Life Sciences Contribution Royal Ontario Museum T O06 Conodont Ultrastructure: The Subfamily Acanthodontinae C)M , Mi i Wi 1 a) hee’ we Ara > ie tT . ‘ i) fat sW. rin ; 1 ) : 1}; ae { FA Pay ‘ W 4 : { hol ntely M bs tt q Yu ta) ta eoag iT a ie 4 (ea ] TA icf 1ehay | eu ‘ihe : { (yy kee ; Da ah i } : | 7 , i ' Ky Ky } tig 4 1%). : tj 1h ae Vi oye AN iRe A why ard a ANNE i] : ”- i} RY f ey) }) at we ate INN Lia i tif : ; yhnae by ‘NY iyi \ | ) Wh 1 Nyy anh yes aye ahha DUAR VEAL TE i Kas 1) ri. A : ee i TA "t i as (0 ay t Vii \ i\ ere Taha iy ip! { \y { ; ! : ie ew ‘ { } 4 iit ey i Mh \ i'n I ele f 7 wae yy | AMR MLGA MAIC UREA / j | Tt ; } ae ry ; ,j ; it ' : A} : 3 ' f } j j LF ) A ; i) } \ : \ : | . | : : } { \ Wns TEAM: | | h he | 7 , wet Mi tt NL AD ING i i \ \ \ \ 1 \f | i at ny i} MY BY YS Vay . . 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ROYAL ONTARIO MUSEUM PUBLICATIONS IN LIFE SCIENCES The Royal Ontario Museum publishes three series in the Life Sciences: LIFE SCIENCES CONTRIBUTIONS, a numbered series of original scientific publi- cations, including monographic works. LIFE SCIENCES OCCASIONAL PAPERS, a numbered series of original scientific publications, primarily short and usually of taxonomic signifi- cance. LIFE SCIENCES MISCELLANEOUS PUBLICATIONS, an unnumbered series of pub- lications of varied subject matter and format. All manuscripts considered for publication are subject to the scrutiny and editorial policies of the Life Sciences Editorial Board, and to review by persons outside the Museum staff who are authorities in the particular field involved. LIFE SCIENCES EDITORIAL BOARD Chairman: W. M. TOVELL Editor: J. Cc. BARLOW Associate Editor: A. R. EMERY Associate Editor: D. W. BARR CHRISTOPHER R. BARNES is a Research Associate, Department of Invertebrate Palaeontology, Royal Ontario Museum, and an Associate Professor in the Department of Earth Sciences, University of Waterloo, Waterloo, Ontario. DOUGLAS J. SLACK is a recent Honours graduate of the Department of Earth Sciences, Uni- versity of Waterloo, Waterloo, Ontario. PRICE: $1.50 © The Royal Ontario Museum, 1975 100 Queen’s Park, Toronto, Canada PRINTED AND BOUND IN CANADA AT THE JOHN DEYELL COMPANY Conodont Ultrastructure: The Subfamily Acanthodontinae Abstract The ultrastructure of representatives of the condont Acanthodon- tinae has been studied with the aid of the scanning electron mic- roscope. Five form species of Scolopodus and one of Ulrichodina are the most common taxa of this subfamily in those faunas from which material was selected: St. George Formation, northern Newfoundland; Baumann Fiord Formation, Ellesmere Island; and Mystic Formation, southern Quebec. These species are typical of Lower and early Middle Ordovician faunas of the Midcontinent Province. Etched longitudinal and transverse sections were studied to determine internal structure for comparison with external mi- cromorphology. The cone-in-cone lamellar structure is modified in certain taxa through secretion of localized lamellae that lengthen the element distally and/or proximally and construct prominent carinae and costae. In other taxa, fine external striae can be de- tected: on internal lamellae representing early ontogenetic stages. Two species (S. emarginatus, S. gracilis) display radial lamellae supporting a close relationship with the Panderodontidae. Most structures of the elements parallel the postero-anterior plane and may be strengthening adaptations in that plane for these simple Comes. Key Words: conodont; ultrastructure; Acanthodontidae; Scolopodus; Ulrichodina; Ordovician. Introduction The study of the internal structures of conodonts has greatly increased with the advent of the scanning electron miscroscope (SEM). High magnifications and various sectioning techniques used by recent workers (e.g., Barnes, Sass, and Monroe, 1970, 1973; Barnes, Sass, and Poplawski, 1973; Lindstrém and Ziegler, 1971; Lindstrom et al., 1972; Miiller and Nogami, 1971; Pierce and Langenheim, 1969, 1970; Pietzner et al., 1968) have provided new data to assist in the taxonomic classification of conodonts. For example, Lindstrém’s (1970) proposed suprageneric classification is partially based on the micromor- phology of the conodont elements. It might be assumed, yet needs to be verified, that those taxa with similar sur- face micromorphology are closely related. It is not known to what extent surface features persist through all growth stages and thus may be preserved in the in- terior of the conodont elements. Even the basic cone-in-cone pattern of cono- dont growth appears to be more complex than earlier believed. For instance, a | different form of lamellae, radial rather than concentric, has recently been de- tected in certain taxa, and there is now evidence that particular concentric lamel- lae did not extend over the entire element (Barnes, Sass, and Poplawski, 1973) in the manner commonly depicted (e.g., Miiller and Nogami, 1971). In a recent study of one of the most common Lower Palaeozoic simple cone genera, Panderodus, both concentric and radial lamellae were noted (Barnes, Sass, and Poplawski, 1973). The inner lateral surface of specimens of Pandero- dus is characterized by longitudinal striae, subparallel to the longitudinal fur- row, that are the surface expression of the radial lamellae. It seemed possible, therefore, that other simple cones exhibiting marked surface striations might possess radial lamellae. A further hint of this possibility was provided by a vague radial pattern shown on the fractured surface of a specimen of Scolopodus gracilis (Barnes and Poplawski, 1973, pl. 3, fig. 7A). Thus, this species and others of Scolopodus were investigated to determine their internal structure. A few other taxa in Lower Ordovician faunas also exhibit surface striations. One of the most common of these is Ulrichodina, and the type species, U. prima, was also selected for examination. This paper thus summarizes the results of the ultrastructure studies of five species of Scolopodus (S. cornutiformis, S. emar- ginatus, S. gracilis, S. multicostatus, S. quadraplicatus) and one of Ulrichodina (U. prima). Taxonomic Status of Scolopodus and Ulrichodina A current revolution in conodont taxonomy involves supressing, where possible, form taxa in favour of multielement taxa. Factors involved in the erection of such taxa include surface micromorphology and the presence, abundance, and distribution of white matter that is usually located in the distal portions of the cusp and denticles (Lindstrom, 1964, pp. 17-22). In his recent revision of certain Lower Ordovician conodonts into multiele- ment taxa, Lindstrém (1971, pp. 40-41) emended the genus Scolopodus to in- clude “hyaline, drepanodiform elements with rounded cross-section and sym- metrical as well as asymmetrical elements. The sides of the elements may be finely costate. The base is not expanded greatly”’. In his work with Baltoscandian conodonts, Lindstrom (1955, 1971) encountered only Scolopodus rex Lind- strom, which comprises a minor proportion of those and other faunas of the North Atlantic Province. However, other species of Scolopodus are dominant components of contemporaneous faunas of the Midcontinent Province (e.g., Barnes, Rexroad, and Miller, 1973; Bergstrom, 1973). This province, which 1s represented in North America, Australia, and Siberia, is interpreted as being developed in epeiric seas with high temperatures and salinities located in tro- pical latitudes (Barnes and Fahraeus, 1975). The North Atlantic Province is regarded as a fauna occupying normal marine environments. While S. rex of the Baltic area is hyaline, i.e., virtually devoid of white matter, the species examined in this study possess variable amounts of white matter. In most, this was confined to the central growth axis and adjacent areas. However, in S. cornutiformis white matter is present generally in the distal three-quarters of the cusp. Thus, the generic definition proposed by Lindstrom (1971) will probably require emendation. Perhaps the erection of a new genus for the scolo- Zz podids discussed herein is justified, but this must await a detailed study of large collections. It is possible that the scolopodids of the European and Midcontinent pro- vinces were closely related during the early Arenigian but became separated with increasing provincialism during that epoch. Alternatively, the scolopodids of the two provinces may be taxonomically different at a suprageneric level. Lind- strom (1970, pp. 231, 233) advocated this view in bringing Scolopodus Pander (including Scolopodus rex; Lindstrom, 1971) to the Oistodontidae of the Chirognathacea, while those scolopodids typical of Midcontinent faunas were assigned to the Acanthodontidae of the Panderodontacea (Table 1). Although not listed by Lindstr6m (1970), it would appear that Ulrichodina also belongs in the Acanthodontidae (Acanthodontinae) on the basis of its morphology, micromorphology, and similar geographic and stratigraphic range, and is thus included in this paper. In previous studies, the only representatives of this sub- family examined by Lindstrom and Ziegler (1971) in their study of ultrastruc- ture in the Panderodontacea were single specimens of the form species A contio- dus iowensis Furnish and cf. A. staufferi Furnish. The detailed ultrastructure of the closely related Panderodontidae has been described by Barnes, Sass, and Poplawski (1973); that of the Chirognathidae was discussed by Barnes, Sass, and Monroe (1973). Table 1. Part of Lindstrom’s (1970) suprageneric classification of conodonts. Scolopodids have been placed in both the Oistodontidae and Acanthodontinae. Superfamily Chirognathacea (Branson and Mehl, 1944) Family Oistodontidae Lindstrom, 1970 Family Chirognathidae Branson and Mehl, 1944 Family Rhipidognathidae Lindstr6m, 1970 Superfamily Panderodontacea Lindstrom, 1970 Family Acanthodontidae Lindstrém, 1970 Subfamily Acanthodontinae Lindstrém, 1970 Subfamily Protopanderodontinae Lindstrém, 1970 Family Panderodontidae Lindstr6m, 1970 Materials and Methods The specimens were obtained primarily from the St. George Formation (Lower Ordovician) of northern Newfoundland, with supplemental material from the Mystic Formation (Middle Ordovician) of southern Quebec and Member B of the Baumann Fiord Formation (Lower Ordovician) of central Ellesmere Is- land, Arctic Canada. They were part of faunas that have been discussed by Barnes and Tuke (1970), Barnes and Poplawski (1973), and Barnes (1974) respectively. The studied specimens represent six form species within two form genera as outlined in Table 2. All the specimens used for internal ultrastructure studies were first embedded in Bioplastic (Ward’s, Rochester, N.Y.) in the desired ori- entation and then ground down with a carborundum grinding wheel. They were buffed to a high polish with the use of a felt disc and tin oxide polishing com- pound, and finally etched with 2N HC1 for approximately 30 seconds before being coated and viewed in the Cambridge Stereoscan Mk. IIa scanning electron microscope at the University of Waterloo. Both longitudinal and transverse sections were prepared for each species. Other sections present oblique views or areas around the basal cavity. Several good specimens were sectioned serially by repeated grinding. Seventy speci- mens (Table 2) were used, the majority for examination of surface micromor- phology but with many selected for internal studies, and from the latter group 27 sections were prepared. All specimens are deposited in the Department of Invertebrate Palaeontology, Royal Ontario Museum, Toronto, Ontario. Table 2. Taxa used in study. No. of No. of Localities and Species Specimens Sections St. George Formation, Newfoundland, (L. Ord.) Scolopodus cornutiformis Branson and Mehl (1933) 9 4 S. emarginatus Barnes and Tuke (1970) 12 4 S. gracilis Ethington and Clark (1964) 4 2 S. multicostatus Barnes and Tuke (1970) fT! 2 S. quadraplicatus Branson and Mehl (1933) 28 8 Ulrichodina prima Furnish (1938) 5 Z Mystic Formation, Southern Quebec, (Mid. Ord. ) U. prima Furnish (1938) 1 1 Member B, Baumann Fiord Formation, central Ellesmere Island, (L. Ord.) S. gracilis Ethington and Clark (1964) Z 4 U. prima Furnish (1938) Z 2 Total 70 27 Ultrastructure of Acanthodontinae The cusp of most conodont elements is constructed of two types of material: hyaline (lamellar) material and white matter (Lindstrom, 1964). Both the hya- line material and the white matter are similar in chemical composition (see Pietzner et al., 1968). Hass and Lindberg (1946, p. 503) concluded that the crystallographic axes and the optic axes of the individual crystallites are coinci- dent, and that the ‘“‘crystal units in each lamella of a conodont are oriented in conformity with the direction in which the conodont grew”. Hyaline and White Matter The hyaline matter of the conodonts considered herein is composed of innumer- able microscopic crystallites arranged into lamellae (Figs. 5D, E; 6C, D, E). When viewed in longitudinal section, the lamellae appear to be composed of crystallites arranged end-to-end with the long axes (c-axes) oriented almost parallel to the long axis of the conodont (Fig. 5D, E). In cross-section, the cry- stallites appear to be oriented side by side, with their c-axes perpendicular to tte plane: of the sectron; to form concentric lamellae (Fig.-6c, p, EE), Each lamella is separated from those adjacent to it by irregular interlamellar spaces but is fused to them irregularly along its length and width (Figs. 4B; 5£; 6p, E). The interlamellar spaces of the studied specimens are not well defined and are usually only inferred from a linear arrangement of voids paralleling the lamella. The etching process may have enhanced their definition. No basic dif- ference, however, was noted in hyaline matter as described by previous workers, nor in the size of crystallites and lamellae as reported by Lindstrom and Ziegler (1971) for specimens of the Acontodontinae. White matter is an opaque white material of virtually identical chemical com- position to the hyaline material, but it differs in several respects. It does not dis- play the regular crystallite arrangement of the hyaline material, but appears virtually structureless. It is, however, permeated by numerous irregular voids (Figs. 3p; 5p, E). These holes are small (less than Q.5um) and apparently are randomly distributed throughout the white matter. The larger, somewhat linear voids do, however, show a very crude alignment, roughly parallel to the inter- lamellar spaces of the hyaline matter, and may indeed be the remnants of these interlamellar spaces. White matter is generally accepted as being a secondary product of reorganized hyaline material. If so, one would expect to find the two substances in the pro- cess of recrystallization. This process is observable in a transition zone along the boundary of the two. The transitional material has been termed incipient white matter by Barnes, Sass, and Monroe (1973). Fig. 5p, E shows this transition in a longitudinal section of §. quadraplicatus, revealing that the transition begins with the appearance of small holes in the crystallites. The interlamellar spaces close and form irregular lines of voids rather than consistent interlamellar spaces. The crystallites lose their hexagonal habit and form agglomerates. This process continues until all apparent crystallite structure is lost and the true white matter is formed. Fig. 1c, D shows the closure of the interlamellar spaces and 2 the formation of irregularly spaced holes within the crystallites and lamellae prior to complete recrystallization. Surface Micromorphology In their study of the ultrastructure of the Panderodontacea, Lindstrém and Zieg- ler (1971) outlined six types of surface ornamentation on their specimens, namely: smooth surfaces, fine striae (<0.7 um), coarse striae and ridges (>0.7 pm), basal wrinkles, longitudinal furrow, and denticles. The last feature (den- ticles) was not observed in this study, since only simple cones were examined. While basal wrinkles are absent, we found all of the other features described by Lindstrom and Ziegler (1971). Smooth surfaces appear in localized areas on some of the specimens studied herein. U. prima displays this feature on the crest of the larger costae and along the anterior edge. S. cornutiformis has smooth surfaces along and close to the anterior edge and displays only a few fine striae posteriorly. Abundant fine striae are found on S. multicostatus, S. emarginatus, S. gra- cilis; ‘and U. prima. (Figs. 2A;-B; 3a; 6A; By, and toa lesser extentvomss. cornutiformis and S. quadraplicatus (Figs. 1A; 5A). The overall pattern of striae is commonly continuous over the length of the conodont, as seen in Figs. 2A, B and 6A, B. However, individual striae seldom extend the entire length of the cusp, tending to merge and pinch out at irregular intervals along it. Fine striae seem to be the surficial representation of the irregular edges of the outermost lamellae. The crystallites forming these lamellae are arranged in roughly parallel rows, thereby forming the fine striae. The fine striae pinch out or merge at some point along their length, because fewer crystallites are required to complete an individual lamella toward the tip of the cusp. The coarse striae and ridges are represented here on specimens of S. cornuti- formis, S. quadraplicatus, S. gracilis, and U. prima (Figs. 1A, B;, 3A; 5A; 6A, B). They are formed by the orientation of lamellae within the cusp and vary from the narrow, sharp ridges and grooves of S. cornutiformis to the broad, shallow ridges of S. gracilis. The methods of building these ridge-groove systems will be discussed below. Only one of the studied species displays a deep longitudinal furrow, S. emar- ginatus (Fig. 2E, arrow). The longitudinal furrow is a narrow and deep postero- lateral groove. It extends inwards almost to the growth axis and runs along the posterior edge to near the tip of the cusp, where it has not yet developed. Lind- strom and Ziegler (1971) suggested that the furrow may represent a site of muscle attachment. Internal Structures Several noteworthy structures are displayed in the various specimens of this study (Table 3). Some of these structures, such as the growth axis and, to some extent, the distribution of white matter, are common to all. Others, such as keels, the longitudinal furrow, radial lamellae, and special concentrations of white matter, are restricted to particular species. The ubiquitous structure is the growth axis. This is a cylindrical tube running Table 3. External and internal features of the taxa studied. 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