peeeinet eG a Trt tava ot OF AAV LLL at tative be rrarened gn nofek me po re ae eee eye restore Howe ook ee near MUS. COMP, ZOOL LIBRARY. FEB 1” 1966 Ostilla PEABODY MUSEUM OF NATURAL HISTORY YALE UNIVERSITY NEW HAVEN, CONNECTICUT, U.S.A. Number 94 December 22, 1965 THE LATE CRETACEOUS COLEOID CEPHALOPOD ACTINOSEPIA CANADENSIS WHITEAVES KARL M. WAAGE PEABODY MUSEUM OF NATURAL HISTORY AND DEPARTMENT OF GEOLOGY, YALE UNIVERSITY ABSTRACT Eighteen new specimens and seven of eight previously reported speci- mens of the coleoid fossil Actinosepia canadensis Whiteaves provide data for redescription and interpretation. The monotypic genus is known only from Late Campanian and Maastrichtian strata in the northern Great Plains region of the United States and Canada. Its gross morphology and shell structure require its inclusion in the teuthidid family Trachyteuthidae, but also suggest relationship, possibly ancestral, to the sepiids. INTRODUCTION Parts of eighteen individuals of the rare coleoid cephalopod Actinosepia canadensis Whiteaves, are among a large collection of invertebrate fossils gathered during studies of the Fox Hills Formation (Maastrichtian) in South Dakota and Wyoming. Only 8 specimens of Actinosepia have been reported previously, all of these are also from the Late Cretaceous of the western interior of North America. The specimens are in various stages of preserva- tion and none are perfect. Collectively they permit a more detailed 2 Postilla Yale Peabody Museum No, 94 morphologic description than now exists for Actinosepia. Certain aspects of the shell and its structure raise questions concerning the systematic position of this monotypic genus, and features of its distribution in the Fox Hills Formation suggest habits differing from those of its cephalopod contemporaries. The dominantly corneous shell of Actinosepia is broad, trans- versely arched, and concave ventrally in its posterior part, the whole resembling the inverted bowl of a spoon (fig. 1). In this respect and in certain details of its structure it is similar to the dorsal layers of the shell of Sepia, but it differs markedly from the sepioid shell as a whole in lacking the characteristic spongy, ven- tral pad of chalky lamellae. Naef (1922, p. 135) interpreted simi- lar sepia-like coleoid shells that lack a ventral pad as teuthidids (Mesoteuthoidea) and extended the term gladius to apply to them as well as to the more familiar, slender teuthoid “pens” to which the term was originally applied. Gladius, as used here in reference to the shell of Actinosepia, is a general term applicable to any dominantly corneous, internal coleoid shell that lacks either a calcareous pad or a true phragmocone. The term pad, a direct translation of the German term Wuist, employed by Appellof (1893) in his classic work on the shell of Sepia, is used in pref- erence to the more common “phragmocone”’ because the latter is an incorrect and subjective extension of a useful term in cephalo- pod morphology. The sepioid pad perhaps may be homologous with part of the cephalopod phragmocone but it is not in itself a chambered cone. For encouraging this redescription of Actinosepia, | am in- debted to Dr. J. A. Jeletzky who made possible the loan of the holotype and other specimens from the Geological Survey of Canada. Dr. Jeletzky kindly read the manuscript, although his views on coleoid phylogeny do not agree with the origin of sepiids suggested as a possibility herein. I have profited from discussions of shell structure with Dr. Copeland MacClintock and from his critical reading of the manuscript. I also wish to thank Drs. W. G. E. Caldwell, W. A. Cobban, A. W. Fischer, R. W. Landes, L. S. Russell and N. F. Sohl for their efforts in helping me locate Figure 1. Reconstruction of Actinosepia canadensis Whiteaves: dorsal aspect and longitudinal profile. Approximately X 24. Based largely on GSC 19888 (Pl. 2). Drawn by Carl Wester. ZOOL Y 1966 LIBRAR Ht ~ Oe NO NN No 10 NO Nagy RD Se) = ( } i Cae) Sl ae ee a ae eee ~~ — 5S ae a ae VA VI EB f Dec. 22, 1965 Actinosepia canadensis Whiteaves t Postilla Yale Peabody Museum No. 94 all but one of the known specimens for this study. Martha Dimock, David Keith and Michael Waldman assisted with preparation of specimens and illustrations; the reconstruction of Actinosepia was drawn by Carl Wester. Grants from the National Science Founda- tion (G-5657, G-18674) that made possible the study of the Fox Hills Formation and its faunas are gratefully acknowledged. OCCURRENCE Specimens of Actinosepia canadensis have been reported pre- viously from three localities; this paper records their occurrence at three additional localities, one of which is a fairly large area that includes a number of individual sites. The distribution and strati- graphic position of these localities is shown in fig. 2. The ini- tial report on Actinosepia is based on four specimens collected - - i Rive, i if ‘ A Le B E R TA e f et ' ‘ OY A—Whiteaves,|897 ! € a South Sos* SASKATCHEWAN C8 —Londes, 1940 \ : : AN 5 See ei a 4 ae lo je a a a aw ee i »> Ik R | Ve, i NORT H \ MONTANA y axe DAKOTA ei _Jensen & igs . C Varnes, | 1964 s I z | ° f ! ~ = ; =e | aay a a Stage and Zone | ata : pees = he a a : ie ‘ i Pn ¥ ; SOUTH z IA |B |C|DIE IF | seer) = x aired Ee! DAKOTA = Sphenodiscus x | et = WYO yy = — | x & ‘ | | Baculites clinolobotus fe rile ai | S - ='m Le m|@ sebp|qwassp =< SEY «ae Sodees Seeeae = ’ a ol=z S}jOstu SsayiydossojdoyH samo y 1¥9|]09}U 4addf~ yO uol¥nqiaysig Sie |O (S|DNPIAIpu! yO ‘OU= S|D4aWNU) UMOUYUN Ty 9807 Jequiy w S|9A98| JOYLO WO4} DidasoUljoV $DO0|J B]qDqoid o aodpDid Ue Hf Tya]JOOTU SafiydOoSoO;doH saddy J9A9| 1}a|JOo1U 4addy wWo4j DIdasouljoy OW OTAXO -— O1pi0d0401g S3JNOZ 39V1IEW4ASSV Saj!W O} 10) = 2 8 8 68 | Didasouljoy $O UOl}DAJUBDUOD |[DIO7 OS 499} OO| on ee i 34a Id TWVYL \ ALIS maaalal lo Sie Lal ind | [0 nikeas! y3gW3w 909° 6A Y3SSWIAW 3NV71 Y3SSEWIL ainsi i _ JIVHS XO4 Y3IMO 1 SW) IUItal 12 Postilla Yale Peabody Museum No. 94 current flowing southwestward through the area was a critical factor in the periodic local presence of a rich bottom fauna. Other paleogeographic features indicate that open sea lay to the south and ESE of the lobate area. The majority of Actinosepia specimens come from the horizon of the Upper nicolleti Assemblage Zone and their geographic con- centration (see fig. 3) is west of the southwestern end of the area occupied by the Upper nicolleti accumulations. The Upper nicolleti Assemblage Zone is the second of two levels of rich fossil assem- blages characterized by an abundance of the scaphitid ammonoid Hoploscaphites nicolleti; it is restricted to a smaller area of distri- bution than the other assemblages in the lower 50 feet of the Fox Hills Formation. The more common associates of H. nicolileti in the upper assemblage are two or three other scaphitids of the genus Discoscaphites, and the pelecypods Oxytoma nebrascana, Proto- cardia subquadrata and Inoceramus fibrosus. Within the Upper nicolleti Assemblage Zone the fossils occur in scattered large cal- careous concretions up to as much as 20 inches in diameter. The zone also includes some small ovoid concretions, generally barren of fossils. At the abrupt western edge of the Upper nicolleti assem- blages in the Moreau River valley the zone changes to an interval from four to eight feet thick, containing numerous small, round to ovoid concretions most of which are unfossiliferous; the Actinosepia specimens are from concretions in this interval. In the Grand River valley to the north the situation is not parallel, inasmuch as the Upper nicolleti zone pinches out westward and its laterally equivalent interval of small concretions is missing from the section, presumably because of nondeposition. Species associated with Actinosepia in the interval of small concretions are mostly the ammonoids Hoploscaphites nicolleti, Discoscaphites cheyennensis, and a large Discoscaphites related to D. nebrascensis. A few clusters of Oxytoma nebrascana occur in the small concretions near the west edge of the Upper nicolleti assemblages but pelecypods, other than a few scattered proto- branchs, are exceedingly rare. A few of the concretions contain claws and carapaces of crustaceans. Fragments of fossil wood also were found, including a ten-foot section of the slender trunk of what is possibly a sabaloid palm (Delevoryas, 1964, p. 585). As the interval of small concretions was not collected systematically Dec. 22, 1965 Actinosepia canadensis Whiteaves 13 throughout its area of outcrop but only sampled at a few localities the frequency of occurrence of Actinosepia is not known. At the locality where five specimens were found (see fig. 3) the outcrop of the interval was searched more thoroughly and over a greater area, approximately half a square mile of intricately dissected river olufis. The density of Actinosepia specimens is thus not great and there is no indication from the fossil distribution that they were gregarious; in this respect they contrast markedly with their ammonoid neighbors to the east, Hoploscaphites nicolleti, whose fossil masses at the same horizon indicate that they were swarm- ing at the time of their death. Although specimens of Actinosepia are few, their geographic grouping at a particular stratigraphic level takes on significance in the context of the strongly patterned distribution of fossils demon- strated for the type Fox Hills. The obvious feature in their distri- bution at the Upper nicolleti level is the location of all but one of the 12 specimens in an area peripheral to rather than within the lobate area of abundant fossil accumulation (fig. 3). The almost complete lack of a molluscan bottom fauna in the peripheral area suggests that bottom conditions were relatively inhospitable and raises the possibility that Actinosepia gladii were preserved here but destroyed by organic activity in the adjacent area with abun- dant benthic molluscs. The facts do not support this possibility. The conspicuous break in mollusc distribution is misleading, as the beds in the peripheral area show the same degree of reworking of sediment by organisms as do those in the highly fossiliferous area. Irregular grade-size mixing, contorted laminae and burrows are common features of the matrix of Actinosepia concretions as well as of the surrounding sediment, and in thin section organic sedi- ment sorting and fecal pellets are abundantly visible. If the fossil accumulations in the Fox Hills Formation reflect the original distribution of living organisms, as is believed (Waage, 1966), and the distribution of Actinosepia is not the result of selective preservation, it is reasonable to suspect that Actinosepia preferred areas peripheral to those with populous molluscan com- munites. Possible reasons for such a preference are numerous but owing to the general lack of even suggestive evidence their recitation would be unrewarding. The only empirical data that may bear on the problem are distributional and concern cephalopod 14 Postilla Yale Peabody Museum No. 94 contemporaries of Actinosepia. These are present in abundance and variety enough to direct attention to competition as a possible factor in the local distribution of Actinosepia. Ammonoids of two kinds, scaphitids and sphenodiscids, make up from 95 to over 99 per cent of the cephalopod fauna in the fossil assemblages of the Fox Hills Formation; scaphitids alone constitute 67 to 99 per cent of the cephalopod fauna in the four lower assemblage zones of the formation (fig. 3). The non- ammonoids that make up the remaining five per cent or less of the cephalopod fauna are Belemitella bulbosa, Nautilus dekayi, and Actinosepia. Unlike Actinosepia, which in the lower Fox Hills is found only at the Upper nicolleti level, the other non- ammonoid cephalopods are a consistent though minor element in all assemblage zones. For the four assemblage zones in question, the percentage of non-ammonoids in the cephalopod faunas from the area of abundant fossils is as follows: Lower nicolleti—0.8 per cent; Limopsis-Gervillia-S.1 per cent; Upper nicolleti-1.5 per cent; Protocardia-Oxytoma—2.2 per cent. If its peripheral area were included the non-ammonoid percentage for the Upper nicol- leti Assemblage Zone would be raised to nearly five per cent by the concentration of Actinosepia. Counts of the cephalopod elements at the Upper nicolleti level are given in Table 1, the localities represented include all the non-ammonoid cephalopods found at that horizon. If the dis- tribution of Actinosepia was influenced by a contemporary cephalopod the numerically dominant scaphitids, particularly H. TABLE 1. Count of cephalopod specimens from collections in and periph- eral to the area of abundant fossils at the horizon of the Upper nicolleti Assemblage Zone. NUMBER OF SPECIMENS From 12 localities From 12 localities in in the area of the area peripheral to CEPHALOPODS nicolleti assemblages — aicolleti assemblages Hoploscaphites nicolleti 202 7 Other scaphitids 56 12 Sphenodiscus 3 0 Nautiloids 2 0 Belemnoids l 0 Actinosepia l Dec. 22, 1965 Actinosepia canadensis Whiteaves 15 nicolleti, are the obvious candidates. The relative rarity of the other non-ammonoid cephalopods make them unlikely candidates. The percentage of non-ammonoids in the cephalopod fauna is lowest in the two assemblage zones that feature an unusual abun- dance of H. nicolleti and this together with the fact that these same two zones have the highest percentage of cephalopod speci- mens in the total fauna (8.8 and 15.1 for the Lower and Upper nicolleti zones respectively ) suggests that the apparent local swarm- ing of H. nicolleti may have had a significant effect on all other cephalopods. The close parallel in molluscan associations, both ammonoid and pelecypod, between the Upper and Lower nicolleti assemblages leads one to expect to find Actinosepia in the areas peripheral to the Lower nicolleti zone, which like the Upper also changes later- ally to an interval with small, generally barren, concretions. But Actinosepia has not been found at this horizon although its pres- ence in the underlying Pierre Shale within 30 miles of the area of Fox Hills fossil assemblages indicates that it had previously appeared as a member of the regional fauna. In summary, Actinosepia’ appears to have been only an occasional inhabitant of the shallow coastal waters in which the type Fox Hills Formation was deposited. Its relatively abundant remains at one horizon are concentrated in otherwise nearly barren beds peripheral to, and on the shoreward side of, a rich molluscan biofacies. The coincidence of this locally restricted occurrence with unusually high productivity of the scaphitid H. nicolleti in the adjacent molluscan biofacies may be significant. However, except for one obviously transported specimen, none of the gladii of Actinosepia known have been found directly associated with an abundance of other fossils. SYSTEMATIC DESCRIPTION CLass CEPHALOPODA SuBcLAss COLEOIDEA Bather 1888 ORDER TEUTHIDIDA Naef 1916 FAMILY TRACHYTEUTHIDAE Naef 1921 Diagnosis: Broad teuthidid gladii with tubercular structure in outer shell laminae over median or greater part of dorsal area; 16 Postilla Yale Peabody Museum No. 94 Late Jurassic (Trachyteuthis, Voltzia) and Cretaceous (Glyphi- teuthis, Libanoteuthis, Actinosepia). Discussion: According to Naef’s diagnoisis trachyteuthids are “bulky mesoteuthoids whose more or less Sepia-like shells are strongly calcified and show knobby roughness on the dorsal mid- region.” (1922, p. 136-137; translation.) In effect, Naef includes in the Trachyteuthidae all teuthidids whose dorsal shell layer shows tubercular structure in any part. All such species appear to have had relatively broad, sturdy gladii, but the degree of calcifica- tion varies considerably even within a single gladius and contrary tc Naef’s implication it is not a diagnostic feature of trachyteuthid gladii. In addition to the type genus, Trachyteuthis von Meyer, Naef (1922, p. 136-141) included Glyphiteuthis Reuss in the family. Subsequently Kretzoi (1942, p. 134) erected the genus Libanoteuthis to include the Lebanese Late Cretaceous species Trachyteuthis libanotica (Fraas)', a device that leaves only European Late Jurassic species in Trachyteuthis. Glyphiteuthis is known only from the Late Cretaceous of Czechoslovakia. With the inclusion of Actinosepia the family Trachyteuthidae becomes a receptacle for Mesozoic coleoid gladii that have tuber- cular shell structure but lack a ventral pad or other kind of phragmoconal part. Whether the family so defined has any validity as a natural group is questionable. The genera noted have charac- teristics other than tuberculation in common; chief among these are 1) the lack of separation of the gladius into middle and side plates by asymptotes and 2) the restriction of broadly rounded conus vanes to half or less of the gladius length. These features are no more indicative of genetic relationship than is the tubercula- tion. Trachyteuthid genera may be related or they may represent variants of more than one teuthidid stock that took to shallow coastal waters and a Sepia-like mode of life. If one accepts the independent development of tuberculation in sepiids and in teu- thidids one must also admit the possibility of its independent development in different teuthidid stocks. ‘Biilow-Trummer (1920, p. 255) refers Geoteuthis libanotica Fraas, the original designation of the type species of Libanoteuthis, to the “?Lias,” but Roger (1946, p. 6, 17) notes that Fraas’ specimen from Hakel and specimens found subsequently at Sahel-Alma are respectively from rocks of Cenomanian and Senonian age. Dec. 22, 1965 Actinosepia canadensis Whiteaves 17 Voltzia palmeri Schevill from the Late Jurassic of Cuba is added provisionally to the trachyteuthids, bringing within the group all tuberculate gladii described to date from the Mesozoic. The provisional status of the assignment stems from the possibility that Voltzia is synonymous with Trachyteuthis and not from the fact that it was described as a sepiid. The specimen of Voltzia palmeri is not available but neither the text nor the illustrations of Schevill’s (1950) description contain evidence that it possessed a pad. What Schevill calls the “phragmocone” is apparently only the filling of a ventral concavity in the central part of the gladius, for in describing the phragmoconal deposit he states (1950, p. 100), “detailed structure not apparent in this material because of bituminous replacement, as is frequent in other fossils from this locality.” Similar axial, ventral concavities in the gladius are observable in many specimens of Trachyteuthis hastiformis (Rup- pell), the common Solenhofen species, and are obviously filled with matrix which may protrude dorsally as an elongate-ova! mound where the substance of the gladius has been removed. That this concavity in Trachyteuthis was not occupied by a cal- cified pad at the time of burial is indicated by the presence of small holdfasts attached to the ventral surface, usually near the axis of the concavity.” The specimen of Voltzia palmeri needs careful restudy; Schevill himself pointed out its superficial resem- blance to Trachyteuthis, and one supposes that he would have referred it to this genus had he not believed that the bitumen- filled, raised area in the center of his specimen was a pad. GENUS ACTINOSEPIA Whiteaves 1897 Type species: Actinosepia canadensis Whiteaves, 1897, by monotypy. Emended diagnosis: Gladius broad, ovoid, arched, with ventral concavity deepening posteriorly; consists of large main body undivided by asymptotes with rounded conus vane flanking *In his original description of Trachyteuthis, von Meyer (1846) notes these holdfasts and attributes them to crinoids; whatever their nature they are a common feature of the Solenhofen trachyteuthids; a good specimen showing the holdfasts and the nature of the axial, ventral concavity in Trachyteuthis is in the U. S. National Museum (USNM 16622). 18 Postilla Yale Peabody Museum No. 94 rear third along weak lateral asymptote. Main body expands for- ward fan-like from apex, attains maximum gladius width about one-third length from anterior end; dorsally, five narrow, longitu- dinal ribs radiate from apex, the stronger median rib protrudes beyond anterior margin in an acuminate tip, weaker laterals impart slight scallop to margin. Gladius substance corneous to corneous- calcareous, in two laminated layers, the ventral smooth, the dorsal with outer laminae tuberculate. Surface of gladius ornamented with fine to coarse tubercles except on conus vanes. Apex poorly known; rostrum, if any, small. Range: Late Campanian and Maastrichtian. Distribution: Great Plains region of southern Canada and northern U.S.A. Discussion: The ovoid plan of the gladius, its five radiating ribs and its acuminate tip were Whiteaves’ basis for suggesting that the coleoid specimens from the South Saskatchewan River “...Seem to indicate a new genus and species of Sepiidae, for which the name Actinosepia Canadensis may not be inappropriate.” (1897, p. 460.) The principal addition to this definition is the presence of an outer layer of tuberculate shell laminae and the resultant nodular ornamentation of most of the dorsal surface of the gladius; a feature noted by Landes (1940, p. 180) on the Alberta specimens but not evident on the four exfoliated specimens available to Whiteaves. Actinosepia cannot be classed as a sepiid, as Whiteaves did, for in spite of its many Sepia-like characters it lacks the ventral pad definitive of that group. As a teuthidid, the tubercular structure justifies its inclusion in the family Trachyteu- thidae ACTINOSEPIA CANADENSIS Whiteaves Fig. 125P)..1, (23; and: 4a, bac: Actinosepia canadensis Whiteaves, 1897, p. 459-460, pl. 2: Landes, 1940, p. 180-181. Material and Measurements: Table 2 lists dimensions and rib angles for the ten more complete specimens of A. canadensis. The dimensions are at best approximations and not direct measure- Dec. 22, 1965 Actinosepia canadensis Whiteaves 19 ments. The external mold, GSC 19888 (see Pl. 2), collected by Landes and used by him (1940, p. 180) in his description, retains more of the form and external ornamentation of the gladius than any other specimen and is the only one preserving the posterior end with the vanes. The length of other specimens was estimated by matching their greatest measurable rib spacing with the correspond- ing spacing on GSC 19888 and measuring the distance along the median rib of the latter from the match point to the posterior end. To this was added the length of gladius preserved (or recon- TABLE 2. Measurements of the ten most nearly complete specimens of Actinosepia canadensis. The estimated measurements are considered minimal. For method of estimation see p. 19. Estimated Estimated width Median-inner Median-outer length at anterior rib rib SPECIMEN (cm) maximum (cm) angle angle Bearpaw Shale Saskatchewan Whiteaves (1897) GSC 5379 (holotype) 21 8.5 We 10° GSC 5379a 22+ 11.0 6° to 6.5° — GSC 5379b 22.0 11.0 6° oo GSC 5379c Mile — Fo) — Bearpaw Shale Alberta Landes (1940) GSC 19888 30 25) Satorseon IE GSC 16395 Pal 10.0 Ta) — Bearpaw Shale Montana Jensen and Varnes (1964) USNM 147231 18.2 8.0 6° to 7° oo Fox Hills Fm. South Dakota (This paper) YPM 24809 23.0 9.4 8° P2ESI= [wey 1S} YPM 24808 20.0 8.6 8° PSY? toy IST YPM 24811 = — 8.5 Sy 20 Postilla Yale Peabody Museum No. 94 structed by extension of growth lines across the median rib) anterior to the match point on the specimen being compared. The sum of these two measurements provides an approximate mini- mum length. Measurement of maximum width is even less accurate as the lateral edges of the gladius are commonly frayed, curled or flattened. The four specimens whose dimensions are judged to be more reliable are GSC 19888, GSC 5379, YPM 24809 and YPM 24808; height-width ratio of these specimens is from 2.3 to 2.5. Features of the anterior half of the gladius are based chiefly on GSC 5379, GSC 5379b, GSC 16395, YPM 24808 and Yim 24809. Data on shell structure and ornamentation came mostly from GSC 19888, USNM 147231, YPM 24811, YPM 24812, and YPM 24810. (YPM = Yale Peabody Museum; GSC = Geological Survey of Canada; USNM = United States National Museum. ) Description: Gladius approximately 2.5 times as long as its maximum width. Range of estimated minimum length of ten best- preserved specimens is 18 to 30 cm. Main body of gladius gently arched transversely; the amount of convexity varies and probably is affected by mode of preservation; in GSC 19888 height/ width= 0.20, in YPM 24809 h/w = 0.22, both these specimens are pre- served in calcareous concretions and appear to retain their original form. The gladius also has a broad asymmetrical arch longitudi- nally, the apex being approximately one third length from posterior end so that curvature is markedly greater on posterior third. (see profile, fig. 1). Five dorsal ribs on the the main body are folds in the gladius that appear as shallow grooves on ventral surface; median rib and adjacent ribs on either side, the inner rib pair, are sharp flexures that stand out prominently from apex to anterior margin, median generally higher and broader than the inner ribs; the outer rib pair are slight flexures that commonly become faint toward anterior margin, particularly on inner shell layers. Inner ribs diverge forward from median rib at angles varying from 6 to 8.5 degrees, outer ribs at angles varying from 10 to 15 degrees. Inner ribs lie nearer outer ribs at approximately two thirds the distance from the median rib to the outer ribs. Ornamentation consisting of tubercles of various size and irreg- ular ridges of coalesced tubercles covers the dorsal surface of the Dec. 22, 1965 Actinosepia canadensis Whiteaves 21 main body of the gladius. Ribs bear large, closely-spaced tubercles, asymmetrically inclined forward and rounded on top; on the bigger A. canadensis specimens these are as much as 3 mm in diameter at the base; some show annular pattern of growth laminae on blunt tops (Pl. 3, fig. 3) indicating either wear or resorption—but most likely the latter, as can be demonstrated for the dorsal tuberculate shell layer in Sepia cuttlebones. Ornament on intercostal areas begins as crowded rows of small tubercles, usually 1 mm or less in size, that closely parallel growth lines; as these grow with the addi- tion of new shell laminae they impinge on one another, the orna- ment pattern becoming increasingly irregular as tubercles grow differentially and/or fuse to form anastomosing nodular ridges (PI. 3, fig. 2). Ornament between inner and outer ribs becomes finer and arrangement of tubercles along growth-lines is obvious even on large gladii; tubercles decrease gradually in size as their rows swing backward with growth lines along lateral edge of main body of gladius. Ornament arises from tubercular structure of outer shell laminae. Where inner laminae are exposed they are smooth or show fine, closely-spaced growth ridges or “lines” which are bent sharply forward along median rib, indicating an acuminate tip. From me- dian rib growth lines curve gently backward and outward to inner rib where they are flexed abruptly backward at an angle of about 40 degrees to longitudinal axis of gladius; at outer rib they flex sightly laterally then curve steeply into the lateral margin of gladius. Lateral vanes border posterior third of gladius, curve down- ward and outward connecting under apex of main body; their combined outline viewed dorsally is nearly semicircular. Along anterior third of juncture of vanes and main body vanes are down- warped to form broad groove that tapers out backward; groove is flanked by narrow tapering ridge along main body (PI. 3, fig. 1). Lateral asymptotes follow inner side of groove and continue back- ward along juncture of vanes and main body; these are the only pair of asymptotes on gladius. Ornament of very fine tubercles spreads into groove from main body, following pattern of growth lines, but does not extend beyond, where vanes are smooth except for fine growth lines that parallel their periphery. In the one speci- men preserving vanes (GSC 19888) they appear thinner than shell of main body. i) NWN Postilla Yale Peabody Museum No. 94 The matrix bearing the posterior end of the gladius in GSC 19888 was X-rayed and excavated as far as possible without destroying it, but no rostrum was found. Some thickening of shell at apex is apparent and the area has been worn or exfoliated; a rostrum may have been present but if so it was probably a small one, for shell laminae visible are not noticeably projected back- ward at the apex. Shell Structure: Shell substance apparently not completely preserved on any specimen; maximum thickness measures 2 mm on flank of median rib USNM 147231; on specimens over 20 cm in length shell in areas between median and inner ribs was prob- ably between 2 and 3 mm thick; shell thins laterally from median rib. Shell laminated, consisting of two opposing sets of laminae which define inner and outer shell layers that are not easily dis- tinguished macroscopically. Relationships of layers are shown in fig. 4 and on Pl. 4, figs. 1 and 2; laminae of inner layer incline upward and forward in longitudinal sections, upward and outward in transverse sections; in corresponding sections laminae of outer layer incline downward and forward, and downward and outward. Laminae of upper layer pass dorsally into tubercular structure which may occupy all of this layer or as little as the upper third. Degree of tuberculation apparently varies among gladii and in Actinosepia Figure 4. Generalized diagram comparing shell layers of Actinosepia with those of dorsal shield of Sepia cuttlebone. A. Tuberculate outer layer, the “Rickenplatte” of Appellof; B. Inner layer, the “Mittelplatte” of Appellof: C. “Innenplatte” of Appell6f, part of the sepiid pad and not present in Actinosepia. Dec. 22, 1965 Actinosepia canadensis Whiteaves 23 different parts of same gladius. Where outer layer thickest, along median rib, its non-tuberculate part is thickest; as layer thins laterally tuberculation becomes progressively more complete. Growth lines and ridges are most distinct on surfaces at and adjacent to the juncture of inner and outer layers; growth lines are apparently the edges of laminae along the juncture of the layers, or their impressions on surfaces of laminae of the opposing layer; broader rounded ridges are small flexures which appear restricted chiefly to the basal non-tuberculate part of the upper layer; ridges not well defined on inner layer, usually discernible at or near juncture with outer layer and probably are reflections of flexures in latter. Ridges parallel ends of laminae and no doubt formed at growing edge of shell. Shell material organic, corneous, slightly to moderately im- pregnated with calcium carbonate. Treatment with ten per cent HCl shows some differential etching of laminae with slight to moderate efflorescence; shell eventually breaks down to fine bits and plates of organic matter. Inner layer contains more organic matrix and is less calcareous than the outer. Landes (1940, p. 181) states that “the calcareous layers of the shell show distinct growth lines. ... The horny layers show no trace of the circumferential growth lines...” The inner shell layer which generally lacks growth ridges or lines except at its juncture with the outer layer appears more “horny” than the latter, but to distinguish the outer layer as calcareous is misleading. In none of the specimens does the degree of impregnation with calcium carbonate approach that of the tuberculate dorsal shield of Sepia. The gladius of A. cana- densis was tough but flexible, no part of it was calcified enough to be rigid. The microstructure of convergent laminae in the shell shows that the inner layer was deposited from below and the outer layer from above and indicates that the gladius was formed in a shell sac, as it is in Sepia. The structural similarity between the dorsal shield of a sepiid shell and the gladius of A. canadensis becomes evident on comparing the latter with Appellof’s (1893) structural analysis of the shell of Sepia. After dividing the cuttlebone into dorsal shield and pad, Appellof (1893, p. 8-19) describes the structure within the dorsal shield, recognizing three distinctive layers, the dorsal plate (Riickenplatte), middle plate (Mittelplatte) and inner 24 Postilla Yale Peabody Museum No. 94 plate (Innenplatte). The dorsal plate is the thicker and character- istically has tubercular structure; shell laminae at the base of the dorsal plate can be seen to incline downward laterally and forward (fig. 4). The dorsal plate thins toward the edges of the dorsal shield, it grows “by the apposition of new layers on its upper side.” (Appellof, p. 19). The much thinner middle plate grows from the underside, its laminae incline upward and outward. The dorsal and middle plates of Sepia are structurally nearly identical to the outer and inner layers, respectively, of the Actinosepia gladius, although they differ in their relative thickness and the degree of calcification. The inner plate of the dorsal shield of Sepia is complex in structure; Appellof (p. 20 and 29) observed that the pad lamel- lae, or “Septa,”’ pass into it without a break; it is thus distinct from the other two layers of the dorsal shield and essentially a part of the pad. Absence of a pad in Actinosepia conceivably could be due to the fact that the delicate pads are relatively easily destroyed, but if a pad was present some remnant of the inner plate should remain on the better-preserved specimens. The fact that the Actinosepia gladius was flexible suggests that any buoyancy apparatus the animal may have had attached to it would also have been flexible; attachment of a rigid, delicate structure like the pad of Sepia to a flexible plate has obvious functional drawbacks. Shape and convexity, shell structure and dorsal ornament are the principal similarities between the sepiid cuttlebone and the gladius of Actinosepia. A less significant, probably superficial, similarity is the pattern of radiating ribs present in some recent and fossil sepiids. These are broad, flat-topped and generally three in number. Remarks: Whiteaves’ four specimens differ enough from most other specimens of Actinosepia to question whether they may be specifically distinct. On these four specimens the angle between the median rib and the inner rib varies from 5.5 to seven degrees; on the gladius from the Bearpaw Shale in Montana, USNM 147231, the same angle is between six and seven degrees. In all other specimens on which it could be measured accurately this angle is more than 7.5 degrees and in the Fox Hills specimens it is consistently in the eight- to nine-degree range. The median- outer rib angle does not exceed 10° in Whiteaves specimens but is Dec. 22, 1965 Actinosepia canadensis Whiteaves 25 12° to 15° in other specimens. A general trend of increasing rib angles with decreasing geologic age is broken by Landes mold, GSC 19888, from the Bearpaw Shale which has a median-inner rib angle of 8 to 8.5 degrees and a median-outer rib angle of 12°. Too little is known about variation within or between populations of A. canadensis to warrant specific separation into two groups on the basis of rib angles alone. There may be slightly finer tuberculate ornament on the Whiteaves specimens but the few scattered remnants of the inner tuberculate laminae preserved are inadequate to demonstrate this conclusively. A better representa- tion of specimens of Actinosepia from a number of horizons is needed before a meaningful evaluation can be made of the rather slight differences apparent in the known specimens. Types: Whiteaves (1897, p. 459) singled out one of the specimens on which he based A. canadensis as “The most perfect of the four ...,” illustrating it with a recognizable line-drawing and basing most of the particulars of his description on it. This is interpreted to be an expression equivalent to the stated designation of a “type” under Article 73b of the 1961 International Code of Zoological Nomenclature; the specimen, GSC 5379, is therefore the holotype and the remaining three specimens, GSC 5379a to c, paratypes. Specimens on which this redescription is based are listed above under the heading Material and Measurements. Of these, GSC 19888 is listed as a hypotype by the Geological Survey of Canada; it is the specimen on which Landes based his supplemental descrip- tion of A. canadensis. RELATIONSHIP TO THE SEPIIDS The similarities of shape and structure between the gladius of Actinosepia and the sepiid cuttlebone can be attributed to paral- lelism resulting from the adoption of sepiid habits by a branch of the trachyteuthid stock. At our present level of knowledge it is reasonable to consider Glyphiteuthis and Actinosepia divergent end members of the trachyteuthids, the former tending toward reduction and attenuation of the gladius, the latter toward increas- ing its breadth, convexity, and strength—that is, becoming more 26 Postilla Yale Peabody Museum No. 94 sepiid-like. It is also reasonable to hold that no true sepiids had yet appeared at this time (Late Cretaceous), for unless unequivocal evidence of a calcified pad in Voltzia can be demonstrated it cannot be considered a sepiid. Rejecting Voltzia as a sepiid reinstates the long established scheme, introduced by Voltz (1830) and elaborated on by many. but most significantly by Naef (1921, 1922), of deriving sepiids from a belemnoid stock, according to Naef, through the succession Belemnosella—Spirulirostra—S pirulirostrina—Belosepia—Sepia. The forms chosen to represent intermediate stages between belemnoids and sepiids are characterized by rostra with impressions or rem- nants of a short curved phragmocone; these range in age from Eocene to Miocene, but Belosepia, Naef’s critical end member of chain, did not survive the Eocene. Wagner (1938, p. 197) describes Sepia agriensis, a gladius preserving what appear to be remnants of a pad, from the Late Eocene, Ludian, and well-pre- served cuttlebones are known from the mid-Oligocene, Rupelian (S. kiscellensis Wagner, S. harmati Szorényi). Sz6rényi (1933, p. 188) maintains that Naef’s phylogeny is negated by species of Archaeosepia from the Eocene, but Wagner (1938, p. 199) believes that neither these nor Belosepia gave rise to true sepiids which he states must have been derived at least by earliest Eocene. If, as is probable, S. agriensis Wagner is a true sepiid, none of the classically accepted ancestors in Naef’s succession are likely to have been the true ancestors. With the more commonly accepted origins of sepiids open to serious question, the possibility that they were derived from the trachyteuthid stock through an Actinosepia-like form deserves con- sideration. The idea of a trachyteuthid origin for sepiids is not new; it was suggested by Fischer (1887, p. 357) who included trachyteuthids in his Sepiophora and considered them transitional with the Chondrophora (teuthidids). Structurally it is a shorter step from Actinosepia to Sepia than from any of the small rostrate genera of the Eocene-Miocene to Sepia. The expanded, convex, dorsally tuberculate gladius is there; it lacks, chiefly, greater calcification and the pad. Functionally the two latter features go hand in hand, rigidity of dorsal shield and a calcified pad. Actinosepia may well have had a buoyancy apparatus in soft tissues under its flexible gladius; Dec. 22, 1965 Actinosepia canadensis Whiteaves 27 if so the step from trachyteuthid to sepiid would entail primarily an increase in rigidity of the shell through greater calcification. Szorényi (1933, p. 185) mentions that in some of the speci- mens of Sepia harmati the pad has survived in the form of a car- bonized substance; judging from her description the only calcified remains of the pad are the bases of pad-lamellae adhering to the inner plate (= Innenplatte of Appellof) on one specimen. This may be an artifact of preservation, but it may also reflect only partial calcification of the pad at this stage in sepiid evolution. As an alternative working hypothesis the possibility of deriving sepiids from trachyteuthids has the advantage of starting back in the Late Cretaceous with a coleoid that apparently already had adopted the sepiid way of life and in addition possessed a dorsal shield of very nearly identical structure. This is consider- ably more than can be said for such forms as Spirulirostra, Belop- tera and the like, whose shells feature the gradual diminution of rostrum without concomitant development of the dorsal shield, and without any changes in the phragmocone that approach very closely the laminate and trabeculate pad of Sepia. Direct deriva- tion of the pad from the phragmocone is a possibility but it is not a necessity; the pad could just as readily have been formed by resumption of calcium carbonate secretion in tissues much changed in structure but essentially homologous with those that in past periods had secreted a true phragmocone. REFERENCES CITED Appellof, A., 1893. Die Schalen von Sepia, Spirula und Nautilus: Kongl. Svenska Vetenskaps-Akademiens Handlingar, v. 25, no. 7, p. 1-106, 12 pls. Bulow-Trummer, E. von, 1920. Cephalopoda dibranchiata. Part 11, in: C. Diener, ed., Fossilium Catalogus, I: Animalia. 313 p. Cobban W. A., 1958a. Two new species of Baculites from the Western Interior region: Jour. Paleontology, v. 32, no. 4, p. 660-665. , 1958b. Late Cretaceous fossil zones of the Powder River Basin, Wyoming and Montana: Wyoming Geol. Assoc. Guidebook 13th Ann. Field Conf., p. 114-119. , 1962. New baculites from the Bearpaw Shale and equivalent rocks of the western interior: Jour. Paleontology, v. 36, no. 1, p. 126-135. Cobban, W. A. and Reeside, J. B. Jr., 1952. Correlation of the Cretaceous formations of the western interior of the United States: Geol. Soc. America Bull., v. 63, p. 1011-1044, 1 pl. Delevoryas, Theodore, 1964. Two petrified angiosperms from the Upper Cretaceous of South Dakota: Jour. Paleontology, v. 38, no. 3, p. 584-586, pls. 95-96. 28 Postilla Yale Peabody Museum No. 94 Fischer, P. H., 1887. Manuel de conchyliologie et de paléontologie con- chyliologique: Paris, F. Savy, p. 340-357. Jensen, F. S., and Varnes, H. D., 1964. Geology of the Fort Peck Area, Garfield, McCone and Valley Counties Montana: U.S. Geol. Survey Prof. Paper 414-F, p. FI-F49. Kretzoi, Miklos, 1942. Necroteuthis n. g. (Ceph. Dibr., Necroteuthidae N. F.) aus dem Oligozan von Budapest und das System der Di- branchiata: F6ldtani KO6zlsny, v. 72, pt. 1, p. 124-138. Landes, R. W., 1940. Paleontology of the marine formations of the Montana group, pt. 2 of Geology of the southern Alberta Plains: Geol. Survey Canada Mem. 221, p. 129-223, pls. 1-8. Meyer, H. von, 1846. (Ueber Trachyteuthis n. g.): Neues Jahrbuch fiir Mineralogie (Stuttgart), p. 598. Naef, Adolf, 1921. Das System der dibranchiaten Cephalopoden und die mediterranen Arten derselben: Mitteilungen aus der zool. Station zu Neapel, v. 22, p. 527-542. , 1922. Die fossilen Tintenfische: Jena, 322 p. Roger, Jean, 1946. Résultats scientifiques de la mission C. Arambourg en Syrie et en Iran (1938-39) —I. Les invertébrés des couches a poissons du Crétacé supérieur du Liban; étude paléobiologique des gisements: Mémories de la Société Géologique de France, new ser., v. 23, Mémoire no. 51, p. 1-92, pl. I-X. Russell, L. R., 1940. Stratigraphy and structure, in Russell, L S. and Landes, R. W., Geology of the southern Alberta Plains: Geol. Survey Canada, Mem. 221, pt. 1, p. 1-128. Schaffer, H., 1958. Ein neues Vorkommen von Sepia vindobonensis Schlb. in Nieder6sterreich: Anzeiger der Osterreichischen Akademie der Wissenschaften, mathematisch-naturwissenschaftliche Klasse, no. 9, p. 141-147. Schevill, W. E., 1950. An Upper Jurassic sepioid from Cuba: Jour. Paleon- tology, v. 24, no. 1, p. 99-101, pl. 23. Szorényi, Erzsébet, 1933. Neue tertiare Sepiinae aus Ungarn nebst Bemer- kungen zur zeitlichen Auftreten und zur Entwicklung der Gattung Sepia: Foldtani Kozlsny, v. 63, p. 183-189, 1 pl. Voltz, M., 1830. Observations sur les Bélemnites: Mém. Soc. d’hist. nat. de Strassbourg, v. 1, p. 1-70. Waage, K. M., 1961. The Fox Hills Formation in its type area, central South Dakota: Wyoming Geol. Assoc. Guidebook, 16th Ann. Field Conf., Symposium on Late Cretaceous rocks, p. 229-240. ,1966. In press. Origin of repeated fossiliferous concretion layers in the Fox Hills Formation, in Symposium on cyclic sedimenta- tion: Kansas Geol. Survey Bull. 169. Wagner, Hans, 1938. Die dibranchiaten Cephalopoden der Mitteloligozanen (Rupélien) Tonschichten von Kiscell und neue Sepiinae aus dem ungarischen Eozin: Annales historico-naturales Musei Nationalis Hun- garici, v. 31, p. 192-199. Whiteaves, J. F., 1897. On some remains of a Sepia-like Cuttlefish from the Cretaceous rocks of the South Saskatchewan: Canadian Ree. Sci., v. 7, p. 459-460, pl. 2. Dec. 22, 1965 Actinosepia canadensis Whiteaves PLATES 29 30 Postilla Yale Peabody Museum No. 94 PLATE 1. Actinosepia canadensis Whiteaves Fig. 1. Holotype (GSC 5379), dorsal aspect;