY, VOLUME 38 Ludlow Bone Bed text-fig. 1. Chronostratigraphy of the Silurian (radiometric dates after Harland et al. 1990) and lithostratigraphy of the Upper Whitclilfe and Downton Castle Sandstone formations (after Bassett et al. 1982) at the type locality for the Ludlow Bone Bed Member at Ludford Corner, Ludlow, Shropshire (loc. 18). to be established (Text-fig. 1). The base of the Downton Group at Ludlow (the base of the Ludlow Bone Bed) was a prime contender for the basal stratotype for this series (Bassett et al. 1982), as was the base of the Skala Series in Podolia, and the Pfidoli Series of the Barrandian area (Prague Basin). There was little support for the Skala section as ‘at this level cyclic dolomites dominate the sequence and correlation with the base of the corresponding Downton and Pfidoli sequences could be achieved only with the use of limited ostracodal evidence’ (Holland 1989, p. 18). Even though the base of the Downton Group could be correlated with graptolitic facies via a complex chain of correlation (Bassett et al. 1982), the marine Pfidoli succession was eventually confirmed as the fourth series of the Silurian (Bassett 1985). The basal boundary stratotype was designated at Pozary near Prague with the base at a level coincident with the base of the Monograptus parultimas Biozone (Kfiz et al. 1986; Khz 1989, 1992). In the Welsh Basin the lithostratigraphical boundary between the Upper Whitclilfe Formation and the Downton Castle Sandstone Formation, corresponds to the base of the Ludlow Bone Bed at Ludford Corner, Ludlow, Shropshire (Text-fig. 1). Ostracodes correlate the base of the Downton Castle Sandstone Formation, via Baltic marine sequences, approximately with the base of the Pfidoli Series at the stratotype in the Czech Republic (Siveter 1978, 1989; Bassett et al. 1982; Siveter et al. 1989; Hansch et al. 1991). Conodont evidence has suggested that the base of the Pfidoli may be slightly higher than the base of the Downton Castle Sandstone Formation at Ludlow (Schonlaub 1986; Aldridge and Schonlaub 1989). The aims of this paper are: MILLER: OSTRACODES AND CONODONTS 343 text-fig. 2. Outcrop of the Downton Group and Ludlow formations in Wales and the Welsh Borderland (after Bassett et al. 1982) showing localities sampled by Miller (1993). 1. To document the detailed distribution of ostracodes and conodonts across the base of the Downton Castle Sandstone Formation at Ludlow and its lateral equivalents, throughout the Welsh Basin. 2. To use conodont and ostracode faunas to test the correlation of the base of the Downton Castle Sandstone Formation across the Welsh Basin. 3. To integrate the results with published palynofacies (Richardson and Rasul 1990) and sedimentological studies at coeval sections. 4. To investigate the correlation of the base of the Pridoli Series, as defined in the Czech Republic, with the base of the Downton Castle Sandstone Formation within the Welsh Basin. METHODS OF STUDY Fieldwork. Slightly calcareous lithologies, bone beds and horizons with decalcified macrofauna or ostracode moulds were sampled from localities across Wales and the Welsh Borderland (Text-hg. 2) covering the lateral equivalents of the base of the Downton Castle Sandstone Formation. The local hthostratigraphical units of Cocks et al. (1992, figs 3-4) are followed unless stated. Some localities exposing strata immediately above or below this level were also sampled. Detailed sedimentary logs were measured at prolific localities with sampling interval dictated by the presence of calcareous horizons or ostracode moulds. For each sample the minimum 344 PALAEONTOLOGY, VOLUME 38 practical thickness of strata was collected (0-01-0T m) and, where possible, approximately 2 kg of sample. However, sample size was often dictated by unstable overhanging strata or vertical cliff exposures. Additional material has been obtained from a number of sources: British Geological Survey (BGS), Dr R. J. Aldridge (RJA), and Dr David J. Siveter (DJS). Dr Aldridge’s samples are suffixed by an asterisk and the original locality numbers retained as they have been used in previous publications (Aldridge 1985; Miller and Aldridge 1993) and the numbers are to be published in a monograph on British Silurian conodonts. Acid preparation. To recover conodonts and other phosphatic microfossils, slightly calcareous lithologies and bone beds were disaggregated in 10 per cent, acetic acid and, if the acid had little or no effect, crushed in a fly press. All residues were sieved at 75 pm and separated into heavy and light fractions using an aqueous solution of sodium polytungstate (manufactured by Sometu, Berlin) at a specific gravity of 2-80. Each heavy residue was picked completely for conodonts. The dry weight of each sample was taken initially and after treatment, to enable numbers of conodont elements per gram to be calculated. Ostracode mould fauna preparation. Samples containing ostracode moulds were split in the laboratory, with care taken to keep part and counterpart together. An approximate calculation of ostracode abundance for each bed was obtained by dividing the total number of ostracode valves and carapaces for each bed by the total surface area viewed. Ostracodes with well preserved external moulds were prepared and cast using silicone rubber (manufactured by Ambersil Ltd., Basingstoke) by the method described by Siveter (1982). LOCALITIES AND HORIZONS 1. Callaughton Mill: roadside exposure, 2-5 km SW of Much Wenlock, Shropshire; SO 6198 9746 (Robertson 1927, p. 86); Whitcliffe Lormation, Downton Castle Sandstone Lormation with bone bed at base; (BGS 18-151). 2. Willey: quarry behind stables, Willey Estate, Willey, 5 km ESE of Much Wenlock, Shropshire; SO 6731 9912 (White and Coppack 1978, text-fig. 1); Whitcliffe Formation, Downton Castle Sandstone Formation with bone bed at base and 3 m above base; (BGS and CGM). 3. Linley: 6-5 km E of Much Wenlock, Shropshire (White and Coppack 1978, text-fig. 3). 3 a. Road from Linley Hall to Linley Brook, E of Linley Bridge; SO 6870 9817 (Robertson 1927, loc. L17); Downton Castle Sandstone; (BGS 18-84). 3b. Linley Brook, 90 m E of Hem Farm; SO 6920 9820 (Robertson 1927, loc. L18); Downton Castle Sandstone Formation; (CGM and BGS 18-85). 3c. Tributary to Linley Brook 1 km E of Linley Bridge; SO 6940 9815 (Robertson 1927, p. 87, loc. LI 9); Downton Castle Sandstone Formation with bone bed; (BGS 18-85). 4. Dean Brook: tributary to R. Severn 6-5 km E of Much Wenlock, Shropshire (White and Coppack 1978, text-fig. 3). 4a. Left bank of Dean Brook at mouth of small dry stream; SO 6955 9915 (Robertson 1927, Iocs LI 3 and 14); Downton Castle Sandstone Formation; (BGS 18-92). 4b. 40 m N of 4c/; SO 6875 9955 (Robertson 1927, loc. L16); Downton Castle Sandstone Formation; (BGS 17-123). 5. Brockton: on B4378, 6-5 km SW of Much Wenlock, Shropshire. 5a. Stream section opposite Ivy Cottage, Brockton, Corve Dale, Shropshire; SO 5755 9388. Whitcliffe Formation; (BGS 54-267). 5b. Road cutting 150 m NE of Brockton cross roads on B4378; SO 579 939; Whitcliffe Formation, Downton Castle Sandstone Formation with bone bed at base; (BGS 19-152). 5c. Old quarry behind old school house, Brockton; SO 5765 9400; Whitcliffe Formation; (RJA). 6. Shipton : junction of B4368 and B4378 on Corve Dale, 9 km SW of Much Wenlock, Shropshire. 6a. Pathside exposure, 30 m SE of B4368; SO 5634 9186; Whitcliffe Formation; (CGM). 6b. Old quarry in farmyard, 150 m at 26° from NE end of St. James Church; SO 5625 9194; Whitcliffe Formation and Downton Castle Sandstone Formation with bone bed at base; (BGS 54-271). 6c. Laneside section, 155 nr at 125° from SW end of St. James Church; SO 5629 9169; Whitcliffe Formation and Downton Castle Sandstone Formation with bone bed at base; (CGM and BGS 54-271). 7. Aston Munslow: Corve Dale, 10 km NE of Craven Arms, Shropshire. la. Swan Inn car park; SO 5124 8658; Whitcliffe Formation and Downton Castle Sandstone Formation with bone bed at base; (BGS 54-120, CGM and RJA). MILLER: OSTRACODES AND CONODONTS 345 lb. Roadside exposure, 120 m NW of 7a; SO 5113 8671 ; Whitclitfe Formation; (CGM and RJA). 8. Diddlebury: roadside exposure on Middlehope road, Diddlebury, Corve Dale, Shropshire; SO 503 858; Whitcliffe Formation; (CGM and RJA). 9. Corfton: roadside cutting, 55 m SE of Sun Inn, Corfton, c. 7 km ENE of Craven Arms, Corve Dale, Shropshire; SO 497 846; Downton Castle Sandstone Formation; (CGM and BGS 54-124). 10. Siefton: c. 5 km E of Craven Arms, Shropshire. 10a. Quarry in Siefton Batch, I km NW of B4368, Corve Dale, Shropshire; SO 4770 8475; Whitcliffe Formation; (CGM). 106. Temporary roadside trench; SO 475 833 to 478 835 (Antia 19796); Whitcliffe Formation and Downton Castle Sandstone Formation. 11. Culmington: old quarry S of new house near Culmington, Shropshire; SO 4745 8150; Downton Castle Sandstone Formation with bone bed at base (BGS records); (CGM and BGS 66-101). 12. Ombury: 4 km SSE of Craven Arms, Shropshire. 12a. Farmyard exposure, 3 km WNW of Onibury Church; SO 425 796; Upper Whitcliffe Formation; (BGS 54-198). 126. Norton road section, NNE of Onibury; SO 4575 7982 (Shaw 1969); Temeside Bone Bed, Temeside Shales, Downton Group; (DJS). 12 c. Locality not constrained, on road from Onibury to Norton; Tilestones (Downtown Group); BGS 22-140). 13. Clungunford: 5 km SW of Craven Arms, Shropshire. 13a. Lane in wood, 3-2 km E of Clungunford; SO 434 789; Whitcliffe Formation; (BGS 54—196). 136. Old quarry, 150 m E of Brandhill Farm, 2 km E of Clungunford; SO 4236 7883; Whitcliffe Formation; (CGM and BGS 54-197). 14. Downton Estate: area around Downton Castle, c. 6 km W of Ludlow, Shropshire. 14a. Bank to SE of Downton Bridge, Downton Estate; SO 4449 7427 (Whitaker 1962); Upper Whitcliffe Formation, Ludlow Bone Bed Member with bone bed at base and Platyschisma Shale Member of Downton Castle Sandstone Formation; (DJS). 146. Weir Quarry, NW bank of the River Teme, c. 275 m NE of Bringewood Forge Bridge, Downton Estate; SO 4560 7525 (Shaw 1969; Richardson and Rasul 1990, loc. I ); Upper Whitcliffe Formation, Ludlow Bone Bed Member with bone bed at base, Platyschisma Shale Member and Sandstone Member of Downton Castle Sandstone Formation; (CGM). 14c. Track section in held to S of Downton Castle Bridge; SO 4442 7402 (Whitaker 1962); Platyschisma Shale Member (including Downton Bone Bed) and Sandstone Member of Downton Castle Sandstone Formation; (collected in 1968 by Dr L. Jeppsson, University of Lund, Sweden). 15. Whitcliffe Quarry: S bank of the River Teme, Ludlow, Shropshire. 15a. 250 m W of Ludford Bridge; SO 5098 7414 (Siveter et al. 1989, loc. 3. If); boundary between Lower Whitcliffe Formation and Upper Whitcliffe Formation at top to convoluted bedding; (CGM and RJA). 156. 40 m W of 15a; SO 5096 7414; same strata exposed as at 15a; (CGM). 15c. 60 m W of 15a; SO 5092 7415; possible boundary between Lower and Upper Whitcliffe formations marked by similar convoluted bedding to 15a; (CGM and RJA). 1 5c/. 120 m W of 15a; SO 5089 7416; Lower and Upper Whitcliffe formations; (CGM and RJA). 16. Whitcliffe: car park to Charlton Arms Hotel, near Ludford Bridge, Ludlow, Shropshire; SO 5116 7416; Upper Whitcliffe Formation, c. 10 m below Ludlow Bone Bed; (RJA). 17. Ludford Lane: N side of Whitcliffe Road (formerly Ludford Lane), Ludlow, Shropshire. 17a. Next to roadsign 90 m W of junction with A49; SO 5116 7413 (Siveter et al. 1989, loc. 3.2b); Upper Whitcliffe Formation, Ludlow Bone Bed Member with multiple bone beds and Platyschisma Shale Member, Downton Castle Sandstone Formation; (CGM, DJS, RJA and BGS). 176. 80 m W of junction with A49; SO 51 17 7413; strata sampled as for 17a. 17c. 70 m W of junction with A49; SO 5118 7413; strata exposed as for 17a, 6, Upper Whitcliffe Formation only sampled. 18. Ludford Corner: at junction of A49 with Ludford Lane, Ludlow, Shropshire; SO 5124 7413 (Siveter et al. 1989, loc. 3.2a); Upper Whitcliffe Formation§, Ludlow Bone Bed Member§ with multiple bone beds, Platyschisma Shale Member and Sandstone Member of Downton Castle Sandstone Formation; only units suffixed by § and the lowermost 0 07 m of the Platyschisma Shale Member sampled. 19. Kington: Hereford and Worcester town c. 25 km SW of Ludlow. 346 PALAEONTOLOGY, VOLUME 38 19 a. Section on N side of Kington by-pass; SO 2998 5706 (Holland and Williams 1985, loc. 5); Upper Whitcliffe Formation, multiple bone beds in Ludlow Bone Bed Member, Platyschisma Shale Member, Sandstone Member of Downton Castle Sandstone Formation. 196. Lane-side exposures on Newton Lane; SO 2902 5716 (Holland and Williams 1985, loc. 3); Upper Whitcliffe Formation, multiple bone beds in Ludlow Bone Bed Member and Platyschisma Shale Member of Downton Castle Sandstone Formation. 20. Netherton : old tramway, SW side of reservoir. Salt Wells Nature Reserve, Primrose Hill, Netherton, Birmingham; SO 9358 8732 (King and Lewis 1912; Ball 1951); Whitcliffe Formation, Ludlow Bone Bed Member of Downton Castle Sandstone Formation; (CGM, RJA and DJS). 21 Abberley: village c. 15 km NW of Worcester, Hereford and Worcester. 21a. Small quarry 50 m S of Abberley Hall; SO 745 663; Whitcliffe Flags Member, Upper Ludlow Formation; (BGS 32-28). 216. Old quarry to E of road 100 m SE of Camp Farm, Great Whitley, near Abberley; SO 7405 6505; Whitcliffe Flags Member, Upper Ludlow Formation; (BGS 28-212). 21c. Woodbury (working) Quarry, 1500 m at 33° from church at Shelsey Beauchamp, Worcestershire; SO 743 637 (Mitchell et al. 1962; Phipps and Reeve 1967); Whitcliffe Flags Member, Upper Ludlow Formation; (BGS 28-215 and 59-146). 21 d. Small quarry 100 m SW of Rodge Hill Farm, Shelsey Beauchamp, Worcestershire; SO 746 622; Whitcliffe Flags Member, Upper Ludlow Formation; (BGS 28-207). 22. Brockhill Quarry: 250 m NNE of Brockhill Farm, Colwall, near Malvern Wells, Hereford and Worcester; SO 7568 4394 (Penn and French 1971, loc. 38); Whitcliffe Flags Member, Upper Ludlow Formation, Downton Castle Sandstone Formation with bone bed at base; (CGM, RJA and BGS 28-281). 23. Perton Lane: exposures to the E of Perton Lane, Perton, 5 km NNW of Woolhope, Hereford and Worcester. 23 a. 20 m S of 3-way road junction at Perton; SO 5971 4035 (Squirrell and Tucker 1960, text-fig. 2, loc. F); Upper Perton and Rushall beds; (CGM, DJS and RJA). 236. 20 m S of 23a at base of cliff section; SO 5969 4031 (Squirrell and Tucker 1967, text-fig. 5. loc. 2); Upper Perton Beds; (CGM and RJA). 24. Prior's Frome: exposures opposite Yew Tree Inn, Prior’s Frome, Woolhope c. 5 km ESE of Hereford, Hereford and Worcester; SO 5662 3901 (Gardiner 1927, text-fig. 4; Squirrell and Tucker 1982; Brandon 1989). 24a. Old quarry face; Upper Perton Beds; (CGM and RJA). 246. To S of old overgrown path; Rushall Beds with bone bed at base; (CGM, RJA and BGS 59-235). 25. Caerswell Farm: 3-5 km SW of Woolhope, Hereford and Worcester; SO 6440 3380; Upper Perton Beds and Rushall Beds with bone bed at base; (CGM and BGS 59-147). 26. Whittock’s End Farm: 550 m W of Whittock's End Farm, 3 km S of Much Marcle, Hereford and Worcester; SO 6540 2990; Rushall Beds with bone bed at base; (BGS 59-147). 27. Rushall: Roadside exposure at Rushall, 3 km ESE of Woolhope, Hereford and Worcester; SO 6410 3481 (Squirrell and Tucker 1967, loc. 18); Upper Perton Beds, Rushall Beds with bone bed at base; (CGM). 28. Bodenham Farm: small quarry immediately to N of Bodenham Farm, 5-5 km SE of Woolhope, Hereford and Worcester; SO 6524 3201 (Squirrell and Tucker 1967, loc. 19); Lower Perton Beds and Upper Perton Beds with bone bed at base. 29. Gorsley: Linton Quarry, 4 km W of Newent, Gloucestershire; SO 6770 2570 (see Lawson (1954) for local lithostratigraphical names); Wenlock Limestone, unconformity. Upper Blaisdon Beds, unconformity. Upper Longhope Beds with phosphatic pebble bed at base, Cliffords Mesne Sandstone with phosphatic pebble bed at base. 30. Longhope: exposures around Longhope Village, Mayhill, Gloucestershire. 30a. Exposure behind Longhope railway station; SO 6910 1901 (Lawson 1955, 1967, 1982); Upper Longhope Beds, Cliffords Mesne Sandstone with phosphatic pebble bed at base. 306. Road cutting on A4136, Longhope Village by-pass; SO 692 186 (Lawson 1982, loc. 19); same strata as for 30a; (RJA). 30c. Stream section at Wood Green; SO 6930 1670 (Lawson 1955, text-fig. 1, loc. C); Upper Longhope Beds, Cliffords Mesne Sandstone with phosphatic pebble bed at base. 31 Tite’s Point: exposures on S bank of Severn Estuary near Berkeley Arms, Purton, Gloucestershire. 31a. Ditch to S of tow path of Purton-Gloucester canal, 180 m at 244° from the Berkeley Arms; SO 6897 0438 (Cave and White 1971); Whitcliffe Formation; (BGS 62-254). MILLER: OSTRACODES AND CONODONTS 347 316. Foreshore of Severn Estuary, 250 m W of Berkeley Arms, Tite’s Point; SO 688 046 (Cave and White 1971, text-fig. 2; Curtis 1982); Upper Leintwardine Formation, Whitclifife Formation, and Downton Castle Sandstone Formation with bone bed at base; (CGM and RJA). 32. Brookend Borehole: Vine Farm, 3 km N of Berkeley, Gloucestershire; SO 6877 0230 (Cave and White 1968, 1978); Elton/Bringewood Beds, Leintwardine Beds, Whitclifife Formation, Downton Castle Sandstone Formation and Thornbury Beds. 33. Brook Flouse: exposure on W bank of Cwm-fifrwd Brook near Brook Cottage, c. 2 km WSW of Llangybi, Usk Valley, Gwent; SN 356 957 (Walmsley 1959, text-fig. 7, 1982); Upper Llangibby Beds and Speckled Grit Beds with bone bed at base; (CGM). 34. Usk: exposures around the town of Usk, Gwent (Walmsley 1959); Speckled Grit Beds with fragmentary fish remains. 34 a. A few metres below the wall in Llandegveth church yard, Llandegveth, 6 5 km SW of Usk; SN 338 957. 346. Old quarry 400 m SW of Llangybi Castle; SN 365 972. 34c. Dingle immediately N of Granary Farm; SN 322 968. 34c/. Stream section 500 m N of Llanddewi Court; SN 316 982. 35. Rurnney Borehole : E of R. Rhymney, c. 1-5 km W of Rumney, Cardiff; ST 2108 7925 (Waters and White 1978); Wenlock Series extending through Ludlow Series including Llanedeyrn Formation, overlain by Raglan Mudstone Formation with fragmentary fish remains at base. 36. Long Mountain: exposures around the Long Mountain, NW Shropshire, c. 8 km W of Welshpool, Powys. 36c7. Wallop Hall : exposure under trees near ruins of Wallop Hall, Lower Wallop, 2-7 km SW of Westbury, Long Mountain, Shropshire; SJ 3150 0725 (Richardson and Rasul 1990, loc. 5); Wallop Hall Member of Causemountain Formation with bone bed. 366. 800 m WSW of March Manor Farm; SN 330 103; Causemountain Formation; (BGS 17-^10). 37. Nantyrhynau Quarry: exposure behind barn, 5 km NNW of Felindre, Powys; SO 1602 8588; Cefn Einion and Clun Forest formations; (CGM and BGS 143-1776). 38. Felindre: village of Felindre, Powys; SO 1698 81 10, c. 13 km W of Clun, Shropshire. 38a. Medwaled Brook: dry stream bed, c. 3 km NNW of Felindre, Powys; SO 1534 8391 to SO 1568 8389 (Earp 1938, p. 138); discontinuous exposures showing general succession through uppermost Cefn Einion Formation into Clun Forest Formation. 386. Stonehouse Dingle: 1 km SE of Felindre, Powys; SO 1712 7983 to 1757 8016 (Earp 1940, p. 7); same strata as for 38a. 38c. Hendre Farm: trackside exposure, 1-7 km NW of Felindre, Powys; SO 1538 8220; Cefn Einion Formation; (CGM). 39. Clun: c. 20 m NNW of Ludlow, Shropshire (Earp 1940). 39a. Within’s Wood: cutting for new forestry path near Within’s Wood, Clun Forest, Shropshire; SO 317 836; Clun Forest Formation with one well-developed bone bed and a succession of thin bone beds. (CGM). 396. Clun Forest: floor of forestry track, near Lydbury North, Shropshire; SO 3176 8317; similar to Green Downton Formation of Holland (1959); (CGM and BGS). 39c. Roadside exposure at Bryn, L2km SE of Cefn Einion, Shropshire; SO 2951 8535; Cefn Einion Formation; (BGS). 39c/. Hurst Mill: exposure next to forestry track in Radnor Wood, c. 1-5 km ENE of Clun, Shropshire; SO 3162 8128; Cefn Einion Formation; (CGM and BGS). 39c. Five Turnings Outlier: old quarry, 280 m E of Black Garn Farm; SO 297 759 (Stamp 1918, p. 237); Cefn Einion Formation with an exposure gap followed by lowest Clun Forest Formation. 40. Knighton: town c. 23 km W of Ludlow, Shropshire. 40a. Old quarry immediately W of bridge on Gwernafifel Estate; SO 273 706 (Holland 1959, p. 462, 1988; Richardson and Rasul 1990, loc. 6); Upper Llan-wen Hill and Platyschisma helicites beds. 406. Stream section SSE of Middle Pitts Cottages; SO 3120 7176 (Holland 1959, p. 463); Upper Llan-wen Hill and Platyschisma helicites beds; (DJS). 40c. Meeting House Lane: discontinuous track and trackside exposures on steep track from Meeting House Farm to Llan-wen Hill ; SO 3023 6940 (Holland 1959; Allender et al. 1960); Upper Llan-wen Hill Beds, Platyschisma helicites Beds (including small bone bed). Green Downton and Yellow Downton formations; (DJS). 41 . Builth Wells: NW of Gwenddwr, on bank of Nant Gwenddwr, 5 km SW of Builth Wells, Powys; SO 061 436 (Straw 1930, p. 84; 1937); Holopella conica Beds and Green Marls. 348 PALAEONTOLOGY, VOLUME 38 42. Cwm Graig Ddu: valley WSW of Builth Wells, 4 km SSE of Garth; SN 968 465 (Straw 1953, p. 217); Holopella conica Beds overlain by Long Quarry Formation (formerly Tilestones) with junction marked by line of quarry workings. 43. Capel Horeb: N side of A 40, 5-5 km ESE of Llandovery; SN 8445 3234 (Cwm Dwr section of Potter and Price 1965; Siveter et al. 1989, loc. 5.8); Upper Roman Camp Formation (= Lower Whitcliffe Formation) unconformably overlain by Long Quarry Formation and Raglan Marls Group; (CGM, RJA and BGS). 44. Sawdde Gorge: river valley c. 10 km SW of Llandovery, Dyfed. 44 a. Exposure in stream bed NW of main bridge over R. Sawdde at Pont-ar-llechau; SN 7280 2447; Lower Roman Camp Formation (= Upper Leintwardine Formation), Long Quarry Formation. 44 b. Small quarry behind Three Horseshoes Inn, Pont-ar-llechau; SN 7279 2446, (Bassett 1982, text-fig. 2, loc. 6); Long Quarry Formation. 44c. Exposure next to forestry track; SN 7372 2418 (Bassett 1982, text-fig. 2, loc. 7G; Siveter et al 1989, loc. 5.5i); Long Quarry Formation. 45. Cennen Valley: 4 km SSW of Llandeilo, Dyfed. 45 a. Cutting W of A476; SN 6100 1908 to 6102 1902 (Siveter et al. 1989, loc. 5.6e); Cennen Formation (= possible uppermost Ludlow Series) and Long Quarry Formation; (BGS and RJA). 45 b. Small quarry above A483, S of Llandeilo; SN 6145 1915 (Siveter et al. 1989, loc. 5.7); Long Quarry Formation. REPOSITORIES Illustrated material with the prefix PM is deposited in the Natural History Museum (London) and with the prefix BGS is deposited at the British Geological Survey (Keyworth). A representative suite of specimens (LEIUG 14555-14566) collected by Miller (1993) is held at the Department of Geology, University of Leicester. Tables of data have been deposited with the British Library, Boston Spa, Yorkshire, UK, as Supplementary Publication No. SUP 14045 (17 pp.). SECTIONS AT LUDLOW, SHROPSHIRE Upper Whitcliffe Formation The base of the Upper Whitcliffe Formation is defined (Holland et al. 1963, p. 123) at the base of the bed above a convoluted horizon at the disused Whitcliffe Quarry (loc. 15u, Text-figs 3-4). Convoluted bedding is well developed at the 'dog-leg’ of the exposure at 15c and for the purposes of this study has been taken as the topmost bed of the Lower Whitcliffe Formation, although the section is faulted and the convoluted bed is considerably thicker at 15c than at 15c/ (Text-fig. 4). As there are no continuous exposures through the Upper Whitcliffe Formation at Ludlow, the sampling interval throughout the formation is irregular and ranges from 0 05 m to approximately 10 m. Localities 15 and 16 are cliff exposures and give an almost complete coverage of the formation (Text-fig. 5). The top of the Upper Whitcliffe Formation is at the base of the Ludlow Bone Bed Member at localities 18 (Text-figs 1, 3, 6), and the formation is approximately 32 m thick at Ludlow (Siveter et al. 1989, text-fig. 30). Conodont distribution. Conodonts were recovered from calcareous to slightly calcareous lithologies which occur sporadically throughout the Upper Whitcliffe Formation. Elements are well preserved and pale amber in colour although some specimens are fragmentary, particularly those from the slightly calcareous lithologies which required crushing to extract the fauna. More than 1800 specimens belonging to nine multielement species were extracted and examined from localities 15 to 18. Conodont-bearing samples contain from twenty to 1056 conodont elements per kg (Text-fig. 7). Conodont faunas from the topmost Lower Whitcliffe Formation and lowermost 5 m of the Upper Whitcliffe Formation (Text-fig. 7) consist dominantly of Ozarkodina excavata and Coryssognathus dubius elements with minor numbers of Panderodus serratus and O. confluens. Other less common species include O. remscheidensis eosteinhornensis , O. remscheidensis ssp. nov. Aldridge, 1985, O. snajdri and O. wimani (PI. 1). At the top of the Upper Whitcliffe Formation these less common species become more frequent and the fauna becomes dominated by C. dubius and O. snajdri with minor numbers of remscheidensis subspecies (notably O. r. eosteinhornensis) and O. cf. crispa \ the latter only in strata 01 5—0-3 m below the top of the formation. In the MILLER: OSTRACODES AND CONODONTS 349 text-fig. 3. Locations of sampled exposures on the Whitcliffe at Ludlow, Shropshire (after Holland et al. 1963, and Siveter et al. 1989). topmost 03 m of the Upper Whitcliffe Formation O. excavata is much less abundant, O. confluens becomes more abundant and P. serratus is no longer present. Relative proportions of the individual elements from the apparatus of O. excavata , calculated for samples that contain more than fifty elements of O. excavata, show insignificant variation in relative percentages of elements (Text-fig. 8). Ostracode distribution. The Upper Whitcliffe Formation has a virtually monospecific ostracode fauna of Calcaribeyrichia torosa (PI. 2, figs 9-12). This species has been found throughout the Upper Whitcliffe Formation (loc. 17a and in samples 15fi/2, 1 5c/3, 17c/l, 18/1) and is mostly confined to decalcified brachiopod coquinas. At localities 17a-c and 18, where the uppermost 0-5 m of the Upper Whitcliffe Formation has been sampled 'bed by bed', only a few isolated specimens of C. torosa have been recovered (samples 17c/ 1 , 18/1, and specimen BGS DEY 3653). C. torosa has been reported from both the Lower Whitcliffe and Upper Whitcliffe formations (Siveter 1974). An internal mould of Hemsiella cf. maccoyiana has been recovered from 015 m below the top of the Upper Whitcliffe Formation at Ludford Corner (loc. 18). Downtown Castle Sandstone Formation The base of the Downton Castle Sandstone Formation is defined at locality 18 at the base of the Ludlow Bone Bed (Holland et al. 1963). The Downton Castle Sandstone Formation has three members (Text-fig. 1) and has been described in detail by Bassett et al. (1982, pp. 6, 14) and Smith and Ainsworth (1989). The upper limit of the Ludlow Bone Bed Member is defined at the top of three closely spaced, millimetre scale, bone beds 0-2 1 m above its base (Bassett et al. 1982, p. 14). These bone beds are discontinuous and the top of the member has not been located accurately at Ludford Lane (Iocs 1 la-b). Only a single bone bed has been located at the same level at locality 18 (Text-fig. 6). The Sandstone Member was not sampled for the present study. Conodont distribution. Conodonts are very rare in the Downton Castle Sandstone Formation, samples containing six to 105 conodont elements per kg, but generally fewer than twenty per kg (Text-fig. 7). Conodont elements have been obtained from bone beds within the Ludlow Bone Bed Member, but elements are extremely fragmentary and abraded making identification difficult (PI. 1, fig. 11). Only fragments of Pa elements of O. confluens and Sa/Sb elements of C. dubius have been identified with any certainty (Miller and Aldridge 1993 ; 350 PALAEONTOLOGY, VOLUME 38 15 b UJ oo £5 31 £2 CL 0. z> LU LL x< ¥1 UJ £ O O 15a 12 m to top of exposure K3I3UGBIK 12 m to top of exposure 15c 0 m 1 - ]Sa/2 ]73/r Poorly exposed 4 m to top ot ,isty2 _ J15*V1 -C-C_s. J D15 ]l5c/2 yv/v^- cicfETcigni^V r-rcnn SEDIMENTS AND SEDIMENTARY STRUCTURES Oangwtuown micsceous 8ne sandstone Conglomerate (ph cephalic and cdbtano daets tn mudstone matrix) wifi rmcscGOus a&ndotnno Interbeds Crow larmnated unite with sharp erosive beses and internal low angle cross lam truss cm g Wavy bsdtorm wr#i podld to low angle crow lamnakons — Streaky to peraftoi lamnsSons 5S Thetodont rich phosphate coaraa aandatone (bone beds) Biotorbsted ©tteton® Convolute bedded Wtstane Paraiei laminated site tone wifi mudstone beds and impersstent tones tone lenses/ beds Dolomite FLORAS AND FAUNAS GRAIN SIZE ABBREVIATIONS Ostracod rich horizons Gastropods Bivalves Inarticulate brachwpods P P P E E E C C C Plant and other organic fragment Eurypssnd fragments Brachiapod rich coqumas m mudstone S sd to tone vf very frie sandstone f Una sandstone C coarse sandstone I tonestone text-fig. 4. Measured logs across the boundary between the Lower and Upper Whitcliffe Formations at Whitcliffe Quarry, Ludlow (Iocs 15cr-c) showing sampled horizons. Log at Locality 15a after Holland et al. (1963, text-fig. 6). The key represents all measured logs for the present study. MILLER: OSTRACODES AND CONODONTS 351 text-fig. 5. Approximate stratigraphical position of sections (thick black lines) and horizons sampled for conodonts and ostracodes through the Lower and Upper Whitcliffe formations on on the Whitcliffe at Ludlow, Shropshire. Total thickness 32 m (Siveter et al. 1989, text-fig. 30). Bed thicknesses given in brackets if known. For detailed sedimentary logs see Text-figures 4 and 6. q_' o z o § o o Q. D o GC O LU LL LL _J o t X <: 1 8 18/1 (5) 1 7 s 16 i-l ^77/2* ■ I (1) 1 LheLudlow Bone Bed 17c/t (2) Texl-ftgure 6 76/1* / 15a 15b 15c 15d - 75/1 * 15a/2 y HO) 73/1* < l5b/2 I5b/l J3l 15c/3 (15) /l5c/2 / (10) ±7— a \ 15c/1 (6-9) and 74/1* Text-figure 4 15d/1 -» (5) this study). Harley (1861) figured a similar fauna; Aldridge and Smith (1985) also reported fragments of O. excavata and Walliser (1966) recorded O. r. eosteinhornensis from the Ludlow Bone Bed Member. Ostracode distribution. A total of 2145 individual ostracode valves and twenty-three specimens of carapaces with co-joined valves has been recovered from the Downton Castle Sandstone Formation at localities 17 and 18 (Text-fig. 9). Individual (mould) specimens are often incomplete and therefore identifiable only to generic level. Relative generic proportions for each bed containing more than ten identifiable ostracodes have been plotted (Text-fig. 9), with ostracode frequency and percentage of carapaces against valves plotted for every bed in the section (Text-fig. 10). The ostracode fauna shows a similar trend in the two parallel sections 10 m apart (Iocs \la-\lb) and also at locality 18. The lowest bed in the Ludlow Bone Bed Member at all three sections contains Frostiella groenvalliana , Londinia arisaigensis, L. fissurata , and Nodibeyrichia verrucosa (PI. 2) in similar relative proportions (Text-fig. 9). In the present study C. torosa has not been found above the Upper Whitcliffe Formation, but Bassett et al. (1982, text-fig. 6) recorded C. torosa within the Ludlow Bone Bed Member at locality 17a. This specimen (BGS MR DEY 3694) has been examined by the author and confirms the occurrence of C. torosa (with coeval F. groenvalliana) at a level 0 08 m above the base of the Ludlow Bone Bed Member. Upper Downton Castle Sandstone Formation 352 PALAEONTOLOGY, VOLUME 38 171? m svf f text-fig. 6. Measured logs across the boundary between the Upper Whitcliffe and Downton Castle Sandstone Formations at Ludford Corner and Ludford Lane (Iocs 17-18), showing sampled horizons. MILLER: OSTRACODES AND CONODONTS 353 text-fig. 7. Conodont ranges and compositions of conodont faunas from the Lower Whitcliffe, Upper Whitcliffe and Downton Castle Sandstone Formations at Ludlow, Shropshire (Iocs 15-18). Positions marked on the lithostratigraphical column are given to the centre of the bed sampled. Bed thicknesses are given in Text-figures 4-6. The coarsening upwards of the sediments in the Ludlow Bone Bed Member and lowermost 015 m of the Platyschisma Shale Member corresponds with an increase in the proportion of Frostiella and a parallel decrease in the proportion of Londinia. Frequency is relatively high and carapaces are most commonly preserved in these strata reaching a maximum of 15 per cent, with respect to the number of valves in sample 17b/ 10. The last occurrence of N. verrucosa and the occurrence of bioturbated, synaeresis-cracked siltstones 0-34 m above the base of the Platyschisma Shale Member corresponds to a horizon above which ostracode frequency becomes very low (< 01 ostracode m2 x 104) but carapaces are still preserved. The onset of cross laminated units with sharp erosive bases corresponds to high frequency ostracode faunas (maximum of 2-0 ostracodes m2 x 1 04) dominated by Frostiella and non-palaeocopes, with Londinia very rare 354 PALAEONTOLOGY, VOLUME 38 Pa Pb M Sa Sb Total elements Sc counted *1 && rW/;. ■ text-fig. 8. Relative proportions of O. excavata elements from the Whitcliffe Group at Whitcliffe Quarry (loc. 15). Samples are arranged in stratigraphical order with the oldest at the base. Sample positions are given in Text-figures 4-5. EXPLANATION OF PLATE 1 Figs 1, 4. Ozarkodina remscheidensis eosteinhornensis (Walliser, 1964). PM X 1164; loc. 8, sample 8/1, Diddlebury, Shropshire; Whitcliffe Formation; Pa element; 1, lateral, and 4, oral views; x 30. Figs 2, 5. Ozarkodina remscheidensis remscheidensis (Ziegler, 1960). PM X 1277 ; loc. 316, sample 316/3, Tite’s Point, Gloucestershire; Whitcliffe Formation; Pa element; 2, lateral, and 5, oral views; x45. Figs 3, 6. Ozarkodina remscheidensis ssp. nov. Aldridge, 1985. PM X 1156; loc. la , sample 78/1*. Aston Munslow, Shropshire; Whitcliffe Formation; Pa element; 3, lateral, and 6, oral views; x45. Figs 7, 10. Ozarkodina wimani (Jeppsson, 1974). PM X 1184; loc. 15c, sample 74/1*, Whitcliffe Quarry, Ludlow, Shropshire; Upper Whitcliffe Formation; Pa element; 7, lateral, and 10, oral views; x85. Fig. 8. Ozarkodina excavata (Branson and Mehl, 1933). PM X 1 193; loc. 20, sample 20/la, Netherton, West Midlands; Upper Whitcliffe Formation; Pa element; lateral view; x 50. Figs 9, 12. Coryssognathus dubius (Rhodes, 1953). PM X 1162; loc. la, sample 39/1*, Aston Munslow, Shropshire; Whitcliffe Formation; Pa element; 9, lateral, and 12. oral views; x 34. Fig. 11. Ozarkodina confluens (Branson and Mehl, 1933). PM X 1188; loc. \la, sample 17a/5, Ludford Lane, Ludlow, Shropshire; Ludlow Bone Bed Member, Downton Castle Sandstone Formation; fragment of Pa element; lateral view; x 22. Figs 13-14. Panderodus recurvatus (Rhodes, 1953). 13, PM X 1170; loc. 10, sample 10/1, Siefton, Shropshire; Whitcliffe Formation; falciform element; unfurrowed lateral face; x 110. 14, PM X 1214; loc. 20, sample 20/la, Netherton, West Midlands; Upper Whitcliffe Formation; similiform element; unfurrowed lateral face; x 85. Figs 15-16. Panderodus serratus (Rexroad, 1967). 15, PM X 1199; loc. 20, sample 20/16, Netherton, West Midlands; Upper Whitcliffe Formation; falciform element; furrowed lateral face; x 50. 16, PM X 1178; loc. 15a, sample 15a/2, Whitcliffe Quarry, Ludlow, Shropshire; Upper Whitcliffe Formation; arcuatiform element; unfurrowed lateral face; x 80. Figs 17, 20. Oulodus sp. 17, PM X 1266; loc. 24a, sample 162/2*, Prior’s Frome, Hereford and Worcester; Upper Perton Beds; Sb element; lateral; x45. 20, PM X 1280; loc. 316, sample 316/3, foreshore of Severn Estuary, Tite’s Point, Gloucestershire; Whitcliffe Formation; Pb element; lateral; x 30. Fig. 18. Walliserodus cf. sancticlairi. PM X 1223; loc. 20, sample 20/16, Netherton, West Midlands; Upper Whitcliffe Formation; symmetrical element; lateral; x 100. Fig. 19. Dapsilodus obliquicostatus (Branson and Mehl, 1933). PM X 1172; loc. 10, sample 10/1, Siefton, Shropshire; Whitcliffe Formation; symmetrical element; lateral; x 100. PLATE 1 MILLER, Silurian conodonts 356 PALAEONTOLOGY, VOLUME 38 (0-7 per cent.). Ostracodes are concentrated as lags at the bases of beds (Text-fig. 6). Carapaces are no longer preserved. THE LUDLOW ANTICLINE AND SURROUNDING AREA The Much Wenlock area Localities in this area have not yielded abundant conodont or ostracode faunas in this study. White and Coppack (1978) recorded the ostracode F. groenvalliana at the base of the Downton Castle Sandstone Lormation, from a horizon marked at Willey (loc. 2) by a bone bed. Their collections (BGS) have been EXPLANATION OF PLATE 2 All specimens are SEM illustrations of silicone rubber casts of external moulds in lateral view, unless stated. Eigs 1-2. Hemsiella cf. maccoyiana. 1, PM OS 14146; loc. 38c, Felindre, Powys; Cefn Einion Formation; tecnomorphic right valve; x 19. 2, PM OS 14093; loc. 146, sample 146/1, Weir Quarry, Downton, Shropshire; Upper Whitcliffe Formation; heteromorphic left valve; x 22. Figs 3^4. Lophoctenella cf. scanensis. 3, BGS RT 336; loc. 46, Dean Brook, Much Wenlock, Shropshire; Whitcliffe Formation; tecnomorphic left valve; x 18. 4, PM OS 14136; loc. 36 a, sample 36a/k, Wallop Hall, Long Mountain, Powys; Causemountain Formation; heteromorphic right valve; x 18. Figs 5-8. Nodibeyrichia verrucosa Shaw, 1969. 5, PM OS 14123; loc. 18, sample 18/2, Ludford Corner, Ludlow Corner, Ludlow, Shropshire; Ludlow Bone Bed Member, Downton Castle Sandstone Formation; tecnomorphic right valve; x 17. 6, BGS SH 3685; loc. 36, Linley Brook, Much Wenlock, Shropshire; Downton Castle Sandstone Formation; heteromorphic left valve; x 14. 7, PM OS 14119; loc. 176, sample Mb /3a, Ludford Lane, Ludlow, Shropshire; Ludlow Bone Bed Member, Downton Castle Sandstone Formation; tecnomorphic left valve; x 35. 8, PM OS 14138; loc. 36 a, sample 36a/M2, Wallop Hall, Long Mountain, Powys; Causemountain Fopmation; heteromorphic left valve; x23. Figs 9-12. Calcaribeyrichia torosa (Jones, 1855). 9, PM OS 14150; loc. 39 d, Radnor Wood, Clun, Shropshire; Cefn Einion Formation; tecnomorphic right valve; x 27. 10, PM OS 14094; loc. 156, sample 15c/3a, Whitcliffe Quarry, Ludlow, Shropshire; Upper Whitcliffe Formation; heteromorphic left valve; xll. 11, BGS DEY 3653; loc. 17 a, Ludford Lane, Ludlow, Shropshire; Upper Whitcliffe Formation; tecno- morphic left valve; x 12. 12, PM OS 6584; loc. 39c, Five Turnings outlier, Clun, Shropshire; Cefn Einion Formation; heteromorphic left valve; xll. Figs 13-14. Londinia arisaigensis Copeland, 1964. Loc. 18, from loose material dumped after the excavation of Ludford Corner, Ludlow, Shropshire in 1988; Downton Castle Sandstone Formation. 13, PM OS 14125; tecnomorphic right valve; x 13. 14, PM OS 14128; heteromorphic left valve; x 12. Figs 15-16. Londinia fissurata Shaw, 1969. 15, PM OS 14098; loc. 17 a, sample \la/5s, Ludford Lane, Ludlow, Shropshire; Ludlow Bone Bed Member, Downton Castle Sandstone Formation; internal mould of an open tecnomorphic carapace; x 15. 16, PM OS 14112; loc. 17a, sample Ma/\2d, Ludford Lane, Ludlow, Shropshire; Platyschisma Shale Member, Downton Castle Sandstone Formation; heteromorphic right valve; x 15. Fig. 17. Non-palaeocope ostracode. PM OS 14120; loc. 176, sample 176/12a, Ludford Lane, Ludlow, Shropshire; Platyschisma Shale Member, Downton Castle Sandstone Formation; x 27. Fig. 18. Leper ditia sp. PM OS 14641 ; loc. 17, from loose material from landslide on Ludford Lane, Ludlow, Shropshire in 1993; Platyschisma Shale Member, Downton Castle Sandstone Formation; x4-3. Figs 19-20. Londinia kiesowi (Krause, 1891). 19, PM OS 14135; loc. 36a, sample 36a/L, Wallop Hall, Long Mountain; Causemountain Formation; tecnomorphic right valve; x 15. 20, BGS SH 3685; loc. 36, Linley Brook, Much Wenlock, Shropshire ; Downton Castle Sandstone Formation ; heteromorphic left valve ; x 1 5. Figs 21-24. Frostiella groenvalliana Martinsson, 1963. 21, PM OS 14113; loc. 17a, sample 17a/26a, Ludford Lane, Ludlow, Shropshire; Platyschisma Shale Member, Downton Castle Sandstone Formation; tecnomorphic left valve; x 13. 22, PM OS 14124; loc. 18, Ludford Corner, Ludlow, Shropshire; Platyschisma Shale Member, Downton Castle Sandstone Formation; heteromorphic left valve; x 13. 23, PM OS 14111; loc. 17a, sample 17a/14a, Ludford Lane, Ludlow, Shropshire; Platyschisma Shale Member, Downton Castle Sandstone Formation; tecnomorphic carapace with open valves; x 9. 24, PM OS 13922; loc. 18, from loose material dumped after the excavation of Ludford Corner, Ludlow, Shropshire in 1988; Downton Castle Sandstone Formation; tecnomorphic left valve; x 17. PLATE 2 MILLER, Silurian ostracodes 358 PALAEONTOLOGY, VOLUME 38 text-fig. 9. Ostracode faunal composition from the Downton Castle Sandstone Formation at Ludford Lane and Ludford Corner (Iocs \la-b and 18). The height of each bar corresponds to the relative thickness of beds from which more than ten identifiable ostracodes were collected. The positions of numbered samples are given in Text-figure 6. MILLER: OSTRACODES AND CONODONTS 359 FREQUENCY (Qstracodes/ mJ X 10*) 18 17b 17a 1 2 i i K35 * 34 33 1 2 1 L Per cent, carapaces/ valves 18 17b 17a 5 10 15 _J I L text-fig. 10. Ostracode frequency and percentage of carapaces with respect to valves for all ostracode samples from the Upper Whitcliffe and Downton Castle Sandstone Formations (Iocs \la-b and 18). 360 PALAEONTOLOGY, VOLUME 38 examined by the author and identifications confirmed. Two abraded Pa element fragments of O. confluens have been recovered from this horizon. F. groenvalliana and L. fissurata are recorded from the Downton Castle Sandstone Formation at Callaughton (loc. 1) and Dean Brook (loc. 46) (Robertson, 1927; White and Coppack 1978, p. 28). White and Coppack (1978, p. 29) reported similar ostracode faunas from Linley (Iocs 3 a-6), remarking that they closely resemble faunas from the old quarry at Willey (loc. 2). The Downton Castle Sandstone Formation at Linley Brook (loc. 3 6), has been sampled by the author and contains abundant F. groenvalliana associated with the gastropod Turbocheilus helicites (J. de C. Sowerby). In one individual calcareous bed at Linley Brook these taxa retain their original calcareous carapaces. The bed has also yielded whole, unabraded conodont specimens of O. confluens and Oulodus sp. Specimens of similar limestone beds from the Downton Castle Sandstone Formation at Dean Brook (loc. 4) are held at the BGS (Keyworth). Ostracode faunas from the Upper Whitcliffe Formation in the Much Wenlock area are dominated by C. torosa , with minor occurrences of H. cf. maccoyiana and Lophoctenella cf. scanensis (PL 2, fig. 3). The ostracode fauna of the Downton Castle Sandstone Formation is dominated by F. groenvalliana with minor occurrences of L. fissurata, L. arisaigensis and a single specimen of Londinia kiesowi (PI. 2, fig. 20). Corve Dale At Brockton (loc. 5b), Shipton (Iocs 6 a-c), and Culmington (loc. 1 1) bone beds have been reported at the base of the Downton Castle Sandstone Formation (BGS records; Turner 1973; Antia 1979a), but are no longer exposed. Ostracode faunas from the Whitcliffe Formation at Brockton (Iocs 5 a-6) and Shipton (loc. 6 a) contain only C. torosa, while those from the Downton Castle Sandstone Formation are almost exclusively dominated by F. groenvalliana with minor proportions of L. arisaigensis, L. fissurata and non-palaeocope ostracodes. F. groenvalliana, although confined to the Downton Castle Sandstone Formation, is not present immediately at the base of the Downton Castle Sandstone Formation at any locality on Corve Dale. Aston M unslow. Two well preserved specimens of C. torosa have been recovered from a bed 0-0-02 m below the top of the Whitcliffe Formation at locality la. A single conodont sample from locality lb (3 m below the top of the formation) is dominated by the conodont O. excavata with O. confluens, C. dubius and minor P. serratus. The two faunas from locality la are very similar to each other, dominated by C. dubius with minor O. confluens, O. snajdri and elements from the remscheidensis plexus. The topmost bed of the Whitcliffe Formation has yielded O. cf. crispa (PI. 3, fig. 8) L63 m of the Downton Castle Sandstone Formation is exposed at locality la, yielding two poorly preserved specimens of F. cf. groenvalliana and L. cf. arisaigensis. O. confluens (Pa and Pb elements) and C. dubius are present in a laterally discontinuous bone bed up to 0 05 m thick at the base of the Downton Castle Sandstone Formation which has produced 122 conodont elements per kg. EXPLANATION OF PLATE 3 Figs 1-2, 4-5. Ozarkodina crispa (Walliser, 1964). 1, 4, PM X 1276; loc. 316 sample 316/7, foreshore of Severn Estuary, Tite’s Point, Gloucestershire; Whitcliffe Formation; Pa element; 1, lateral, and 4, oral views; x 60. 2, 5, PM X 1263; loc. 24 a, sample 162/2*, Prior’s Frome, Hereford and Worcester, Upper Perton Beds; Pa element; 2, lateral, and 5, oral views; x45. Figs 3, 6-12. Ozarkodina cf. crispa. 3, 6, PM X 1187; loc. 17a, sample 77/2*, Ludford Lane, Ludlow, Shropshire; Upper Whitcliffe Formation; fragment showing cavity and posterior termination of Pa element; 3, lateral, and 6, oral views; x 120. 7, 10, PM X 1244; loc. 24a, sample 24a/2a, Prior’s Frome, Hereford and Worcester; Upper Perton Beds; Pa element; 7, lateral, and 10, oral views; x 50. 8, 11, PM X 1160; loc. la, sample 7a/4, Aston Munslow, Shropshire; uppermost bed of Whitcliffe Formation; Pa element; 8, lateral, and 11, oral views; x 40. 9, 12, PM X 1189; loc. 18, sample 18/1, Ludford Corner, Ludlow, Shropshire; Upper Whitcliffe Formation; Pa element; 9, lateral, and 12, oral views; x40. Figs 13, 16. Ozarkodina cf. snajdri. PM X 1189; loc. la, sample 7a/ 1, Aston Munslow, Shropshire; Whitcliffe Formation; Pa element; 13, lateral, and 16, oral views; x40. Figs 14—15, 17-18. Ozarkodina snajdri (Walliser, 1964). 14, 17, PM X 1190; loc. 24a, sample 24a/2a, Prior's Frome, Hereford and Worcester; Upper Perton Beds; Pa element; 14, lateral, and 17, oral views; x 50. 15. 18, PM X 1191; loc. 33, sample 33/3, Brook House, Usk, Gwent; Upper Llangibby Beds; Pa element; 15, lateral, and 18, oral views; x 60. PLATE 3 MILLER, Ozarkodina 362 PALAEONTOLOGY, VOLUME 38 Downton to Onibury area The Downton Bridge locality (14a) is no longer exposed, but collections made by Dr David J. Siveter in 1982 include F. groenvalliana, L. arisaigensis and non-palaeocope ostracodes from a bed immediately above the base of the Downton Castle Sandstone Formation. Like the basal bed of the Ludlow Bone Bed Member at Ludlow, carapaces of F. groenvalliana are present, although N. verrucosa is absent. The Downton Bone Bed (loc. 14c) within the Platyschisma Shale Member (Whitaker 1962) has yielded abraded conodonts, dominantly Pa elements of O. confluens, also elements of C. dubius with minor O. excavata, O. r. eosteinhornensis and Oulodus sp. At Onibury (loc. 12a) and Clungunford (Iocs 13a, 136) C. torosa has been found in the Upper Whitcliffe Formation. Locality 126 at Onibury has yielded L.fissurata from the Downton Castle Sandstone Formation. Weir Quarry , Downton. The ostracode fauna from the Upper Whitcliffe Formation is very sparse with only H. cf. maccoyiana and C. torosa present. No conodonts have been recovered. Ostracode faunas of the Downton Castle Sandstone Formation are very sparse reaching a maximum frequency of 0-2 ostracodes m2 x 101 but generally fewer than 0T ostracodes m2 x 104. Only three beds yielded more than ten ostracodes and these had very similar faunas of dominant F. groenvalliana , with rare specimens of L. arisaigensis, L. fissurata and non palaeocope ostracodes. The basal bone bed yielded a conodont fauna dominated by Pa elements of O. confluens with C. dubius, fragments of Oulodus sp. and two Pa elements of O. excavata. Other localities The base of the Downton Castle Sandstone Formation has been recognized at Kington (Iocs 19a-6) where multiple bone beds are developed in the Ludlow Bone Bed Member (Holland and Williams 1985). No conodonts and only a single specimen of H. cf. maccoyiana has been collected from the uppermost Upper Whitcliffe Formation (loc. 19a). A distinctive bed of limestone nodules in the Upper Whitcliffe Formation at Netherton (loc. 20) contains abundant P. serratus, C. dubius, O. excavata, O. confluens, a minor proportion of P. recurvatus and single specimens of O. r. eosteinhornensis and Walliserodus cf. sancticlairi (PI. 1, hg. 18). The bed at the top of the formation contains P. serratus, O. excavata and large, abraded specimens of O. confluens. Only 0-32 m of the Downton Castle Sandstone Formation is exposed at Netherton and has yielded conodont collections consisting almost exclusively of C. dubius elements and a single Pa element of O. confluens. A single ostracode specimen of F. cf. groenvalliana has been collected by Dr David J. Siveter from the lowermost Downton Castle Sandstone Formation (Siveter 1989; Hansch et al. 1991). SOUTHERN WELSH BORDERLAND INLIERS Abberley and the Malverns No localities in this area yielded abundant conodont or ostracode faunas in the present study. Material (BGS collections) has been examined and includes abundant examples of C. torosa from the Upper Ludlow Formation at Woodbury Quarry (loc. 21c). There are no examples of the H. maccoyiana material that Mitchell et al. (1962) indicated to be present. Exposures of the Whitcliffe Flags Member of the Upper Ludlow Formation around the village of Abberley (Iocs 21a-6, d) have also yielded specimens of C. torosa. At Brockhill Quarry (loc. 22), a single conodont sample from the Whitcliffe Flags Member yielded O. excavata, C. dubius and O. confluens in ascending order of abundance. Woolhope inlier Perton Lane. Non-palaeocope ostracodes have been recovered from the topmost Upper Perton Beds and a single specimen of H. cf. maccoyiana recovered from a coquina 0 06 m below the top of the beds. Two samples from locality 236, 4 m below the top of the Upper Perton Beds contain O. excavata , C. dubius, O. confluens and P. serratus, also rare examples of O. wimani, O. r. eosteinhornensis and O. snajdri (PI. 1). A sample 0T5 m below the top of the Upper Perton Beds contains only C. dubius, O. confluens and O. excavata. Ostracode moulds from the Rushall Beds are stained rusty brown, occur almost exclusively in the coarse bases of hning-upwards beds and are poorly preserved due to the coarse nature of the sediment. Plant and eurypterid fragments are commonly associated and ostracode frequency is low, ranging from 0 02-01 8 m2 x 104. The lowermost 0-5 m of the Rushall Beds contains a relatively consistent ostracode fauna dominated by non-palaeocopes, together with approximately equal proportions of Londinia and Frostiella. MILLER: OSTRACODES AND CONODONTS 363 F. groenvalliana, L. arisaigensis and L.fissurata are present, with a specimen of Nodibeyrichia sp. recovered from a sample 015 m above the base of the Rushall Beds. MO m above the base of the Rushall Beds the fauna is dominated by non-palaeocopes, with minor proportions ( < 1 5 per cent.) of Londinia and Frostiella. Approximately 1-5 m above the base of the Rushall Beds the fauna consists of equal proportions of Frostiella , Londinia, and non-palaeocope ostracodes. The only carapace recovered from this section is that of L.fissurata from 1-5 m above the base of the Rushall Beds. Prior s Frome. An old quarry face (loc. 24a) exposes 2-96 m of the Upper Perton Beds. Conodont faunas from the lower metre of the exposure are characterized by O. excavata, C. dubius, O. confluens , P. serratus and P. recurvatus in ascending order of abundance. A limestone bed 01 m thick, near the base of the exposure has also yielded O. r. eosteinhornensis , O. r. ssp. nov., O. wimani , and O. crispa (PI. 3, fig. 5). Samples from the upper 2 m of the Upper Perton Beds contain an abundance of Panderodus elements, together with C. dubius , O. excavata and O. confluens. A single internal mould of C. torosa has been recovered from approximately 0 8 m below the top of the Upper Perton, Beds. The junction between the Rushall Beds and the underlying Upper Perton Beds is no longer exposed; the present exposure gap of 0-5 m has been estimated using a published photograph of the section (Gardiner 1927, pi. 39, text-fig. 2). Conodonts obtained from the Rushall Beds are fragmentary, abraded and consist dominantly of C. dubius', O. confluens is less common and O. excavata , P. recurvatus and O. cf. snajdri are rare. Other localities. The BGS record bone beds from the base of the Rushall Beds, on the eastern margin of the Woolhope inlier at Caerswell Farm (loc. 25), Whittock’s End Farm (loc. 26) and Rushall (loc. 27). Calcaribeyrichia torosa and non-palaeocopes have been recovered from the uppermost Upper Perton Beds at Rushall (loc. 27). May Hill inlier Localities in this area have not yielded abundant ostracode and conodont faunas for the present study. A single conodont sample from the Upper Longhope Beds of the Longhope by-pass road cut (loc. 30 b) is dominated by Pa elements of O. confluens, together with elements of O. excavata , C. dubius and small numbers of P. serratus and Oulodus sp. Tortworth inlier Tites Point. The Whitcliffe Formation directly overlies the Upper Leintwardine Formation and is marked at the base by an intraformational conglomerate. Only poorly preserved, often abraded and fragmentary conodont specimens have been recovered from the Whitcliffe Formation, ranging in frequency from sixty-one to 6961 elements per kg. The percentage of C. dubius elements gradually increases upwards through the formation; the percentage of O. confluens and O. excavata fluctuate greatly throughout the formation and show no regular pattern. All samples contain a predominance of Pa elements of O. confluens compared with other elements in its apparatus. One sample contains only the Pa elements of O. confluens and another contains twice as many Pa elements of O. confluens as the total of all the other elements of its apparatus. Panderodus elements are last present 7-5 m below the top of the Whitcliffe Formation. Rare taxa include O. crispa, which was found only in a sample 17 m below the top of the Whitcliffe Formation (PI. 3, fig. 1). There are rare occurrences of O. snajdri, O. r. ssp. nov. and O. r. remscheidensis. Only 1-7 m of the Downton Castle Sandstone is exposed at Tite’s Point, and has not yielded conodonts or ostracodes for the present study. Other localities. The Brookend Borehole (loc. 32) covered the base of the Downton Castle Sandstone Formation (Cave and White 1968, 1978) but has not been sampled for the present study. Usk inlier The Upper Llangibby Beds and Speckled Grit Beds of the Usk area are distinct lithologically from the Upper Whitcliffe Formation and Downton Castle Sandstone Formation, respectively. The original lithostratigraphy of Walmsley (1959) has, therefore, been used for the present study rather than the mixture of lithostratigraphical units from Walmsley (1959) and from the Ludlow area (Bassett et al. 1982) as used by Barclay (1989) and Cocks et al. (1992). 364 PALAEONTOLOGY, VOLUME 38 Brook House. Three phosphatized internal moulds of the ostracode H. cf. maccoyiana have been recovered from conodont preparations from the Upper Llangibby Beds (loc. 33) and external moulds of C. torosa and H. cf. maccoyiana recovered by members of the Ludlow Research Group in 1992. Conodonts from the Upper Llangibby Beds are small, fragmentary and range in frequency from thirty-five to 236 elements per kg. Collections from the lower, more calcareous part of the exposure have similar faunas characterized by C. dubius , O. confluens and O. excavata. Less common species, also conlined to the base of exposure, include Oulodus sp., O. r. ssp. nov. and O. snajdri (PI. 3, fig. 1 5). The highest sample collected from approximately 3-5 m below the top of the Upper Llangibby Beds, contains only C. dubius and O. confluens. Approximately 04 m of the Speckled Grit Beds, exposed in a small overgrown bank on the south side of the lane to the west of the bridge, have yielded O. confluens and C. dubius. Other localities. Localities at Llandegveth Church (loc. 34a), Llangybi Castle (loc. 346), Granary Farm (loc. 34c) and Llanddewi Court (loc. 34 d) previously displayed Speckled Grit Beds with fragmentary fish remains (Walmsley 1959) but none of these is now exposed. The base of the Raglan Mudstone Formation in the Rumney Borehole (loc. 35) is marked by a 0 06 m bed containing abundant fish remains and shell fragments, a level taken to correlate with the Ludlow Bone Bed (Waters and White 1978). EAST CENTRAL AND SOUTHWEST WALES Long Mountain In the Long Mountain area the base of the Downton Castle Sandstone lithologically, but correlates with a level within the upper part of Causemountain Formation (Palmer 1970, 1973). Wallop Hall. 4-75 m of the Wallop Hall Member, Causemountain Formation are exposed, showing a gradual transition in macrofauna from parallel laminated siltstones, rich in articulate brachiopods, below a thin bone bed (bed K) to very fine sandstones characterized by gastropods, inarticulate brachiopods and plant fragments above the bone bed (Text-fig. 11). Ostracodes, preserved only as moulds of disarticulated valves, range in frequency from 0 01 to 1-35 ostracodes m2 x 10J (Text-fig. 12). Most ostracode specimens have been collected above the bone bed (bed K); faunas below that level are sparse (Text-fig. 12). Ostracode specimens below the bone bed are predominantly C. torosa with rare H. cf. maccoyiana and L. cf. scanensis\ all three species are also present above the bone bed, and last appear within bed M (Text-fig. 12). Londinia arisaigensis and L.fissurata first occur just below the bone bed. On the bedding plane surface of the bone bed (Bed K), C. torosa , LophocteneUa sp., N. verrucosa , L. arisaigensis , L. fissurata, F. groenvalliana , and non-palaeocope ostracodes are present. 0-0-25 m above the bone bed the fauna is dominated by Londinia with minor proportions of Nodibeyrichia , FrostieUa and non-palaeocopes. Beds 3P and 3Q contain abundant Londinia , but the other ostracode collections from beds more than 0-25 m above the bone bed are dominated by non-palaeocopes with minor Londinia , Nodibeyrichia and FrostieUa. Eight well-preserved C. dubius conodont elements have been recovered from bed K. Formation cannot be distinguished the Wallop Hall Member of the Chin to Felindre area Nantyrhynau Quarry. This locality (loc. 37) was discovered in 1986 by the BGS during field mapping for the Montgomery Sheet. The field report stated that the boundary between the Cefn Einion and Clun Forest formations was exposed within the quarry, at the base of a calcareous bed approximately 2-5 m below the top of the section. The calcareous bed yielded two O. excavata Pa elements and the ostracodes C. torosa , H. cf. maccoyiana , LophocteneUa sp., L. arisaigensis , L.fissurata and FrostieUa sp. Other localities. A section through the Clun Forest Formation was recently exposed when a new forestry path was cut at Within's Wood (loc. 39a). A well developed bone bed is present and is followed by a succession of eight, one millimetre thick bone beds. F. groenvalliana , non-palaeocope ostracodes and a specimen of Londinia sp. have been recovered from a rottenstone below the level of the bone beds. Abraded conodont elements of O. confluens and C. dubius have been recovered from the well developed bone bed which yielded 216 conodont elements per kg. Localities in the vicinity of Felindre at Medwaledd Brook (loc. 38a) and Stonehouse Dingle (loc. 386), provide discontinuous exposures through the uppermost Cefn Einion Formation and the lowermost Clun Forest Formation (Earp 1938, 1940), but provided no conodont or ostracode material for the present MILLER: OSTRACODES AND CONODONTS 365 text-fig. 1 1 Measured logs of the Wallop Hall Member, Causemountain Formation at Wallop Hall, Long Mountain (loc. 36a), showing sampled horizons (A-Z, a-y) and sketch of the exposure showing position of logged sections. 366 PALAEONTOLOGY, VOLUME 38 text-fig. 12. Ostracode faunal composition, frequency and ranges of species from the Wallop Hall Member, Causemountain Formation at Wallop Hall, Long Mountain (loc. 36a). Only samples with ten or more valves present are included. MILLER: OSTRACODES AND CONODONTS 367 study. A locality at Hendre Farm (loc. 38c) has yielded H. cf. maccoyiana (PI. 2, fig. 1) and L. arisaigensis from the Cefn Einion Formation. A forestry cutting in the Clun Forest (loc. 39 b) has yielded L. arisaigensis , L. fissurata, non-palaeocope ostracodes, and Leperditia sp. from a lithology similar to the Green Downton Formation of Holland (1959). Calcaribeyrichia torosa has been recovered from the Cefn Einion Formation at Bryn (loc. 39c) and Hurst Mill (loc. 39 d). Knighton Meeting House Lane. Collections made by Dr David J. Siveter from the Platyschisma helicites Beds are described herein as the locality (40c) is no longer exposed. No conodont or ostracode faunas have been found from the Llan-wen Hill Beds at this locality. The lowermost bed of the Platyschisma helicites Beds contains C. torosa , H. cf. maccoyiana , L. arisaigensis , L. fissurata and abundant non-palaeocope ostracodes. Higher in the P. helicites Beds, L. arisaigensis , L. fissurata, and two specimens of Frostiella sp. have been obtained. The Green Downton Formation contains L. arisaigensis and L. fissurata. Other localities. Collections made by Dr David J. Siveter from the now overgrown P. helicites Beds at Middle Pitts Cottages (loc. 40 b) include L. arisaigensis , N. verrucosa , and non-palaeocope ostracodes. Southwest Wales The unconformable base of the Downton Group, progressively oversteps older and more deformed rocks in a westerly direction, until west of Flandeilo the Downton Group overlies Ordovician strata (Potter and Price 1965; Squirrell and White 1978; Bassett 1982). Focalities reported to expose this unconformity at Builth Wells (loc. 41), Cwm Graig Ddu (loc. 42) and the Sawdde Gorge area (Iocs 44a-c) have yielded no conodont or ostracode faunas for the present study. Capet Horeb Quarry. No conodont or ostracode specimens have been recovered from the Upper Roman Camp Formation, a correlative of the Tower Whitchffe Formation (Potter and Price 1965). F. groenvalliana and non- palaeocope ostracodes have been recovered from the Fong Quarry Formation. The conodont specimen reported by Aldridge (1985) as O. r. eosteinhornensis has been re-examined and identified by the present author as a fragment of O. confluens. Coryssognathus dubius, O. excavata , and P. serratus also occur in the same sample. Cennen Valley. In the road cut (loc. 45a), the Fong Quarry Formation overlies unconformably the Cennen Formation (Potter and Price 1965; Squirrell and White 1978, text-fig. 2b; Bassett 1982; Siveter et al. 1989), but the section is now completely overgrown. Authors have used differing lithostratigraphical nomenclature, but the stratigraphy employed by Siveter et al. (1989) is adopted herein. A thickness of 3-55 m of the Cennen Formation rests unconformably on the older Trichrug Formation (a full list of macrofauna is given in Squirrell and White 1978, table 3). Ostracodes were identified by the author (BGS collections) as F. cf. groenvalliana , L. cf. scanensis, and C. torosa. Conodont samples collected by Dr R. J. Aldridge when the section was fully exposed, proved to be barren. F. groenvalliana and H. cf. maccoyiana have been recorded 9-83 m above the base of the overlying Fong Quarry Formation (Squirrell and White 1978, table 3). PAFAEOENVIRONMENTS Upper Whitcliffe Formation and lateral equivalents Watkins (1979) and Bassett et al. (1982) interpreted deposition as subtidal on a proximal shelf, mostly within wave base, shallowing towards the top of the formation with coquinas representing storm events. Allen (1985, p. 90) also recognized storm-related planar to hummocky lamination, cross-lamination and current ripples. Conversely, Richardson and Rasul (1990) proposed a deepening towards the end of deposition of the Upper Whitcliffe Formation at Downton (loc. 14 b), based on palynofacies. The thickness of upper Ludlow strata is much greater in east central Wales 368 PALAEONTOLOGY, VOLUME 38 than on the shelf and probably reflects subsidence of the outer shelf and shelf margin of the Welsh Basin (Bassett et al. 1982). Palynofacies at Downton, Long Mountain and at Knighton all show a change towards more open sea floras towards the top of the Ludlow Series (Richardson and Rasul 1990). Sedimentological evidence suggests a shallowing stratigraphically upwards through the Llan- wen Hill Beds at Knighton (Holland 1959, p. 475). The Ludlow Series in south-west Wales, traditionally regarded as part of the basinal facies of the Welsh Basin (Holland 1962, text-fig. 1), has also been described as a sandy shelf facies (Potter and Price 1965). A proximal land area probably existed to the south during deposition of the Upper Roman Camp Formation at Capel Horeb, from which plant debris drifted into a shallow sea (Siveter et al. 1989, p. 97). The depositional environment of the Cennen Formation near Llandeilo has been interpreted as very shallow marine (Squirrell and White 1978). Breaks in the succession occur near the top of the Ludlow Series in the Cennen Valley, but the succession is continuous at the Sawdde Gorge (Squirrell and White 1978). The apparent ‘early’ occurrence of F. groenvalliana in the Cennen Formation of the Cennen Valley was attributed to ‘occurrence in this area in late Ludlow times of a lithofacies comparable with that of the Downton Series’ (Squirrell and White 1978, p. 9). The composition of conodont samples that have undergone significant post-mortem sorting reflect the hydrodynamic regime, rather than the original faunal composition (McGofT 1991). It seems unlikely that samples from the base of the Upper Whitcliffe Formation at Ludlow (loc. 15) have undergone significant post-mortem sorting, as elements are well preserved and relative proportions of individual elements of O. ex cavata remain almost constant, thus reflecting original apparatus composition (Text-fig. 8). Elements from the uppermost metre of the Upper Whitcliffe Formation contain a dominance of C. dubius and O. confluens , often present almost exclusively as abraded specimens of Sa/Sb and Pa elements respectively. Post-mortem sorting seems to have significantly affected these samples as the Sa/Sb and Pa elements of the respective species are the most robust in the apparatus and therefore most likely to withstand the abrasion associated with sorting. Conodont faunal variations (Text-fig. 7) probably reflect a combination of changes in faunal abundances and hydrodynamic regimes. The preservation of the conodont fauna indicates a more turbulent environment towards the top of the Upper Whitcliffe Formation compared with the basal 5 m. This increased turbulence could be associated with the shallowing interpreted by Watkins (1979) and Bassett et al. (1982). General trends in conodont faunal composition towards the top of the Ludlow Series are similar at Aston Munslow (loc. la), Woolhope (Iocs 23-24) and Usk (loc. 33) and may also indicate shallowing. The fauna from the topmost bed of the Whitcliffe Formation at Aston Munslow, dominated by C. dubius with minor proportions of O. confluens, O. snajdri , and O. cf. crispa , is almost directly comparable with that from sample 18/1, 0T-0T5 m below the top of the Upper Whitcliffe Formation at Ludford Corner, Ludlow (loc. 18), differing only in the absence of remscheidensis plexus elements. Conodont elements from the Upper Longhope Beds at Longhope (loc. 306) and throughout the Whitcliffe Formation at Tite’s Point (loc. 316) have probably undergone significant sorting; the collections are dominated by abraded Pa elements of O. confluens. Abrasion and winnowing indicate that, compared with the rest of the shelf, a more turbulent environment existed in this area during deposition of the Whitcliffe Formation. Downton Castle Sandstone Formation The marked sedimentological, macro- and microfaunal change at the base of the Ludlow Bone Bed Member has been explained by a sudden regression and subsequent transgression (Allen and Tarlo 1963; Allen 1974; Antia and Whitaker 1978; Antia 1979«, 1980; Bassett et al. 1982; Richardson and Rasul 1990). Smith and Ainsworth ( 1989, p. 898) explained the deposition of the Ludlow Bone Bed Member by ‘repeated storm reworking during a period of reduced sediment supply, probably associated with a raised sea level’. Hummocky cross-stratification has been documented from the Sandstone Member at Ludford Corner and suggests shallow deposition (water depths of a few MILLER: OSTRACODES AND CONODONTS 369 metres), possibly in a shoreface environment dominated by storms (Siveter et al. 1989; Smith and Ainsworth 1989). Richardson and Rasul (1990) stated that the lowermost Downton Castle Sandstone Formation at Ludlow contains a greater proportion of land-derived sporomorphs than the coeval section at Weir Quarry, Downton, although Ainsworth (1991) noted that these differences could be explained by preferential winnowing of the smaller acritarchs from the larger spores. Richardson and Rasul (1990, p. 681) suggested that distribution patterns could have been affected by a ‘pattern of distributionary channels delivering high concentrations of land-derived sporomorphs in a non-uniform fashion along an irregularly prograding shoreline’. Ainsworth (1991) questioned Richardson and Rasul’s (1990) palynofacies interpretations suggesting that more recent sedimentological interpretations (Smith and Ainsworth 1989) indicated storm dominated environments in which onshore and offshore sediment movements probably influenced proportions of microplankton and spores. Jeram et al. (1990) documented trigonotarbid arachnids from the Ludlow Bone Bed Member at Ludford Corner (loc. 18), which are the earliest reported undoubted land animals and indicate a proximal land area. Localized variations of lithofacies at the base of the Rushall Beds in the Woolhope inlier have been proposed to indicate shoals in a shallow sea (Gardiner 1927). The bone bed at the base of the Rushall Beds has been interpreted as a lag concentrate formed during marine regression, and the Rushall Beds interpreted as a marginal marine deposit on a prograding sandy shore which is succeeded by subtidal mud flats (Allen 1985; Brandon 1989). The Platyschisma helicites Beds in the basin at Knighton have no basal bone bed and are thicker than the equivalent Platyschisma Shale Member on the shelf at Ludlow, suggesting continuous deposition in the basinal region (Bassett et al. 1982; Allen 1985). Palynofacies variations at Wallop Hall (loc. 36 a) indicate a gradual change to more inshore environments between the late Ludlow and the early Pridoli, followed by a gradual change to a more offshore setting and a subsequent return of more onshore conditions (Richardson and Rasul 1990). A similar but less pronounced palynofacies curve has been documented at Knighton (Richardson and Rasul 1990). Concentrations of the inarticulate brachiopod C. implicata at the top of the Upper Llan-wen Hill Beds at Knighton (Iocs 40 a, c ), also provide an environmental link with similar beds in the uppermost Upper Whitcliffe Formation at Downton (loc. 14a) and Kington (Iocs 19a, b) (Holland 1962, 1988). By the end of the Silurian, ‘ostracodes had occupied most of the marine environments and taken up most of the life-styles known from modern ostracodes’ (Siveter 1984, p. 71). Based on evidence from elsewhere in Europe and also in North America, Siveter (1984, p. 73) suggested that in the marine to restricted marine transition of the British Downton Group that ostracodes ‘for the first time began adapting to salinity changes that included reduced salinity, brackish water, and hypersaline conditions’. The species present in the Upper Whitcliffe and Downton Castle Sandstone formations cannot be directly compared taxonomically with Recent ostracodes. However, to assess their palaeoenvironmental and biostratigraphical potential, one can compare other reported occurrences of the same late Silurian species. Frostiella groenvalliana has been reported in a wide range of environments (Hansch et al. 1991), from the deeper water, outer shelf areas of the Leba elevation, Poland (Tomczykowa and Witwicka 1974) and the Kaliningrad region, Estonia (Kaljo and Sarv 1976) to fully marine carbonate facies of Scania, Sweden (Martinsson 1962, 1963, 1967). Sarv (1968, 1971) and Kaljo and Sarv (1966) demonstrated the incoming of F. groenvalliana within a fully marine succession in the east Baltic. F. groenvalliana has been reported from basal part of the Downton Castle Sandstone Formation in the basinal area of the Welsh Basin at Clun, Knighton and Long Mountain (Shaw 1969; present study), across the ‘shelf’ area of Shropshire (Shaw 1969; Siveter 1974, 1978, 1988, 1989; White and Coppack 1978; Hansch et al. 1991; present study), at Woolhope and Capel Horeb, Llandovery (present study) and in the Scout Hill Flags of the Lake District (Shaw 1971). Because of its apparently wide facies tolerance, the sudden appearance of F. groenvalliana at the base of the Ludlow Bone Bed Member is therefore unlikely to be influenced entirely by a marked facies change at that level. Londinia arisaigensis has been reported from Arisaig, Nova Scotia from both limestones and 370 PALAEONTOLOGY, VOLUME 38 shales (Copeland 1960, 1964). In the Welsh Basin L. arisaigensis has been recovered from the Downton Castle Sandstone Formation and its lateral equivalents across the ‘shelf’ area throughout Shropshire and at Woolhope and from the ‘basinal’ area at Long Mountain and Knighton (Shaw 1969; Siveter 1974, 1978, 1989; present study). The same species has been recovered also from the Cefn Einion Formation at Clun (present study) and the Causemountain Formation at Long Mountain (Shaw 1969), and therefore appears to have been tolerant of a wide range of environments. L.fissurata has been reported only from the Welsh Basin (Shaw 1969; Siveter 1974, 1978, 1989) commonly associated with L. arisaigensis (present study). Nodibeyrichia verrucosa is considered by Hansch and Siveter (1994) to be conspecihc with Nodibeyrichia jurassica (Gailite, 1967) the index species for the late Pfido’h Ohessare ‘Stage’ of Saaremaa, Estonia; it is commonly found in faunally rich and diverse open shelf, marine environments (Sarv 1968, 1971; Kaljo 1970; Meidla and Sarv 1990; Nestor 1990; Hansch and Siveter 1994). In the Welsh Borderland, N. verrucosa is restricted to the Much Wenlock, Ludlow, Downton, Knighton and Long Mountain areas (Shaw 1969; Siveter 1974, 1978; present study), areas which embrace both the shelf and basin areas of the Welsh Borderland. Calcaribeyrichia torosa , the characteristic ostracode of the Upper Whitcliffe Formation in the Welsh Borderland, is found in the lateral equivalent to the Downton Castle Sandstone Formation at Long Mountain (Shaw 1969; present study) and on the shelf at Ludlow (Bassett et al. 1982). It is also present in the Underbarrow, Kirkby Moor, and Scout Hill Flags of Cumbria (Shaw 1971). Beyrichia cuspidata (Gronwall, 1867), a species characteristic of the marine upper Ludlow of Scania, has been noted as a possible synonym for C. torosa (Siveter 1989). The ostracode taxa characteristic of the Upper Whitcliffe and Downton Castle Sandstone formations appear to be tolerant across a wide range of environments; the marked turnover in ostracode faunas at the base of the Ludlow Bone Bed Member is, therefore, unlikely to be entirely facies related. In the more offshore basinal area of the Welsh Borderland at Long Mountain, the ostracode faunal change is not as sudden as at Ludlow (Shaw 1969; Text-hg. 12). This gradual ostracode faunal change is consistent with coeval gradual palynofacies changes (Richardson and Rasul 1990). The abundance of some ostracode taxa, for example C. torosa , therefore appears to be partly environmentally controlled. Changes in ostracode frequencies, preservation, and faunal compositions (Text-figs 9-10) are coeval with fine scale sedimentological changes in the Ludford Lane section, and these factors are possibly related. The ostracode faunas from the Rushall Beds at Perton Lane (loc. 23a) are concentrated in the coarse bases to fining upwards units. Smith and Ainsworth (1989) proposed that similar beds in the basal metre of the Platyschisma Shale Member at Ludlow were the products of storms; therefore, it is possible that the ostracodes at Perton were selectively winnowed and concentrated by storm action. Local factors also appear to affect the presence and frequency of ostracode faunas in the Downton Castle Sandstone Formation, which at Downton (loc. 146) contains a very sparse ostracode fauna compared with Ludford Corner, only 5 5 km to the east, when sedimentological evidence (present study) does not suggest vast differences in lithofacies. The sedimentology of the Downton Castle Sandstone Formation, which yields very few ostracodes, at Aston Munslow is distinct from coeval levels at Ludford Lane, as the sediment coarsens upwards much more rapidly, and lacks multiple bone beds in the lowermost 0-3 m. The Rushall Beds at Perton Lane (loc. 23) are characterized by plant-rich fine sandstones and siltstones with ostracodes, while at Prior’s Frome (loc. 24), only 2-5 km to the SE, they comprise conglomerates, very fine sandstones and mudstones but lack ostracodes. Ostracodes are common at localities characterized by an abundance of land plant fragments and/or land derived sporomorphs, for example the Rushall Beds at Perton (loc. 23a) and the Downton Castle Sandstone Formation at Ludford Lane (loc. 17). This may explain why the Downton Castle Sandstone Formation at Downton (loc. 146), with a lower percentage of land derived sporomorphs compared with Ludford Lane (Richardson and Rasul 1990) also contains a rather sparse ostracode fauna. It is, therefore, possible that high percentages of palynomorphs, land plant fragments, and ostracodes are related phenomena. High frequencies MILLER: OSTRACODES AND CONODONTS 371 of land-derived sporomorphs could have been the result of proximal distributary channels delivering sediment along an irregularly prograding shoreline (Richardson and Rasul 1990). Ostracode faunas recovered from a limestone bed at Linley Brook (loc. 3 6) are very similar to faunas from beds 1 7a/28 and 176/24 in the Platyschisma Shale Member at Ludlow (Text-figs 9-10). Ostracode collections from these limestone beds are also similar to collections from the Downton Castle Sandstone Formation at Willey (White and Coppack 1978). It is, therefore, possible that the Much Wenlock and Ludlow areas experienced similar environmental conditions at the time of deposition of the Downton Castle Sandstone Formation. However, unabraded conodont specimens recovered from one of these limestone beds at Linley Brook (loc. 36) are unusual, as conodont specimens recovered from the Downton Castle Sandstone Formation across the Welsh Borderland are usually heavily abraded (PI. 1, fig. 11); the possibility that these abraded specimens have been transported or reworked from older strata cannot be discounted. These calcareous beds with well preserved conodont elements suggest a marine environment in the Much Wenlock area in which conodonts of the genera Oulodus and Ozarkodina existed during deposition of the Downton Castle Sandstone Formation. Original calcareous ostracode valves obtained from these beds are unusual as ostracodes are only present at these levels elsewhere in the Welsh Borderland as decalcified moulds. Leperditiid ostracodes are often regarded as shallow water restricted forms (Siveter 1984). Leperditia sp. occurs within the Green Downton Formation at Clun (loc. 396) and in a glacial erratic from the Vale of Wigmore, which suggests that by late Downton times the Welsh Basin had become so restricted that only leperditiid ostracodes together with inarticulate brachiopods such as Lingula sp. could exist. A single specimen of Leperditia sp. has been recovered from loose material from the Platyschisma Shale Member of the Downton Castle Sandstone Formation at Ludford Lane (PI. 2, fig. 18). CORRELATION Britain The base of the Ludlow Bone Bed at Ludford Corner (loc. 18) defines the base of the Downton Group (Holland et al. 1963), formerly regarded as the base of the Downtonian Stage. At the stratotype section (loc. 18) this horizon is marked by the onset of vertebrate sand deposition which has been used to correlate this lithostratigraphical level across the Welsh Borderland to Much Wenlock (Robertson 1927; White and Coppack 1978), Corve Dale (Shergold and Shirley 1968), Downton (Whitaker 1962), Netherton (Stamp 1923; Ball 1951), Kington (Holland and Williams 1985), the Malvern-Abberley Hills (Phipps and Reeve 1967), Woolhope (Squirrell and Tucker 1960), May Hill and Gorsley (Lawson 1954, 1955), Tite’s Point (Cave and White 1971), Usk (Walmsley 1959) and Cardiff (Waters and White 1978). Bone beds are developed within the Platyschisma Shale Member of the Downton Castle Sandstone Formation, at Weir Quarry Downton (loc. 146) and Ludford Lane (Text-fig. 6); although they are not as well developed as the Downton Bone Bed (loc. 14c; Whitaker 1962), they are possible correlatives. In the absence of a basal bone bed, Antia (19796) used the first occurrence of F. groenvalliana and the disappearance of distinctive Upper Whitcliffe brachiopods to indicate the local base of the Downton Castle Sandstone Formation at Siefton (loc. 106). Bone beds at the base of the Downton Castle Sandstone Formation and its lateral equivalents across the shelf area rarely extend laterally into coeval succes- sions in east central Wales (Straw 1930). Only at Wallop Hall, Long Mountain (loc. 36a) is a thin bone bed developed at a comparable level within the Causemountain Formation (Palmer 1973). The ostracode succession of Neobeyrichia lauensis (Kiesow, 1888) -C. torosa -F. groenvalliana -Leperditia sp. has been recognized in the Ludlow and Pfidoli Series of Shropshire and east central Wales, and used for correlation (Straw 1930; Shaw 1969; Siveter 1978, 1989). Other correlations of the base of the Downton Castle Sandstone Formation into east central Wales are based on macrofaunas. For example, the basal Platyschisma helicites Beds at Knighton (the local equivalent to the Downton Castle Sandstone Formation) have a similar lithology to the underlying Upper Llan-wen Hill Beds, but can still be identified on the basis of a faunal change from articulate 372 PALAEONTOLOGY, VOLUME 38 brachiopod-doniinated faunas to gastropod, bivalve and inarticulate brachiopod faunas (Holland 1959, 1962). Similar faunal successions have been described from the area around Clun and Kerry (Earp 1938, 1940). The base of the Downton Castle Sandstone Formation at Ludlow is coincident with changes in the macro- and microfaunas (Bassett et al. 1982, text-fig. 6). The microfaunal changes displayed by the ostracode faunas offer a potential for biostratigraphical correlation of the base of the Downton Group in Britain. As discussed above, this changeover in ostracode fauna is unlikely to be entirely due to the facies change at this level as these species are known elsewhere in a wide range of environments. Calcar ibeyrichia torosa appears to be environmentally controlled (see above) and it cannot be used as a definitive indicator of Ludlow strata within Britain. L. arisaigensis , although common in the Downton Castle Sandstone Formation, has been recovered at Clun and Long Mountain during the present study from levels taken by Cocks et al. (1992) to correlate with the Upper Whitcliffe Formation, and thus possibly has only limited correlation potential. L. fissurata is confined to the Downton Castle Sandstone Formation (and its lateral equivalents) and could prove biostrati- graphically useful. Nodibeyrichia verrucosa is restricted to the lowermost 0-34 m of the Downton Castle Sandstone Formation at Ludlow, and therefore has potential for correlation with other areas of the Welsh Borderland. F. groenvalliana is more abundant than N. verrucosa and is geographically more widespread. In Britain it is widespread at the base of the Downton Castle Sandstone Formation and its lateral equivalents (see above) and can, therefore, be used to indicate basal Downton strata across the Welsh Borderland and into the Lake District. The only potential anomaly in an otherwise consistent scheme in Britain is the reported occurrence of F. groenvalliana in the Cennen Beds (?uppermost Ludlow) of the Cennen Valley, Wales (Squirrell and White 1978; Bassett et al. 1982; Siveter 1989). The presumed Ludlow age for the Cennen Formation is based on the occurrence of the characteristic Ludlow trilobite Calymene neointermedia and the brachiopod Sphaerirhynchia cf. wilsoni in the lower part of the Cennen Beds (Squirrell and White 1978). However, most species in the Cennen Formation, including the characteristic Upper Leintwardine brachiopod Hyattidina canalis, also occur in the Tilestones (Long Quarry Formation) (Squirrell and White 1978, table 3). The Cennen Valley section is no longer exposed, although the author has examined material at the BGS (Keyworth). The specimens of Frostiella are not well preserved and are almost exclusively internal moulds. Well preserved external moulds are needed for positive identification and the specimens are here considered to be best referred to F. cf. groenvalliana. The species itself is not lithofacies related, so it is unlikely that a lithofacies comparable with the Downton Group could account for the occurrence of it in the Cennen Formation of the Cennen Valley in late Ludlow times (cf. Squirrell and White 1978, p. 9). The ostracodes Lophoctenella cf scanensis and C. torosa are also present but do not unequivocally indicate a Ludlow age (see earlier discussion). The uppermost Ludlow age for the Cennen Beds is therefore unproven, and F. groenvalliana is here considered restricted to the Downton Group of Britain until the Cennen Beds can be shown to be unequivocally Ludlow in age. The upper and lower contacts of the Cennen Formation are uncomfortable, and it is possible that it is a local unit at the base of the Downton Group. Frostiella groenvalliana does not always occur immediately at the base of the Downton Castle Sandstone Formation as at Linley (Iocs 3 a-c). Brockton (loc. 5), Culmington (loc. 11), Downton (loc. 146), Clun (loc. 39 a) and Llandovery (loc. 43). Without detailed bed by bed collections, the assumption that the base of the Downton Castle Sandstone Formation is at the level of the first occurrence of F. groenvalliana at Siefton (Antia 19796) is therefore unsubstantiated. ‘The fauna below does contain some species (e.g. Lingula minima and L. kiesowi) which are commonly found in the Downtonian’ (Antia 19796, p. 127) which suggests that the base of the Downton Castle Sandstone Formation at Siefton is possibly at a level below the first occurrence of F. groenvalliana. The first occurrence of F. groenvalliana at Wallop Hall is coincident with a thin (1 mm) bone bed within the Causemountain Formation (Text-figs 1D12). Closely spaced ostracode samples across this level show a gradual change from a fauna similar to that of the Upper Whitcliffe Formation MILLER: OSTRACODES AND CONODONTS 373 at Ludlow to a fauna comparable with that of the Downton Castle Sandstone Formation (Text-fig. 9). Nodibeyrichia verrucosa is confined to the lowermost 0-34 m of the Downton Castle Sandstone Formation at Ludlow and first occurs (with F. groenvalliana) at the base of bed K, at Wallop Flail (Text-fig. 12). On this basis, the base of the Downton Castle Sandstone Formation should be correlated with the base of bed K within the Causemountain Formation at Wallop Flail (loc. 36 a). Similar ostracode faunas from assumed basal Pffdoli horizons at Knighton (Iocs 406-c), and Nantyrhynau Quarry, Clun (loc. 37) offer potential for correlation of the base of the Downton Castle Sandstone Formation from the shelf at Ludlow to the westernmost part of the Ludlow outcrop (Text-fig. 13). BASIN SHELF SAMPLED HORIZON Catcarbeyrichia CLUN NANTYRHYNAU OUARRY (loc. 37) basal bed of Clun Forest Formation (10cm) KNIGHTON MEETING HOUSE LANE (loc 40c) basal bed erf Platyschisma hel Idles Beds (2cm) LONG MTN WALLOP HALL (loc. 36) bedding plane o< bone bed within Causemountain Formation LUDLOW LUDFORD LANE (loc 17) basal bed of Downton C as tie Sandstone Formation (2cm) text-fig. 13. Comparison of ostracode faunas from individual beds at assumed basal Pndolf horizons along a shelf-basin transect of the Welsh Basin. The bone beds at Within’s Wood (loc. 39c) occur above the first occurrence of F. groenvalliana , indicating that these bone beds correlate above the base of the Downton Group and within the Clun Forest Formation. The bone beds are possible correlatives of similar bone beds in the Clun Forest Formation at Bishop’s Castle (Allender 1958; Allender et al. 1960), the Platyschisma helicites Beds at Meeting House Lane at Knighton (loc. 40c), and the Platyschisma Shale Member at Downton (loc. 14c). Conodonts recovered from the lowermost bone bed at Within’s Wood (loc. 39c) are also similar to conodont collections from the Downton Bone Bed (loc. 14c). International correlation The base of the Pridoli Series is defined at Pozary near Prague (Bassett 1985), within bed 96 at a level coincident with the first occurrence of Monograptus parultimus (the base of the parultimus Biozone). The stratotype section has been sampled in detail for graptolites, chitinozoans, conodonts, trilobites, bivalves and brachiopods (Jaeger et al. 1981; Paris 1981; Krfz el al. 1983, 374 PALAEONTOLOGY, VOLUME 38 1986; Paris and Khz 1984; Khz 1989, 1992). Graptolites are the most important biozonal fossil group for the type Phdoh and allow detailed correlation of the Pfidoli Series throughout the Prague Basin. Conodonts. The stratigraphically important conodont taxa O. r. eosteinhornensis and O. crispa have been recovered from the section at Pozary. O. r. eosteinhornensis ranges from c. 2 m below the base of the Phdoh Series at Pozary, to a level above the top of the Pridoli Series (Chlupac et al. 1980; Khz et al. 1983). O. crispa is stratigraphically restricted to the uppermost Ludlow Series at Pozary, appearing only in beds 87-91, and last occurs at a level 0 5 m below the base of the Pridoli Series (Khz 1989, text-fig. 67). There is a similar situation throughout the Barrandian Basin: O. crispa last occurs just below the base of the parultimus Biozone at Lochov Marble Quarry, Lochov Cephalopod Quarry, Hvizdalka, Kolednik Quarry and at Kosov (Khz et al. 1986; Khz 1992). Conodonts from the Upper Whitcliffe Formation at Ludlow offer a direction correlation between the Welsh and Prague basins. Rare specimens of O. r. eosteinhornensis occur in collections from the uppermost Ludlow Series at Ludlow and at other localities across the Welsh Borderland (Collinson and Druce 1966; Aldridge 1975, 1985; Aldridge et al. 1980; Aldridge and Schonlaub 1989; present study); the subspecies has also been recovered from the Ludlow Bone Bed Member at Ludlow (Walliser 1966). The stratigraphical ranges of O. cf. crispa and O. r. eosteinhornensis overlap at the top of the Ludlow Series at Ludlow (Text-fig. 7). However, O. crispa has a much shorter stratigraphical range in both the Welsh and Prague basins, and therefore has greater correlative potential. Until the present study, only one reported occurrence of O. cf. crispa (PI. 3, fig. 3) had been documented from Britain, 0-3 m below the Ludlow Bone Bed at Ludford Lane, Ludlow (Aldridge and Smith 1985; Aldridge and Schonlaub 1989). This occurrence marked the first (and last) occurrence of O. crispa in the Welsh Basin and therefore could be correlated only with the first occurrence of O. crispa at Pozary, at a level 2-75 m below the top of the Ludlow Series. Consequently it has been suggested (Schonlaub 1986; Aldridge and Schonlaub 1989), that the base of the Pfidoli Series at Ludlow occurs at a level above the Ludlow Bone Bed. Two specimens of O. crispa have been recovered from the Upper Whitcliffe Formation as part of the present study, one at Tite’s Point, Severn Estuary (PI. 3, fig. 1) and another at Prior’s Frome in the Woolhope inlier (PI. 3, fig. 2). A broken specimen of O. cf. crispa (PI. 3, fig. 9) has been recovered from sample 18/1 at Ludford Corner (loc. 18), and a specimen of O. cf. crispa recovered from the topmost bed of the Upper Whitcliffe Formation at Aston Munslow, Shropshire (PI. 3, fig. 8). This latter specimen has similar dentition, cavity shape and outline to unequivocal specimens of O. crispa, although the curved posterior termination to the element is not well developed (PI. 3, fig. 8). These new occurrences confirm the presence of O. crispa in the Welsh Basin towards the end of deposition of the Upper Whitcliffe Formation, and more importantly provide a range for O. cf. crispa at Ludford Corner and Ludford Lane. O. cf. crispa can now be shown to range from 0T 5—0-3 m below the base of the Downton Castle Sandstone Formation at Ludlow (Text-fig. 7). This new conodont evidence from Ludlow and other localities in the Welsh Borderland, confirms that base of the Pfidoli Series in Britain is very close to the level of the base of the Downton Castle Sandstone Formation. Taken in isolation, the occurrence of O. cf. crispa in the topmost bed of the Upper Whitcliffe Formation at Aston Munslow indicates that the base of the Pfidoli Series is at least as high as the base of the Downton Castle Sandstone Formation and possibly at a level above its base. In the latter case, without the key graptolite M. parultimus it would not be possible to pinpoint the level of the base of the Pfidoli Series in Britain. O. crispa follows O. snajdri stratigraphically and is thought to be a direct phylogenetic descendant (Aldridge and Schonlaub 1989). O. snajdri is considered to be restricted to the Ludlow Series (Aldridge and Schonlaub 1989, text-fig. 172), even though Spathognathodus aff. snajdri has been recovered from the Aigu Member of the Kaugatuma Formation of Estonia (Viira 1982). The base of the Kaugatuma Formation is considered coincident with the base of the Pfidoli Series, as M. ultimus occurs at the base of the formation in the south-east Baltic (Kaljo 1990). Viira (1982) was not able to distinguish S. snajdri from S. crispa. However, O. crispa is now regarded as confined to MILLER: OSTRACODES AND CONODONTS 375 SUBMARINE GOTLAND WELSH NOVA MAINE HOBURG BORDERLAND SCOTIA USA 1 SCAN LAI BANK I PODOLIAl NE BALTIC (ESTONIA) C and SE BALTIC (LATVIA and LfTHUANIA) IPOLANDI IBOHEMIAI North America using ostracode, graptolite and conodont faunas. The correlations of the local lithostrati- graphical units are based on Bassett et al. (1982; 1989) and Siveter (1989). G, refers to the occurrence of the key ostracode F. groenvalliana within a formation; P, denotes the presence of the graptolite M. parultimus\ C, indicates the presence of the conodont O. crispa. The symbols are not intended to indicate exact stratigraphical positions and the columns are not drawn to scale. the Ludlow Series of the Baltic (Mannik and Viira 1990); thus the material that Viira (1982) identified as Spathognathodus afif. snajdri probably includes specimens of O. snajdri from the Pridoli Series. If O. snajdri is considered to be a predecessor to O. crispa , the occurrence of O. cf. snajdri above the base of the Rushall Beds at Prior’s Frome suggests that there the base of the Pridoli Series should be at least as high as the last occurrence of O. snajdri. Conodont faunas from the Barrandian Basin (Schonlaub 1986) indicate that O. snajdri and O. crispa occur together. Ozarkodina snajdri also occurs higher than O. crispa in the Whitcliflfe Formation at Tite’s Point and the Upper Perton Beds at Prior's Frome. In the Welsh Basin the first appearance of O. crispa stratigraphically follows that of O. snajdri , though their stratigraphical ranges overlap, and O. snajdri continues into the Pridoli Series. It must also be noted that the specimens of O. cf. snajdri in the Rushall Beds at Prior’s Frome are abraded and the possibility that the specimens have been reworked cannot be discounted. The occurrence of O. cf. snajdri above the base of the Rushall Beds cannot, therefore, be taken as an indication that the base of the Pridoli Series should be placed above the base of the Rushall Beds at Prior’s Frome. Ostracodes. The ostracodes in the type section for the base of the Pridoli Series in the Barrandian area are provincial and in need of further study (Kriz 1989; Siveter 1989; Hansch 1993); therefore, direct correlation with British ostracode faunas cannot be made. Using the ostracode F. groenvalliana and graptolites, the base of the Downton Castle Sandstone Formation can be correlated to Maine, Nova Scotia, Podolia, Scania, Gotland, the Baltic, Poland and Bohemia (Martinsson 1967; Siveter 1978, 1989, text-fig. 164, and references therein ; Bassett et al. 1982). Text- figure 14 summarizes the chain of correlation based on Bassett et al. (1982, text-fig. 7; 1989) and Siveter (1989, text-fig. 164), including conodont data and recent information from Podolia. The correlative link between ostracode and graptolite faunas occurs in the Kaliningrad region of the Baltic which then provides a link with the graptolite biozonal schemes of Polish and hence. 376 PALAEONTOLOGY, VOLUME 38 Bohemian successions. F. groenvalliana and the key graptolite M. parultimus occur together only in the Kaliningrad region, but at separate stratigraphical levels in the Dubovskoe borehole; the first occurrence of the former occurs 68 m higher than the first occurrence of the latter (Kaljo and Sarv 1976, text-fig. 1; Hansch et al. 1991). The first occurrence of F. groenvalliana has been recognized within the fully marine Aigu Member of the Kaugatuma Formation of Estonia (Kaljo and Sarv 1966; Sarv 1968, 1971). At Ohesaare on Saaremaa, where the base of the Kaugatuma Formation is shown as coincident with the base of the parultimus Biozone, F. groenvalliana has also been reported 8 m above the base of the formation (Bassett et at. 1989, text-fig. 123). In Lithuania the first occurrence of F. groenvalliana coincides with the lowest sample taken within the Kaugatuma Regional Stage (4 m above its base) in the Stoniskiai borehole (Sarv 1977, text-fig. 7). In the Pajevonis 13 borehole of Lithuania, M. parultimus is reported at the base of the Minija Formation (Paskevicius 1979). Accepting the correlation of the base of the Minija Formation with the base of the Kaugatuma Stage (Bassett et al. 1989, text-fig. 118), this indicates that F. groenvalliana and M. parultimus first appear at approximately the same level in Lithuania. Martinsson (1964) reported Frostiella lebiensis at a restricted range of 68 1 -75-694-40 m in the Leba 1 borehole in northern Poland. F. lebiensis is now recognized as a synonym of F. groenvalliana (Hansch et at. 1991); the species occurs within the Lower Podlasie Beds of Poland (Text-fig. 14). Tomczyk (1968) recorded graptolites from Polish boreholes including the Lebork Borehole where M. ultimus directly follows M. formosus. Recovery from most of the Polish boreholes is incomplete, except for the Lebork borehole where it is almost complete. Tomczyk (1968) used the upper limit of M. formosus to define the boundary between the Ludlow and the Podlasie Beds. The correlation chart for the Polish Silurian (Tomczykowa and Witwicka 1974, text-fig. 2) based on ostracode, graptolite, and trilobite evidence, places the last occurrence of M . formosus in the Leba 1 borehole at a level between 800 and 850 m, at least 230 m below the occurrences of F. groenvalliana ( lebiensis ) reported by Martinsson (1964). The first occurrence of F. groenvalliana is therefore consistently above the level of the base of the parultimus Biozone, most notably at Kaliningrad which is the only locality where the two species occur in the same section. Since Bassett et al. (1982) outlined the correlation of the base of the Downton Castle Sandstone Formation across Europe, further information has become available on the distribution of the ostracode F. groenvalliana and the resolution of graptolite biozonal schemes has been increased. A number of potential problems regarding the correlation noted by Bassett et al. (1982) can now be addressed. 1. ‘There is currently some discrepancy in the interpretation of the ranges of graptolites associated with the lowest Downton ostracode assemblages in Poland’ (Bassett et al. 1982, p. 18). Ostracode assemblages from the Lower Podlasie Beds in Poland correlate within the ultimus Biozone but occur above horizons containing M. formosus (Tomczyk 1968, 1970; Tomczykowa and Witwicka 1974). Levels with M. formosus were formerly regarded as being within the ultimus Biozone, although the taxonomy of the formosus group was poorly known (Teller 1969; Jaeger 1977). The graptolite biozonation for the Pridoli in the Prague Basin (Jaeger 1986) shows that the range of M. formosus spans the Upper Ludlow fragmentalis Biozone and the Pridoli parultimus and ultimus biozones. The ultimus Biozone has now been subdivided into a (lower) parultimus Biozone and (upper) ultimus Biozone, as M. parultimus and M. ultimus are almost certainly successive members of a lineage (Jaeger 1986). Occurrence of the ostracode F. groenvalliana above levels containing M . formosus is not therefore inconsistent with the occurrence of F. groenvalliana above the base of the parultimus Biozone. 2. Various reviews of the correlation of the Silurian of the East Baltic (Kaljo and Sarv 1966; Kaljo 1970, 1978) have expressed differing opinions as to the correlation of the base of the Downton Group with the Kaugatuma and underlying Kuressaare beds (Bassett et al 1982, p. 18). Kaljo (1979) correlated the base of the Kuressaare Beds with the base of a broad formosus-ultimus graptolite interval, with F. groenvalliana entering slightly higher in the succession (at the base of the Kaugatuma Beds), suggesting that the base of the Kaugatuma Beds is approximately coincident with the base of the ultimus graptolite Biozone (Bassett et al. 1982). The latest correlative schemes MILLER: OSTRACODES AND CONODONTS 377 for the Silurian of the Baltic place the Kuressaare Formation at the top of the uppermost Ludlow formosus Biozone and the base of the Kaugatuma Formation coincident with the base of the parultimus Biozone (Bassett et al. 1989, text-fig. 118; Kaljo 1990, text-fig. 2). 3. The position of the base of the Minija Formation in the East Baltic is marked as uncertain (Bassett et al. 1982, text-fig. 7) and possibly at a level below the base of the ultimas Biozone. Bassett et al. (1982, p. 17) reported that the basal ‘Downton’ ostracode fauna in Latvia and Lithuania entered at or closely above the base of the Minija Formation, but it is unclear from what authority this has been cited. Paskevicius (1982) and Sidaraviciene (1986) confirmed that F. groenvalliana is present at the base of the Minija Formation in the Stoniskiai, Vidukle and no. 1 10 (Arjogal profile) boreholes of Lithuania. If the base of the Minija Formation is below the base of the parultimus Biozone (see Bassett et al. 1982, text-fig. 7) then the correlation using F. groenvalliana is wrong. The latest published correlation chart for the Silurian of the Baltic (Bassett et al. 1989, text-fig. 118) places the base of the Minija Formation coincident with the base of the parultimus Biozone, but a dotted line is used as there is still a degree of uncertainty concerning the exact position of the base of the formation. Dr David J. Siveter (pers. comm.) has examined material from Podolia and considers F. modesta Abushik, 1971, conspecific with F. groenvalliana. This further extends the geographical distribution of the species to Podolia where it occurs 17 m above the base of the Rashkov Formation (Abushik et al. 1985; Koren' et al. 1989). Ozarkodina crispa last occurs 5 m above the base of the Rashkov Formation in Podolia (Abushik et al. 1985; Koren' et al. 1989, text-fig. 105). Conodont evidence therefore suggests that the base of the Pridoli Series is at a level at least 5 m above the base of the Rashkov Formation. This provides an additional example of F. groenvalliana closely strati- graphically following O. crispa , but with no overlap in their ranges (cf. Ludford Corner, Ludlow). According to Viira (1982) and Schonlaub (1986) it is possible that O. crispa ranges into the lowermost Kaugatuma Formation of the east Baltic and, therefore, occurs above levels containing F. groenvalliana. As discussed above, O. crispa is now considered to be confined to the Upper Paadle Formation, at a level below the Kaugatuma Formation (Miinnik and Viira 1990). Frostiella groenvalliana is not always present at the base of the hthostratigraphical units shown in Text-figure 14. However, the distribution is remarkably consistent across the whole of Europe, with F. groenvalliana always occurring above the base of the parultimus Biozone and occurrences of O. crispa and never below these levels. The evidence currently available therefore suggests that F. groenvalliana is restricted to the Pridoli Series. The correlation of the base of the Downton Castle Sandstone Formation in the Welsh Borderland with the base of the Pridoli Series in the Czech Republic using the ostracode F. groenvalliana is regarded as approximate in terms of the detailed stratigraphical resolution of the present study. The correlation is indirect as the two key species are both present only at Kaliningrad, and then at different stratigraphical levels (see above; Kaljo and Sarv 1976). Lithostratigraphical correlation between local units has to be used to provide the link between ostracode and graptolite faunas. Often there is a degree of uncertainty regarding these correlations, for example with the position of the base of the Minija Formation in western Latvia and western Lithuania. Sampling in Baltic, Scanian, Polish and North American sections has not been carried out to the same high resolution as at the stratotype for the base of the Pridoli Series at Pozary, or at Ludlow in the present study. More detailed sampling is therefore needed on and around the stratigraphical level at the base of the parultimus Biozone to recover more detailed records of F. groenvalliana and to enable occurrences to be more accurately tied in with the base of the parultimus Biozone. With only a limited sample size, borehole data does not often permit detailed studies of these faunas. Borehole recovery is seldom complete, and important faunas may have been lost. Indirect and approximate correlation using ostracodes and graptolites (Text-fig. 14) suggests that the base of the Pridoli Series in Britain is coincident with the base of the Downton Castle Sandstone Formation. Conodont faunas from the uppermost Upper Whitcliffe Formation at Ludlow and across the Welsh Borderland offer a direct correlation with the Barrandian Basin and suggest that the base of the Pridoli Series in Britain is at least as high as the base of the Downton Castle 378 PALAEONTOLOGY, VOLUME 38 Sandstone Formation and possibly a little higher than this. At present, the exact position of the base of the Pridoli Series in Britain cannot be demonstrated because of the absence of the key graptolite species M. parultimus ; the current state of knowledge on British, European and North American conodont, ostracode and graptolite correlations suggests that the base is coincident with the base of the Downton Castle Sandstone Formation at Ludlow. Acknowledgements. This research was carried out under the tenure of NERC studentship GT4/89/GS/056. I thank Drs R. J. Aldridge and David J. Siveter for provision of additional material, and for their supervision. I am grateful to Mr W. Teasdale for the use of facilities in the Department of Geology, University of Leicester, Mr R. Branson for his assistance with scanning electron microscope studies and photographic techniques, and Mr A. Swift for advice in the laboratory. I also thank Drs L. R. M. Cocks and J. E. Whittaker for their help and use of the facilities at the Natural History Museum. Dr J. 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G. miller Department of Geology University of Leicester Leicester, LEI 7RH, UK Present address Typescript received 1 February 1994 Revised typescript received 29 September 1994 Department of Palaeontology Natural History Museum Cromwell Road London, SW7 5BD, UK THE TYPE SPECIES OF THE BRACHIOPOD YUNNA N ELLI N A FROM THE DEVONIAN OF SOUTH CHINA by MA XUEPING Abstract. Yunnanellina hanburyi, the type species of the genus, is widely distributed in South China. Study of the external and internal features of abundant specimens from three sections in central Hunan indicates that other previously described nominal species and subspecies of Yunnanellina from the Upper Devonian of South China, are junior synonyms of the type species. Y. hanburyi is very varied in both external form and internal structures. Internally, the septalium may be open, or covered anteriorly by a connectivum. This connectivum shows a systematic change with time and, on this basis, three morphotypes have been established which comprise the Y. hanburyi lineage. The stratigraphical range of the lineage can be correlated with the upper crepida Zone (Early Famennian). Rhynchonella hanburyi Davidson, 1853, the type species of Yunnanellina Grabau, 1931, is widely distributed in South China. Davidson’s original material includes only five specimens, four of which possess two plications in the sulcus, with one, a juvenile, too immature to have developed a sulcus or fold. Kayser (1883) noticed some uniplicate specimens and correctly assigned them to Davidson’s species as a varietal form. But since 1931, more species and subspecies, some of which have been introduced in the literature as mutations or varieties, have been described from the Upper Devonian of South China. These are Yunnanellina hanburyi mut. lata Grabau, 1931 ; Y. uniplicata Grabau, 1931; Y. triplicata Grabau, 1931; Y. hanburyi mut. sublata Tien, 1938; Y. triplicata var. latiformis Tien, 1938; Y.obesa Tien, 1938; Y . heyuanzhaiensis Fang in Fang and Zhu, 1974 (= Y. xintianensis Zhao in Yang et al. 1977); Y. uniplicata mesosulcata Liu in Liu et al. 1982 and Y. undatussulcus Li, 1987. All the above nominal species or subspecies were established solely on different external features, especially the number of sinal plications and general outline. The validity of these taxa has not as yet been tested. Nevertheless, the binomials Yunnanellina hanburyi , Y. uniplicata and Y. triplicata have frequently appeared in the Chinese literature. Sartenaer (1971) gave a fairly thorough treatment of Yunnanellina and discussed forms labelled Yunnanellina from most parts of the world. He redescribed the type species based chiefly on the type material deposited in the Natural History Museum in London, and material in the United States National Museum in Washington, D.C. This redescription was largely based on external characters. Regarding the internal structure, Sartenaer pointed out (p. 204) that the ‘septalium [was] short, deep, wide, amphora-shaped and uncovered’. This description was based on only one sectioned specimen and as such can not be taken as definitive. Xu (1979) discussed the stratigraphical distribution of the genus and gave a Famennian age for the Yunnanellina- Yunnanella fauna. The present study is an attempt to clarify the taxonomy of Yunnanellina hanburyi and related forms from South China and to demonstrate its intraspecific and stratigraphical variations in internal morphology. MATERIAL AND METHODS Yunnanellina is very abundant in Hunan, especially in the centre of the province, where Upper Devonian strata with abundant benthic fossils are well developed, making it the most important (Palaeontology, Vol. 38, Part 2, 1995, pp. 385-405, 2 pls| © The Palaeontological Association 386 PALAEONTOLOGY, VOLUME 38 text-fig. 1. Location map of the study area. 1, Xikuangshan section (samples beginning with the letter L). 2, Chongshanpu section (T). 3, Jiangjiaqiao section (C). area for research into the Upper Devonian of China. Numerous specimens of Yunnanellina , most of which are well preserved, have been collected from three sections in central Hunan (Text-fig. 1). Thirty-six specimens were sectioned, of which twenty-two have been serially sectioned to reveal the systematic change in internal structure. Most of the sections were recorded as acetate peels. The distance between each adjacent peel was usually taken at c. 0-3 mm. Detailed microstructure was added to the camera lucida drawings of the outline of the internal structure through examination of the peels under a microscope. The illustrated acetate peels were selected to show significant changes in the internal structure. The thirty-six sectioned specimens include twelve of ‘ Y. uniplicata\ eighteen of ' Y. hanburyi', and six of ' Y. triplicate. In the following text, these three 'species' are expressed as uniplicate, biplicate and triplicate forms, respectively. All specimens illustrated in the text-figures and plates are deposited in the Department of Geology, Peking University. TAXONOMIC DISCUSSION OF YUNNANELLINA FROM SOUTH CHINA Ten species and subspecies of Yunnanellina have been described from the Upper Devonian of South China. The following list gives the features by which they were distinguished. 1. Y. hanburyi (Davidson, 1853): with two plications in the sulcus. 2. Y. h. mut. lata Grabau, 1931 : with flatter shell than Y. hanburyi. 3. Y. h. mut. sublata Tien, 1938: similar to Y. h. mut. lata , but smaller. 4. Y. uniplicata Grabau, 1931 : one plication in the sulcus. 5. Y. u. mesosulcata Liu in Liu et al., 1982: with a furrow on the sinal plica and correspondingly a small median plica present in the interspace on the fold. 6. Y. triplicate i Grabau, 1931 : with three plications in the sulcus. 7. Y. t. var. latiformis Tien, 1938: with a flatter shell than Y. triplicata. 8. Y. obesa Tien, 1938: a rather broader obese form with three plications in the sulcus. MA XUEPING: YUNNANELLINA FROM SOUTH CHINA 387 9. Y. heyuanzhaiensis Fang in Fang and Zh u. 1974 ( = Y. xintianensis Zhao in Yang et al. 1977?): with four plications in the sulcus. 10. Y. undatussulcus Li, 1987: with two or three plications in the sulcus, which is concave in the middle part. Most of the above species or subspecies were originally defined on the basis of only a few or even a single specimen. Davidson’s original material was purchased from a Chinese drugstore, and the original locality and stratum can not be determined. It is questionable that the material is from Guangxi Province. Grabau’s material, which also has questionable provenance, was used by him to establish two new species and a subspecies chiefly based on differences in the number of the sinal plications. Most subsequent Chinese workers followed this example and named species and subspecies based on minor differences in external morphology. The present study shows that all the above species and subspecies belong to the type species, Y. hanburyi. However, this idea is not new. Kayser (1883) included his uniplicate form in Y. hanburyi (Davidson). Tien (1938, p. 46) considered that his Y. cf. triplicate! Grabau (based on one specimen) ‘is not only a direct derivative of the biplicate form- Y. hanburyi, but also foreshadows the quardriplicate form. If we could prove this in the future when more materials are available, I would prefer to regard all them as varieties of Y. hanburyi because they are all essentially identical, apart from the number of the plicae in the sinus and on the fold’ (quoted from Tien’s original English text). Sartenaer (1971) did not consider the species Y. triplicata and Y. uniplicata to be valid as they entered the range of variability of Y. hanburyi , but this was not discussed in depth. I have the following evidence to reject the other species and subspecies. 1. Specimens from the same sample show different shapes and possess different numbers of plications in the sulcus. If the number of sinal plications and general shape of a shell is taken as the most important criterion for species recognition, this would lead to many ‘species’ and ‘subspecies’ in a given sample, which is unlikely according to modern concepts in biology. This is demonstrated by sample C-C, for example (Text-fig. 2a-d). Uniplicate, biplicate and triplicate forms are present, and one specimen shows five plications in the sulcus. This would require the erection of four text-fig. 2. Variation in external morph- ology. a-d, sample C-C; all anterior views of uniplicate (a), biplicate (b), triplicate (c) and pentaplicate (d) speci- mens (PUM92032-42). E, sample C-D; PUM92043, showing a parietal plica on the right slope, f-g, sample L-D3xt; showing transverse shell (PUM92044) and high sinal tongue (PUM92045). h, sample LI 7; PUM92046, with two strong central plicae and a faint plica on each side, of which the plica on the left may be considered as a parietal one. 388 PALAEONTOLOGY, VOLUME 38 text-fig. 3. Scatter diagram showing length-width and length-thickness relationship. Legends 1-4 refer to uniplicate, biplicate, triplicate and quadriplicate specimens, respectively. Reference lines (dashed) are drawn for comparison of different samples. A, sample LI 7. B, sample C-LL ‘species’ on account of the number of sinal plications. But, only the rarity of specimens would preclude the quadriplicate or pentaplicate forms from being a separate species because they are basically identical with the uni-, bi- and triplicate forms. Secondly, different shapes are present in the uni-, bi-, and triplicate forms. In the biplicate form, ‘ Y. hanburyi', ‘ Y. h. mut. lata' and ‘ Y. h. mut. sublata' can be recognized; in addition, there is still a globose form similar to ‘ Y. obesa' in general shape, but different from it in the number of sinal plications (this again would be a new ‘species’). A similar case is for the triplicate form including ‘ Y. triplicata', ‘ Y. t. var. latiformis ’ and ‘ Y. obesa' . Actually flat forms {'lata', ‘ sublata ' and ‘ latiformis ’) are composed of most immature specimens. Certainly, some flat specimens could be adults because their frontal commissure is highly elevated by plications, a feature of maturation (see section on General Morphology). 2. Occasionally in a sample, one or two specimens of bizarre morphology may be present. I have observed specimens with the sulcus protruding to a high tongue, or with a transverse or very globose shell, or with parietal plications, which are normally absent (Text-fig 2e-h). Several more examples of abnormal growth are shown in Plate 1, figures 7-8, 21-22. The specimens in Plate 1, figures 7-8 would represent ‘ Y. uniplicata mesosulcata' Liu with a furrow on the strong sinal plica and, correspondingly, a small median plica present in the interspace on the fold. The specimens in Plate MA XUEPING: YU N N AN ELLIN A FROM SOUTH CHINA 389 1, figures 21-22 show a similar case with, in addition, the right plica on the fold (or left plica in sulcus) bifurcating anteriorly. 3. The growth curve shows basically the same pattern for specimens of uniplicate, biplicate and triplicate forms in the same sample (Text-figs 3-4). width -21 -19 -17 -15 h!3 + + / / / / + + + + ++ ++ + 'itv% / V X t •/ / w/l= 1 ••4 J • , + + * c + +L +r + / -11 • ✓ + y + T* » * - •• + + -I* k. A1 *• t/l=1/2 10 _L 12 length(mm) 14 16 18 20 14- §1 2-1 c O ~ioH 81 6 4-1 width -21 -19 -17 -15 -13 Mi B + + . • ^ ■+*» * . / +/ / • U ** * ' ** • ® T •• ••• . +X *•< / • •/ VW/I=1 / •* • • / -9 X / C *f » • • • r *+ + • i • • %••?+ : *JL* *.! t/l= Vs 10 length 12 14 16 + K + +- 10 8- 6 41 text-fig. 4. Scatter diagram showing L-W and L-T relationship. Legend as for Text-figure 3. a, sample C-C. B, sample C-D. 4. Like external features, internal structures also vary between specimens in a single sample, e.g. sample C-H. In this sample in the uniplicate form, the connectivum (i.e. cover plate over the septahum; see Sartenaer 1969) may appear when the septalium disappears in some specimens; in others it may cover the septahum and persist in front of the septahum; other specimens may not have a connectivum or may just possess a semiconnectivum (see below). In the biplicate form, the connectivum is not present. The internal characters, like the external morphology, are therefore quite varied. These internal variations apparently do not represent separate species or subspecies, otherwise the uniplicate form with similar general shape in one sample (as in sample C-H) would have to be further subdivided into ‘species’ or ‘subspecies’. In conclusion, the Yunnanellina specimens from the Upper Devonian of South China appear to belong in the same species Y. hanburyi. Such species as Pugnax Utah (Marcou), P. postmodica- 390 PALAEONTOLOGY, VOLUME 38 formis, P. hunanensis and P. chaoi described from Shaoyang by Ozaki (1939) probably also belong to the type species. This is especially the case if Ozaki's (1939) specimens are confirmed to be Famennian in age, rather than Visean as was originally reported (see Yang et al. 1977, p. 389). GENERAL MORPHOLOGY OF YUNNANELLINA HAN BURYI External morphology The external structure of Yunnanellina hanhuryi has been extensively described by many previous workers (Grabau 1931; Tien 1938; Wang et al. 1964; Sartenaer 1971). However, these authors have concentrated chiefly in describing the ornament. Here I present a brief description of other aspects. Shape and growth. Y. hanburyi is usually dorsibiconvex, but the ventral valve is more convex at the umbo. The general outline is triangular. Width, length and thickness dimensions of Yunnanellina are characterized by simple linear growth (Text-figs 3-4). In young shells width and length are seen to be nearly equal. When the shell is very small, length is even greater than width, but in adult forms width increased more rapidly than length. The greatest thickness is at the frontal commissure because it is highly elevated there by plications. This feature is a reflection of growth stage (Text- fig. 5). In the young stage, the shell is much flatter; the plications are not present, with only numerous striae covering the whole shell surface; the greatest thickness is not at the frontal commissure, but near the mid-length. Because of the influence of the growth pattern, the thickness of specimens in a sample is very variable, making this character poorly correlated with length or width. Beak and pedicle opening. Yunnanellina hanburyi possesses deltidial plates and a small palintrope (Text-fig. 6). The pedicle opening is oval. The beak is usually slightly incurved. EXPLANATION OF PLATE 1 Figs 1-15. Yunnanellina hanburyi Morphotype 1. 1, sample L12/0-7-0-8; ventral view of a juvenile specimen (PUM92080) showing greater length than width. 2-5, sample L12/0-0T ; dorsal view of a triplicate specimen (PUM92063), anterior views of biplicate specimens (PUM92081-83); note the variation. 6, sample L12/0 4— 0 5; showing teeth of a biplicate specimen (PUM92084). 7-8, sample C-H; anterior and ventral views of PUM92085 showing the presence of a small central plication on the fold and corresponding anterior furrow on the sinal plication. 9-10, sample L12/0-7-0 8; dorsal and anterior views of a uniplicate specimen (PUM92086). 1 1, sample C-H ; anterior view of a uniplicate specimen (PUM92087). 12, sample L12/0-7-0-8; internal mould of brachial valve of a uniplicate specimen (PUM92088) showing adductor muscle scars. 13-14, sample C-H; anterior and ventral views of biplicate specimen (PUM92089). 15, sample C7-2; anterior view of a large quardriplicate speciment (PUM92090). Figs 16-25. Yunnanellina hanburyi Morphotype 2. 16-17, sample C-E; dorsal and anterior views of a juvenile specimen (PUM92091). 18, sample C-C; anterior view of PUM92092. 19-20, sample C-D; dorsal and anterior views of immature specimen (PUM92093). 21-22, sample C-G, PUM92094; ventral and dorsal views showing abnormal growth of sinal plications; note a faint median furrow present in the sulcus and small median plica in the interspace on the fold ; one lateral plica bifurcates at the front into two weak ones. 23-24, sample LI 9/0; anterior and ventral views of a biplicate specimen (PUM92095). 25, sample LI 9/0; dorsal view of a triplicate specimen (PUM92096) showing pattern of striation. Figs 26-29. Yunnanellina hanburyi Morphotype 3. Sample L-D3xt; anterior and ventral views of quadriplicate and triplicate specimens (PUM92097-98). All figures x 2, except fig. 1, x 3 and fig. 6, x 4. PLATE 1 MA XUEPING, Yunnanellina 392 PALAEONTOLOGY, VOLUME 38 text-fig. 5. Growth stages as reflected by the outline of the frontal commissure. Drawn from specimens PUM92047-53 from the same sample (C-D). text-fig. 6. Pedicle opening and related structures from juvenile (d) to adult (a) stages, dp = deltidial plate; p = palintrope. a, sample C-E, PUM92054. b, sample LI 7, PUM92055. c, sample C-C, PUM92056. d, sample C-D, PUM92057. Specimens of a and b uniplicate, whereas in the latter two, the sulcus has not developed and sinal plication cannot be defined. table 1 . Relative proportion of various forms of Y. hanburyi in different samples (arranged in stratigraphical order). Uniplicate Biplicate Triplicate Sample N % n2 % n3 % Morphotypes L-D3xt 20 — — 6 300 13 650 Morphotype 3 C-A 11 — — 7 63-6 4 36-4 C-C 116 35 30-2 75 64-7 5 4-3 Morphotype 2 C-D 83 67 80-7 16 19 3 — — C-E 63 53 84 1 9 143 — — L17 45 10 22-2 26 57-8 8 17-8 C-G 18 7 38-9 9 500 2 111 C-H 76 65 85-5 10 13-2 i 13 Morphotype 1 Plications. One to five plications may be present in the sulcus of Yunnanellina hanburyi. Specimens with one to three sinal plications are most common. However, in a given sample, usually only one of the three forms is predominant (Table 1). Specimens with four or five sinal plications are very rare. There are, on average, two plications on each side in the uniplicate, biplicate, or triplicate form. This character does not seem to vary stratigraphically. Internal structure Nomenclature used for the description of the internal structure in serial sections is shown in Text- figure 7. Cardinalia. Teeth are supported by a pair of dental plates. The dental cavity is variable in size. This feature does not show any systematic change with time, but in ‘ Y. uniplicata the dental plates seem nearly consolidated with the shell wall. The inner socket ridge is more prominent than the outer. MA XUEPING: YUNNANELLINA FROM SOUTH CHINA 393 text-fig. 7. Nomenclature for the internal structure in transverse serial sections, cb = crural base; c = connectivum; dc = dental cavity; dp = dental plate; h = hinge plate; isr = inner socket ridge; s = septum; se = septalium; t = tooth. text-fig. 8. The herringbone-shaped connectivum with a divided crest. See also Plate 2, figure 8. 2mm The latter is low, its inner face being crenulated. The hinge plates are horizontal, divided by the septalium. The septalium may be wide or narrow. Stratigraphically lower specimens usually show a wide septalium, while those from upper levels have a narrow one. The septalium is usually open posteriorly, being uncovered or covered anteriorly by a connectivum. This is the first record of a connectivum in Yunnanellina. In some specimens this structure may be just an extension halfway to the midline from each of the hinge plates, here called a semiconnectivunr, in others, it may not be present. The connectivum is actually a joint plate resulting from further development of the semiconnectivum. The unification makes it appear slightly concave, planar, or herringbone-shaped. In the latter form, a divided crest may exist (Text-fig. 8). Lophophore support. Crural bases are located at the junction of the hinge plates and the septalium. They begin at the posterior end of the hinge plates, and extend anteriorly giving rise to the freely projecting crura. Crural bases, which are usually clearly defined, are triangular, point downward, and have, in cross-section, a tail extended horizontally outward. Muscle attachment. Yunnanellina does not possess a cardinal process. Adductor muscle scars in the brachial valve are well impressed in a mould specimen (Text-fig. 9). Posterior adductors are heart- shaped, separated by a low, rounded septum. Anterior adductors are horn-shaped. 394 PALAEONTOLOGY, VOLUME 38 text-fig. 10. Transverse peels of Y. hanburyi Morpliotype 1, showing broad septalium (a) and the absence of connectivum (b). Sample T12, a biplicate specimen (PUM92058). SYSTEMATIC PALAEONTOLOGY Order rhynchonellida Kuhn, 1949 Family yunnanellidae Rzhonsnitskaya, 1956 Genus yunnanellina Grabau, 1931 Type species. Rhynchonella hanburyi Davidson, 1853, p. 356, pi. 15, figs 10-11. Range. Famennian. Rare occurrences of Frasnian (Yang et al. 1977) and Visean (Ozaki 1939) ages have been reported, but these need confirmation. Distribution. South China (abundant), Northwest China (rare), ?Kazakhstan, ?Novaya Zemlya (Russia). Remarks. The combination Ywmanella hanburyi was first utilized by Grabau (1923-24, p. 195). However, the genus Ywmanella was neither described nor given a type species in this paper (contrary to Tien 1938, p. 48). It was only in 1931 that Grabau thoroughly described the genus MA XUEPING: YUNNANELLINA FROM SOUTH CHINA 395 text-fig. 1 1. Transverse serial sections of biplicate Y. hanburyi Morphotype 1. Numbers refer to distance in mm from ventral apex, a, sample C-H, PUM92059. B, sample LI 2/0-01, PUM92060 (shell compressed). Yunnanella and designated Y. synplicata Grabau as the type species of Yunnanella. Yunnanellina was proposed as a subgenus of Yunnanella , with Rhynehonella hanburyi Davidson as the type species (Grabau 1931). Subsequently both Yunnanella and Yunnanellina have become two well-used names in the Chinese literature, because they are very abundant and good markers of Famennian strata in South China. However, in the Treatise (McLaren in Moore 1965) Yunnanella and Yunnanellina are listed as junior synonyms of Nayunnella Sartenaer, 1961 and Yunnanella Grabau, 1923, respectively, a proposal which I do not support. Yunnanellina Grabau, 1931 can be easily distinguished on superficial evidence from Yunnanella Grabau, 1931 by the presence of its finer striae arising independently and continuing over the plications. In the latter, the plicae are formed anteriorly by a single enlarged strica, or two or more united striae. In addition, the striae of Yunnanellina increase in number chiefly by multibifurcations and cover more densely the shell surface. In Yunnanella , however, the shell surface is covered by relatively coarse and sparse striae characterized by both bifurcation and intercalation. The internal structure of the latter needs detailed study before comparisons can be made with the former. Stratigraphically this species can be divided into three chronological morphotypes based on the variation pattern of the connectivum, especially in the biplicate form, and in the septalium. Yunnanellina hanburyi Morphotype 1 Plate 1, figures 1-15; Plate 2, figures 1-3, 7; Text-figures 10-13 Diagnosis. Specimens of Yunnanellina hanburyi in which the biplicate form does not possess a connectivum. The septalium of all specimens is broad and rounded. Description. In the biplicate form, dental plates are well developed. Dental cavities are large, oval in shape. In the brachial valve, hinge plates are usually horizontal, separated by the septalium. Crural bases are small, not well-defined. The most important feature is the absence of a connectivum anteriorly over the septalium. In the uniplicate form, the shell is strong. Dental plates are thick, more or less consolidated with the shell wall, leaving the dental cavities very narrow, small, or even slit-like. The septalium is still broad and rounded, but posteriorly it becomes very narrow. Crural bases are usually well-defined; in some specimens, they may 396 PALAEONTOLOGY, VOLUME 38 text-fig. 12. Transverse serial sections of uniplicate Y. hanburyi Morphotype 1. Note the small size of the dental cavity. Sample C-H. a, PUM92061 b, PUM92062. Compare with Plate 2. figure 7. text-fig. 13. Three serial sections of triplicate Y. hanburyi Morphotype 1. Sample L12/0-0T, PUM92063. (Also shown in PI. 1, fig. 2; PI. 2, fig. 2). MA XUEPING: YUNNA N ELLIN A FROM SOUTH CHINA 397 text-fig. 14. Transverse serial sections of uniplicate Y . hanburyi Morphotype 2. a, sample C-C, PUM92064. b sample L19/0, PUM92065. extend for a short distance laterally. The connectivum is present in some specimens, but in others it may be just a semiconnectivum. The connectivum may cover the septalium exactly or stretch farther forward than the septalium. The crus is triangular, point down in cross section, pointing ventrally and slightly anteriorly. In the triplicate form, a semiconnectivum is present. It seems that the end of the crura are curved ventroposteriorly so that the crura and the hinge plates with crural bases are shown in the same section. 398 PALAEONTOLOGY, VOLUME 38 text-fig. 15. Transverse serial sections of biplicate Y. hanburyi Morphotype 2. Note the narrowness of the septalium. a, sample C-C, PUM92066. b, sample L19/O2-0-4, PUM92067. Material. Over 145 specimens: from the middle part of the Chang lungchieh Shale, near Laojiangchong village, Xikuangshan area: L 1 0/7-9 (one specimen); Lll (fragments); L12 (1-7 m thick, over fifty specimens, some of which are in good state of preservation; the biplicate form is predominant); from the lower part of the Famennian, near Tingziling, about 4 km east of Chongshanpu: T12 (two specimens); T13 (two specimens); from the lower part of the Famennian, near Chenjiayuan, about 4 km east of Jiangjiaqiao: C7-2 (two specimens); C-H (eighty-five specimens). EXPLANATION OF PLATE 2 Figs 1-3, 7. Yunnanellina hanburyi Morphotype 1. 1, sample L12/0-0T; showing the absence of connectivum of a biplicate specimen (PUM92060). 2, same specimen as PI. 1, fig. 2; showing broad and rounded septalium. 3, sample L12/06; a biplicate specimen (PUM92077) showing right hand hinge plate and crural base, but without connectivum medially (towards the left on photograph). 7, sample C-H; showing a uniplicate specimen (PUM92062) with connectivum. Figs 4, 6, 8. Yunnanellina hanburyi Morphotype 2, 4, sample C-D; showing a biplicate specimen (PUM92078) with the connectivum. 6, sample L17; showing a triplicate specimen (PUM92072) with very narrow septalium; note that the position of the crural base is on the hinge plate and not at the junction of the hinge plate and the septalium. 8, sample C-E; showing a uniplicate specimen (PUM92079) with a herringbone- shaped connectivum; note the divided crest. Fig. 5. Yunnanellina hanburyi Morphotype 3. Sample L-D3xt; a triplicate specimen (PUM92068) with V-shaped septalium and outward disposition of the crural base. All figures x 75, except figs 1 and 7, x 30; c = connectivum; cb = crural base; h = hinge plate; s = septum; se = septalium. PLATE 2 MA XUEPING, Yunnanellina 400 PALAEONTOLOGY, VOLUME 38 text-fig. 16. Transverse serial sections of triplicate (a) and biplicate (B) Y. hanburyi Morphotype 3. Sample L-D3xt. a, PUM92068, also partly shown in Plate 2, figure 5. b, PUM92069. Yunnanellina hanburyi Morphotype 2 Plate 1, figures 16-25; Plate 2, figures 4, 6, 8; Text-figures 14-15 Diagnosis. Yunnanellina in which all specimens possess a connectivum. A narrow and deep septalium is common. Description. In this morphotype, the uni- and biplicate specimens are predominant. In the uniplicate form, the dental cavity is larger than that in Morphotype I . Dental plates are well developed in all forms. The septalium is usually narrow and deep, V-shaped or vase-shaped. In this case, crural bases are usually not located at the junction of the septalium and the hinge plates but lie outward in the hinge plates. Some specimens from sample C-C may show a broad and rounded septalium. A connectivum is present in all forms. In the uniplicate form, the connectivum may be herringbone-shaped in stratigraphically higher specimens; it may be plane or slightly concave in stratigraphically lower specimens. Material. In total about 400 specimens, most of which are in a good state of preservation : upper part of the Changlungchieh Shale, near Laojiangchong village: L 1 5/0-55 (one specimen); L15/1-7 (three specimens); L17 (about forty specimens); LI 7/ IT (about ten specimens on slab); LI 9/0 (seventeen specimens); L 19/0-0-2 (nine specimens); L 19/0-2-0-4 (thirty specimens); LI 9/0-35 (three specimens); L 19/0-4—0-6 (three specimens); L20/1-7-2-0 (two specimens); near Chenjiayuan village: C-G (eighteen specimens); C-E (sixty-eight specimens); C-D (ninety specimens); C-C (one hundred and twenty specimens). Yunnanellina hanburyi Morphotype 3 Plate 1, figures 26-29 ; Plate 2, figure 5; Text-figure 16 1938 Yunnanellina hanbruyi mut. sublata Tien, pp. 45 — 46, pi. 6, figs 3-5. 1938 Yunnanellina cf. triplicata Grabau; Tien, p. 46, pi. 6, fig. 8. 1938 Yunnanellina triplicata var. latiformis Tien, p. 47, pi 6, fig. 6. 1938 Yunnanellina obesa Tien, p. 48, pi. 6, fig. 7. MA XUEPING: Y U N N AN EL LI N A FROM SOUTH CHINA 401 LI 7, uniplicate (PUM92070) and triplicate (PUM92071); L17/1T (PUM92073); C-G (PUM92074); C-H, biplicate (PUM92075) and C-C, triplicate (PUM92076). Diagnosis. Specimens of Y. hanburyi with a semiconnectivum and usually a narrow and deep septalium. Description. Shell usually small All specimens so far found are bi- and triplicate. Internal structure is weak. Dental plates are well developed. Septalium is usually narrow and deep. A semiconnectivum is present in all forms. text-fig. 18. Slratigraphica! distribution of hanburyi and correlation of the Xikuangshan (1) an£* Jiangjiaqiao (2) sections. Data of black dots are adopted from Houer al. (1988). Legend: 1. shale; 2. mudstone; 3, marl; 4. limestone; 5, nodular limestone; 6, limestone with argillaceous bands; 7, oolitic limestone. Sinopora sp. o Cyrtiop sis d avid soni o Spin a try]) a sp. ■oC. graciosa o P ly chomaletoechia shetienchiaoensis o C- spiriferoides Cyrlospirifer sp. o Alhyi o o Produclellana sp. a o Cyrlospirifer subextensus o C- pekinensis o Ply chomaletoechia sp- 402 PALAEONTOLOGY, VOLUME 38 (2) ±k± lit - 50 - 40 - 30 - 20 - 10 - 0m L21 L19 „ LI 5 '1 a 3 o <3 L-D3Xt & a ft* L12 4! L10 | L9 o L5 o o H 6 © ft. &- 3Z”Z a FTT J_--L XT 1 1 77 TT , / / / ) 7 r / l , ( i , , / x / / , l , / , , / / , / , . / ~T / , / 7 , / / , / , , / , / / , / , , / , / f , / , , / / / , , / / / f , / , / 7 / , , / 7^ / , / > ( x / , / , / , / / , / , / / /_ / ^ i > , * .i i XL! H i » i = = _L = 1 = ; = I = 1 = 1 , / , / ( / , , / , / / , / . / / / , / , f l / , ( , , / . / / / — ~~ “7 7" J , / , / / , / , / . / ^ ■ r i T7T C-A 0J Ch o _c a. C-B s C-C 6 C-D ^ O rC a u C-E g C-F C-G a> C-H 4- > o X! a 5- l o C7 C4 3 -O e a Cl text-fig. 18. Stratigraphical distribution of Y.hanburyi and correlation of the Xikuangshan (1) and Jiangjiaqiao (2) sections. Data of black dots are adopted from Hou et al. (1988). Legend: 1, shale; 2, mudstone; 3, marl; 4, limestone; 5, nodular limestone; 6, limestone with argillaceous bands; 7, oolitic limestone. MA XUEPING: YUNNANELLINA FROM SOUTH CHINA 403 Material. Thirty-one specimens from the Tutzutang Member, near Laojiangchong village: L-D3xt (twenty specimens); and from near Chenjiayuan village: C-A (eleven specimens). VARIATION IN THE CONNECTIVUM AND SEPTALIUM WITH TIME Morphotype 1 . In the biplicate form, the connectivum is not present, or it occurs as a very short inward extension from the hinge-plate. This has been verified in the five sectioned specimens from the three stratigraphical sections (Text-fig. 17). In the uniplicate form, the connectivum is very varied, as discussed above for sample C-H. The only sectioned triplicate specimen possesses a semiconnectivum. The septalium in all the forms is broad and rounded. Morphotype 2. The connectivum is present in all the specimens. It is usually planar in the biplicate and triplicate forms. The uniplicate form of this morphotype may be further subdivided into two varieties. The stratigraphically lower variety is characterized by a planar connectivum as seen in specimens from both the Xikuangshan and Chongshanpu sections. The stratigraphically higher variety is characterized by a herringbone-shaped connectivum. The septalium of this morphotype is usually narrow and deep in the lower part, but becomes broader higher up the stratigraphical section. Morphotype 3. This morphotype possesses a semiconnectivum. The septalium is variable in shape, usually V- to U-shaped in cross-section. STRATIGRAPHY AND DISTRIBUTION OF Y. HANBURYI In central Hunan, the Upper Devonian includes the Shetianqiao and the Xikuangshan formations. The Xikuangshan Formation is composed of three members (Tien 1938). The lower member is the Chang lungchieh Shale, about 100 m thick, which consists of grey-green shales, thinly-bedded marls and minor limestones. The lower part possesses abundant corals and a common rhynchonellid, Hunanotoechia tieni (Ma, 1993), of late Frasnian age. The upper part (about 50 m thick) hosts abundant Yunnanellina hanburyi and cyrtospiriferids. The overlying member is the Tutzutang Limestone (about 2CM10 m thick), in which Y. hanburyi is present in its lower part. The uppermost member is the Makunao Limestone (about 200 m thick), which is rich in brachiopods, including cyrtospiriferids and Ywmanella. It is separated from the Tutzutang Limestone by the thin Nitangli iron ore bed (1-2 m thick). Yunnanellina hanburyi first occurs about ten metres above the Frasman/Famennian boundary as found in the Xikuangshan, Jiangjiaqiao and Chongshanpu sections (Text-fig. 18). The boundary can be recognized from the first occurrence of Icriodus deformatus Han, a conodont which is present in the lower triangularis Zone in South China (Jia et al. 1988). But, at the Xikuangshan section, it is associated with I. iowaensis , a species beginning to occur in the middle triangularis Zone in South China (Bai Shunliang, oral communication). The occurrence of Palmatolepis glabra in bed LI I (Hou et al. 1988) may indicate the upper crepida Zone. The upper occurrence of Y. hanburyi probably still lies within the upper crepida Zone because of the presence of this zonal species at the base of the Tutzutang Member (Hou et al. 1988). This is further supported by data from the Qidong section in Hunan Province, where the Yunnanellina fauna is displaced by the Ywmanella fauna at the top of the crepida Zone (Wang and Bai 1988). Therefore, the entire range of Y. hanburyi may well coincide with the upper crepida Zone. At the Jiangjiaqiao section, no conodont data are available, but there are abundant brachiopods, including Y. hanburyi, cyrtospiriferids and productids. Using the three morphotypes of Y. hanburyi, it is possible to correlate this section with the Xikuangshan section. Obviously, the rate of sedimentation in the Jiangjiaqiao area was much higher than that in the Xikuangshan area because the former sequence is much thicker. 404 PALAEONTOLOGY, VOLUME 38 CONCLUSIONS The variations in both external and internal structures of Yunnanellina hanburyi (Davidson, 1853) have been thoroughly described based on abundant specimens collected from central Hunan. It is concluded that the other nominal species and subspecies founded later from South China are all junior synonyms of Y. hanburyi. This demonstrates that care must be taken in using external features alone to establish new species, especially when few specimens are to hand. Internal structure is usually considered to be reliable feature for taxonomy, but some species, like Yunnanellina hanburyi , may show a wide range of variations in the internal structure, even in specimens from the same sample. Better understanding of this kind of species (variable in both external and internal structure) can only be achieved through the study of numerous specimens whose locality and stratum are clearly known. When the morphology of a brachiopod is well understood, it could, potentially, enable finer subdivision of its stratigraphical range. Acknowledgements. I thank Professor Bai Shunliang (Department of Geology, Peking University) who identified the conodonts and reviewed the first draft of this paper; Li Xingqian and Gan Xuehong of Peking University, who aided in field and partly in laboratory work. An anonymous referee is greatly thanked for critically reviewing the typescript and suggesting many improvements to the paper. This work was supported by grants to Professor Bai from the State Education Committee Foundation and National Natural Science Foundation of China. REFERENCES davidson, t. 1853. On some fossil brachiopods, of the Devonian age, from China. Quarterly Journal of the Geological Society , London , 9, 353-359. fang yunsen and zhu xiangshui 1974. Brachiopoda. 287-479. In geological bureau of yunnan province (ed. ). Fossil Atlas of Yunnan. Yunnan People’s Press, Vol. 1, 864 pp.; Vol. 2, 296 pis. [In Chinese]. grabau, A. w. 1923-24. Stratigraphy of China , Part /, Palaeozoic and older. Geological Survey of China, 528 pp. — 1931. Devonian Brachiopoda of China. Palaeontologia Sinica , Series B , 3, 1-454. hou hong-fei, ji qiang and wang jinxing 1988. Preliminary report on Frasnian-Famenman events in South China. 63-69. In mcmillan, n. j., embry, a. f. and glass, d. j. (eds). Devonian of the World. Memoirs of the Canadian Society of Petroleum Geologists , 14 (3). JIA HUI-CHEN, XIAN SI-YUAN, YANG DE-LI, ZHOU HUAI-LIN, HAN YING-JIAN, CHEN ZHEN-HUAN, WANG JIN-XING, wang rui-gang, wang shi-tao, zhang zhen-xian and wei ming 1988. An ideal Frasnian/Famennian boundary in Ma-anshan, Zhongping, Xiangzhou, Guangxi, South China. 79-92. In mcmillan, n. j., embry, a. f. and glass, d. j. (eds). Devonian of the World. Memoirs of the Canadian Society of Petroleum Geologists , 14(3). kayser, e. 1883. Devonische Versteinerungen aus dem sudwestlichen China. 75-102. In Richthofen, f. p. w. von. China, Volume 4. D. Reimer, Berlin, 288 pp. kuhn, o. 1949. Lehrbuch der Palaeozoologie. E. Schweizerbartsche, Stuttgart, v-f 326 pp. li you-xin 1987. A new species of Genus Yunnanellina from Upper Devonian of Lingling, Hunan. Acta Palaeontologia Sinica , 26, 323-325. [In Chinese with English summary], liu zu-han, tan zheng-xiu and ding ya-ling 1982. Brachiopoda. 172-216. In hunan geological bureau (ed.) Palaeontological Atlas of Hunan. Geological Publishing House, Beijing, 997 pp. [In Chinese]. ma xue-ping 1993. Hunanotoechia : a new Late Devonian rhynchonellid brachiopod from Xikuangshan, Hunan, China. Acta Palaeontologica Sinica , 32, 716-724. [In Chinese with English summary], MOORE, r. c. (ed.) 1965. Treatise on invertebrate paleontology. Part H. Brachiopoda. Geological Society of America and University of Kansas Press, Boulder, Colorado and Lawrence, Kansas, 927 pp. ozaki, k. 1939. Some Lower Carboniferous brachiopod fossils from central Hunan, China. Institute of Natural Science of Shanghai , Memoir 2, 225-252. rzhonsnitskaya, m. a. 1956. Semeystvo Pentameridae i sem. Camarotoechiidae. Materiaty po Paleontologii Novy Semeystva i Rody, Novaya Seriya , 12, 49-50, 53-55. [In Russian]. MA XUEPING: YUNNANELLINA FROM SOUTH CHINA 405 sartenaer, p. 1969. Late Upper Devonian (Famennian) rhynchonellid brachiopods from western Canada. Bulletin of the Geological Survey of Canada, 169, 1-269. — 1971. Redescription of the brachiopod genus Yunnanella Grabau, 1923 (Rhynchonellida). Smithsonian Contributions to Paleobiology, 3, 203-218. tien, c. c. 1938. Devonian Brachiopoda of Hunan. Palaeontologia Sinica, New Series B, 4, 1-192. wang K. and bai shunliang 1988. Faunal changes and events near the Frasnian-Famennian boundary of South China. In McMillan, n. j., embry, a. f. and glass, d. j. (eds). 71-78. Devonian of the World. Memoirs of the Canadian Society of Petroleum Geologists, 14 (3). wang Y., jin y. G. and fang D. w. (eds). 1964. Brachiopod fossils of China. Science Press, Beijing, 111 pp., 136 pis. [In Chinese]. xu han-kui 1979. The brachiopod Yunnanella-Yunnanellina fauna from the Upper Devonian of Hunan. Acta Stratigraphica Sinica, 3, 123-126. [In Chinese], yang de-li, ni shi-zhao, chang mei-li and zhao ru-xuan 1977. Brachiopoda. 303-470. In HUBEI institute of geosciences et al. (eds). Palaeontological Atlas of Central-Southern China. Geological Publishing House, Beijing, 856 pp. [In Chinese]. Typescript received 27 January 1993 Revised typescript received 28 October 1993 MA XUEPING Department of Geology Peking University Beijing, 100871 China CHAROPHYTE BIOSTRATIGRAPHY OF THE PURBECK AND WEALDEN OF SOUTHERN ENGLAND by MONIQUE FEIST, ROBERT D. LAKE and CHRISTOPHER J. WOOD Abstract. The distribution of charophyte assemblages in the Purbeck and Wealden sequence of southern England has been established from borehole samples from the Weald and from outcrop material collected in Dorset, Wiltshire and on the Isle of Wight. Of the twenty-one taxa represented, three are new: Globator rectispirale, Clypeator britannicus and Sphaerochara andersonii ; three new combinations are proposed : Globator praecursor, Globator protoincrassatus and Atopochara triquetra. The Chinese Valanginian species Flabellochara xiangyunensis is recognized for the first time in Europe. In the context of the phylogeny of the Family Clavatoraceae, G. rectispirale represents the Jurassic ancestor of the Globator lineage and a separate origin is suggested for both Flabellochara and Clypeator. The correlations established with the Tethyan realm locate the Jurassic-Cretaceous boundary within the Lulworth Formation of the Purbeck Limestone Group; in this context, the whole ‘Purbeck’ sequence of Swindon (Wiltshire) is attributed to the Upper Tithonian. The distribution of Clavatoraceae indirectly confirms the contemporaneity of the Boreal Galbanites kerberus and Titanites anguiformis with the Tethyan ‘ Durangites' ammonite zones. For the Wealden Supergroup, the charophyte data affirm the Hauterivian-Barremian boundary at the base of the upper division of the Weald Clay and the Upper Barremian is identified at the base of the Vectis Formation of the Isle of Wight. The charophytes of the Purbeck and Wealden successions of southern England have received little attention since they were first recognized by Forbes (1851) in the Purbeck Beds of Mupe Bay (Dorset). A preliminary report on the Purbeck Beds Characeae was published by Reid and Groves (1916), who established the genus Clavator , subsequently discussed by Groves (1924). The only detailed study of Purbeck charophytes to date has been by Harris (1939) who reviewed previous work and provided descriptions of assemblages from the Dorset coast and inland sections, as well as from the Vale of Wardour and quarries at Swindon (Wiltshire). More recently. Barker et al. (1975) discussed the depositional environment of the Charophyte Chert at the base of the Great Dirt Bed, 4 m above the base of the Purbeck Beds at Portesham Quarry (Dorset) and described the supposed new species Clavator westii from indeterminate Clavatoracean material. Harris (1939), on the basis of studying ‘Middle’ and ‘Upper’ Purbeck charophyte associations, stated that they did not exhibit major evolutionary changes and concluded that ‘ these beautiful little fossils [gyrogonites] are likely, in general, to have only slight stratigraphic value’. In contrast to this view, further research on charophyte gyrogonites, following the pioneer work of Peck (1957) and Grambast (1972, 1974), has revealed their stratigraphical importance for dating and correlating Cretaceous and Palaeogene non-marine deposits. Preliminary studies of charophytes recovered from cored boreholes in the Weald showed that part of the Purbeck sequence could be attributed to the Berriasian Stage and that the upper part of the Weald Clay of the Wealden Supergroup belonged to the Barremian Stage (Feist in Lake et al. 1987). In this paper we present the results of our research to date on the charophyte biostratigraphy of the Purbeck and Wealden outcrop and subcrop successions of southern England. These results have been directly integrated with the ostracod zonal and faunicycle scheme of Anderson (1985), as charophytes and ostracods are commonly found associated in the same sample. We also review evolutionary trends among the charophyte family Clavatoraceae. (Palaeontology, Vol. 38, Part 2, 1995, pp. 407—142, 2 pls| © The Palaeontological Association 408 PALAEONTOLOGY, VOLUME 38 MATERIALS The greater part of the charophyte specimens was separated from the residues of microsamples taken from cored boreholes in the Weald; most were taken from the ostracod collection of the late Dr F. W. Anderson at the British Geological Survey. For the Dorset, Isle of Wight and Swindon localities, new material collected by M. Feist from exposure has been studied, in addition to specimens from the Natural History Museum (London) and Senckenberg Museum (Frankfurt am Main, Germany). The borehole material from the Weald, the types of the new taxa described herein and the specimens figured in Plate 1, figures 1-2 and 4-8 are housed at the British Geological Survey, Keyworth, UK; the specimens figured in Plate 1, figures 16-17 at the Natural History Museum, London, UK; and the specimen figured in Plate 1, figure 9 at the Senckenberg Museum, Frankfurt am Main, Germany. The other samples are deposited at the Laboratoire de Paleobotanique, Universite de Montpellier II, France, under the symbol CF. EVOLUTIONARY TRENDS AMONG THE CL A V ATOR ACEAE The Clavatoraceae is a Mesozoic charophyte family characterized by the gyrogonite having a supplementary calcified cover of vegetative elements, known as the utricle. As shown by Grambast (1974) in his analysis of three phylogenetic lineages through the Cretaceous, it is the utricle that underwent evolutionary change. These lineages represent such remarkable examples of progressive evolution that they have been interpreted by Martin-Closas and Serra-Kiel (1991) as ‘evolutionary species’ ( sensu Wiley 1978). However, this concept has no formal taxonomic status and is not appropriate to biostratigraphical studies. The Clavatoraceae are subdivided into three subfamilies, according to the wall structure and the symmetry of the utricle. In the Echinocharoideae and Atopocharoideae, the utricle wall is composed of only one layer of three symmetrically arranged cells. In the former subfamily, the utricle comprises unjoined cells, whereas in the latter the cells are coalescent and entirely cover the gyrogonite inside. Our material comprises three representatives of the Atopocharoideae: the genera Globa tor , Perimneste and Atopochara. The Clavatoroideae differ from the two former subfamilies by the complexity of the utricle wall, which comprises two layers, with internal canals in the most evolved species, and by a bilateral symmetry. A three-fold symmetry can become superimposed secondarily, as in Triclypella. Most Clavatoraceae from southern England belong to this subfamily, namely Nodosoclavator , Clavator , Flabellochara , Clypeator, Triclypella and Ascidiella. The new data from the Purbeck charophyte floras of southern England complement existing data on the Globator lineage, and allow us to propose a separate origin for the two genera of the Flabellochara-Clypeator lineage (Grambast 1970, 1974). Our new data for P. horrida and A. triquetra do not modify the evolutionary succession outlined by Grambast (1967) for the Perimneste- Atopochara lineage, and so will not be discussed in this section. Globator lineage This series shows the evolution from the Tithonian Globator rectispirale to the Barremian G. trochiliscoides by reduction in the number of utricle cells and by progressive acquisition of spiralling (PI. 1, figs 1—8). Only the oldest forms have so far been found in southern England. G. rectispirale sp. nov. is the oldest and most primitive representative of the Globator lineage; each utricle comprises twenty-four vertical cells, without any indication of spiralling, when viewed both laterally and apically (PI. 1, figs 1, 5). It is found in the Fairlight Borehole at 317-6-317-9 m. As reported below, the occurrences of this form outside the British Isles, have all been attributed to the Upper Tithonian. G. praecursor (Mojon) comb. nov. occurs at 2960-2963 m in the Fairlight Borehole, and equivalent beds in the Warlingham, Broadoak and Brightling boreholes. It has the same utricle structure with twenty-four cells, but the upper elongated cells have begun to spiral (PI. 1, figs 2, 6). FEIST ET A L.\ CHAROPH YTE BIOSTRATIGRAPHY 409 This form has been dated as Lower Berriasian in the Goldberg Formation in the Jura Mountains, where it is the index species of Mojon’s Zone Ml. Accordingly, the Jurassic-Cretaceous boundary can be recognized in southern England between the beds with G. rectispirale and with G. praecursor, near to the base of the Purbeck sequence. G. protoincrassatus (Mojon) nov. comb, occurs at 293-2-293-5 m in the Fairlight Borehole, as well as in Bed 70 of Clements (in Cope et al. 1969) of the higher part of the Soft Cockle Member of the Lulworth Formation of Dorset. The utricle is still composed of twenty-four cells, but the three basal cells are shorter and the upper ones have become even more strongly spiralled (PI. 1, figs 4, 8). This taxon is the index-species of Mojon’s Zone M2, considered to be Lower Berriasian. The subsequent stages of the Globator lineage, which have been reported from Spain (Grambast 1966, 1974; Martin-Closas and Grambast-Fessard 1986) and North America (Peck 1957) are missing in the Purbeck-Wealden succession of the British Isles; this absence may be explained by a local excess in salinity and lack of calcium carbonate in Hastings Beds and Weald Clay times. Flabellochara and Clypeator lineages The subdivision of the Flabellochara-Clypeator lineage proposed here differs from Grambast’s phylogeny, in that Clypeator is not considered to be a descendant of Flabellochara because at various localities it has been found that Flabellochara appeared later than Clypeator. However, the main phylogenetic tendencies are the same as those demonstrated by Grambast (1970). In the oldest of the Clavatoraceae, Nodosoclavator sp., only the internal layer of the utricle is developed, and is composed of nodules covering the spiral cells of the gyrogonite. Nodosoclavator appeared in the Oxfordian (Feist and Schudack 1991) and persisted until the Barremian. In the Upper Tithonian, Clypeator (C. discordis) appeared. In this genus, the central basal cell of each side of the utricle is subdivided and the lateral pore occupies a central position (PI. 2, figs 5-6). The evolutionary trend continued by lengthening and spiralling of the upper basal cells, from the late Tithonian, when C. discordis appeared, to the Albian C. caperatus and C. lusitanicus. Triclypella (PI. 2, figs 1-3) represents a side branch of Clypeator (Grambast 1970). In the present state of knowledge of the few documented Upper Jurassic charophyte floras, the only possible transitional form between Nodosoclavator and Clypeator would be Echinochara peckii. However, the latter differs fundamentally from Clypeator in its utricle structure, built on a six-rayed mode of symmetry (Peck 1957; Grambast 1974), instead of the bilateral symmetry of Clypeator, and devoid of a nodular internal layer. The Clypeator and Clavator-Flabellochara lineages seem to have derived from an as yet undiscovered common Late Jurassic ancestor. The Clavator-Flabellochara lineage starts with Clavator aft', reidii , found in the Upper Tithonian; ‘aff. ’ indicates that the utricle is not yet completely constituted (PI. 1, figs 9-10); the vegetative cells do not reach the apex of the ‘nodosoclavatoroid gyrogonite’ (sensu Schudack 1990, for Nodosoclavator). In the Lower Berriasian Clavator reidii , the two-layered utricle is attained ; it consists of vertical cells originating from a basal very short cell and joining themselves at the apex (PI. 1, figs 11-13). Within populations of C. reidii, incompletely constituted utricles morphologically similar to C. aff. reidii are commonly found. However, these morphotypes do not represent the Tithonian species, because, in the latter, the utricle never reaches the apex of the gyrogonite, whereas, in the Berriasian, populations of Clavator generally include typical specimens with complete utricles. Such populations are found notably in the Hils Serpulit of north-western Germany (Feist and Schudack 1991). The immature morphotypes can be regarded as reminiscent of the ancestral Tithonian stage. Flabellochara was derived from Clavator by addition of two cells on each adaxial side of the utricle and by the development of radiating, instead of vertical, upper cells. In Flabellochara (PI. 1, figs 14-21), the small cells surrounding the lateral pores always remain small, unlike in Clypeator. 410 PALAEONTOLOGY, VOLUME 38 SYSTEMATIC PALAEONTOLOGY The three families in existence during Late Jurassic to Early Cretaceous times are all represented. As commonly found for this time, Clavatoraceae are dominant, both in number of species and abundance, the Porocharaceae and Characeae remaining small and unornamented forms. Overall, twenty-one species have been identified in our material. Family porocharaceae Grambast, 1962 Subfamily porocharoideae Grambast, 1961 Genus porochara Madler, 1955 Porochara maxima (Donze) Donze, 1958 Plate 2, figure 21 1955 Aclistochara maxima Donze, p. 289, pi. 13, figs 6-7. 1958 Porochara maxima Donze, p. 180. Distribution and range in southern England. Weald: Warlingham Borehole (6121 m), upper part of the Broadoak Calcareous Member, Lulworth Formation. This level was referred to the Netherfield ostracod faunicyle (Anderson in Worssam and Ivimey-Cook 1971 ; Anderson 1985). The Berriasian age of this horizon is deduced from records of the species from other areas. Other occurrences. Berriasian of the Jura (Donze 1955; Mojon 1989), Spain (Brenner 1976; Schudack 1987a) and Sardinia (‘ Musacchiella maxima ’) of Colin et al. (1985). EXPLANATION OF PLATE 1 Figs 1, 5. Globator rectispirale sp. nov. Fairlight Borehole, Sussex, 3 1 7-6 — 3 1 7-9 m; Broadoak Calcareous Member. 1, MPK 8888, para type; apical view. 5, MPK 8919, holotype; lateral view. Figs 2, 6-7. G. praecursor (Mojon) comb. nov. Fairlight Borehole, Sussex; Broadoak Calcerous Member. 2, MPK 8889; depth 296 0-296-3 m; apical view. 6, MPK 8920; depth 2960-296-3 m; lateral view. 7, MPK 8891; depth 293-2-293-5 nr; lateral view. Figs 3-4, 8. G. protoincrassatus (Mojon) comb. nov. 3, CF 2911-1; Swanage, Dorset; upper Soft Cockle Member; lateral view. 4, 8, Fairlight Borehole, Sussex, 293-2-293-5 m; Broadoak Calcareous Member. 4, MPK 8890; apical view. 8, MPK 8921; lateral view. Figs 9-10. Clavator aff. reidi Groves. Exposure III, Town Gardens Quarry, Swindon, Wiltshire; Chara Marls; lateral views; 9, SMF 44798. 10, CF 279 1 b- 1 . Figs 11-13. Clavator reidi Groves. Fairlight Borehole, Sussex, 280T-280-4 m; Broadoak Calcareous Member; lateral views. 11, MPK 8892. 12, MPK 8895. 13, MPK 8896. Figs 14—15. Flabellochara grovesi (Harris). Lulworth Formation, Plant and Bone Beds Member; lateral views. 14, MPK 8893; Fairlight Borehole, Sussex, 2734 m. 15, MPK 8894; Broadoak Borehole, Sussex, 71-50-72-00 m. Figs 16-17. Flabellochara grovesi (Harris). NHM V 26181-3 and NHM V 26181-4; Poxwell Road cutting, Dorset; Bed 33; lateral views. Figs 18-21. Flabellochara xiangyunensis Wang et ah Wadhurst Clay; lateral views. 18-19, Wadhurst Park No. 3 Borehole. 18, MPK 8897; 7-3-7-6 m. 19, MPK 8898; 6-7-7 0 m. 20, MPK 8899; Glynleigh Borehole, 59-00-59-50 m. 21, MPK 8900; stream section near Warninglid. All x 45, except figs 14, 19 and 20, x48, and fig. 18, x43. PLATE 1 FEIST et al., charophytes 412 PALAEONTOLOGY, VOLUME 38 Family clavatoraceae Pia, 1927 Subfamily atopocharoideae Peck, 1938, emend. Grambast, 1969 Genus globator Grambast, 1966 Globator rectispirale Feist, sp. nov. Plate 1, figures 1-5 1971 Globator maillardi (Saporta); Ramalho, pi. 32, fig. 7. 1981 Globator maillardi Saporta; Benest, p. 1288. 1985 Globator cf. maillardi De Saporta; Benest, p. 363. 1989 Globator maillardi praecursor Mojon, pars, Mojon in Detraz and Mojon, p. 54, lines 8-9. Holotype. MPK 8919, British Geological Survey, Keyworth (PI. 1, fig. 5). Paratype. MPK 8888 (PI. 1, fig. 1). Type horizon and locality. Lulworth Formation, Broadoak Calcareous Member, Fairlight Borehole, Sussex, 3 17-6-3 17-9 m. Derivation of name. From the shape of the upper cells of the utricle, which are quite straight in the new species, but always spiral to some extent in other Globator representatives. Diagnosis. Utricle of Globator composed of three units, each comprised of one central basal cell, bearing three upper cells, flanked by two lateral basal cells each bearing an upper cell. Length of the central basal cells equal to 50-52 per cent, of the utricle length. Upper cells straight, and do not reach the apex. General shape globular to ovoid. Dimensions: 775-1025 pm long, 675-825 pm wide; L/W ratio varying from 11 to 14. Remarks. This Tithonian species of Globator differs from other representatives of the genus by its utricle with very large basal cells and completely straight upper cells. It represents the most primitive grade of the Globator lineage. Distribution and range in southern England. Weald: Fairlight Borehole (3 17-6-3 17-9 m), Broadoak Calcareous Member, Lulworth Formation, below the correlative of the Mountfield Adit Limestone. Mojon's identified ostracods in the associated residue ( Cypridea dunkeri papulata (aberrant), Damonella pygmaea , Fabanella boloniensis , Mantelliana purbeckensis and Rhinocypris jurassica) indicate Ostracod Assemblage 1 of Anderson (1985). Only known record to date. Other occurrences. Algeria: Chellala Mountains, Mahjouba Formation (Tithonian), from 50-60 m below beds with an A2/A3 calpionellid subzonal assemblage (Benest 1981, 1985). Southwest Portugal: Brouco section, Sintra area, Tnfravalanginian’ beds with Anchispirocyclina (Ramalho 1971). These beds were referred to the Lower Cretaceous on ostracod evidence; however, Mantelliana purbeckensis , the species on which this correlation is based (Rey et al. 1968), appeared in the Weald in the ostracod assemblage of the Gypsiferous Beds (Anderson 1985). The former beds are now considered to be Upper Jurassic (Rey, pers. comm. 1991), which agrees with the presence of Upper Tithonian calpionellids in the lower Anchispirocyclina beds in the Algarve (Rey 1982, 1983). Globator praecursor (Mojon) comb. nov. Plate 1, figures 2, 6-7 1987 Globator maillardi (Saporta); Feist in Lake et al., p 14. FEIST ET A L. \ CHAROPHYTE BIOSTRATIGRAPHY 413 1989 Globator maillardi prae cursor ; Mojon in Detraz and Mojon, p. 53, figs 5m-5r, non p. 54, lines 8-9. 1991 Globator maillardi prae cursor'. Feist and Schudack, p. 502. Holotype. Detraz and Mojon (1989, fig. 5m). Emended diagnosis. Utricle of Globator composed of three units each comprised of one central basal cell, bearing three upper cells, flanked by two lateral basal cells each bearing an upper cell. Length of central basal cells equal to 33-34 per cent, of the utricle length. Upper cells oblique, slightly curved and reaching the apex. General shape ovoid. Dimensions: 850-1000 /nn long, 600-700 //in wide. L/W ratio varying from 1-4 to 1-8. Remarks. This form is remarkably stable in its different morphological characters in localities as distant as Jura, north-west Germany and southern England. A combination of this wide geographical distribution and a very short stratigraphical range makes G. praecursor a charophyte index for the basal Berriasian. These factors combine to justify raising this form to specific rank. Distribution and range in southern England. Weald: Warlingham Borehole (625- 1 m), Fairlight Borehole (296 0-296-3 m), Broadoak Borehole (111 50—1 1 2 00 m) and Brightling No. 27 Borehole (270 6 m). All occurrences were in the Broadoak Calcareous Member, Lulworth Formation; in the Broadoak Borehole they were from immediately above the Mountfield Adit Limestone. Mojon’s identifications of the ostracods in the Fairlight Borehole sample include Cypridea dunkeri inversa and Fabanella bo/oniensis, indicating Ostracod Assemblage 2. Other occurrences. French and Swiss Jura: G. praecursor is the index species of the Lower Berriasian Ml charophyte Zone of Mojon (in Detraz and Mojon 1989), the base of which yields the Lower Berriasian marine ostracod Protocythere revili and palynofloras of Berriasian affinities. Germany, Lower Saxony Basin: lower part of the Serpulit (Feist and Schudack 1991). Globator protoincrassatus (Mojon) comb. nov. Plate 1, figures 3^1, 8 1989 Globator maillardi protoincrassatus Mojon in Detraz and Mojon, p. 55, figs 5E-5L. 1991 Globator maillardi protoincrassatus '. Mojon et al., p. 502. Holotype. Detraz and Mojon (1989, fig. 5e). Emended diagnosis. Utricle of Globator composed of three units each comprised of one central basal cell, bearing three upper cells, flanked by two lateral basal cells each bearing an upper cell. Length of central basal cells equal to 29-30 per cent, of the utricle length. Upper cells slightly spiral, joining at the apex. Dimensions: 850-1 150 pm long, 600-850 pm width. L/W ratio varying from LI to 1-7. Remarks. This form differs from G. praecursor by its shorter basal cells and more acute curvature of its upper cells, and from G. maillardi (Saporta) Grambast, by its larger basal cells and more twisted upper cells. The range of the new species is restricted to the Lower (not basal) Berriasian. The distinctive morphology and short stratigraphical range of Mojon’s subspecies support it being raised to specific rank. Distribution and range in southern England. Weald: Fairlight Borehole (293-2—293-5 m), Broadoak Calcareous Member, Lulworth Formation. Mojon identified Cypridea dunkeri inversa and Fabanella boloniensis from the same residue, indicating Ostracod Assemblage 2. Dorset: Swanage, upper Soft Cockle Member, bed 70 of Clements (in Cope et al. 1969). 414 PALAEONTOLOGY, VOLUME 38 Other occurrences. French Jura : G. protoincrassatus is the index species of the Lower Berriasian M2 charophyte Zone of Mojon (in Detraz and Mojon 1989), dated by ammonites (in a marine intercalation) to the Pseudosubplanites grandis Zone, P. grandis Subzone (Clavel et al. 1986; Hoedemaeker 1991). Germany: Lower Saxony Basin, upper part of the Serpulit (Feist and Schudak 1991). Genus perimneste Harris, 1939 Perimneste horrida Harris, 1939 1939 Perimneste horrida Harris, p. 54, pis 13-15; pi. 16, figs 6, 8-9. Distribution and range in southern England. According to Harris (1939) the species is common in the ‘Middle’ and ‘Upper Purbeck Beds’ of Dorset. The material of this species published by Harris and preserved at the Natural History Museum, London, comprises predominantly vegetative remains. Utricles are present at Durdle Door and Moigne Down. Other occurrences. This species is common in the Berriasian of the Jura Mountains (Donze 1958; Mojon and Strasser 1987), Spain (Brenner 1976; Schudack 1987a) and Germany (Schudack 1990; Feist and Schudack 1991). It is unknown outside Europe. Genus atopochara Peck, 1938, emend. Peck, 1941 Atopochara triquetra (Grambast) comb. nov. Plate 2, figure 9 1967 Atopochara trivolvis Peck, pars; Grambast, pi. 3, fig. 14. 1968 Atopochara trivolvis triquetra Grambast, p. 8, pi. 3, fig. 16. 1981 Atopochara trivolvis Peck triquetra Grambast; Musacchio, p. 474, pi. 5, fig. 9. 1981 Atopochara trivolvis triquetra Grambast; Zhang et al., p. 153, pi. 1, figs 1-6. 1982 Atopochara trivolvis triquetra Grambast; Wang and Lu, p. 94, pi. 2, figs 9-13. 1982 Atopochara trivolvis Peck ssp.; Feist in Huckriede, p. 187, pi. 6, fig. 4. 1983 Clypeator europeus Grambast, pars', Kampmann, pi. 18, fig. la. 1985 Atopochara trivolvis triquetra Grambast; Jiang et ah, p. 166, pi. 1, fig. la-c 1986 Atopochara trivolvis subsp. triquetra Grambast; Martin-Closas and Grambast-Fessard, p. 38, pi. 8, figs 7-12. 1987a Atopochara trivolvis triquetra Grambast; Schudack, p. 135. pi. 6, figs 1-4. 19876 Atopochara trivolvis triquetra Grambast; Schudack, p. 16, pi. 2, figs 1-5. 1987 Atopochara trivolvis subsp. triquetra Grambast; Martin-Closas and Peybernes, p. 699, fig. 2:5-6. 1988 Atopochara trivolvis triquetra (Peck) Grambast; Mojon, pi. 2, figs a-e. 1989 Atopochara trivolvis triquetra Grambast; Schudack, p. 415, pi. 2, figs 1-6. 1991 Atopochara trivolvis triquetra Grambast; Lu and Yuan, p. 377, pi. 1, figs 3-6. Holotype. C. 633. 16, Montpellier University (Grambast 1968, pi. 3, fig. 16). Diagnosis. Utricle of Atopochara , composed of three basal cells, the two left hand ones bearing three upper cells and the right hand one bearing two upper cells and, in most cases, a slight antheridial cast. Upper cells twisted. Utricle subsurface visible between cells. Utricle showing a triangular and irregular outline when seen from apex or base. Dimensions of paratypes: utricle length, 656-924 //m; utricle width 632-973 //m; average cell number, 33; average antheridia number, 3; antheridium diameter, 73-218 /im. Remarks. This form represents an evolutionary grade of the Perimneste- Atopochara lineage. During the sixty million years from the Berriasian to the Campanian, this lineage shows progressive FEIST ET AL. : CHAROPHYTE BIOSTRATIGRAPHY 415 evolution of the utricle with the condensation of the primarily ramified basal cells, the spiralization of the upper cells, and the regression and eventual disappearance of the antheridial casts, which are exceptionally preserved in Perimnesle. A. triquetra is characterized by rather distinct basal branching (portions of the underlying layer being apparent), well spiralized upper cells, and a vestigial antheridial cell persisting in one branch. Two forms can be recognized. In the primitive form, the primary basal cells may be present and the characteristic antheridial sculpture still persistent; in the advanced form, the primary basal cells have disappeared and the ancestral antheridiae are represented only by short sterile cells with a smooth surface (Grambast 1967, 1974). In A. trivolvis, the utricle structure is quite condensed (the subsurface is no longer visible) and the lower right hand fork still shows a vestigial antheridium, but reduced to a spot without any structure. A. triquetra is a species with world-wide occurrences, ranging from Lower to Upper Barremian, A. trivolvis from Upper Barremian to Lower Aptian. It seems justified to raise A. trivolvis triquetra , which differs from A. trivolvis by distinct characters as well as by its range, to species rank. Distribution and range in southern England (primitive form). Weald : Warlingham Borehole (430 0 m), lower part of the upper division of the Weald Clay, above Bed 3, associated with Ascidiella iberica and therefore considered to be Lower Barremian (see above; Feist and Grambast-Fessard 1991, p. 194, fig. 3b). Distribution and range in southern England (advanced form). Isle of Wight: Cowleaze Chme, basal part of the Vectis Formation, attributed to the Upper Barremian. Other occurrences (primitive form). Spain: Upper Flauterivian-Lower Barremian of Maestrazgo (Grambast 1968, 1974; Martin-Closas and Grambast-Fessard 1986; Martin-Closas and Salas 1988, 1989) and Cameros Basin (Schudack 1987a). The attribution to the Barremian is based on correlations of marginal non-marine Tethyan sequences with distal marine deposits dated by ammonites, nannofossils and planktonic foraminifers (Martin-Closas and Salas 1989). Switzerland: a similar dating, based on palynology, was given by Mojon and Medus (1990) for specimens of A. triquetra primitive forms, albeit identified from thin sections in which the distinctive characteristics of the species do not appear clearly (cf. Mojon 1988, pi. 1, figs g-h). Other occurrences (advanced form). Southern Jura : a recent report of this form in the succession of La Ruchere, dated by orbitoline foraminifers and palynofloras (Mojon 1988; Mojon and Medus 1990) is a new and important record, extending the known range of the San Carlos charophyte Zone of Grambast (1974), previously restricted to the Upper Barremian, into the Lower Aptian. Spain: Maestrazgo, Upper parremian-Aptian (Martin-Closas and Grambast-Fessard 1986; Martin-Closas and Salas 1989). Other occurrences (evolutionary stage not recorded). Barremian of Germany (Schudack 19876), Spain (Schudack 1987a, 1989), Argentina (Musacchio 1971, 1979) and China (Wang and Lu 1982; Jiang et al. 1985). Subfamily clavatoroideae Pia, 1927, emend. Grambast, 1969 Genus clavator Reid and Groves, 1916, emend. Harris, 1939 Clavcitor reidi Groves, 1924 Plate 1, figures 9-13 1916 Clavator Reid and Groves, p. 253, pi. 18. 1924 Clavator reidi Groves, p. 116. Remarks. This species is well represented in the Purbeck Group of southern England. Among the Clavatoraceae, it represents an early stage of the Flabellochara-Clypeator lineage, first described by 416 PALAEONTOLOGY, VOLUME 38 Grambast (1974). C. reidi seems to be derived from Nodosoclavator by the intermediate of C. aff. reidi, the utricles of which present a bilateral symmetry but are not completely closed at the apex. Distribution and range in southern England. Weald: Warlingham Borehole (6 1 2-3—6 1 4-8 m), Fairlight Borehole (273-7— 274-0 m, 280 1-280-4 m and 28 1 0—28 1 -3 m; C. aff. reidi at 296 0-296-3 m) and Broadoak Borehole (71-5-72 0 m). All occurrences in the upper part of the Broadoak Calcareous Member, Lulworth Formation. Dorset: Durdle Door, just below the Cinder Bed Member, Lulworth Formation; Worbarrow Tout, just above the Cinder Bed, Durlston Formation; Swanage, Mammal Bed to 5 m above the Cinder Bed; Poxwell Road Cutting (NHM material). Wiltshire; (identified with ‘aff.’) Swindon, exposure III of Sylvester-Bradley (1941); ‘Swindon Series’, Cythere Marls and Chara Marls. Other occurrences. Switzerland: Bienne (Jura), Lower Berriasian Goldberg Formation (Hafeli 1966; Mojon and Strasser 1987). France: Saint-Claude (Jura) and Marseille region, Purbeck Beds attributed to the Berriasian on ostracod evidence (Mojon 1989). Spain: Maestrazgo, Berriasian beds dated by dasyclads (Canerot 1979). Northern Portugal: (‘ C lava tor cf. reidi'). Lower Cretaceous (Rey et ah 1968; Ramalho 1971). Germany: Lower Saxony Basin, upper part of the Serpulit (Feist and Schudack 1991), attributed to the Berriasian by correlations with the Mlb charophyte zone established in the French and Swiss Jura; these correlations are supported by ostracod and miospore evidence (Dorhofer and Norris 1977 ; Detraz and Mojon 1989; Feist and Schudack, 1991). Genus flabellochara Grambast, 1959 Flabellochara grovesi (Harris) Grambast, 1962 Plate 1, figures 15-17 1939 Clavator grovesi Harris, p. 46, pi. 10, figs 1-12; pis I 1-12; pi. 17, figs 8-13. 1962 Flabellochara grovesi (Harris) Grambast, p. 69. Remarks. The specimens from Brouco (Portugal) attributed to F. grovesi (Ramalho 1971, pi. 33, fig. 6) have been reinterpreted by Schudack (1990) as Clypeator discordis , which co-occurs with Globator rectispirale. The beds in question, previously considered to be Lower Cretaceous, are now assigned to the Jurassic (Upper Tithonian). F. grovesi has not so far been recorded from Germany; published records of this species refer to Clypeator discordis. Distribution and range in southern England. Weald: Fairlight Borehole (273-4-273-7 m and 280T-280-4 m). The lowest occurrence is in the Robertsbridge faunicycle (‘Lower’ Purbeck), but nine faunicycles above the upper limit of Cypridea dunkeri papulata. Dorset: ‘Middle’ and ‘Upper Purbeck Beds’ of Durdle Door, Worbarrow Tout, Mupe Bay and Poxwell Road Cutting (see Appendix 2). Other occurrences. This species occurs in most of the classic ‘Purbeck’ successions attributed to the Berriasian. The species is restricted to the lower and middle Berriasian (Detraz and Mojon 1989). Jura (France and Switzerland): Goldberg Formation and Mergel-und-Kalk-Zone (Hafeli 1966; Grambast 1970; Mojon and Strasser 1987; Detraz and Mojon 1989). Spain: various areas and localities (Brenner 1976; Martin-Closas and Grambast-Fessard 1986; Schudack 1987a). Sardinia: La Cala d’lnferno, Purbeck beds (Pecorini 1969; Colin et al. 1985). Flabellochara xiangyunensis Wang et al., 1976 Plate 1, figures 18-21 1976 Flabellochara xiangyunensis Wang et al., p. 68, pi. 1, fig. 1 FEIST £7/IL:CHAROPHYTE BIOSTRATIGRAPHY 417 Remarks. This species has not previously been recorded outside China. Such wide distribution is not rare in charophytes, and other wide-ranging forms include the genera Atopochara (A. trivolvis, A. triquetra ), Peckisphaera (P. verticillata ) and Clypeator ( C . discordis). Distribution and range in southern England. Weald: Wadhurst Park No. 3 Borehole (6-7 — 7-6 m), Glynleigh Borehole (59-0-59-5 m) and Kitchenham Dam Borehole (2813 m). All occurrences are in the Wadhurst Clay. Other occurrences. Yunnan Province, China: Valanginian (Wang et al. 1976; Wang and Lu 1982). Genus clypeator Grambast, 1962, emend., 1970 Clypeator combei Grambast, 1970 Plate 2, figure 4 1970 Clypeator combei Grambast, p. 1967, pi. 3, figs 1-5. Remarks. From the records presented here, the range of C. combei , previously reported only from the Lower Barremian, extends from Upper Hauterivian into the Upper Barremian. Distribution and range in southern England. Weald: Warlingham (4304 m), Ripe ( 1 59-5—1 600 m) and Hailsham (29-5-30 0 m) boreholes. This species occurs in the beds above the main occurrences of Small- ‘ Paludina\ below (Ripe, Hailsham) and above (Warlingham) Bed 3 of the Weald Clay (Lake and Young 1978; Worssam 1978). The borehole records range from Upper Hanterivian to Lower Barremian. Isle of Wight: Cowleaze Chine, in the basal part of the Vectis Formation (Upper Barremian). Other occurrences. Spam: Maestrazgo, ‘Lower Barremian’ (Grambast 1970, 1974; Martin-Closas and Salas 1989). The attribution to Lower Barremian was by Grambast (1974), probably on the basis of charophyte evolutionary stages. Clypeator britannicus sp. nov. Plate 2, figures 7-8 Holotype. MPK 8906, British Geological Survey, Keyworth (PI. 2, fig. 8). Paratype. MPK 8905 (PI. 2, fig. 7). Type horizon and locality . Grinstead Clay (Valanginian), Kingsclere Borehole, Hampshire; 306-6 m (holotype) and 305-7 m (paratype). Diagnosis. Utricle of Clypeator characterized by the position of the lateral pores in the lower third of the utricle length, the lateral shields being composed of ten to eleven triangular cells radiating from the lateral pores. Dimensions: length varying from 475 to 625 pm, width from 500 to 625 /mi. L/W ratio varying from 0-9 to IT. Remarks. The Clypeator phylogenetic lineage (Grambast 1970) is characterized by the development of intermediate cells between the basal and upper cells. The new species represents a new grade, intermediate between the Berriasian Clypeator discordis and the Hauterivian-Barremian C. combei. In the new species, the lateral pores are in the lower third of the length of the utricle, as they are in C. discordis , but in the latter the intermediate and basal cells are approximately of the same size and rectangular shape. In contrast, C. britannicus has intermediate cells which resemble the upper ones, and which are elongated and slightly undulated. By this character, the new species resembles C. combei , but differs from it in the low position of the lateral pores. Distribution and range in southern England. Hampshire : so far recognized only from its type locality (see above). 418 PALAEONTOLOGY, VOLUME 38 Clypeator discordis Shaikin, 1976 Plate 2, figures 5-6 1970 Clypeator sp. Grambast, p. 1965, pi. 1, fig. 3. 1976 Clypeator discordis Shaikin, p. 82, figs 9-10. Distribution and range in southern England. Wiltshire: Town Gardens Quarry, Swindon. In the succession established by Sylvester-Bradley (1941), the species ranges through the major part of the Purbeck sequence; in its lowest occurrence, in the Lower Pebbly Beds, it is associated with ostracods of the Quainton-Stair faunicycles (1. P. Wilkinson in litt. 1991). Using Anderson's (1985) ostracod evidence, these faunicycles, which constitute ostracod Assemblage 1, are older than the Swindon faunicycle which, in the Fairlight Borehole, contains the (inferred) Tithonian Globator rectispirale. C. discordis thus appears in the Upper Jurassic. Other occurrences. Portugal: Brouco section. The specimen, named Flabellochara grovesi and figured by Ramalho ( 1971, pi. 33, fig. 6), has been re-identified as Clypeator discordis (Schudack 1990). The attribution of the Brouco section to the Tithonian on the occurrence of Globator rectispirale (see above) confirms that the first appearance of C. discordis is in the Upper Jurassic. This species is common in the Berriasian of Europe (see Schudack 1 987a, 1990; Feist and Schudack 1991). It has also been reported from the Valanginian of Sichuan Province, China (Fluang 1985) and from the Hauterivian and Barremian of the Pre-Dobrogean Depression in Ukraine (Shaikin 1976). EXPLANATION OF PLATE 2 Figs I -3. Triclypella calcitrapa Grambast. Ripe Borehole, Sussex, 1 54 00— 1 54- 50 m; Weald Clay. 1, MPK 8901 ; lateral view, showing one of the three faces with central pore. 2, MPK 8922; basal view, showing the triradiate symmetry of the utricle. 3, MPK 8923; dorsal (adaxial) face, showing the high position of the lateral pores. All x 45. Fig. 4. Clypeator combei Grambast. MPK 8902; Ripe Borehole, 1 54-00—1 54-50 m; Weald Clay; lateral view, showing one of the two faces of the utricle; x45. Figs 5-6. Clypeator discordis Shaikin. Town Garden Quarry, Swindon; Lower Pebbly Beds; lateral views, showing the basal cell subdivided; x 60. Figs 7-8. C. britannicus sp. nov. Kingsclere Borehole, Hampshire, 306 6 m; ?Grinstead Clay equivalent. 7, MPK 8905, paratype; dorsal view, showing the low position of the lateral pores; x45. 8, MPK 8906, holotype; lateral view, showing lateral pore and short basal cell; x48. Fig. 9. Atopochara triquetra Grambast, advanced form. CF 2777a-7; Cowleaze Chine, Isle of Wight; lower Vectis Formation; x 43. Fig. 10. Ascidiella iberica Grambast. MPK 8907; Warlingham Borehole, Sussex, 430 0 m; Weald Clay, upper part ; lateral view ; x 25. Figs 1 1-16. Sphaerochara andersoni sp. nov. Ripe Borehole, Sussex, 1 5400—1 54-50 m; Weald Clay. 11, MPK 8908, holotype; lateral view; x 60. 12, MPK 8909, paratype; lateral view; x 48. 13, MPK 8910, paratype; lateral view; x 45. 14, MPK 891 1, paratype; apical view of a germinated specimen; x 45. 15, MPK 8912, paratype; basal view; x 42. 16, MPK 8913, paratype; apical view; x 45. Fig. 17. Latochara sp. A. CF 2792b- 1 ; Town Gardens Quarry, Swindon; Upper Marlstones; lateral view; x 45. Figs 18-19. Mesochara sp. A. Fairlight Borehole, Sussex, 2810-281-3 m; Broadoak Calcareous Member; lateral views. 18, MPK 8914. 19, MPK 8915. Both x 70. Fig. 20. Latochara sp. B. MPK 8916; Warlingham Borehole, Sussex, 581 -7 m; Greys Limestones Member; lateral view; x 66. Fig. 21. Porochara maxima Donze. MPK 8917; Warlingham Borehole, Sussex, 61 21 m; Arenaceous Beds Member; lateral view; x 48. Figs 22-27. Peckispliarea verticillata Peck. Cowleaze Chine, Isle of Wight; lower Vectis Formation. 22-24, 26, CF 2111 & 1 to a3, a4; lateral views; 25, CF 2777a-5; apical view. 27, CF 2777a-6; basal view. All x 45. Fig. 28. Aclistochara sp. A. MPK 8918; Warlingham Borehole, Sussex, 614-2 m; Broadoak Calcareous Member, lateral view; x 70. PLATE 2 FEIST et al., charophytes 420 PALAEONTOLOGY, VOLUME 38 Genus triclypella Grambast, 1969 Triclypella calcitrapa Grambast, 1969 Plate 2, figures 1-3 1969 Triclypella calcitrapa Grambast, p. 881, pi. 1, figs 1-7. Distribution and range in southern England. Weald : this species is commonly associated with C. combei in the beds above the Small - Paludina' Limestone beds of the Weald Clay of the Weald. In the Ripe Borehole, the species occurs in beds at 154 0 to 1 54-5 m, dated palynologically as Hauterivian (Feist and Batten 1990). It also occurs in equivalent beds in the Hailsham Borehole (Text-fig. 2). In the Warlingham Borehole, it occurs at 430-0-430-7 m; in the sample from 430-0 m, it co-occurs with Ascidiella iberica , which is considered to be lower Barremian. The species has not been recorded from the topmost Wealden Beds Vectis Formation of the Isle of Wight; its range thus seems restricted to the highest Hauterivian-Lower Barremian. Other occurrences. Spain: north-central and eastern Spain, "Lower' (but not 'basal') Barremian (Grambast 1970, 1974; Schudack 1987a; Martin-Closas and Salas 1989). The species ranges from the Hauterivian to the Barremian (Wang and Lu 1982). Genus ascidiella Grambast, 1966 Ascidiella iberica Grambast, 1966 Plate 2, figure 10 1966 Ascidiella iberica Grambast, p. 2210, pi. 1, figs 1-6. Distribution and range in southern England. Weald: the species was found only in the Warlingham Borehole (430-0 m), in a sample from above Bed 3 of the Weald Clay, which is considered to be Lower Barremian from its position 1-4 m above the lowest horizon dated by angiosperm pollen (Hughes and McDougall 1990, fig. 3) and dinocysts (Harding 1990) as Barremian. Other occurrences. Spain: eastern Maestrazgo (Combes et at. 1966), above beds containing Hauterivian- Barremian foraminifers; Cameros Basin (Schudak 1987a), above beds with ostracods indicating the same age. Although considered to be of early Barremian age, it is therefore possible that the species ranges down into the upper Hauterivian. Family characeae, Agardh, 1824 Subfamily charoideae Al. Braun apttd Migula, 1897 Genus peckisphaera Grambast, 1962 Peckisphaera verticillata (Peck) Grambast, 1962 Plate 2, figures 22-27 1937 Chara verticillata Peck, p. 84, pi. 14, figs 30-33 1962 Peckisphaera verticillata (Peck) Grambast, p. 78. Distribution and range in southern England. Isle of Wight; Cowleaze Chine, the fossiliferous bed at the base of the Vectis Formation (attributed to the Upper Barremian - see below). Other occurrences. USA: Rocky Mountains, common in the Upper Jurassic and Lower Cretaceous (Peck 1957). East Asia: China, Triassic (Jiang et al. 1985; Lu and Luo 1990); Mongolia, Upper Cretaceous (Karczewska and Ziembinska-Tworzydlo 1970). Spain: Barremian (Schudack 1987a, 1990). FEIST ET A L. \ CHAROPHYTE BIOSTRATIGRAPHY 421 Subfamily nitelloideae Al. Braun apud Migula, 1897 Genus sphaerochara Madler, 1952, emend. Horn af Rantzien and Grambast, 1962 Sphaerochara undersold sp. nov. Plate 2, figures 1 1-16 Holotype. MPK 8908, British Geological Survey, Keyworth (PI. 2, fig. 11). Paratypes. MPK 8909-8913 (PI. 2, figs 12-16). Type horizon and locality. Weald Clay, Hauterivian, Ripe Borehole, Sussex, 154 0-154-5 m. Derivation of name. The species is dedicated to the late Dr F. W. Anderson, in token of gratitude for having preserved numerous charophyte specimens during his work on the Purbeck and Wealden ostracods of southern England. Diagnosis. Gyrogonite of Sphaerochara , characterized by its ellipsoid to cylindroid shape, the length-width ratio varying from IT to T5. Lower part of the basal plate superficial, bearing a central nodule. Dimensions: length 425-600 //m, width 375-525 /tm. Eleven to twelve circum- volutions seen in lateral views. Remarks. By its prominent apical rosette and its thick basal plate, superficial at the basal pore level, the new species clearly belongs to Sphaerochara. It differs from other species assigned to that genus by its elongated, instead of, the more common, spherical shape. In this character, S. andersoni resembles S. bicarinata Yang from the Minhe Formation of north-west China (Hao et al. 1983), but this latter species is significantly smaller. Distribution and range in southern England. Weald: Warlingham Borehole (430-0 m, 430-4 m and 430-7 m). Ripe Borehole (154 0-154-5 m) and Hailsham Borehole (16-50-17-99 m). All these occurrences are in the lower portion of the upper Weald Clay. Forms resembling S. andersoni (assigned here to S. aff. andersoni) but with a more globular shape, are present in the Wadhurst Clay, in the Wadhurst Park No. 3 Borehole ( 59-0—59-5 m), and the Robertsbndge Borehole, Sussex ( 12-2—12-3 m). Flampshire: Kingsclere Borehole (306-6 m), Grinstead Clay. SUCCESSION OF THE CHAROPHYTE ASSEMBLAGES AND BIOSTRATIGRAPHICAL IMPLICATIONS Charophytes occur intermittently in the Purbeck and Wealden successions of southern England; on the whole, each standard stage can be characterized by a particular assemblage, but abundance, preservation and diversity vary throughout the succession. The abundant and diverse Purbeck floras enable a biozonation to be established for the Jurassic-Cretaceous transition but other intervals, such as the detritic, and/or marine and weakly calcareous deposits either do not contain charophytes or contain only poorly calcified specimens without stratigraphical significance. We have considered as undefined zones, or as interregna, these intervals which, however, are well documented elsewhere and thus permit an appraisal of the entire Upper Jurassic-Lower Cretaceous charophyte zonation. The local charophyte zones introduced here are based on the first occurrences of successive index-species in the succession. The index species are chosen from the best dated and most widely distributed species of the assemblages. An ‘interregnum’ represents the time-interval between the last occurrence of the index species of the previous zone and the first occurrence of the index species of the following one. 422 PALAEONTOLOGY, VOLUME 38 PURBECK LIMESTONE GROUP Stratigraphy The Purbeck Limestone Group of southern England constitutes a predominantly non-marine succession of limestones and mudstones spanning the Jurassic-Cretaceous boundary. This sequence rests on marine sediments (Portland Group) of late, but not latest, Jurassic age. It is found in two main depositional areas, a Western or Wessex Basin to the west of the Portsdown structure and an Eastern or Wealden Basin to the east of this structure (Anderson 1985, fig. 1). Wessex Basin. The stratotype is the section in Durlston Bay, Swanage (Melville and Freshney 1982, fig. 16), where the group attains its maximum thickness (House 1989, table 7) and, except for the basal and topmost beds, is superbly exposed (for section details see Clements in Cope et a/. 1969; Clements 1993). The junction in the Isle of Purbeck between the 'Purbeck Beds’ as originally defined and the overlying Wealden Beds (Supergroup) is gradational (Strahan 1898; Arkell 1947a, p. 148); recent research has shown that the base of the type Wealden Beds as recognized in the Wealden Basin must be located within rather than at the top of the Purbeck sequence (Morter 1984; Lake and Shephard-Thorn 1987). Following Clements (1993) and standard British Geological Survey (BGS) practice, two formations are recognized in the stratotype Purbeck Limestone Group in this paper, the Lulworth and Durlston formations (Townson 1975) in ascending order, with the base of the latter being taken at the base of the near-marine Cinder Bed Member. The succession was earlier divided informally into the now redundant lower, middle and upper Purbeck Beds (Forbes 1851), which were used, extensively, both in this country and abroad, until comparatively recently (e.g. Anderson 1985). Within each of the original three subdivisions, distinctive groups of beds were recognized and named, based on a combination of their lithological character and fossil content. These groups of beds have member status (Clements 1993) within the two component formations. The Cherty Freshwater Member near the top of the Lulworth Formation is the source of much of the well- preserved Purbeck charophyte material described by Harris (1939), notably Flabellochara grovesi and Perimneste horrida. Wealden Basin. In the Wealden Basin, the Purbeck strata crop out in three faulted inliers, where the gypsiferous basal beds have been exploited for gypsum; they have also been penetrated by several deep cored boreholes (for details see Lake and Shephard-Thorn 1987). The occurrence of a shell- rich unit (Cinder Bed Member, Text-Fig. 1), characterized by oysters, and the near-marine ‘ Protocardia' major molluscan association (Morter 1984) allows the succession to be subdivided into the same two formations (Fulworth and Durlston) recognized in the Wessex Basin, although the member nomenclature adopted is different (Fake and Shephard-Thorn 1987, table 3). Charophytes indicating a Berriasian age for the Broadoak Calcareous Member of the Lulworth Formation have already been reported by Feist (in Lake et al. 1987) and are further discussed later in this paper. Near the base of this member there is a marker horizon of local importance, the Mountfield Adit Limestone, also referred to later in the text. The succession of lithologies and inferred depositional environments of the Purbeck Group in the Wealden Basin, however defined, is essentially comparable with that found in the Wessex Basin (Worssam and Ivimey-Cook 1984 and references therein; Anderson 1985, p. 3, fig. 5). The two successions are generally held to be at least broadly correlative and contemporaneous, despite somewhat controversial palynological evidence to the contrary (Wimbledon and Hunt 1983; Hunt 1985, 1987; Norris 1985), which suggests that the base of the Purbeck succession is significantly younger in the southern Weald (Brightling Mine, Fairlight Borehole) than it is in Dorset. Batten (pers. comm. 1992) emphasizes the geographical proximity between Dorset and the Weald at the time, and also the fact that there is good evidence for a more or less synchronous climatic change from arid to humid throughout that part of Europe. He considers that the differences in palynological assemblages between apparently lithostratigraphically correlative successions may FEIST ET AL.: CHAROPHYTE BIOSTRATIGRAPHY 423 FAIRLIGHT BROADOAK WARLINGHAM ASHDOWN BEDS GREY LIMESTONES MEMBER " Arenaceous beds MEMBER "CINDE r'bEDS MEMBe'r PLANT AND BONE BEDS MEMBER BROADOAK CALCAREOUS MEMBER GYPSIFEROUS BEDS MEMBER ' PORTLAND BEDS" ^Porochara maxima ' Clavalor reidi Clavalor reidi G praecursor - Clavalor alt. reidi - Clavalor reidi — Highest algal limestone _G^praecur_sor_ ? ? ? M.A.L. ■Transition sequence ? Toly pel la Flabellochara cf. grovesi Clavator reidi Flabellochara grovesi Clavator reidi C. protoincrassatus G praecursor ■ 300 Clavator a ft. reidi - G. rectispirale m 0 10 20 30 40 50 60 text-fig. 1 . Lithofacies correlation between Warlingham, Broadoak and Fairlight boreholes, modified after Morter (1984), showing key charophyte records. M.A.L., tentative position of Mountfield Adit Limestone. result from a more hostile environment in Dorset compared with the Weald. Allen and Wimbledon (1991) noted that the same sequence of events ( Classopollis pollen decline, Cypridea posticalis occurrence, quasi-marine Cinder Bed and percentage increase in the kaolinite component of the clay mineral assemblages) can be recognized in both areas, which suggests that the base of the Purbeck is not diachronous. Marginal areas. Purbeck strata are also found in marginal areas relative to the two main depositional basins, namely in Wiltshire in the Vale of Wardour and in three outliers near Swindon 424 PALAEONTOLOGY, VOLUME 38 (Sylvester-Bradley 1941; Arkell 1947a, 1947&, 1948; Wimbledon 1976), as well as in outliers in Oxfordshire and near Aylesbury, Buckinghamshire (Barker 1966; Bristow 1968; Wimbledon 1980; Radley 1992). The correlation between the Swindon and Aylesbury successions and the Dorset stratotype remains uncertain (see Barker et al. 1975; Morter 1984), but Anderson (in Worssam and Ivimey-Cook 1971) considered that at least the lower part of the Swindon Purbeck succession pre- dates the Purbeck stratotype and correlates with the higher part of the Portland Stone Formation. Of the marginal localities, only the Swindon succession is considered in this paper. The Purbeck succession cored in the Kingsclere Borehole in the western part of the Wealden Basin exhibits a succession intermediate between that of the Dorset stratotype and that of the marginal developments near Aylesbury. The Purbeck Limestone Formation succession at Swindon. In the classic Great (now Town Gardens) Quarry near Swindon, a complex succession of marls, limestones and pebble-beds (including at least one limestone with marine fossils), the so-called 'Swindon Series’ (Keeping 1883), rests with an erosional contact on the Swindon Sand and Stone Member of the Portland Stone Formation. Stratigraphical details of the sections then exposed, together with an extensive review of previous measured sections, were given by Sylvester-Bradley (1941) and later summarized by Arkell (1947 b, 1948). The bed nomenclature used in this paper follows that introduced by Sylvester-Bradley, his bed numbers being given in parentheses after the bed names. The basal 2 m of the ‘Swindon Series’, comprising a basal pebble bed [Lower Pebble Bed (2)], a marlstone unit [Lower Marlstones (3)], an ostracod-rich marl [Cythere Marl (4)] and terminating in a limestone with marine bivalves and gastropods [Swindon Roach (5)] were separated by Wimbledon (1976) as the Town Gardens Member and assigned to the top of the Portland Stone Formation. The overlying 10 m succession was assigned to the Purbeck Limestone Formation. This succession comprises two units of marlstones [Middle (6) and Upper (8) Marlstones] alternating with units of sandy marls with well-preserved freshwater ostracods and reworked limestone pebbles [Middle Pebbly Bed (7) and Upper Pebbly Beds (9)], these being overlain by two limestones [Boxy Tufa (10) and Swindon Flags (12)] with an intercalated unit of earthy marls [Chara Marls (11)] containing abundant ostracods and charophytes. Arkell (1948, p. 202) recorded an additional unit overlying the Swindon Flags consisting of marl with limestone rubble, which had not been noted previously. In the present study, charophyte assemblages have been examined from the Lower Pebbly Bed, Cythere Marl, Middle Pebbly Bed, Upper Pebbly Beds and Chara Marls. The identification of the taxa present and the biostratigraphical interpretations arising therefrom differ significantly from those published by Harris (1939; in Sylvester-Bradley 1941). Charophyte succession The most representative succession of charophyte occurrences was found in borehole samples from the Weald. In contrast, on the Dorset coast, only the beds of the uppermost Lulworth Formation to the lowest Durlston Formation have yielded charophytes. In the Fairlight Borehole, the Broadoak Calcareous Member can be subdivided into three local zones, based on the first occurrences of the successive chronological species of Global or ; the succeeding beds are referred to a fourth zone. As discussed below, the Jurassic-Cretaceous boundary lies between local charophyte zones 1 and 2. Zone 1. This is defined as the interval between the first occurrences of Global or rectispirale and G. praecursor\ the zone is represented in the lowest part of the Broadoak Calcareous Member (Lake and Holliday 1978) which appears in the Fairlight Borehole and may be provisionally interpolated in the Warlingham and Broadoak boreholes, below the occurrences of G. praecursor. The only FEIST ET AL.: CHAROPHYTE BIOSTRATIGRAPHY 425 occurrence of G. rectispirale is at 3 17-6-3 17-9 m in the Fairlight Borehole. An important additional species is Clavator aff. reidi (utricles incompletely constituted). By direct correlation. Zone 1 (as recognized in the Fairlight Borehole) corresponds to the lower part of the Swindon ostracod faunicycle of Assemblage 2 of Anderson (1975). The Swindon succession, which is referable to the underlying Assemblage 1, is provisionally included in the charophyte Zone 1, albeit in the absence of Globator praecursor (see below). Outside southern England, the zone is identifiable by the occurrence of G. rectispirale in the Seba Mahjouba Formation of the Chellala Mountains (Algeria), 50 m below beds referred to the Upper Tithonian A2-A3 calpionellid Zone (Benest 1981), which is correlated with the Late Tithonian 1 Durangites' ammonite Zone. The lower part of the Portuguese ‘ Infra valanginian’ (Rey et al. 1968; Ramalho 1971) which has yielded G. rectispirale and Clypeator discordis may be equivalent to this zone. Rey (in litt. 1991) considers that these beds should now be attributed to the Upper Jurassic (Tithonian). In terms of ammonite zones, the basal part of the Broadoak Calcareous Member, which is the stratotype of the charophyte local Zone 1, has been inferred to correlate with the Titanites anguiformis Zone (Wimbledon 1980 and this paper). Charophytes thus indirectly confirm the Boreal-Tethyan correlations of the anguiformis and ‘ Durangites' ammonite zones. Zone 2. This is defined as the interval between the first occurrences of Globator praecursor and G. protoincrassatus ; the zone is found represented in the lower-middle part of the Broadoak Calcareous Member. The lowest occurrences of G. praecursor are at 296-0-296-3 m in the Fairlight Borehole, at 625-3 m in the Warlingham Borehole, at 111-50-112 00 m in the Broadoak Borehole and at 270-6 m in the Brightling No. 27 Borehole. An important additional species is Clavator reidi. By direct correlation, Zone 2 (as recognized in the Fairlight Borehole) corresponds to the ostracod faunicycles between Swindon (pars) and the upper part of the Lower Soft Cockle (Anderson 1975). Outside the British Isles, Zone 2 corresponds approximately to the Ml charophyte Zone defined by Detraz and Mojon (1989) in the Jura Mountains and referred to the basal Berriasian. Zone 2 is also identifiable in the lower part of the Serpulit of the Lower Saxony Basin (Schudack 1991; Feist and Schudack 1991). Zone 3. This is defined as the interval between the first occurrences of Globator protoincrassatus and Flabellochara grovesi ; the zone is identified in the upper part of the Broadoak Calcareous Member (Lake and Holliday 1978); the former species occurs in the Fairlight Borehole at 293-2-293-5 m depth. An important additional species is Clavator reidi (primitive and advanced forms). Zone 3 is directly correlated with the Lower Soft Cockle (upper part). Upper Soft Cockle, Penshurst and Ringstead ostracod faunicycles. The zone is recognized by the occurrence of G. protoincrassatus in the topmost Soft Cockle Member of Dorset (Bed 70 of Clements in Cope et al. 1969; Clements 1993). Outside southern England, Zone 3 corresponds to the Lower Berriasian M2 charophyte zone defined by Detraz and Mojon (1989) in Switzerland, dated by ammonites of the Pseudosubplanites grandis Zone (Clavel et al. 1986; Hoedemaeker 1991). Zone 3 is also identifiable in the upper part of the Serpulit of the Lower Saxony Basin (Feist and Schudack 1991 ). Zone 4. This is defined as the interval between the first occurrence of Flabellochara grovesi and the last occurrence of Clavator reidi. The zone spans the highest Broadoak Calcareous Member, the Plant and Bone Beds, Cinder Bed, Arenaceous Beds and Greys Limestones members (Lake and Holliday 1978). The lowest record of Flabellochara grovesi is at 28 1 0—28 1 -3 m in the Fairlight Borehole. Important additional species are Porochara maxima , Perimneste horrida and Clavator reidi. The base of Zone 4 in the Fairlight Borehole is directly correlatable with the Robertsbridge ostracod faunicycle of Anderson ( 1975). In Dorset, the lowest occurrence of this zone is identifiable in the Cherty Freshwater Member; its upper part includes the Cinder Bed [Member] which is correlated with the Praetollia runctoni ammonite Zone (Casey 1973). 426 PALAEONTOLOGY, VOLUME 38 WEALDEN SUPERGROUP Stratigraphy The Wealden Supergroup (Series) in the type area consists of two broad subdivisions, the Hastings Beds below and the Weald Clay above. The former comprises an alternating sequence of formations (and locally members) which are dominantly argillaceous or of variable grain-size but with a significant arenaceous content (Ashdown Beds-Upper Tunbridge Wells Sand; cf. Text-Fig. 3). Whilst the clay subdivisions are thought to represent lacustrine/lagoonal environments, the intervening ‘sands’ show fluvial/alluvial associations. In the Hastings Beds, important transgressive events are recognized at the bases of the Wadhurst Clay and the Grinstead Clay and the major facies-change below the Weald Clay may reflect another of more regional significance (Allen and Wimbledon 1991). The Wealden Group of the Wessex Basin is generally poorly understood. The Wessex Formation, of alluvial/fluvial facies with few known lithostratigraphical or faunal markers, comprises sandstones and variegated mudstones (Hesselbo and Allen 1991). The Hauterivian-Barremian boundary has been placed approximately at the levels of the 'Pine Raft’ of the Isle of Wight and of the 'Coarse Quartz Grit’ of Dorset, on palynological evidence (Hughes and McDougall 1989). On the Isle of Wight, the Wessex Formation is succeeded by the lagoonal Vectis Formation, grey shelly mudstones, which has been correlated with the upper part of the Weald Clay (Anderson 1967; Stewart 1981). The Kingsclere (Hants) Borehole (National Grid Reference SU 4984 5820) (discussed later) apparently encountered red mottled beds of Wessex Formation facies overlying grey beds of Wealden aspect, but the effect of the sub-Aptian unconformity above is unclear. One possibility is that the variegated beds may reflect an expansion of those seen in the highest Hastings Beds and Weald Clay at outcrop (mid-Tunbridge Wells Sand-equivalent and above). Hughes et al. (1979) recognized Barremian palynomorphs in the highest part of the sequence at Kingsclere. Subdivision of the Weald Clay The scheme of subdivision adopted here follows that developed in the southern outcrop (Lake and Young 1978; Lake et al. 1987; Young and Lake 1988), following the work of Topley (1875, p. 102) and Thurrell et al. (1968, p. 24). The lithological marker horizons recognized within the dominantly clay sequence are as follows: 7 Sandstone(s) 6 Larg Paludina' limestone 5 Sandstone(s) 4 Larg q-' Paludina' limestone 3 Sandstone(s) 2 Small-' Paludina ’ limestones and ' Cyrena' limestones 1 Horsham Stone The Large-' Paludina' limestone units are individually restricted in vertical range, but the other horizons may comprise more than one intercalation within the sequence. For example. Bed 2 (clays with Small-' Paludina ' limestones and ' Cyrena ’ limestones) was found to have only a broad ‘zonal’ equivalence (Text-Fig. 2). Bed 4 (the lower of two commonly occurring Large-' Paludina' limestones) was, however, shown to be characterized by the ostracod Cypridea bogdenensis in the Gillmans faunicycle and therefore forms a useful marker horizon. In the Warlingham Borehole, Worssam and Ivimey-Cook (1971) attributed to 'Topley’s Bed 5’ a complex tripartite succession comprising, in ascending order: (a) 2T m of glauconitic sandstones with a brackish-marine molluscan fauna; (b) 0 8 m of shaly mudstones containing a bed of glauconitic sand with quartz pebbles; (c) 4-3 nr of sediments of terrestrial to freshwater aspect containing, in the basal metre, rootlet beds, Unio and charophytes. A sample (431 -4 m) from above the pebble bed in unit b yielded Barremian angiosperin pollen (Hughes and MacDougall 1990) and dinocysts (Harding 1990); the FEIST ET AL.\ CHAROPHYTE BIOSTRATIGRAPHY 427 WARLINGHAM Mudstone Red and green mottled beds Sandy intercalation in mudstone Siltstone and sandstone Ironstone prominent Estheriid honzon Large "Paludma" horizon Small "Paludina" honzon (isolated) Pellet bed r 0 -10 - 20 - 30 - 40 - 50 metres text-fig. 2. Lithofacies correlation between the Warlingham, Ripe and Hailsham boreholes in the Weald Clay, modified after Lake and Young (1978), showing key charophyte records. charophytes at the base of unit c are thus demonstrably Barremian. The Hauterivian-Barremian boundary falls in the interval between this sample and a sample from near the base of the sandstones (433-8 m) which gave a Hauterivian date (Hughes and MacDougall 1990. In this paper we specifically restrict ‘Topley’s Bed 5’ to the glauconitic sandstones between 431-8 m and 433-9 m. Moreover, it is evident that this bed underlies Topley’s Bed 4 as defined above (Bed 6 in the original borehole classification) and should more properly be numbered ‘ Bed 3 ’ ; albeit 428 PALAEONTOLOGY, VOLUME 38 Charophyte species e $ s. ® -9 U ii I 1 s e C 45 f g a 2 ^ ^ ® s s. i. 2 FORMATIONS ■1 2 • -9 .2 (3 o Itilllllil 2 | <0 .O O CD 1 1 U. Q. illllll &f r- u Charophyte Zones southern England 0*tr«cod launal Assemblages Stages Vectis Formation equivalent to topmost Weald Clay Weald Clay above Bed 3 Weald Clay above Bed 2 Upper Tunbridge Wells Sand and lowest Weald Clay Grinstead Clay and ? Lower Tunbridge Wells Sand Wadhurst Clay Ashdown Beds Durlston Beds Lulworlh Beds Atopochara triquetra (advanced) Ascidiella iberica Tridypella calcitrapa Interregnum 7 ■ 9 Clypeator britanicus Flabellochara xiangyunensis Interregnum 4 - 6 Flabellochara grovesi Globator protoincrassatus Global or praecursor Globator rectispirale 11 10 15 (pars) 10-12 9 (pars) 8-9 2-3 2 (pars) 1 -2 Late Banemian Early Banemian Valanginian Bemasian Late Trthonian text-fig. 3. Charophyte succession in the Purbeck and Wealden beds of southern England and correlation with the ostracod Assemblages of Anderson (1985). Dashed lines refer to related unspecified forms. there is a thin sand at the top of unit c. The transition from brackish-marine to freshwater conditions above this bed clearly marks a significant event at or about the Hauterivian-Barremian boundary (Allen 1989; Allen and Wimbledon 1991). This amendment to the classification of the Warlingham sequence invites reassessment of the correlation with other occurrences of Bed 3 (and subordinate units) which show brackish influences at outcrop in the Weald (Worssam and Ivimey-Cook 1971, p. 29; Worssam 1978, p. 8). FEIST ET A L. \ CHAROPHYTE BIOSTRATIGRAPHY 429 Charophyte succession ( Hastings Beds and equivalent strata) Above the Cinder Bed Member, there are large gaps in the charophyte succession. The Ashdown Beds, as well as the Lower and Upper Tunbridge Wells Sands, have yielded only insignificant charophyte material. Undefined Zone 5 — Interregnum 4-6. This corresponds to the interval between the last occurrence of Clavator reidi and the first occurrence of Flabellochara xiangyunensis in the Wadhurst Clay of the Weald. This Zone has not yet been recognized in Dorset. The interval represented by Zone 5 corresponds to the highest part of the Durlston Formation and to the Ashdown Beds, which are interpreted as fluvial deposits (Allen 1989), not favourable to the preservation of charophytes. Taxa identified from this zone comprise Tolypella sp., Peckisphaera knowltoni (Seward) Schudack, and incompletely calcified utricles of Flabellochara (see Appendix 1 for sample location). The Ashdown Beds are currently dated as Berriasian-early Valanginian on palynological evidence (Allen and Wimbledon 1991). Zone 6. This is defined as the interval between the first occurrence of Flabellochara xiangyunensis in the Wadhurst Clay of the Weald and that of Clypeator britanicus. The lowest occurrence of F. xiangyunensis is at 59-00-59-50 m depth in the Glynleigh Borehole. An important additional species is Sphaerochara aff. andersoni. Zone 6 has been identified in Wadhurst Park No. 3 Borehole at an horizon in the upper part of the Wadhurst Clay corresponding to the Hawkhurst ostracod faunicycle. On the basis of the occurrence of Flabellochara xiangyunensis. Zone 6 can be broadly correlated with the Valanginian F. xiangyunensis-Clypeator zongjiangensis Zone established by Wang and Lu (1982) in China. With regard to the European biozonation. Zone 6 seems to correspond to the Embergerella stellata Zone, defined by the first occurrence of this species in the Lower Valanginian of Maestrazgo (north- east Spain), dated by orbitoline foraminifers (Martin-Closas and Salas 1988). This dating is compatible with the age attributed to the Wadhurst Clay by Allen and Wimbledon (1991). Zone 7. This is defined as the interval corresponding to the range of Clypeator britannicus, recorded in the Kingsclere Borehole from 305-7-306-6 m; this is above beds between 31 1 -8—354-8 m with ostracod assemblages which indicate a correlation with the whole of the Wadhurst Clay (Anderson and Shephard-Horn 1967). Because this taxon has not been recognized elsewhere, only the evolutionary stage reached enables its occurrence to be dated tentatively. Apparently transitional between the Berriasian, Clypeator discordis and the upper Hauterivian-Barremian, C. conibei, C. britannicus can be inferred to be of Valanginian-early Hauterivian age. A probable Valanginian age is, however, only compatible with its occurrences in the Kingsclere Borehole, taking the tentative classification of the beds in question as equivalent to the Grinstead Clay (cf. Lees and Taitt 1945; Anderson 1985). Undefined Zone 8 = Interregnum 7-9. This corresponds to the interval between the last occurrence of C. britanicus and the first occurrence of Triclypella calcitrapa in the middle part of the Weald Clay in the Weald (Warlingham Borehole). This interval is provisionally inferred to equate with the Upper Tunbridge Wells Sand and much of the lower part of the Weald Clay, which have not yielded charophytes. Following the current dating of the various lithological subdivisions of the Wealden Beds (Allen and Wimbledon 1991), this interval may include the upper part of the Valanginian Embergerella stellata Zone and the Upper Hauterivian Globator trochiliscoides (primitive form) Zone defined in the Tethyan areas (Martin-Closas and Salas 1989). 430 PALAEONTOLOGY, VOLUME 38 Charophyte succession ( Weald Clay and equivalent strata) Charophytes of zonal significance occur above Bed 2 and its correlatives in the Weald Clay of the Weald and also at the base of the Vectis Formation, in the Isle of Wight, the latter representing the highest occurrence of charophytes in the Mesozoic of southern England. Zone 9. This is defined as the interval between the first occurrence of Triclypella calcitrapa and the first and only occurrence of Ascidiella iberica in the Weald (Warlingham Borehole, 430-0 m). The zone is present in beds immediately below and above the top of the Small - Paludina' Beds, including Bed 3. Important species are Clvpeator combei and Sphaerochara andersoni. Zone 9 has been identified in the Warlingham, Ripe and Hailsham boreholes, near the base of the upper part of the Weald Clay. Palynofloras from the Ripe Borehole (Feist and Batten 1990) and from the Warlingham Borehole (Hughes and McDougall 1989) indicate that this zone may straddle the Hauterivian-Barremian boundary. Zone 10. This is defined as the interval between the first and only occurrence of Ascidiella iberica and that of Atopochara triquetra (advanced) in southern England. The zone is present, in the lower part of the upper division of the Weald Clay, in beds above the equivalent of Bed 3 in the Warlingham Borehole, where A. iberica occurs at 430 0 m. The base of Zone 10 can be dated imprecisely (as late Hauterivian/early Barremian) from records of the index species in Spanish localities. The occurrence of A. iberica in the Warlingham Borehole indicates an early Barremian age. Important species are Atopochara triquetra (primitive), Clvpeator combei , Triclypella calcitrapa and Sphaerochara andersoni. Zone 10 corresponds to the El Mangraner charophyte Zone of Grambast (1974), defined in north-east Spain and also identifiable in the Pre-Dobrogean Depression, Ukraine (Shaikin 1976). The El Mangraner Zone ranges from the Lower Barremian to possibly the Upper Hauterivian from foraminifer evidence (Martin-Closas and Peybernes 1987; Martin-Closas and Salas 1989). Zone 11. This is defined as the interval based on the range of Atopochara triquetra (advanced). The zone is represented in the Cowleaze Chine Member at the base of the Vectis Formation, in the Isle of Wight. Important additional species are Clvpeator combei , Triclypella calcitrapa and Peckisphaera verticillata. Zone 11 corresponds to the late Barremian San Carlos charophyte Zone of Grambast (1974) and is identifiable in the La Ruchere section in the Jura (Mojon 1988) dated by foraminifers (Schroeder in Mojon 1988) as Early Aptian. The occurrence of advanced forms of A. triquetra is considered as more significant than that of the persistent accompanying species C. combei , previous records of which limited its range to the lower Barremian (Grambast 1970; Martin-Closas and Salas 1989). This interpretation fits with palynofloras characterizing the upper Barremian (Feist and Batten 1990). THE PURBECK GROUP AND THE PROBLEM OF THE JURASSIC-CRETACEOUS BOUNDARY The most complete charophyte succession in the Purbeck Group has been found in the boreholes from the Weald. In Dorset, only the sequences from the upper Soft Cockle to the Intermarine members have yielded charophytes so far, well above the level where the base of the Berriasian has been placed (Allen and Wimbledon 1991). Weald The Purbeck strata of the Weald rest on marine Portlandian, but the age, based on ammonite data, of the highest marine sediments below the contact varies throughout the basin. In the Fairlight Borehole and in the gypsum mines in the southern Weald, the Gypsiferous Beds rest, locally with FEIST ET AL. \ CHAROPHYTE BIOSTRATIGRAPHY 431 erosional contact (Brightling Mine), on sandstones of the Glaucolithites glaucolithus Zone, i.e. equivalent to the middle part of the Portland Sand Formation of Dorset. By contrast, in the Warlingham Borehole (northern Weald), the Gypsiferous Beds rest on the lower part of the Portland Stone Formation, Galbanites ( Kerberites ) kerberus Zone; it has been suggested (Wimbledon 1980) that there was no hiatus between the highest marine Portlandian and the onset of Purbeck facies sedimentation, implying that the lower part of the Purbeck Beds in this area correlated with the Titanites anguiformis Zone Portland Freestone of Dorset. Although these data could be taken to demonstrate that the onset of Purbeck facies was diachronous within the Wealden basin, Worssam and Ivimey-Cook (1984) argued that this apparent diachroneity might have resulted from a non-sequence in the southern part of the area caused by intra-Portlandian movement of the Portsdown-Paris Plage Swell and that the beginning of Purbeck-type sedimentation (as distinct from the date of the highest underlying marine Portlandian) might be essentially synchronous throughout the basin. The Broadoak Calcareous Member of the Lulworth Formation can be subdivided biostrati- graphically by means of three successive species of the Globcitor lineage. The inferred Tithonian local charophyte Zone 1 is recognized by the presence of G. rectispirale in the basal part of the Member in the Fairlight Borehole, while the Lower Berriasian local charophyte Zone 2, characterized by G. prae cursor, is represented in four boreholes: Fairlight, Warlingham, Broadoak and Brightling (see Appendix 1). The boundary between zones 1 and 2 appears to occur at about the level of the Mountfield Adit Limestone (Lake and Holliday 1978, fig. 3), i.e. near the base of the Broadoak Calcareous Member and a short distance above the Gypsiferous Beds Member. G. protoincrassatus, which succeeds G. praecursor in the lower part of the Lower Berriasian, has also been found in the Weald, but only in the Fairlight Borehole. The fact that charophyte Zone 1 was recognized only in the Fairlight Borehole does not seem sufficient evidence to demonstrate that Purbeck sedimentation began earlier in the southern Weald; the beds spanned by local charophyte Zone 2 in the Warlingham Borehole, in the northern Weald, are situated 30 m above the marine Portland Beds and this interval has yielded ostracods belonging to Assemblage 1 of Anderson (1985) as in the basal Purbeck beds of the Fairlight Borehole, corresponding to local charophyte Zone 1. Dorset The dating, in terms of both Tethyan and Boreal ammonite biostratigraphy, of the onset of non- marine (Purbeck facies) sedimentation and of the various members comprising the Purbeck Group remains unresolved. Recent interpretations of the possible correlations between the marine and non-marine successions are based on global sea-level changes (Hoedemaeker 1991, fig. 1 ), but some additional evidence is provided by palynomorphs and magnetostratigraphy. Hunt (1985) drew the base of the Apiculatisporis verbitskayae miospore Biozone near the top of a group of thin limestones at an horizon only 3 m above the base of the Cypris Freestones Member. In a subsequent paper (Hunt 1987, fig. 11.2), he took this floral change to mark the base of the Berriasian. It is possible that these limestones approximate to the level of the Mountfield Adit Limestone of the Weald, which marks the boundary between local charophyte zones 1 and 2 and the inferred position of the Tithonian-Berriasian boundary (see above). It is noteworthy that a significant change in the miospore assemblage in Purbeck appears to coincide with a change in the charophytes in the Weald. However, the Cypris Freestones palynomorphs and the overlying ostracods are stated to permit correlation with the Pseudosubplcinites grandis ammonite Subzone of the Berriasian stratotype (Allen and Wimbledon 1991; Wimbledon, pers. comm. 1994), implying that the base of the Berriasian as understood here (i.e. the base of the underlying Berriasella jacobi ammonite Subzone) lies below the Cypris Freestones and possibly approximates to the base of the Purbeck Limestone Group. This latter interpretation is supported by preliminary magneto- stratigraphical studies of the Purbeck stratotype (Ogg et al. 1991), but does not agree with the 432 PALAEONTOLOGY, VOLUME 38 correlations of Hoedemaeker (1991, fig. 1), who equated the greater part of the basal Purbeck succession below the Cypris Freestones with the terminal Tithonian ‘ Durangites' ammonite Zone. In Dorset, samples collected from the lower part of the Lulworth Formation were barren of charophytes and there is therefore no direct evidence for the recognition of the Jurassic-Cretaceous boundary. The type material of the supposed new taxon Clavator westi Costin (in Barker et al. 1975) from the Charophyte Chert, near the base of the Lulworth Formation at Portesham Quarry, is indeterminate (see discussion in Appendix 2). The lowest occurrence of determinable charophytes is in the upper part of the Soft Cockle Member at Durlston Bay; Bed DB70 (Clements, in Cope el al. 1969; Clements 1993) has yielded Globator protoincrassatus , which is the index of local charophyte Zone 3 and of Mojon’s Zone M2 in the Jura, and is lower (but not basal) Berriasian and equivalent to the Pseudosubplanites grandis Subzone of the grandis ammonite Zone. This dating is supported by early Berriasian miospores and dinoflagellates in a sample from the top of Bed 43 in the lower part of the Soft Cockle Member (Batten et al. in Lord and Bown 1987). Charophyte Zone 4 covers the interval from the Cherty Freshwater Member to the Intermarine Member. The charophyte assemblage, with Flabellochara grovesi, is that studied by Harris (1939). By comparison with the Jura and north-western Germany, the Dorset succession from the Soft Cockle to the Intermarine members is attributable to the Lower, not basal, Berriasian. Wiltshire The dating of the ‘Swindon Series’ has always been a matter of controversy (Sylvester-Bradley 1941, 1942; Arkell 1942). Wimbledon (1980, fig. 15) showed the Town Gardens Member divided between the kerberus and anguiformis zones (by implication assigning the Swindon Roach to the latter zone), with the overlying Purbeck Limestone Formation also placed in the anguiformis Zone, but there is no hard evidence for this interpretation (Wimbledon, pers. comm. 1992). The marine Swindon Roach, despite its general lithological and faunal similarity to the anguiformis Zone Roach of the Isle of Portland (particularly in the occurrence of the ‘Portland screw’ Aptyxiella portlandica) has so far yielded no ammonites. Arkell (1942) considered that the ‘Swindon Series’ equated with the ‘Middle Purbeck’ by reference to the charophytes, which he noted were particularly characteristic of and common in the ‘Middle Purbeck’ of Dorset, but which he mistakenly stated were not found below in the ‘Lower Purbeck’. However, Sylvester-Bradley (1942) and all subsequent workers (see above) have emphasized that the ostracods point unequivocally to a correlation between the ‘Swindon Series’ and the basal Purbeck of Dorset, whilst not excluding the possibility of the Swindon succession being a Purbeck-facies equivalent of the highest Portland Beds. The entire succession, which contains Cypridea dunkeri papulata throughout, belongs to the lowest Lower Purbeck ostracod assemblage (Assemblage 1), comprising the Quainton, Warren, Ridgeway and Stair faunicycles in ascending order (Anderson 1985, fig. 5), of which the first three were recognized at Swindon by Anderson. The absence of any members of the Cypridea granulosa granulosa-C. granulosa fasciculata lineage in the higher part of the ‘Swindon Series’ rules out any correlation of these beds, particularly the Chara Marls, with the charophyte-rich higher part of the Lulworth Formation. The general consensus is to correlate the entire ‘Swindon Series’ with the uppermost member (Portland Freestone) of the Portland Stone Formation of the Dorset coast, together with the basal beds of the Dorset Purbeck sequence (Caps, Dirt Beds and Broken Beds). This means that the charophyte assemblages at Swindon are older than any other charophytes discussed here from the British Purbeck, with the possible exception of the largely indeterminate material described from the Charophyte Chert of Portesham Quarry (Barker et al. 1975; and this paper). The Town Gardens Quarry at Swindon provides the northernmost exposure of Purbeck strata in Britain that yields charophytes. A preliminary study of the charophyte floras (Harris in Sylvester- Bradley 1941) identified Flabellochara grovesi and Clavator reidi , indicating a broad correlation with the ‘Middle Purbeck Beds’ of Dorset. Re-evaluation of the charophytes has now shown that the entire succession is characterized by Clypeator discordis and the primitive form Clavator aff. reidi. FEIST ET AL.\ CHAROPHYTE BIOSTRATIGRAPHY 433 all specimens formerly attributed to Flabellochara grovesi having been misidentified. By extrapolation from the Brouco section, Portugal, where Clavator discordis co-occurs with Globator rectispirale, and on the basis of the occurrence of Clavator afif. reidi , the Swindon succession, including the Chara Marls near the top, is tentatively assigned to the Tithonian local charophyte Zone 1, albeit in the absence of the zonal index. This new interpretation is supported by the ostracod evidence, which places the Swindon succession in ostracod Assemblage 1, i.e. equivalent to the basal stratotype Purbeck succession below the Cypris Freestones. It also agrees with the correlation scheme presented by Hoedemaeker (1991, fig. 1), in which the three ostracod faunicycles (Quainton, Warren and Ridgeway) recognized by Anderson (1985) at Swindon are equated with the terminal Tithonian ‘ Durangites' ammonite Zone. There is no evidence at Swindon for the Lower Berriasian local charophyte Zone 2. CONCLUSIONS For the first time, a stratigraphical study based on charophytes has been undertaken of the whole of the Purbeck and Wealden sequence of southern England. In contrast with previous views, this group provides a useful tool for subdividing and correlating the non-marine sequences between the Portland Stone and the base of the Lower Greensand. We have subdivided the succession into eleven local charophyte zones, of which two (zones 5 and 8) must remain uncharacterized intervals at present. This new zonal scheme provides useful correlations between successions in the Weald, Dorset and Wiltshire. Because of the wide distribution of most species at this time, direct correlations can be established between the Boreal and Tethyan realms. The Upper Tithonian local charophyte Zone 1 and the Lower Berriasian local charophyte zones 2, 3 and 4 established here can also be recognized in the Tethyan Realm. Two key indirect correlations can be made between the charophyte local zonal scheme for the Purbeck Limestone Group and marine successions in the Tethyan and Boreal Realms. The zonal index of the Globator rectispirale local charophyte Zone 1 can be recognized in Algeria below beds with an A2/A3 calpionellid assemblage, correlated with the Upper Tithonian ‘ Durangites' ammonite Zone of the Tethyan Realm. The Flabellochara grovesi local charophyte Zone 4 embraces the Cinder Beds Member at the base of the Durlston Formation. This bed is taken to correlate with the Praetollia runctoni ammonite Zone at the base of the Ryazanian Stage of the Boreal Realm and has been equated approximately with the base of the Strambergella occitanica ammonite Zone of the Tethyan Realm. The Jurassic-Cretaceous boundary can be inferred on charophyte occurrences (the boundary between local charophyte zones 1 and 2) to be located near the base of the Broadoak Calcareous Member of the Lulworth Formation of the Purbeck Limestone Group of the Weald. The boundary is situated at about the level of the Mountfield Adit Limestone, which may approximate to the basal group of limestones of the Cypris Freestones Member of the stratotype Purbeck Group succession in Dorset and the base of the Apiculatisporis verbitskayae miospore Zone. The Jurassic-Cretaceous boundary is understood here as the base of the Berriasian Stage of the Tethyan Realm, i.e. (following Anon. 1975) the base of the Berriasella jacobi Subzone of the Pseudosubplanites grandis ammonite Zone. If the base of the Berriasian approximates to the base of the Cypris Freestones, the new charophyte data accord with Hoedemaeker’s (1991, fig. 1) correlation diagram. Thus, the gypsiferous basal beds could represent the Tithonian ‘ Durangites' Zone (Tidalites de Vouglans of the Jura) and the base of the Cypris freestones could equate with the base of the (Berriasian) Goldberg Formation, within which the Globator lineage was first recognized. The charophyte biostratigraphy supports the previous ostracod-based correlations between the Purbeck and Wealden successions of Dorset and the Weald respectively. A reassessment of the charophyte and ostracod data from the Town Gardens Quarry, Swindon, allows this succession to be attributed tentatively to the Upper Tithonian local charophyte Zone 1 and equated indirectly with the " Durangites ' ammonite Zone of the Tethyan Realm. This succession is divided between the Galbanites kerberus and Titanites anguiformis ammonite zones (Wimbledon 1980); the charophytes 434 PALAEONTOLOGY, VOLUME 38 thus provide indirect evidence of the contemporaneity of these boreal ammonite zones with the Tethyan ‘ Durangites' Zone. For the Wealden Supergroup, the charophyte data, supported by preliminary palynological indications from Professor D. J. Batten, allow us to locate the Hauterivian-Barremian boundary near the base of the upper division of the Weald Clay in the Weald. The Upper Barremian is identified in an equivalent of the topmost Weald Clay, at the base of the Vectis Formation of the Isle of Wight. In addition to these stratigraphical results, the work has provided new data on charophyte evolution. The oldest and most primitive representative of the Globator lineage has been found in the Fairlight Borehole. On the other hand, correlations establish the presence of the genus Clypeator in the Upper Jurassic; this supports the views of Martin-Closas and Serra-Kiel (1991), who considered the Upper Jurassic to be a period of charophyte diversification. The appearance of Clypeator before Flabellochara suggests that the two genera have a separate origin. The study of Jurassic-Cretaceous charophytes from southern England is far from complete and the local zonal scheme presented here must be regarded as provisional. Further collecting from the incompletely sampled Purbeck Limestone Group of Dorset should lead to refinements of the zonal scheme for this part of the succession. Future investigations could examine the extent to which changes in taxonomic diversity and degree of calcification are controlled by palaeoenvironmental changes. Acknowledgements. We are grateful to Professor D. J. Batten for permission to integrate palynological data, to Dr H. Capetta, B. Sigand and Dr I. Wilkinson for their expertise in respectively determining selachian fish remains, mammal teeth and ostracods, and to Dr P. O. Mojon for kindly providing us with critical specimens. Professor M. R. House, Dr H. C. Ivimey-Cook and Dr E. R. Shephard-Thorn are thanked for their suggestions on field work which were most helpful. We thank R. N. Mortimore for assistance in the field. Dr A. Coe for her comments on an early draft of the manuscript and Mr J. A. Ross for information on the borehole successions in the Weald Clay. Information on the Fairlight Borehole and figures of MPK specimens are published with the permission of the Director, British Geological Survey, Keyworth. 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Geology of the country around Brighton and Worthing. Memoir of the British Geological Survey, 1 1 5 pp. MONIQUE FEIST Laboratoire de Paleobotanique Institute des Sciences de l’Evolution, USTL Place Bataillon 34095 Montpellier, France ROBERT D. LAKE British Geological Survey Keyworth, Nottingham NG12 5GG, UK CHRISTOPHER J. WOOD Typescript received 13 September 1993 20 Temple Road Revised typescript received 12 January 1995 Croydon, Sussex CR01 HT, UK APPENDIX 1 - DISTRIBUTION OF CHAROPHYTES IN BOREHOLES IN THE PURBECK AND WEALDEN OF SOUTHERN ENGLAND The distribution of charophyte species found in borehole material is described in descending order. Sample numbers with the prefix Mik(M), MPA and SAM refer to the British Geological Survey collections at Keyworth, NHM numbers to the National History Museum, London, SWF to the Senckenberg Museum, Frankfurt, and CF to the Laboratoire de Paleobotanique, Universite de Montpellier. Warlingham Borehole, Surrey (Worssam and Ivimey-Cook 1971) This includes the most complete succession of charophyte floras and is taken as a reference section, supplemented by data from the Purbeck Group in the Fairlight Borehole. Weald Clay, lower portion of the upper part 430 0 m. Samples Mik(M) 1068 and SAM 884: Ascidiella iberica, Atopochara triquetra (primitive), Triclypella calcitrapa, Sphaerochara andersoni. 4304 m. Sample Mik(M) 2493: Clypeator combei, T. calcitrapa, S. andersoni, stems. 430-7 m. Sample Mik(M) 1074 and SAM 886: T. calcitrapa, S. andersoni. Ashdown Beds 573-6 m. Sample Mik(M) 1545: Small-sized gyrogonites of Characeae, Tolypellal 581-7 m. Sample Mik(M) 1558: Characeae genus et species indet. Purbeck Group (all samples from the Lulworth Formation) 612-1 m. Sample Mik(M) 1758 and SAM 1346 (ex Bp 4971): Porochara maxima, Clavatoraceae gen. et sp. indet., stems. 612-3-612-4 m. Sample Mik(M) 1759: Clavator reidi (one utricle, with slightly spiralized cells), Porochara maxima, stems. 440 PALAEONTOLOGY, VOLUME 38 6 1 4-2—6 1 4-4 m. Sample Mik(M) 1760: Latochara sp., C. reidi (utricles with well spiralized cells), Aclistochara sp., stems. 6 1 4-8 m. Sample Mik(M) 1775 and SAM 1360 (ex Bp 5012): C. reidi (utricles with spiralized cells). 625-3 m. Sample Mik(M) 1856 and SAM 1403: Globator praecursor, Clavator aff. reidi. 6319 m. Sample SAM 1424: C. aff. reidi. Ripe Borehole, Sussex (Lake and Young 1978) Weald Clay 15400-154-50 m. Sample Mik(M) 3927 and MPA 25418: Triclypella calcitrapa, Sphaerochara andersoni , Clypeator combei. 1 59-50 1 6000 m. Sample Mik(M) 3935 and MPA 25419: Clypeator combei. Hailsham Borehole , Sussex (Lake and Young 1978) Weald Clay 1 6-50 — 1 700 m. Sample Mik(M) 3736: T. calcitrapa , S. andersoni. 29-50-30 00 m. Sample Mik(M) 3780: C. combei. 38 00-38-50 m. Sample Mik(M) 3790: T. calcitrapa. Wadhurst Park No. 3 Borehole , Sussex (Anderson and Shephard-Thorn 1967) Wadhurst Clay 6- 7-7-0 m. Sample Mik(M) 1987 and SAM 3779: Flabellochara xiangyunensis, Sphaerochara aff. andersoni. 7- 3— 7-6 m. Sample Mik(M) 1993 and SAM 3781 : Flabellochara xiangyunensis. 1 6-8—1 7-0 m. Sample Mik(M) 2026: Flabellochara sp. indet. Glynleigh Borehole, Sussex (Lake and Young 1978) Wadhurst Clay 59-00-59-50 m. Sample Mik(M) 3697 : Flabellochara xiangyunensis , Sphaerochara atf. andersoni. Kingsclere Borehole, Hampshire (Lees and Taitt 1945) ?Grinstead Clay (equivalent) 305- 7 m. Sample Mik(M) 2489, ex. Mik(M) 301 : Clypeator britannicus. 306- 6 m. Sample Mik(M) 2490, ex. Mik(M) 327-9 : Clypeator britannicus, Sphaeorchara aff. andersoni. Robertsbridge Bypass No. 15 Borehole, Sussex (OS TQ 7391 2523) Wadhurst Clay 2-9-3 0 m. Sample 15/6, University of Brighton, CF 2773b. Stiff olive-grey, slightly shaly clay: Flabellochara sp. (incompletely calcified utricles), Sphaerochara aff. andersoni. 12-2—12-3 m. Sample 15/18, University of Brighton, CF 2773a. Dark greenish shaly clay with fossil shell fragments: Sphaerochara aff. andersoni. Kitchenham Dam Borehole No. K4, Sussex (OS TQ 6816 1313) Wadhurst Clay 28-30 m. Sample per University of Brighton, CF 2774/1 . Light greenish grey, partly friable clay: Flabellochara xiangyunensis. Fairlight Borehole, Sussex (Holliday and Shephard-Thorn 1974) Purbeck Group (Plant and Bone Beds Member) 263-3-263-7 m. Sample Mik(M) 4159: ITolypella. Purbeck Group (Broadoak Calcareous Member) 273-4-273-7 m. Sample Mik(M) 4192: Flabellochara cf. grovesi. 273-7-274 0 m. Sample MPA 25422: Clavator reidi (with vertical cells), Flabellochara grovesi. 280- 1 280-4 m: Flabellochara grovesi, Clavator reidi (spiralized). 28 1 -0—28 1 -3 m: F. grovesi, C. reidi, small-sized Characeae, oospores. 293-2-293-5 m. Sample MPA 25425: Globator protoincrassatus. 296-0-296-3 m. Sample MPA 25426: G. praecursor, Clavator aff. reidi. 3f 7-6-317-9 m: Globator rectispirale, nodosoclavatoroid utricles. FEIST ET A L.: CHAROPHYTE BIOSTRATIGRAPHY 441 Broadoak Borehole, Sussex (Lake and Holliday 1978) Purbeck Group (Broadoak Calcareous Member) 71 -50-72-00 m. Sample Mik(M) 4333: Clavator reidi (vertical cells). 1 1 1-50-1 12 00 m. Sample Mik(M) 4296: Globator praecursor. Brightling No. 27 Borehole, Sussex (Anderson and Bazley 1971) Purbeck Group (Broadoak Calcareous Member) 270 6 m. Sample Mik(M) 2651 : G. praecursor. APPENDIX 2-DISTRIBUTION OF CHAROPHYTES IN PURBECK AND WEALDEN OUTCROPS IN SOUTHERN ENGLAND For the Purbeck Limestone Group, specimens were collected by MF in the classic sections along the Dorset coast and at two localities in the Swindon Marshes: Town Garden Quarry, Swindon and the Upwey section. Sediments collected in the basal Purbeck beds of the Isle of Portland did not yield any charophytes. MF has also revised the specimens from the same areas that are housed in the Natural History Museum (specimen numbers prefixed BMNH-Y), notably the important material studied by Harris (1939). Wealden charophyte floras have been collected from a quarry near Capel, Surrey, and on the south-west coast of the Isle of Wight (specimens CF, charophyte collections, University of Montpellier). The distribution of charophyte floras found at outcrop is given below. Wealden Supergroup Cowleaze Chine. South-west coast of the Isle of Wight (OS SZ 444 801). There are three levels with charophytes, at the base of the Vectis Formation (Stewart 1981). CF 2777b. 170 m west of Cowleaze Chine; dark grey marls: Atopochara triquetra (advanced), Clypeator combei , Peckisphaera verticillata. CF 2777a. 150 m west of Cowleaze Chine; dark grey marls below a bed of light grey sands 0 3 m thick: charophyte flora as above. CF 2776. 0T m above the sand bed; dark grey marls, with white mollusc shells and fish teeth: C. combei. Butterley Brickworks Pit (formerly Clock House Pit). Capel, Surrey (Worssam 1978) (OS TQ 175 384). CF 2771. Weald Clay, below Bed 3, bed 33 in Worssam (1978, p. 16). Charophytes were collected in 1986 from a shaly clay below a sandstone with Ophiomorpha : Sphaerochara sp. Stream section, 500 m east of Freechase. Near Warninglid, Sussex (OS TQ 2442 2518). E276, British Geological Survey, Keyworth. Wadhurst Clay, sample of purple shales from beds high in the formation : Flabellochara xiangyunensis. Fairlight section. Sussex. Hastings Beds, ‘Fairlight Clay’, Sample BMNH-V1070: Peckisphaera knowltoni (Seward) Schudack; internal mould of a ?Characeae. Purbeck Limestone Group of Dorset Durdle Door. CF 2781a-b. Lulworth Formation: Broken Beds and Caps: ostracods. No charophyte seen. Harris (1939): Below chert: Perimneste horrida. CF 2781. Just below the Cinder Bed [Member], in the Lulworth Formation. Marl with gypsum. CF 2781c: Flabellochara grovesi, Clavator reidi. CF 278 Id: Flabellochara grovesi. Durlston Bay, Swanage. (OS SZ 040 786). Neale and Mojon sample. Higher part of Soft Cockle Member, Lulworth Formation: Bed DB 70 of Clements (in Cope et al. 1969; Clements 1993): Globator protoincrassatus. Worbarrow Tout. See Ensom (1985). CF 2783. Above the Cinder Bed [Member], in the Durlston Formation: Porochara sp., Clavator reidi. 442 PALAEONTOLOGY, VOLUME 38 Mupe Bay. See Arkell (1947a). Harris (1939) reported Perimneste horrida from this locality, probably from the Charophyte Chert, Cherty Freshwater Member, Lulworth Formation. CF 2785. 08 m above the chert, and below the Cinder Bed [Member]: Flabellochara grovesi. Durlston Bay. Swanage (Clements in Cope et al. 1969; Clements 1993; El Shahat and West 1983). CF 2779a-b. Mammal Bed, in the Marly Freshwater Member, Lulworth Formation: Porochara sp., Clavator reidi. CF 2780b. Above the Cinder Bed, in the Durlston Formation: Porochora sp., Clavator reidi. Portesham Quarry. Near Abbotsbury (OS SY 61 1 859). Harris (1939) reported Perimneste Itorrida , Clavator reidi and C. (i.e. Flabellochara) grovesi (holotype) in ‘Portesham or near Portesham’, from Reid and Groves collection. Portesham Quarry is the type locality of Clavator westi (Barker et al., 1975). The type material of this supposed new taxon comprises nodosoclava- toroid utricles and vegetative fragments which could correspond to any Clavatoroideae: ‘C. westi ’ cannot therefore be considered as a species in the traditional sense of charophyte taxonomy (Feist and Grambast- Fessard 1991). Sample BMNH-V26280, Reid and Groves Collection: Clavator reidi. Poxwell Road cutting. Dorset. Bed 33 of Sylvester-Bradley (1949). BMNH-V26181: Flabellochara grovesi. Purbeck Limestone Group of Swindon Marshes Town Gardens Quarry. Swindon, Wiltshire. Section after Sylvester-Bradley (1941). CF 2789a. ‘Lower Purbeck Beds’. Exposure II. Lower Pebbly Beds (base): Clypeator discordis. Ostracoda: Cypridea dunkeri papulata. Foraminifera: Lenticulina muensteri. CF 2789b. 0-3 m above: Clavator aff. reidi. CF 2790. Cythere Marl: Clypeator discordis. ‘Middle to Upper Purbeck Beds’. Exposure IV. Middle Pebbly Bed. Sample TCQ-IV, collected by Dr H. Malz, Senckenberg Museum, Frankfurt a. Main and sample CF 2792 : Latochara aff. bitruncata, nodosoclavatoroid utricles, Clypeator discordis. Exposure III. Chara Marls. Sample TGQ-III of H. Malz and sample CF 2791a, at the base of the marls: Clypeator discordis , Clavator aff. reidi (with vertical and slightly spiralized cells). Sample CF 2791b-c (laterally, at the top of the marls): Clypeator discordis , Clavator aff. reidi , nodosoclavatoroid utricles. Purbeck Limestone Group of the Vale of War dour, Wiltshire (see Harris 1939). Chicksgrove quarry, near Tisbury. Sample CF 2788, grey shaly marls, 1 m above the Portland Stone: Latochara aff. bitruncata, Clavatoraceae gen. et sp. indet. LOWER CAMBRIAN REEFAL CRYPTIC COMMUNITIES by ANDREY Yu. ZHURAVLEV and RACHEL WOOD Abstract. Phanerozoic reefs were differentiated into distinctive open surface and cryptic communities from their first appearance. During the Lower Cambrian, cryptic communities were surprisingly diverse with small, solitary chambered archaeocyath sponges, calcified cyanobacteria and a microburrowing (?)metazoan being the most ubiquitous and abundant elements. Putative primitive cnidarians, spiculate sponges and various problematica were also common crypt dwellers. Several species of archaeocyath sponge, as well as cribricyaths, the calcified cyanobacteria Chabakovia spp. and possibly boring sponges, were obligate cryptobionts. Lower Cambrian crypts offered a habitat of reduced environmental stress, and they housed a substantial proportion of the total biotic diversity of early reefs. Cryptic communities were composed of solitary, pioneering organisms and displayed no succession. Lower Cambrian crypts were small, short-lived structures compared with most modern reefal crypts, and were sites of extensive syn-sedimentary cementation supporting the conjecture that crypts did not remain open for long before partial or total occlusion. There is ample evidence, however, of a soft-bodied cryptos and of intense competition for space, as organisms commonly form multiple overgrowths or chains of individuals. On a sub-zonal scale, the vast majority of archaeocyath species appear simultaneously in both open surface and cryptic niches, suggesting that Lower Cambrian crypts did not serve either as 'safe-havens’ harbouring formerly open surface inhabitants or as ‘brood-pouches’ of evolutionary innovation. One of the most striking aspects of modern coralgal reefs is their differentiation into distinctive open surface and cryptic communities (Jackson and Buss 1975; Jackson 1977; Jackson and Winston 1982; Choi and Ginsburg 1983; Choi 1984; Kobluk 1988). Whilst phototrophic organisms dominate on exposed, open surfaces, filter and suspension-feeding organisms flourish within hidden, or cryptic niches. Of these, encrusting sponges and ectoprocts are particularly abundant as they appear to be the best overgrowth competitors (Jackson and Winston 1982), but solitary organisms such as serpulids, foraminiferans and brachiopods are also conspicuous, even though they occupy little space (Jackson 1977). Any association of aggregating skeletal organisms will form cavities or crypts within its framework, as well as generating abundant debris which present attractive undersurfaces for colonization. Such primary crypts provide relatively well-protected niches shielded from direct exposure to local environmental pressures, such as wave scour, irradiation and predation. Unoccupied substratum is rare in crypts and overgrowths are common, suggesting that, as at the open surface, competition for space is intense. Nutrient supply and oxygen availability (provided by sufficient water flow) are critically important to modern cryptic communities (Kobluk and James 1979; Choi and Ginsburg 1983), with competition for food and competitive networking being the principal determinants which maintain high diversity (Jackson and Buss 1975). Cryptic niches are extremely important within modern reef ecosystems, as many organisms are far more abundant in crypts than on open surfaces and some may be obligate cryptobionts. Crypts can thus house a significant proportion of the total biotic diversity of a reef. In addition, modern reefal caves and grottoes have attracted a celebrated status for the ancient affinities of their biotas (Jackson et al. 1971). These crypts house putative relict communities of Mesozoic reef-building calcified demosponges (‘sclerosponges’) and thecidioid brachiopods (Jackson et al. 1971; Wood 1990). Such large cryptic niches have been suggested to be refugia or 'safe havens’ to which once- [Palaeontologv, Vol. 38, Part 2, 1995, pp. 443-470, 3 pls| © The Palaeontological Association 444 PALAEONTOLOGY, VOLUME 38 widespread organisms have retreated in the face of new competition (Jackson et al. 1971 ; Vermeij 1985). Others have suggested that crypts may be the crucibles or ‘brood-pouches’ of evolutionary innovation which spawn new forms that subsequently colonize the open surface (Kobluk and James 1979). Despite their acknowledged importance in modern reefs, cryptic biotas within fossil reefal buildups have been the subject of limited study (see summaries in Kobluk 19816, 1988). Cryptic communities often go unrecognized in palaeoecological analyses. Although isolated communities have been well documented, it has not yet been established when a distinctive cryptos first developed within reef ecosystems. Nor have any studies been devoted to detailing patterns of temporal development within the cryptos as distinct from open surface communities. Here, we have attempted to describe the cryptos in the earliest known Phanerozoic reefs and to document its development. The oldest Phanerozoic reefs known are from the ‘Nemakit-Daldynian’ (= Manykaian; earliest Cambrian; some 544 Ma according to Bowring et al. 1993) and were pure calcified cyanobacterial mounds. The first metazoan reefs formed with the appearance of archaeocyath sponges within calcified cyanobacterial communities at the base of the Tommotian (530 Ma; Bowring et al. 1993). This consortium was joined later in the Lower Cambrian by other calcified heterotrophs such as radiocyaths and coralomorphs. Lower Cambrian reefal communities usually developed as a series of bioherms in fairly energetic shallow shelf seas (Wood et al. 1992 a), and showed no succession apart from initial stabilization of substrates by the growth of calcified cyanobacteria (Hart 1992) or a consortium of pioneer archaeocyaths and calcified cyanobacteria (Kruse et al. in press). Where archaeocyaths were present, bioherms were often dominated by only one or two modular, branching species, implying the rapid colonization and subsequent growth of only a limited number of larval spat falls (Wood et al. 1992 a, 1993). These bioherms were essentially soft-substrate communities, with few massive or encrusting organisms. Early reef communities persisted until the virtual demise of the archaeocyaths at the end of the Toyonian, some 520 Ma (Bowring et al. 1993), although calcified cyanobacteria continued to build reefs for the remainder of the Cambrian. Reefs known from the base of the 'Nemakit-Daldynian’ to the end of the Toyonian, a period of approximately 25 million years, thus present a coherent ecosystem in which to study the temporal development of cryptic communities. Crypts are known to have been exploited early in the history of reefs: organic-walled microfossils ( Huroniospera sp. and Gunflintia sp.) and haematitic problematica ( Frutexites sp.) have been noted from crypts within lithified algal mat sequences from the Early Proterozoic Odjick Formation, Canada (Hofmann and Grotzinger 1985), and Turner et al. (1993) noted Renalcis- like cryptobionts in the pre-Vendian Neoproterozoic reefs of the Little Dal Group in northwestern Canada. The first Phanerozoic cryptic communities are documented from the middle Lower Cambrian (Kobluk and James 1979; Kobluk 1981c, 1985; Rees et al. 1989; James and Gravestock 1990; Frohler and Bechstadt 1992; Wood et al. 1993). These cryptic biotas show, however, marked differences in composition. The cryptos described from the Botomian Poleta Formation in Nevada (Kobluk 1981c), the early Toyonian Forteau Formation in Labrador and Newfoundland (Kobluk and James 1979) and the Upper Shady Dolomite in Virginia (Kobluk 1985) have only rare, if any, recorded archaeocyath sponges, even though they have revealed otherwise diverse and unique biotas. In contrast, late Atdabanian cryptic biotas from the Flinders Ranges, South Australia (James and Gravestock 1990) and Zuune Arts, Mongolia (Wood et al. 1993) contain abundant archaeocyath sponges, as well as calcified cyanobacteria, putative primitive cnidarians and various problematic forms. Additionally, reported total cryptobiontic diversity and abundance is very variable. These isolated descriptions suggest that cryptic communities were common and well differentiated in Lower Cambrian reefs and deserve systematic study. Here, we have examined representative reefal communities from throughout the Lower Cambrian. Early cryptic communities were surprisingly well developed, and show biotic and ecological features quite distinct from contemporary open surface communities. We have attempted to highlight these ecological differences by considering differences in morphology and in systematic ZHURAVLEV AND WOOD: CRYPTIC COMMUNITIES 445 text-fig. 1. Schematic diagram of different cryptic niche types determined within Lower Cambrian reefal buildups. distribution. In addition, we present quantitative data to test between the competing hypotheses of cryptic niches as ‘safe havens’ for relict faunas, or as ‘brood pouches’ of evolutionary innovation. METHODS This study is the result of the examination of over 1500 oriented thin-sections from 38 localities embracing ‘Nemakit-Daldynian’ to middle Toyonian bioherms from the Siberian Platform, South Urals, Altay Sayan Fold Belt, Mongolia, South Australia, Antarctica and North America (see Appendix: Localities 1-38). We have documented only demonstrably in situ elements of the cryptic biota. Although sediment infills within crypts often contain bioclastic debris (such as small shelly fossils, trilobite fragments, brachiopod valves, sponge spicules and echinoderm ossicles), this material is often equally abundant in the non-crypt micrite and interbiohermal sediments of reefal sequences. We have excluded such skeletal material from our analyses except where preferential enrichment within crypts is evident. We follow the terminology outlined by Kobluk (1988) and the biostratigraphy of Mansy et al. (1993) given in Table 1. Most of the material described herein is housed in the Palaeontological Institute, Russian Academy of Sciences, Moscow (PIN) with supplementary material from the Northern Territory Geological Survey, Darwin, Australia (NTGS), the Sedgwick Museum, Cambridge (SM), and the National Museum of Wales, Cardiff (NMW). VARIETY AND FORM OF CRYPTS A surprising variety of cryptic niches was present within Lower Cambrian buildups (Text-fig. 1), whose size ranged from a few millimetres in diameter to several decimetres in some cases. Many 446 PALAEONTOLOGY, VOLUME 38 table 1. Biostratigraphy and correlation of Lower Cambrian (Tommotian to Toyonian) in the studied localities studied using archaeocyath zonation (modified from Mansey et al. 1993) Stage Zone Siberian Platform Altay-Sayan Australia Mongolia North America Zhuravleva et al. 1969, 1976 (revised) Osadchaya et al. 1979 Zhuravlev and Gravestock in press Voronin et al. 1982 Mansy et al. 1993 Toyonian 3 Erbocyathus heterovallum Tegerocyathus edelsteini 2 Irinaecyathus shabanovi Archaeocyathus okulitchi Beds Irinaecyathus rat us A rchaeocya th us kusmini Archaeocyathus abacus Beds Tegerocyathus greenlandensis Pycnoidocyathus pearylandicus Beds i * Claruscyathus solidus' Not established Archaeocyathus altanticus Beds Botomian 3 Not established Syringocyathus aspectabilis Syrinocnema favus Beds Pycnoidocoscinus serratus Tabulaconus kordeae 2 Terycyathellus altaicus Not established Claruscoscinus Jritzi Metacyathellus caribouensis 1 Rozanovicvathus alexi Beds Clathricoscinus Ethmophyllum whitneyi Sekwicyathus nahanneinsis Carinacyathus squamosus Botomocyathus zelenovi Atdabanian 4 Fansycyathus lermontovae Arturocyathus borisovi Jugalicyathus tardus Alataucyathus jaroschevitschi Tabulacyathellus bidzhaensis Pretiosocyathus subtilus Beds Not established 3 Nochoroicyathus kokoulini Nalivkinicyathus cyroflexus Spirillicyathus tenuis Warriootacyathus wilkawillinensis 2 Carinacyathus pinus Gordonicyathus howelli 1 Retecoscinus zegebarti Nochoroicyathus mariinskii Tommotian 4 Dokidocyatlius lenaicus Tumuliolynthus primigenius 3 2 Dokidocyatlius regularis i Nochoroicyathus sunnaginicus ZHURAVLEV AND WOOD: CRYPTIC COMMUNITIES 447 text-fig. 2. A SM X25956; transversely folded cup of Pycnoidocyathus latiloculatus (Hill) with rich cryptic fauna of Tumuliolynthus irregularis (Bedford and Bedford) (top), Archaeopharetra sp. (centre) and Metaldetes lairdi (Hill) (bottom). The development of synsedimentary cement (lower left) has distorted the growth of Archaeopharetra sp. (arrowed) and the cement has also served as a substrate for an encrusting Khasaktia-Yike organism and later generations of irregular archaeocyaths; Locality 32 (Botomian 3); x 5. B, NMW 95.2G.1 ; probable boring excavations of the ceiling of a crypt, showing scalloped edges. The crypt is formed by Cambrocyathellus tchuranicus, Zhuravleva and has been subsequently colonized by Archaeolynthus polaris (Vologdin) and Renalcis jacuticus , Korde; Locality 2 (Tommotian 1); x 6. c, PIN 3848/701; fungal hyphae on the undersurface of Okulitchicyathus discoformis (Zhuravleva); Locality 3 (Tommotian 2); x0-3. primary growth framework crypts were formed by upright solitary, branching or laminar reef- building organisms, such as archaeocyath sponges (PI. 1, fig. 1), radiocyaths (PI. 1, fig. 5), coralomorphs (PI. 1, fig. 6) and calcified cyanobacteria (PI. 1, fig 3). Areas beneath toppled or reworked skeletal debris also provided shelter crypts (PI. 1, fig 4). Selective removal of pockets of sediment by currents or storms within accumulations of reefal debris also formed secondary crypts by early lithification of the remaining sediment. Such crypts may have initiated as open burrow systems (PI. 1, fig. 2). No crevice crypts have been noted, but this may be due their small size and difficulty of recognition. Peculiar sheet-like cracks have, however, been noted within the ‘Nemakit- Daldynian’ stromatolites of the Chapel Island Formation in southeastern Newfoundland (Myrow and Coniglio 1991). The lower parts of crypts were often infilled with homogenous or finely laminated micrite, together 448 PALAEONTOLOGY, VOLUME 38 with minor amounts of terrigenous material and variable quantities of bioclastic debris. Sediment infills, which may postdate some cement generations, were commonly microburrowed (PI. 1, figs 1 and 4), and may be layered and graded indicating episodic sedimentation. The upper parts of crypts may be filled with further generations of early and late cements. The presence of a variety of cements indicates that crypts developed in well-oxygenated and agitated conditions (James et al. 1976). Early cements were a ubiquitous feature of Lower Cambrian crypts, with microcrystalline and fibrous rimming cements being especially common (PI. 1, fig. 1; Text-fig. 2a). The in situ skeletal cryptobionta was attached to the walls and ceilings of the crypts, and encrusted framebuilders, other cryptobionts or the surfaces of synsedimentary cements (Text-fig. 3). LOWER CAMBRIAN CRYPTOBIONTS AND THEIR DISTRIBUTION Sessile crypt os Archaeocyaths. Archaeocyaths were aspiculate calcified sponges, which formed a high-Mg calcite skeleton via calcification of a collagenous template (Zhuravlev 1989; Wood 1990). They were probably closely related to demosponges (Debrenne and Zhuravlev 1992). Archaeocyaths displayed a variety of growth forms although solitary and low integration branching forms were by far the most common (Wood et al. 1992a). They appeared at the base of the Tommotian on the Siberian platform, after which they diversified rapidly to reach an acme in the Botomian. During the late Botomian-early Toyonian their diversity plummeted and only two species are known from the post Lower Cambrian (Wood et al. 1992 b). Archaeocyaths were a common to abundant faunal element in Lower Cambrian reefs, forming EXPLANATION OF PLATE 1 Types of Lower Cambrian reefal crypt Fig. 1. NTGS 810028; a domal cup of Sakhacyathus subatus (Zhuravleva) forming a crypt colonized by Renalcis jacuticus Korde; the first generation of geopetal micrite infill is burrowed and followed by a second layer; all sediment infill postdates R. jacuticus encrustation and the precipitation of fibrous calcite; the remaining pore-space is filled with sparry calcite; Locality 3 (Tommotian 2); x 5. Fig. 2. NTGS 810038; self-supporting cavity-system formed by synsedimentary lithification of a burrow system, possibly further enhanced by scour; parts of the crypt wall have been colonized by Renalcis jacuticus Korde (arrowed); Locality 5 (Tommotian 3); x6. Fig. 3. PIN 4451/90; crypt ceilings formed by rafts of the calcified cyanobacteria Razumovskia uralica Vologdin; the resultant crypts were colonized by pendent colonies of Epiphyton fruticosum Vologdin and juvenile individuals of the archaeocyath Spirocyathella kyzlartauense Vologdin (arrowed); Locality 25 (Botomian 1); x 7. Fig. 4. PIN 3848/702; shelter crypts formed by toppled cups of the archaeocyaths Dictyocyathus bobrovi Korshunov (top left), Nochoroicyathus anabarensis (Vologdin) (top centre and right) and Heckericyathus heckeri (Zhuravleva) (centre); crypts have been colonized by Renalcis jacuticus Korde, Archaeolynthus polaris (Vologdin) (lower centre), and Dictyocyathus bobrovi Korshunov; the geopetal micrite infills within the toppled archaeocyath cups have been extensively microburrowed; Locality 7 (Atdabanian 1); x 4. Fig. 5. PIN 3482/401; chain of pendent solitary archaeocyath individuals ( Nochoroicyathus changaiensis (Vologdin) (upper right), Cambrocyathellus pannonicus (Fonin) (centre) and Ajacicyathina gen. et sp. indet. (bottom) forming under the skeleton of the branching radiocyath Girphanovella georgensis (Rozanov); several individuals of the cribricyath Striatocyathus sajanensis Vologdin and Jankauskas are also present; Locality 19 (Atdabanian 4); x 5. Fig. 6. PIN 3848/703; framework crypt formed by the encrusting coralomorph Khasaktia vesicularis Sayutina; cryptobionts include pendent archaeocyaths Neoloculicyathus sibiricus (Sundukov) (centre and lower left), Dictyocyathus bobrovi Korshunov (upper left), the coralomorph Hydroconus sp. (upper and lower left); this cryptic fauna was subsequently encrusted by the calcified cyanobacterium Renalcis jacuticus Korde; Locality 7 (Atdabanian 1); x 10. PLATE 1 ZHURAVLEV and WOOD, Lower Cambrian reefal crypts 450 PALAEONTOLOGY, VOLUME 38 text-fig. 3. Schematic block diagram of a typical Lower Cambrian crypt. 1, archaeocyaths; 2, synsedimentary cements; 3, calcified cyanobacteria; 4, coralomorphs; 5, microburrowing metazoan; 6, bioclastic debris, including sponge spicules. up to 50 per cent, of the total rock volume of some bioherms. Most were attached by an epitheca to hard substrates, such as calcified cyanobacteria or archaeocyath, radiocyath and coralomorph skeletons. Some large solitary, regular individuals, although initiating upon small ephemeral hard substrates, may have been rooted in lime mud. Many had abundant exocyathoid buttresses which served for both stabilization and binding and as competitive exclusion structures (Brasier 1976; Debrenne and Zhuravlev 1992; Wood et al. 1992 a). Most irregular forms tend to be in growth □ TABULACYATH1DA 0 KAZACHSTANICYATHIDA 0 ARCHAEOCYATH IDA □ COSCINOCYATHIDA □ MONOCYATHIDA □ AJACICYATHIDA B LOWER CAMBRIAN LOWER CAMBRIAN LOWER CAMBRIAN LOWER CAMBRIAN text-fig. 4. Total number of archaeocyath species within each order in a, total bioherm community, b, cryptic communities only, c, percentage of each order within total communities, d, percentage of each order within cryptic communities only. Community proportions are averaged for each stage. ZHURAVLEV AND WOOD: CRYPTIC COMMUNITIES 451 table 2. Distribution of cryptobionts through the Lower Cambrian. X marks the certain occurrence of cryptic forms. ? marks the probable first appearance. * refer to James and Gravestock (1990) for detailed descriptions. Tommotian Atdabanian Botomian Toyonian ‘Nemakit- Cryptobionts Daldynian’ 1234 1234 123 123 Non-calcified bacteria Calcified cyanobacteria Korilophyton Aitgulocellularia Botominella Renalcis Tarthinia Girvanella Obruchevella Epiphyton Tubomorphophyton Gordonophyton Kordephyton Bija Chabakovia Wetheredella ‘ Encrusting microfossils’* ‘Calcareous microspheres’* Fungi Archaeocyaths: Monocyathida Ajacicyathida Archaeocyathida Kazachstanicyathida Coscinocyathida Tabulacyathida Cribricyaths Coralomorphs : Cysticyathus Hydroconus Khasaktia Rackovskia Aploconus Tabulaconus Labyrinthus Microburrowers Siliceous sponges Calcarean sponges Stenotheocids Archaeotrypa Pellets Unidentified borings Grazers Microborings < X- X- X ?-- X- X- ?-- X- X- X- -X- X- X- X- X X X- X- X X X---- X X X - X x X X-- X X — - - X X X---X X X x X X X---X X---X X---X x x ? X X X — X---- - - X X position, where branching individuals were often bound together to form bafflestones and laminar forms bindstones. Reworked archaeocyath skeletal debris was also a common component of inter- biohermal sediment. Contrary to previous accounts (Kobluk and James 1979; Kobluk 1981o, 1985), archaeocyaths were abundant cryptobionts; in most communities studied between 20-60 per cent, of the species represented were cryptic (Text-fig. 4). Monocyathid archaeocyaths appeared as an element in 452 PALAEONTOLOGY, VOLUME 38 o i — 0. > n o T1 T2 T3 T4 A1 A2 A3 A4 B1 B2 B3 TNI TN2 LOWER CAMBRIAN text-fig. 5. Percentage of cryptic regular and irregular species as a proportion of the total numbers of regulars and ir- regulars within individual bioherm com- munities. Community proportions are averaged for each stage. cryptic faunas in the Tommotian 1, with regular (Ajacicyathida) and irregular forms (Archaeo- cyathida) following in the Tommotian 2 (Table 2). Representatives from all six archaeocyathan orders (sensu Debrenne and Zhuravlev 1992) were present in crypts, but in markedly different proportions. Irregular archaeocyaths (Archaeocyathida, Kazachstanicyathida) formed between 7-80 per cent, (averaging approx. 35 per cent.) of the total bioherm community (Text-fig. 4c), yet between 30-100 per cent, (averaging approx. 55 per cent.) of the cryptic community (Text-fig. 4d). A far greater proportion of the irregular order Archaeocyathida and the regular orders Monocyathida and Coscinocyathida are represented in any one cryptic community than members of the regular orders Ajacicyathida and Tabulacyathida (Text-fig. 4a-b). During the early Lower Cambrian often all irregular archaeocyaths (archaeocyathids) present in any one community were both open surface and crypt dwellers (Text-fig. 5). Ajacicyathids were only a minor component of the cryptos, even though they were the most species-rich order in open surface communities (Text-fig. table 3. Differences in morphology and abundance between organisms which occur as both open surface inhabitants and cryptobionts. Biota Open surface Crypt Archaeocyaths Reef-builders Small, solitary irregulars predominantly and thalamid regulars modular irregulars + large regulars Abundant exothecal tissue Renalcis and Globular, compact Delicate branching, Epiphyton- groups arborescent Chabakovia Absent Present Khasaktia Sheath-like, encrusting Conical, small attachment site Microburrowing Rare Abundant (?)metazoan Cribricyaths Absent Abundant Hydroconozoans, Rare Common Labyrinthus and Rackovskia Archaeotrvpa ? Present Wetheredella ? Present ZHURAVLEV AND WOOD: CRYPTIC COMMUNITIES 453 4b, d). We have noted only one occurence of a tabulacyathid : Putapacyathus regularis Bedford and Bedford, which occurs in both the open surface and cryptic community (Locality 30; Botomian 3). For all communities where sufficient data is available, the Fisher Exact Test shows statistically significant underrepresentation of ajacicyathids, and significant enrichment of archaeocyathids within crypts at the 5 per cent, level. The diversity of archaeocyaths within Lower Cambrian cryptic communities was highly variable. Some communities show no cryptic archaeocyaths (localities 12 (Atdabanian 3) and 18 (Atdabanian 4)) whereas others were almost entirely cryptic, e.g. locality 22 (Botomian 1). Here, of the seven cryptic species, five were coscinocyathids (PI. 2, fig. 5). Although this community has yielded a total fauna of seventeen species, many of these forms were uncommon. In addition to differences in systematic distribution, cryptic archaeocyaths display distinct morphological differences from those typical of open surface, frame-building communities (Table 3). Firstly, all cryptic archaeocyaths have porous septa. Savarese (1992) argues that such forms were adapted hydrodynamically to low turbulence conditions, which is supported by the fact that modern cryptic niches generally create lower energy settings than the open environment. Secondly, Kobluk and James (1979, p. 203) noted that the rare archaeocyaths found in the lower Toyonian reefs of Labrador (Locality 36) were small and ‘poorly organized'. We note too that cryptic forms were often small, but have detected no evidence for any differences in their rate of growth compared with open surface conspecifics. Their small size appears to result from their reduced longevity, i.e. many were young individuals. Most interesting, however, is that those archaeocyath species which possessed both modular and solitary phenotypes, consistently displayed modular forms on open surfaces but solitary organizations in crypts (see Appendix for specific details). The only exception to this is Cambrocyathellus proximus, which was present in a modular state in both open surface and cryptic niches within the Tommotian 2 and Tommotian 3 reefs of Siberia. The encrusting, modular species Altaicyathus notabilis (PI. 2, fig. 6), Dictyofavus araneosus (PI. 2, fig. 2) and Zunyicyathus sp., however, appear to be obligate cryptobionts together with the chambered, encrusting forms Polythalamia americana and P. perforata Debrenne and Wood (PI. 2, fig. 3). When present, these forms were very abundant. Many cryptic archaeocyaths (both regulars and irregulars) show abundant exothecal tissue (epitheca and buttresses), which was probably necessary to secure firm attachment to the ceiling or walls of a crypt (PI. 1, fig. 6; PI. 2, figs 1-2). The pronounced ability to produce abundant exothecal tissue in the orders Monocyathida and Archaeocyathida might thus explain their preferential occupation of crypts. Archaeocyaths clearly preferred attachment to hard substrates, and pendent chains of individuals have been noted in larger crypts (PI. 1, fig. 5). Some archaeocyath individuals also show growth in a series of distinct morphological phases, where each phase appears as rapid growth followed by complete cessation (PI. 3, fig. 4). This might be related to periodic, possibly seasonal, environmental fluctuations. Calcified cyanobacteria. Calcified cyanobacteria were abundant in many Cambrian platform carbonates, and constructed reefal buildups throughout this period even after the extinction of the majority of archaeocyaths (Rees et al. 1989; James and Gravestock 1990; Wood et a/. 1992u). They were often associated with micrite, and may form a substrate for the attachment of other organisms. James and Gravestock (1990) have suggested that the micrite between Rena/cis colonies was originally a cement similar to modern sea-floor cements. Calcified cyanobacteria occurred as framework constructors in the form of substantial upright bushes or rafts, as encrustations around reef dwellers and as pendent colonies in crypts. All forms may have trapped sediment and many were common as facultative cryptobionts (e.g. PI. 1, figs 1-3). Renalcis , Angulocelhdaria , Chabakovia , Gordonophyton and Epiphyton were especially abundant in crypts, but only Chabakovia was a preferential cryptobiont. Renalcis and Tarthinia had a botryoidal external form, consisting of rounded compartments with micritic, fibrous or peloidal walls. Individual colonies are difficult to discern but all these forms 454 PALAEONTOLOGY, VOLUME 38 produced dense accumulations or crusts up to 5 mm thick. Girvanella formed encrusting sheets or rafts of intertwined microtubules. Korilophyton, Angulocellularia, Chabakovia, Gordonophyton , Epiphyton and Tubomorphophyton all formed dendritic colonies with bifurcating branches and micritic walls. Of these, Gordonophyton and Chabakovia were the most volumetrically important constituent in crypts (PI. 2, fig. 4). Epiphyton , with short, compact branches (PI. 1, fig. 3), and Tubomorphophyton, with hollow branches, were also common in crypts, whilst Kordephyton, which formed branches of radiating fine tubes, inhabited crypts but was generally a relatively uncommon component in Lower Cambrian bioherms. The previously problematic form Wetheredella, noted in the Toyonian reefs of Labrador (Kobluk and James 1979), was suggested by Riding (1991) to be a calcified cyanobacterium. This has been confirmed by the finding of Recent analogues in the mildly alkaline crater lakes of Indonesia, where an identical form grows in crypts and crevices between folliaceous calcified red algae (Kazmierczak and Kempe 1992). Other Lower Cambrian calcimicrobes noted to be cryptic have probably been misidentified. The calcimicrobe named Serligia noted in crypts from the Toyonian of Labrador (Kobluk and James 1979) is probably a fragment of Botominella. Likewise, the form Cavifera of Kobluk (1985) probably represents a coiled tube of Obruchevella sp. The form described by Myrow and Coniglio (1991) as Frutexites sp. is referable to Angulocellularia, and was probably a weakly calcified cyanobacterium. Kobluk and James (1979) noted that Renalcis and Epiphyton-growp calcified cyanobacteria exhibited phenotypy, showing globular and compact morphologies when growing upright on open surfaces, but delicate branches in an arborescent mode in crypts (Table 3). We confirm this observation. EXPLANATION OF PLATE 2 Fig. 1. PIN 3848/704; a rich cryptic community within a crypt formed by the calcified cyanobacteria Renalcis jacuticus Korde (upper left) and Epiphyton scapulum Korde (upper right); the cyanobacterial shrubs have been encrusted by the coralomorph Khasaktia vesicularis Sayutina, and the archaeocyaths Neoloculicyathus sibiricus (Sundukov), Dictyocyathus bobrovi Korshunov, and Erismacoscinus oymuranensis A. Zhuravlev; pockets of micrite within the crypt have been extensively microburrowed ; Locality 7 (Atdabanian 1); x 4. Fig. 2. PIN 4221/51 ; cavity created by the abundant secondary skeleton of the archaeocyath Anaptyctocyathus oppositus (Gravestock) and encrusted by the same species, as well as Dictyofavus araneosus (Gravestock) and the calcarean sponge Dodecaactinella cynodontota Bengtson and Runnegar (arrowed); these cryptic forms were subsequently engulfed by the secondary skeleton of A. oppositus'. Locality 14 (Atdabanian 3); x 5. Fig. 3. PIN 4451/69; crypt formed under a calcified cyanobacterial colony encrusted by the chambered archaeocyath Polythalamia perforata (Vologdin), which was subsequently completely overgrown by Clathricoscinus popovi Vlasov; Cryptic Cribricyathus sp. is also present (right); Locality 22 (Botomian 1); x 10. Fig. 4. PIN 3848/705 ; crypts formed by the calcified cyanobacterium Gordonophyton durum (Korde) encrusted by the archaeocyaths Dictyocyathus bobrovi Korshunov, Ajacicyathina gen. et sp. indet. and the calcified cyanobacterium Renalcis jacuticus Korde; Locality 7 (Atdabanian 1); x 12. Fig. 5. PIN 4451/91; a cryptic community of the chambered archaeocyaths Capsulocyathus irregularis (Zhuravleva), Tylocyathus bullatus (Zhuravleva), Clathricoscinus popovi Vlasov the cribricyath Cribricyathus sp. (top left and bottom right) and the calcified cyanobacterium Tubomorphophyton sp.; Locality 22 (Botomian 1); x 5. Fig. 6. PIN 4451/92; small crypts within a cyanobacterial bioherm, colonized by tiny individuals of the archaeocyath Altaicyathus notabilis Vologdin (arrowed), a weakly calcified coralomorph (lower right), and Epiphyton sp. and Renalcis sp.; Locality 34 (Botomian 3); x 10. Fig. 7. SM X24900; a cryptic individual of the coralomorph Khasaktia intermedia Sayutina, with an attached cryptic archaeocyath fauna of small individuals of Alataucyathus jaroschevitschi Zhuravleva (left), Nochoroicyathus changaiensis (Vologdin) (centre) and juvenile cups of Cambrocyathellus tuberculatus (Vologdin); Locality 20 (Atdabanian 4); x 3. PLATE 2 ZHURAVLEV and WOOD, Lower Cambrian crypts and communities 456 PALAEONTOLOGY, VOLUME 38 Coralomorphs. Early Cambrian calcified putative cnidarians, known as coralomorphs (Jell 1984), are represented by slender, irregular polygonal tubes or open cups and may occur as solitary individuals or small modular colonies (Zhuravlev et al. 1993). All forms were encrusting and many had extensive attachment areas. Of the ten early Cambrian coralomorph genera, at least seven were known from crypts (Table 2). Five were solitary forms ( Cystieyathus , Khasaktia , Hydroconus , Aploconus and Tabulaconus), with Rackovskia and Labyrinthus bearing a modular habit, although the biological affinity of the latter is uncertain (Kobluk 1979). The earliest coralomorph, Cystieyathus , was cryptic and appeared in the lower Tommotian. Hydroconus (appearing in the Tommotian 4), the branching form Rackovskia (Atdabanian 4) and Labyrinthus (Toyonian 1) were commonly cryptic, whereas Khasaktia , Aploconus and Tabulaconus were both open surface and cryptic dwellers (PI. 2, fig. 7; PI. 3, figs 1, 6). Khasaktia is the only coralomorph to show phenotypy (Table 3). On open surfaces, it forms an extensive encrusting sheet, whereas in crypts it forms a conical, open cup originating from a small attachment site (PI. 3, fig. 1). Cribricyaths. Cribricyaths were simple, usually solitary, narrow, conical or horn-shaped calcareous tubes with a bilaterally symmetrical cross-section. Although common in Lower Cambrian reefal sequences they remain largely problematic (Jankauskas 1972). Cribricyaths were obligate and abundant cryptobionts (PI. 1, fig. 5; PI. 2, fig. 5), appearing first in the Atdabanian 1 and disappearing from the record in the Toyonian 1 (Table 2). Siliceous sponges. Siliceous spicules of hexactinellid sponges first appeared in the Tommotian 1. Such spicules were common components of Lower Cambrian reefal sediments, and some crypts appear to be particularly enriched, perhaps representing disaggregated cryptobiontic sponges. Calcar ean sponges. Tor Herm, in the Australian Flinders Ranges (Locality 16; Atdabanian 4) yields an abundant encrusting sponge, described by Reitner (1992) as a pharetronid calcarean named Gravestockia pharetroniensis. The skeleton of this sponge, however, consists of triradiate spicules corresponding with the well known Cambrian form Dodecaactinella. This form is a common cryptobiont and often grew attached to the holdfast structures of cryptic archaeocyaths (PI. 2, fig. 2; PI. 3, fig. 2). Problematica. Various Lower Cambrian problematica are known only from reefal crypts (Table 2) and many are described from only one locality. These include ‘spherical algae’ (Kobluk 1985), ‘encrusting microfossils’ and ‘calcareous microspheres’ (James and Gravestock 1990), Archaeo- trypa (Kobluk 1984) and stenothecoids. Stenothecoids became common in bioherms from the early Atdabanian onwards. They were asymmetrical, bivalved organisms with a sinuous alimentary canal, and may represent a separate phylum (Rozov 1984). Most of the brachiopods and brachiopod-like forms noted from Lower Cambrian crypts (Kobluk and James 1979; Kobluk 1985) are stenothecoids, although brachiopods are indeed also rarely present. The ‘globular foraminifera’ identified by Kobluk (1985) are probably compartments of Tarthinia. Uncalcified biota. There is evidence for the presence of soft-bodied, encrusting organisms within Lower Cambrian crypts. Distorted areas on the undersurfaces of archaeocyath skeletons are noted, but in the absence of any preserved attached biota (PI. 3, fig. 3). These areas were subsequently bioimmured by calcified cryptobionts. In addition, in Locality 19 (Atdabanian 4), cryptobionts are frequently surrounded by an extensive crystalline area which may represent the remains of uncalcified microbial or bacterial encrustations. ZHURAVLEV AND WOOD: CRYPTIC COMM UNITIES 457 Vagrant crypt os Microburrowing (l)metazoan. Developments of spar-filled tubular or fenestrate fabric which branch at irregular intervals with numerous blind side branches are extremely common within pockets of micrite in Lower Cambrian reefs, especially within crypts (PI. 1, fig. 4; PI. 2, fig. 1). The diameter of the tubes is 100-500 /un, and the burrows extend within archaeocyath intervalla and pore-spaces. These forms first appeared in the 'Nemakit-Daldynian’ (R. A. Wood and P. D. Kruse, pers. obs.) and continued to be abundant throughout the Lower Cambrian (Table 2). Similar fabrics have been described from syndepositional crypts in the Lower Cambrian bioherms of the Forteau Formation of Labrador (Kobluk and James 1979), from late Atdabanian buildups of western Mongolia (Wood et al. 1993) and from mid-Ordovician bioherms of the Chazy Group of eastern Canada (Pratt 1982; Desrochers and James 1989). Kobluk and James (1979) and Wood et al. (1993) suggested them to be the traces of deposit-feeding worms. The presence of deposit feeders in crypts indicates, as noted by Kobluk and James (1979), that the crypt-infills were soft and that sediment accumulated while the crypts were still able to support life. Macroburrows. Macroburrows developed in some micrite crypt infills, often beneath the attached cryptos, and may contain pockets packed with consolidated and cylindrical faecal pellets (PI. 3, fig. 1). These burrows and pellets first appear in the Tommotian 2 (Table 2). Passive stowage of pellets within vacated regions of a burrow system is well known from the Recent and is generally attributed to the activity of infaunal worms (Schafer 1972). Planolites , Torrowangea , Teicliichnus , Paleophycus and three unidentified traces have also been noted (Kobluk and James 1979) from the crypts of the Toyonian 1 bioherms of Labrador (Locality 36). Endolitliic cryptos Borers. Kobluk (1981c) and Kobluk and James (1979) noted that although micro- and macroborers were present by the late Lower Cambrian (Toyonian 1), they had not invaded the cryptic habitat. In this study we have found possible evidence of bioerosion in the lowermost Tommotian reefs of Ulakhan-Sulugur (Locality 2). Here, probable borings are present on the walls and ceilings of crypts, and excavate lithified micrite as well as the cryptic biota of Renalcis jacuticus and Archaeolynthus polaris (Text-fig. 2b). The borings appear to have scalloped edges similar to modern sponge borings, but no excavated chips have been noted. Similar structures have been noted from Atdabanian 2 crypts (Locality 16), where the secondary skeleton of pendent archaeocyaths has been bioeroded (PI. 3, fig. 5). This style of bioerosion has only been noted in crypts, and was clearly present in metazoan reefs from their inception. Kobluk (1985) described sinuous microborings ( 14-20 pm diameter) from the Upper Shady Dolomite, Virginia. These borings show no evidence of branching, reproductive bodies or septation. Similar microborings have been ascribed to the endolithic cyanobacterium Endoconchia by Bengtson et al. (1990). Fungi. The first cryptic fungi are noted in the Tommotian 2 (Locality 3), where a dense, cotton-like mass of long, slender, branched tubes (0-3-10 mm diameter) covers the undersurfaces of the disc- shaped archaeocyath Okulitchicyathus discoformis (Text-fig. 2c). The relatively large size and flattened morphology of these tubes exclude them from being boring bacteria. Their size and distinct septation suggest them to be the hyphae of fungi (ascomyctes or oomyctes). ECOLOGY OF LOWER CAMBRIAN CRYPTS Competition for space in Lower Cambrian reefs must have been severe to produce differentiated and distinct open surface and cryptic communities. This is confirmed by the observation that 458 PALAEONTOLOGY, VOLUME 38 cryptobionts commonly formed multiple overgrowths or chains of individuals in crypts (PI. 1, fig. 5; PI. 2, fig. 1), indicating that much of the crypt surface was covered with both calcified and non-calcified organisms. The small patches of hard substrate provided by pendent archaeocyaths may have been the only areas available for colonization by later generations of cryptobionts. There is also evidence for encrustation of crypt-forming archaeocyaths during their life, as their calcareous skeletons show evidence of distortion in response to attached calcified and non-calcified cryptobionts (PL 3, fig. 3). The development of the cryptos was thus contemporary with framebuilder growth, and chains of pendent cryptobionts are also noted to have grown synchronously (PI. 3, fig. 6). The apparent diversity and abundance of life in any one crypt appears to have been a function of overall community diversity, the size of the crypt and the length of time crypts were available for colonization. The zone-averaged diversity of archaeocyath species within the cryptos through the Lower Cambrian shows a marked decline from the Tommotian 2 onwards (Text-fig. 4b). When analysed, however, as a percentage of total community diversity, no such trend is apparent (Text- fig. 6); crypt diversity, at least as reflected by the richness of the archaeocyath fauna, appears to be broadly a function of overall community diversity. Yet individual Lower Cambrian communities show a tremendous range of cryptobiont diversity, both within and between different communities. For example, the very dense bioherms formed by the calcified cyanobacterium Razumovskia in Eastern Sayan (Localities 11, 12 and 18) possess extremely small cryptic niches, and except for calcified cyanobacteria a cryptic biota was absent in spite of a rich open surface community of 20-45 archaeocyath species. In contrast, the large crypts formed during the mid late Tommotian of Siberia (localities 3-5) housed a diverse and abundant cryptos. Although this phenomenon is difficult to quantify, large cavities contain more abundant biotas with higher diversities, and also show more examples of multiple overgrowths and chains of individuals (e.g. PI. 1, fig. 5; PI. 2, fig. 1). EXPLANATION OF PLATE 3 Fig. I. PIN 3848/706; a secondary crypt formed by a cryptic individual of the coralomorph Khasaktia vesicularis Sayutina, which has been colonized by a further individual of the same coralomorph; the crypt was later infilled with nucrite, which has subsequently been burrowed; some burrows show the stowage of faecal pellets; Locality 8 (Atdabanian 2); x 5. Fig. 2. PIN 4221/52; a cryptic individual of the encrusting calcarean sponge Dodecaactinella cynodontota Bengtson and Runnegar forming a further crypt colonized by pendent Ajacicyathina gen. et sp. indet. (left) and Archaeocyathina gen. et sp. indet. (right); the archaeocyath Metaldetes ferulae Gravestock and the calcified cyanobacterium Chabakovial sp. are attached to the cup of Archaeocyathina; Locality 15 (Atdabanian 3); x 7. Fig. 3. PIN 3848/707; distortions caused by the attachment of Hydroconus sp. (right) and uncalcified biota (arrowed) to the undersurface of the archaeocyath Dictyosycon gravis Zhuravleva; this fauna developed underneath the toppled cup of Arturocyathus varlamovi A. Zhuravlev and Renalcis jacuticus Korde; Locality 7 (Atdabanian 1); x 15. Fig. 4. PIN 3848/708; a succession of cryptic, encrusting archaeocyath individuals Neoloculicyathus sibiricus (Sundukov), and Ajacicyathina gen. et sp. indet. (bottom), encrusted by the calcified cyanobacterium Gordonophyton durum (Korde) and Renalcis jacuticus Korde; Locality 7 (Atdabanian 1); x 15. Fig. 5. PIN 4221/53; probable borings with scalloped edges, within a spicule-rich mud-infilled crypt inhabited by the archaeocyaths Rozanovicoscinus stellatus Gravestock and Ajacicyathina gen. et sp. indet; the boring has excavated both lithified micrite and the secondary skeleton of a pendent archaeocyath; Locality 16 (Atdabanian 4); x 12. Fig. 6. PIN 445 1 /93 ; interacting cryptic growth of two cups of Hydroconus sp. and a solitary individual of the archaeocyath Loculicyathus tolli Vologdin; Locality 23 (Botomian 1); x 5. Fig. 7. PIN 3848/709; abundant individuals of the chambered form Cellicyathus sp. within an individual crypt; Locality 33 (Botomian 3); x 10. PLATE 3 ZHURAVLEV and WOOD, Lower Cambrian crypts and communities 460 PALAEONTOLOGY, VOLUME 38 LOWER CAMBRIAN text-fig. 6. The percentage of cryptic species within the total bioherm com- munity through the Lower Cambrian. Community proportions are averaged for each stage. Although the total diversity of cryptic archaeocyaths may be high for any one community, individual crypts, especially those of limited size, were often dominated by a limited number of species (e.g. PI. 3, fig. 7). This suggests that, as on open surfaces, crypts were colonized rapidly by a limited number of larval spat falls. On modern hard substrates, solitary organisms are poor space competitors as they generally have small areas of attachment and lack specific competition mechanisms (Jackson 1977, 1985; Hughes 1989). They appear to be more dependent upon disturbance processes to provide suitable sites for settlement and growth than modular organisms. Small size, rapid growth rates and short generation times favour generalist, opportunist or fugitive life strategies (Jackson 1977). However, many solitary species occur throughout a wide range of modern cryptic habitants, whereas most modular forms, especially the best competitors for space, are more limited in the range of depths and substrates that they occupy (Jackson 1977). In Jamaica, modern foliaceous coral undersurfaces routinely survive tens to hundreds of years (Hughes and Jackson 1980) and are dominated by dense growths of clonal animals and plants (Jackson 1977; Jackson and Winston, 1982). In contrast, shorter-lived substrates, such as Pinna shells, are sparsely colonized by scattered serpulids and bryozoans. Jackson (1985) thus proposed that the ratio of modular to solitary species is a function of substrate longevity and, indeed, studies on community development in modern reefal crypts (e.g. Choi 1984) demonstrate that over time an ecological succession takes place from solitary, generalist forms to modular, encrusting organisms. No such succession has been noted in Lower Cambrian crypts. Lower Cambrian cryptic systems seem to have been dominated by organisms with solitary organizations, be they archaeocyaths, cribricyaths or coralomorphs, often together with multiple generations of calcified cyanobacterial colonization. Solitary archaeocyaths, which were out-competed by the larger, branching forms on the open surface, were competitively superior in crypts. Although the modular species Altaicyathus notabilis , Dictyofavus araneosus and Zunyicyathus sp. can be abundant in crypts, they were often engulfed by the extensive growth of the secondary tissue of solitary forms (PI. 2, fig. 2). Modular soft-bodied forms such as siliceous sponges may, however, have been very important competitors in Lower Cambrian crypts. The continued dominance of solitary archaeocyaths within crypts throughout the Lower Cambrian is especially noteworthy as modular archaeocyaths became increasingly available during this period (Wood et al. 1992a). This, together with the limited number of species present within any one crypt, might suggest that Lower Cambrian crypts were short-lived structures compared with modern reefal crypts, and may have suffered frequent disturbance. These ecological observations are supported by the fact that cryptobionts are noted to grow against and be distorted by the precipitation of synsedimentary cements (Text-fig. 2a). Such cements would have grown rapidly, and would have reduced markedly the size of the cavities as well as leading eventually to the total occlusion of crypt openings. ZHURAVLEV AND WOOD: CRYPTIC COMMUNITIES 461 Although it is difficult to quantify the longevity of individual Lower Cambrian bioherms and their crypts, the small size and dominant solitary to low integration organizations of the framebuilding metazoans (archaeocyaths, radiocyaths and coralomorphs) also suggests that they were relatively short-lived communities (Wood et al. 1993). Both Lower Cambrian crypts and their occupants were small compared with modern examples. Modern reef cavities may be vast, and will contain cryptobionts exhibiting a considerable range of sizes. The Lower Cambrian reef ecosystem was thus markedly different from its modern counterpart, with the rapid establishment of an aggregating open surface community of heterotrophs and phototrophs and an attendant cryptos with short generation times, in areas of relative environmental instability (Wood et al. 1992