Paleo Bios Museum of Paleontology University of California. Berkeley _________________________ISSN 0031-0298________________________ Number 3^_____________________________________________December 18, I98O OSTEOPYGIS SP., A MARINE TURTLE FROM THE LATE CRE- TACEOUS MORENO FORMATION OF CALIFORNIA by DAVID E. FOSTER1 ABSTRACT An osteopygine toxochelyid turtle from the marine Cretaceous of Cali- fornia is the first Pacific appearance of the family and extends the geographic range of the group beyond previously known North Atlan- tic, North American "Western Interior Sea", and South American oc- currences. The uncertain presence of nasal bones in this genus may require a reassessment of the traditional derivation of the genus Evquelinnesia from Osteopygis. INTRODUCTION At the February, 1979, meeting of the Western Association of Ver- tebrate Paleontologists, Dr. Arthur E. Staebler of California State University (Fresno) and Mr. Chad Staebler presented the Museum of Paleontology of the University of California with a skull and as- sociated humerus of a turtle from the marine Cretaceous Moreno For- mation of central California. Several months later, the Staeblers supplied post-cranial elements of the same specimen. This specimen, an osteopygine toxochelyid, unambiguously ex- tends the known geographic range of the family into the Pacific. Current understanding of the Toxochelyidae is based primarily upon two major works by Zangerl (1953, 1971) who reviewed the entire family in 1953. Distilling the nomenclatorial complexities of previous wor- kers (notably Cope; see Hay, 1908), he recognized three major subfamilies the Toxochelyinae, the Lophochelyinae, and the Osteopyginae. Zangerl (1971) revised the subfamily Osteopyginae, emending his diagnosis of this group, and summarizing the known geographic record of the Toxo- chelyidae. As established by Zangerl, the Osteopyginae consists of two mono- typic genera, Osteopygis Cope and Evquelinnesia Dollo. 'Museum of Paleontology, University of California, Berkeley, Cali- fornia 9^720 2 PALE0B10S NO. 31* These are united in the subfamily by the presence of extensive secon- dary palates and massive jaw symphyses, with Erquelinnesia presenting the greater development in these two features. Zangerl did not include Chinese material assigned to Osteopygis (Bohlin, 1953) in his reviews. Boh!in (1953) described three new species of Osteopygis that constitute the first Asian record of the family. The validity of these identifications is discussed below. Knowledge of the skull of Osteopygis is limited. Only three skulls and a snout fragment are known, and no description other than that of the snout fragment has ever been published. Abbreviations used herein are: AMNH - American Museum of Natural History, NJSM - New Jersey State Museum, UCMP - University of California Museum of Paleontology, YPM - Yale Peabody Museum; cm - centimeters. SYSTEMATIC PALEONTOLOGY Order Testudines Infraorder Cryptodira Family Toxochelyidae Subfamily Osteopyginae Osteopygis sp. Material - UCMP 123616: a crushed, but complete skull with attached mandible, two humeri, three peripheral plates, one scapula, and nu- merous unidentifiable bone fragments of probable limb and digital origin. Locality and Hori2on: UCMP 123616 comes from UCMP locality V-79088, an exposure of the Moreno Formation slightly northwest of Panoche Creek, Fresno County, California. Additional locality data are on file at the University of California Museum of Paleontology. The Moreno Formation, which has been extensively described elsewhere (Anderson, 1958; Payne, 1951), is generally divided into four members. In ascending stratigraphic order, these are the Dosados Sand and Shale, the Tierra Loma Shale, the Marca Shale, and the Dos Palos Shale. UCMP 123616 comes from the Dosados Sand and Shale, a yellow-brown shale which weathers fragmentarily into a brittle gravel. Most of the Moreno Formation is Late Cretaceous, but the uppermost Dos Palos shales might be of Paleocene age (Payne, 1951)- The present specimen is thus considered to be Maestrichtian. DESCRIPTION Cranial - The skull (Plates A1,2; Fig. la-c) is extensively distorted and much of the bone is shattered by the growth of gypsum crystals. As preserved, it is dorsoventrally compressed, as well as transversely sheared. The mandible, the dorsal ramus of the scapula, and some un- identifiable limb fragments are crushed against the skull. 1980 CRETACEOUS MARINE TURTLE 3 In dorsal view (Fig. 1c, 7a), the outline of the skull is clearly similar to that of the other Osteopygis specimens, with a compara- tively pointed snout region and slightly bowed post-orbital region. Of particular interest are the prefrontal bones, which have been lifted and distorted from their original positions (Plate Al, Fig. 7a). These probably bordered the narial opening, although a small groove-1ike depression is present between the anterior border of each prefrontal and the corresponding surface of the narial opening. The possibility that small nasal bones were present on this specimen thus cannot be overlooked. While the closely related Erquetinnesia has nasal bones, other specimens of Osteopygis show no evidence of this condition. The presence of nasal bones in osteopygine turtles will be discussed more fully below. In lateral view (Fig. lb), the tip of the crista supraoccipitalis has been reconstructed in a manner agreeing with known specimens of Osteopygis. Due to extensive crushing, reconstructed skull height had to be estimated. A recently discovered, uncrushed skull of Osteopygis (NJSM 11872) reveals that its height in proportion to length is significantly lower than that found in cheloniids or chelydrids, turtles traditionally linked with the Toxochelyidae. The lower pro- portional value was used in the reconstruction of UCMP 123616. A fossa temporalis inferior Is clearly visible, although its poor state of preservation does not permit the identification of any truly distinguishing characters. Likewise, the emargination of the jugal and quadratojugal are uncertain, although it is clear that the orbito-temporal roof was quite extensive. As in recent cheloniids, the squamosal tips lap up against the paroccipital processes. Reconstructed quadrate placement was de- teremined by the rami of the lower jaw, which are virtually undis- torted. The articulating surfaces have been restored at an angle more or less perpendicular to the sagittal midline of the skull, as in Osteopygis. In Erquetinnesia, these have been restored as dir- ecting slightly inward (Zangerl, 1971). Regrettably, a detailed description of the basicranium is not possible from the present specimen. Nevertheless, a distinctive depression in the ventral surface of the basioccipital (Plate A2, Fig. la) like that seen in Osteopygis (NJSM 11872) is present. In palatal view (Plate A2, Fig. la, 7b), the dominating feature is the lower jaw, which is crushed against the palate. Transverse shearing has displaced it from the quadrate condyles, buckled the right quadrate and opisthotic to the left, and separated the left quadrate condyle and pterygoid from the remaining dorsal process of the quadrate and opisthotic bone. As a result of the crushing, the exoccipital and supraoccipital bones are pressed flat and skewed to the left. The occipital condyle may be directed more basally than it was in life. Only the right fenestra temporalis inferior is exposed. The lower jaw obscures the anterior extent of this opening. The low tomial ridge is one of the most distinctive features of UCMP 123616. It is a character which is shared by the other speci- mens of Osteopygis and Erquetinnesia, and may be considered a de- PALEOBIOS NO. 3U Figure 1. Reconstruction of the skull of Osteopyg-is sp. based upon UCMP 123616 with additions from NJSM 11872. a) palatal view; b) lateral (right) view; c) dorsal view. Abbrevia- tions: bo, basioccipital; bs, basisphenoid; ex, exocci- pital; fr, frontal; ju, jugal; mx, maxillary; na, nasal; op, opisthotic; pa, parietal; pal, palatine; pf, prefron- tal; pm, premaxillary; po, postorbital; pt, pterygoid; qj, quadratojugal; qu, quadrate; so, supraoccipital; sq, squamosal; vo, vomer. Dashed lines indicate features not determinable from UCMP 123616. 1980 CRETACEOUS MARINE TURTLE 5 rived character of the Osteopyginae. It is clear that UCMP 123616 posesses a secondary palate, although not nearly as posteriorly expanded as that found in Erquelinnesia. The symphysis of the mandible hinders assessment of the extent of the palate, but a marked depression is present in the palatal surface, dorsally roofed with bone. The posterior extent of the symphysis of the lower jaw exactly corresponds with this depression, suppor- ting the interpretation of this structure as a secondary palate. The extent of the secondary palate agrees well with that of Osteo- pygis (NJSM 11872). Figure 2. Outline of the lower mandible of Osteopygis sp., in ventral view; UCMP 123616. The mandible of UCMP 123616 (Fig. 2) is complete in outline, al- though lacking in detail; almost none of the original bone surface is present. The lower jaw is virtually undistorted, with the excep- tion of a slight bend in the right ramus just anterior to the artic- ular condyle. The mandibular symphysis extends h}% of the sagittal length of the mandible, compared to the 58% of the mandibular length occupied by the symphysis of Erquelinnesia (Zangerl , 1971)- The comparatively slender rami and condyles agree better with the lower jaws of Os- teopygis than wi th Erquelinnesia. Most chelonioid mandibles show a slight swelling at the point PALEOBIOS NO. Ik where the rami of the lower jaw effectively become a triturating surface; this swelling is usually formed by a combination of the dentary and surangular. While the suture lines of these bones can- not be traced on UCMP 123616, the swellings are clearly visible. It is reasonable, in light of the probable relationships of the bones, to postulate a surangular and angular lengthening to account for the comparatively long, slim, jaw rami. Table I is a compilation of measure- ments of the skull of UCMP 123616. Table I. Measurements taken on the skull of Osteopygis sp., UCMP 123616 Measurement Size (cm) Length, condyle to premaxi1laries 11.6 Length, quadrates to premaxi1laries 10.5 Width, widest point of the skull, 9-1 cm posterior to the premaxi11ary 10.6 Diameter, orbits, at widest point 3.5 Width, between orbits, h cm posterior to the premaxi11ary 2.9 Width, right side of right quadrate to left side of left quadrate 10.2 Width, squamosal tips (reconstruction) 10.8 Length, total 14.5 Snout angle 79° Postcranial - UCMP 123616 includes two complete humeri. The right is so severely weathered as to make it unsuitable for study. The left (Fig. 3a-d) is uncrushed and retains much of the original bone sur- face, overlain by a thin, transparent sheet of gypsum. Proximally, in dorsal view (Fig. 3b), the capitulum is completely obliterated, although the rounded foundation of its base remains, clearly revealing its original location and dimensions. The angle it forms with the shaft of the humerus conforms with the chelonioid "angle alpha" described by Zangerl (1953), a morphology/function com- plex considered intermediate between that found in fresh water tur- tles such as chelydrids and that found in recent marine turtles. The toxochelyid humerus has been described as intermediate between chelydrid and cheloniid conditions (Zangerl, 1953; Hay, 1908; Wie- land, 1900). Ventrally (Fig. 3a), the trochanteric fossa between the two crests is not nearly the deep excavation in UCMP 123616 that it is in Maaroclemys Gray, although it more closely approximates this than it does that of Chelonia Brongniart. The radial crest is both reduced and more ventro-distally located in UCMP 123616 than in Macroatemys, but does not attain the condition seen in Cheton-ia, in which the radial crest is nearly ventral, at the base of the capi- tulum. More distally, the humerus of UCMP 123616 has a much thicker waist that does that of a chelydrid, and is more like that of a cheloniid, but with none of the attendant flattening. The shape of the shaft 1980 CRETACEOUS MARINE TURTLE Figure 3- Left humerus of Osteopygis sp., UCMP 123616. a) ventral view; b) dorsal view; c) proximal view; d) lateral view; Abbreviation: ec, ectepicondylar groove. (Fig. 3d) is intermediate between the "S" - shaped curves of the chelydrids, and the almost linear shafts of the cheloniids. The dis- tal third of the shaft curves ventrally, somewhat more distally, and less radically, than does that of Maoroclemys. The distal end of the humerus shows an ectepicondylar groove, but the articulating surfaces are obscured by some unidentifiable bone fragments. The scapula has a distinctive pinching of the neck, visible at the base of the shorter, dorsal scapular process in ventral view (Fig- k). Readily-identifiable carapacial elements consist of three peri- pheral plates (Fig. 5a-c, 6a-c), but little of the original bone surfaces remain, and substantial weathering has rounded any sharp corners. Rib pits are clearly present in all three. The plate shown in Fig. 5 is 7-9 cm long, and a maximum of 6.2 cm wide, with a greatest depth of 2.5 cm. These dimensions correspond with those of more posteriorly oriented peripherals, and the plate is assumed to fall within peripherals nos. 9 - 11. The lateral margins of the plates are gently convex, and show remnants of the intermarginal sulci. 8 PALEOBIOS NO. 3k Figure h. Reconstructed left scapula of Osteopygis sp.3 UCMP 123616. a) anterior view; b) posterior view. The plate shown in Fig. 6 has undergone substantial erosion, and Ion gitudinal distortion. It has a maximum length of 6.9 cm and a max- imum width of 5.2 cm, with a depth of 3-1 cm. Its cross section (Fig. 6c) identifies it as one of plates h - 6. The shape of the ventral edge is unique; the great emargination of this ledge at the rib pit may be partially due to erosion. Frequently some slight emargination occurs at rib pits in toxochelyids (see Lytotoma angusta Wieland, 1904, 1980 MARINE CRETACEOUS TURTLE 9 Figure 5- Peripheral plate of Osteopygis sp., UCMP 123616. a) cross sectional view; b) dorsal view; c) proximal view. Figure 6. Peripheral plate of Osteopygis sp., UCMP 123616. a) ventral view; b) dorsal view; c) cross sectional outline. 10 PALE0BI0S NO. 3k and Toxochelys barbevi, Zangerl, 1953) but it is never as extensive as in the present specimen. In dorsal view (Fig. 6b), there are a pair of excavations in the plate; their origin is suspect, because no such morphological feature has been reported in other turtles. Figure 7- Outline specimen drawing of Osteopygis sp., UCMP 123616. a) dorsal view; b) ventral view. Abbreviations: fti, fossa temporalis inferior; 1, limb fragment; m, mandible; n, nares; o, orbit; oc, occipital condyle; otr, orbito-temporal roof; q, quadrate condyles; s, scapula; sr, skull roof 1980 CRETACEOUS MARINE TURTLE il DISCUSSION I dentificat ion - Identification of UCMP is based in large part upon the morphology of the humerus and certain skull features. The humerus is the "thalassoid" type of humerus (Wieland, 1900), and conforms well to the toxochelyid morphology/function complex described by Zangerl (1953)- The extensive secondary palate and massive mandi- bular symphysis clearly place UCMP 123616 in the subfamily Osteopyginae, as established by Zangerl (1953, 1971). Within the Osteopyginae, the extreme length of the secondary palate and mandibular symphysis of Erquelinnesia preclude referral of UCMP 123616 to that genus. Rather, the moderate length of the secondary palate, the low tomial ridge, the massive mandibular symphysis, as well as the general outline of the skull most closely approximate those found in Osteopygis, to which UCMP 123616 is referred. Specific identification of UCMP 123616 cannot be determined. There are simply not enough diagnostic characters to either sustain or disprove referral to the one species in Osteopygis, 0. emarginatus. Biogeography - As stated above, UCMP 123616 constitutes the first unam- biguous published record of the Toxochelyidae from the Pacific. A prior account (Bohlin, 1953) pf discoveries from the Sino-Swedish Asian ex- pedition establishes three new Asian species of Osteopygis based upon fragmental shell material of late Cretaceous age from North Kansu, China. This work, however, falls short of documenting the occurrence satisfactorily because: 1. Bohlin, himself, states "It is even doubtful if these turtles can be referred to North American genera...American species described by Hay are at least twice as large as those from Kansu..." (Bohlin, 1953); 2. The quality of the description and material are not sufficient to accurately diagnose the specimens more exactly than at the infra- ordinal level. It is interesting to note that osteopygine toxochelyids are known only from marine rocks, while the deposits of Ug-Tokhoi, the North Kansu lo- cality which is the provenance of the Chinese material, are non-marine. In sum, then, it is not clear what family of chelonian is repres- ented by the Chinese material. For this reason, UCMP 123616 is the first unambiguous Pacific record of the family. A Pacific, North American "Western Interior Sea", and North Atlantic distribution suggests that the Toxochelyidae was far more cosmopoli- tan than previously thought. An unpublished record of a South Amer- ican occurrence of the Osteopyginae usstains this conclusion (Gaffney, pers. comm.). This does not necessarily contradict the morphological interpretations of Zangerl; a near shore turtle may achieve a wide- ranging distribution along a coastline. Nasal bones and phylogeny - The presence or absence of nasal bones in osteopygine toxochelyids has been a matter of some confusion. Zangerl, 12 PALEOBIOS NO. 3A in his 1953 diagnosis of the Osteopyginae, stated that "probably no nasal bones" were present in members of the subfamily. In his 197' "emended diagnosis" he changed his position to "nasal bones present." Nasal bones are a primitive character in chelonians, and many groups have independently lost them. In the Osteopyginae, they are a small, thin sheet of bone, poorly sutured to the prefrontals (Zangerl, pers. comm.). Evquelinnesia evidently has them relictly (Zangerl, 1971), but it is important to note that in both YPM 913 and NJSM 11872, the two specimens posessing the best preserved snouts, there is no evidence to suggest the presence of nasals. Nasal bones are at best equivocably present in UCMP 123616, and for this reason the genus Osteopygis is here considered not to posess nasals. The consequence of this hypothesis is that the subfamilial diagnosis of Zangerl must again be emended with respect to nasals. Because nasal bones may or may not be present in osteopygine toxochelyids, the character is best omitted from the diagnosis of the subfamily. If nasal bones are found to be variably present in Osteopygis, this morphological dichotomy within the genus should be relected in the taxonomy of the group. For the present, however, such a systematic re- vision would be extravagant, given the small number of specimens and the uncertainty of the nasal bone identification. ACKNOWLEDGEMENT I am most grateful to Dr. Arthur E. Staebler and Mr. Chad Staebler as well as to their institutional sponsor, California State University (Fresno) for making the specimen available for study at the Museum of Paleontology. Furthermore, I thank Dr. E.S. Gaffney for constructive advice and stimulating conversations about turtles, as well as for gen- erously providing comparative material. Comparative material was also provided by the Yale Peabody Museum and the New Jersey State Museum. Drs. J.H. Hutchinson, J.T. Gregory, and Mr. M. Wilson provided useful criticisms of the manuscript. Likewise, Mr. R.A. Laws and Dr. D.E. Sa- vage contributed to an appreciated editorial effort. This study was supported, in part, by the AMNH Theodore Roosevelt Memorial Fund, the Sigma Xi Scientific Research Society, and by the University of Califor- nia Museum of Paleontology. This manuscript was reviewed by Dr. Eugene S. Gaffney and Dr. Rainer Zangerl. 13 PALEOBIOS NO. 3h LITERATURE CITED Anderson, F.M. 1958. Upper Cretaceous of the Pacific Coast. Geol. Soc. Mem. 77:51-55. Baird, D. 196^4. A fossil sea turtle from New Jersey. New Jersey State Museum Investigations 2:1-26. Bohlin, B. 1953- Fossil Reptiles from Mongolia and Kansu. Reports from the Scientific Expedition to the Northwestern provinces of China; the Sino-Swedish Expedition, Publication no. 37; Ver- tebrate Paleontology 6. Statens Etnografiska Museum, Stockholm Gaffney, E.S. 1972. An illustrated glossary of turtle nomenclature. Am. Mus. Novit. (2486): 1-33- Hay, O.P. 1908. The fossil turtles of North America. Carnegie In- stitute of Washington, Publication no. 75. Payne, M.B. 1951- Type Moreno Formation and overlying Eocene strata on the west side of the San Joaquin Valley, Fresno and Merced Counties, California. California Department of Natural Resources, Division of Mines, Special Report no. 9> PP- 1-29. Wieland, G.R. 1900. Evolution of the testudinate humerus. Am. J. Sci. 9(S4):k\l-h2h. ----- 1904. The structure of upper Cretaceous turtles of New Jersey: Lytoloma. Am. J. Sci. 18(105):183-196- Zangerl, R. 1953- The turtles of the family Toxochelyidae. Part IV. The vertebrate fauna of the Selma Formation of Alabama. Fieldiana Geol. Mem. 3:137-277- ---- 1971. Two toxochelyid sea turtles from the Landenian sands of Erquelinnes (Hainaut), Belgium. Inst. Roy. Soc. Natur. Bel. Mem. 169:\-12. 1980 CRETACEOUS MARINE TURTLE 1A Plate A. The skull of Osteopygis sp., UCMP 123616, X 0.62. Al Dorsal View A2 Ventral View PALEOBIOS back issues may be ordered by mailing a check (made payable to PALEOBIOS) to: Editor, PALEOBIOS Department of Paleontology University of California Berkeley, California 9^720 USA All back issues are $0.50 each (which includes postage). Numbers 4,6,7,10, 13,15,16,19 and 29 are not currently available. Printed by C-J Graphics, Inc., Berkeley, Californ