550 5 fi GEOLOGY LJBRARY n.s. no. 46 h i ELDI ANA Geology NEW SERIES, NO. 46 The Dermal Armor of the Cyamodontoid Placodonts (Reptilia, Sauropterygia): Morphology and Systematic Value Olivier Rieppel £§ February 28, 2002 CSi Publication 1517 E PUBLISHED BY FIELD MUSEUM OF NATURAL HISTORY CD AT llRBANA-CHAMrVftljjJrmation for Contributors to Fieldiana WU GEOLOGY General: /;i'/Hfc//7J\V^.primarily a journal for Field Museum stafi members and research associates, although manuscritA^MiJjutnattiliated authors may be considered as space permits. TheTOUrnal carries a page charge of $65.00 per printed page or fraction thereof. Payment of at least 50% of page charges qualifies a paper for expedited processing, which reduces the publication time. Contributions from staff. research associates, and invited authors will be considered for publication regardless of ability to pay page charges, however, the full charge is mandatory for nonaffiliated authors of unsolicited manuscripts. Three complete copies of the text (including title page and abstract) and of the illustrations should be submitted (one original copy plus two review copies which may be machine copies). No manuscripts will be considered for publication or submitted to reviewers before all materials are complete and in the hands of the Scientific Editor. Manuscripts should be submitted to Scientific Editor, Fieldiana, Field Museum of Natural History, Chicago, Illinois 60605-2496, U.S.A. Text: Manuscripts must be typewritten double-spaced on standard-weight, 8V2- by 11 -inch paper with wide margins on all four sides. If typed on an IBM-compatible computer using MS-DOS, also submit text on 5V4-inch diskette (WordPerfect 4.1, 4.2, or 5.0, MultiMate, Displaywrite 2, 3 & 4, Wang PC, Samna, Microsoft Word, Volks- writer, or WordStar programs or ASCII). For papers over 100 manuscript pages, authors are requested to submit a "Table of Contents," a "List of Illustrations," and a "List of Tables" immediately following title page. In most cases, the text should be preceded by an "Abstract" and should conclude with "Acknowledgments" (if any) and "Literature Cited." All measurements should be in the metric system (periods are not used after abbreviated measurements). The format and style of headings should follow that of recent issues of Fieldiana. For more detailed style information, see The Chicago Manual of Style (13th ed.), published by The University of Chicago Press, and also recent issues of Fieldiana. References: In "Literature Cited," book and journal titles should be given in full. Where abbreviations are desirable (e.g., in citation of synonymies), authors consistently should follow Botanico-Periodicum-Huntianum and TL-2 Taxonomic Literature by F. A. Stafleu & R. S. Cowan (1976 et seq.) (botanical papers) or Serial Sources for the Biosis Data Base (1983) published by the BioSciences Information Service. Names of botanical authors should follow the "Draft Index of Author Abbreviations, Royal Botanic Gardens, Kew," 1984 edition, or TL-2. References should be typed in the following form: Croat, T B. 1978. Flora of Barro Colorado Island. Stanford University Press, Stanford, Calif., 943 pp. Grubb, P. J., J. R. Lloyd, and T. D. Pennington. 1963. A comparison of montane and lowland rain forest in Ecuador. I. The forest structure, physiognomy, and floristics. Journal of Ecology, 51: 567-601. Langdon, E. J. M. 1979. Yage among the Siona: Cultural patterns in visions, pp. 63-80. In Browman, D. L., and R. A. Schwarz, eds., Spirits, Shamans, and Stars. Mouton Publishers, The Hague, Netherlands. Murra, J. 1946. The historic tribes of Ecuador, pp. 785-821. In Steward, J. H., ed., Handbook of South American Indians. Vol. 2, The Andean Civilizations. Bulletin 143, Bureau of American Ethnology, Smithsonian Institution, Washington, D.C. Stolzi-, R. G. 1981. Ferns and fern allies of Guatemala. Part II. Polypodiaceae. Fieldiana: Botany, n.s., 6: I— 522. Illustrations: Illustrations are referred to as "figures" in the text (not as "plates"). Figures must be accompanied by some indication of scale, normally a reference bar. Statements in figure captions alone, such as "X0.8," are not acceptable. Captions should be typed double-spaced and consecutively. See recent issues of Fieldiana for details of style. All illustrations should be marked on the reverse with authors name, figure number(s), and "top." Figures as submitted should, whenever practicable, be 8V2 by 1 1 inches (22 X 28 cm) and may not exceed 1 \Vi by I6V2 inches (30 X 42 cm). Illustrations should be mounted on boards in the arrangement to be obtained in the printed work. This original set should be suitable for transmission to the printer as follows: Pen and ink drawings may be originals (preferred) or photostats; shaded drawings must be originals, but within the size limitation; and photostats must be high-quality, glossy, black and white prints. Original illustrations will be returned to the corre- sponding author upon publication unless otherwise specified. Authors who wish to publish figures that require costly special paper or color reproduction must make prior arrangements with the Scientific Editor. Page Proofs: Fieldiana employs a two-step correction system. The corresponding author will normally receive a copy of the edited manuscript on which deletions, additions, and changes can be made and queries answered. Only one set of page proofs will be sent. All desired corrections of type must be made on the single set of page proofs. Changes in page proofs (as opposed to corrections) are very expensive. Author-generated changes in page proofs can only be made if the author agrees in advance to pay for them. © This paper meets the requirements of ANSI/NISO Z39.48-1992 (Permanence of Paper). FIELDIANA Geology NEW SERIES, NO. 46 The Dermal Armor of the Cyamodontoid Placodonts (Reptilia, Sauropterygia): Morphology and Systematic Value Olivier Rieppel Department of Geology Field Museum of Natural History 1400 South Lake Shore Drive Chicago, Illinois 60605-2496 U.S.A. Accepted November 7, 2001 Published February 28, 2002 Publication 1517 PUBLISHED BY FIELD MUSEUM OF NATURAL HISTORY © 2002 Field Museum of Natural History ISSN 0096-2651 PRINTED IN THE UNITED STATES OF AMERICA KOUKfUBmY Table of Contents Abstract 1 Introduction 1 Material 2 The General Structure of the Cyamo- dontoid Dermal Armor 2 Ontogeny and Phylogeny of the Cyamo- dontoid Dermal Armor 3 Systematic Paleontology 6 Genus Cyamodus Meyer, 1863 6 Genus Henodus Huene, 1936 10 Genus Placochelys Jaekel, 1 902 11 Genus Psephoderma Meyer, 1858a,b 14 Genus Psephosaurus Fraas, 1896 20 Genus Psephosauriscus n. gen 21 A Comparison of the Dermal Armor in Cyamodontoid Placodonts and Tur- tles 32 Functional Anatomy of the Dermal Ar- mor in Placodonts 36 Discussion and Conclusions 38 Acknowledgments 39 Literature Cited 39 List of Illustrations 1 . Life reconstruction of a hypothetical cyamodontoid 4 2. Carapace fragment and isolated osteo- derm of cf . Psephoderma 5 3. Plastron fragment of Psephosauriscus sinaiticus Haas 6 4. Plastron fragment of Psephosauriscus sinaiticus Haas 7 5. Detail of carapace of Cyamodus hilde- gardis Peyer 7 6. A juvenile specimen of Psephoderma alpinum H.v. Meyer 8 7. Carapace fragment referred to Cyamo- dus kuhnschnyderi Nosotti and Pinna .... 8 8. Carapace fragments referred to Cyamo- dus kuhnschnyderi Nosotti and Pinna .... 9 9. Carapace fragment referred to Cyamo- dus kuhnschnyderi Nosotti and Pinna .... 10 10. Dermal armor of Cyamodus hildegar- dis Peyer 11 1 1 . Marginal osteoderms of the carapace of Cyamodus hildegardis Peyer 11 1 2. Carapace fragment of Placochelys pla- codonta Jaekel 12 13. Gastral rib and plastron fragments of Placochelys placodonta Jaekel 13 14. Left lateral margin of the carapace of Psephoderma alpinum H.v. Meyer 14 15. Dermal armor of Psephoderma alpin- um H.v. Meyer 15 16. Osteoderm shape and structure in the carapace of Psephoderma alpinum H.v. Meyer 16 17. Osteoderm shape and structure in the carapace of Psephoderma alpinum H.v. Meyer 17 18. Carapace of Psephoderma sculptata n. sp 18 19. Isolated osteoderms from the carapace of Psephoderma sculptata n. sp 19 20. Carapace fragment of Psephosaurus suevicus Fraas 22 21. Carapace fragments and isolated osteo- derms of Psephosaurus suevicus Fraas 23 22. Carapace fragments of Psephosauriscus mosis Haas 24 23. Osteoderm shape and structure in the dermal armor of Psephosauriscus mos- is Haas 25 24. Plastron fragment referred to Psepho- sauriscus mosis Haas 26 25. Carapace of Psephosauriscus ramonen- sis n. sp 27 26. Osteoderm shape and structure in the dermal armor of Psephosauriscus ra- monensis n. sp 28 27. Plastron of Psephosauriscus ramonen- sis n. sp 29 28. Dermal armor of Psephosauriscus sin- aiticus Haas 30 29. Carapace fragments referred to Psepho- sauriscus sinaiticus Haas 31 30. Carapace fragment referred to cf. Pse- phosauriscus rhomhifer Haas 32 31. Pectoral girdle of Henodus chelyops 33 List of Charts 1 . Morphological differences in the dermal armor of Testudines and Cyamodontoi- dea 35 The Dermal Armor of the Cyamodontoid Placodonts i kept ilia. Sauropterygia): Morphology and Systematic Value Olivier Rieppel Abstract The dermal armor of cyamodontoid placodonts is described and discussed in detail. A review of all available data on the ontogeny and phylogeny of the cyamodontoid dermal armor pre- cedes the discussion of its value in placodont systematics. The cyamodontoid dermal armor is known from Middle to Upper Triassic fossil remains found in the Germanic and Alpine Triassic and at various circum-Mediterranean localities, most notably Makhtesh Ramon in the Negev, as well as in southern China. This paper recognizes five, possibly six species of cyamodontoids from the Middle Triassic of Makhtesh Ramon, two of them new. The morphology of the cyamodontoid dermal armor is compared in detail to the morphology of the turtle shell. The similarity is shown to be superficial only. The study concludes with comments on the functional anatomy of the cyamodontoid dermal armor. Introduction The history of the investigation of sauroptery- gians from the Germanic Triassic goes back to the beginning of the 19th century. Large, black, shiny tooth plates have been reported from the upper Muschelkalk of Bayreuth (Bavaria, southern Ger- many) since 1809 (Weiss, 1983; 1806 following Miiller, 1979), the year when Count Georg von Munster (1776-1844) started the systematic col- lection of vertebrate fossils from these deposits. The first skull was collected in 1824, described by Munster in 1 830, and named by Agassiz ( 1 833- 45) as a new genus of pyenodont fish, Placodus. It was left to Owen (1858) to discover the reptil- ian affinities of that genus. In 1863, H.v. Meyer reviewed the then avail- able knowledge on placodonts and recognized two basic groups, which he named "Macrocephali" and "Platycephali," respectively (see also Braun. 1862). Meyer (1863) thereby captured a number of essential characteristics separating two clades of placodonts that today are known as the Placo- dontoidea (Nopcsa, 1923) and Cyamodontoidea (Peyer & Kuhn-Schnyder, 1955), respectively (Rieppel & Zanon, 1997). The skull of cyamo- dontoids (Rieppel. 2001) is rather low and broad, characterized by flaring upper temporal arches and squamosals that project far back beyond the dorsal head of the quadrate. The premaxillary ros- trum may be short and rounded and carrying pre- maxillary teeth, or it is slender, elongate, and edentulous, with margins that may have been cov- ered by a horny sheath. The maxillary and pala- tine dentition is reduced to a variable degree, and only the posterior palatine teeth are expanded into distinctly enlarged tooth plates. In his review, Meyer (1863) considered placodont skulls only, since at that time another important distinction be- tween the two clades had not been recognized. Whereas osteoderms are (Placodus: Drevermann, 1933) or are not (Paraplacodus: Rieppel, 2(KX)a) present in the Placodontoidea. osteoderms always develop and combine to form a turtle-like body armor in the Cyamodontoidea. Throughout their history, placodonts remained restricted to the Middle and Upper Triassic of the Tethyan faunal province. Their remains are found in deposits of the shallow epicontinental sea of the Germanic basin and of intraplatform basins FIELDIANA: GEOLOGY, N.S., NO. 46, FEBRUARY 28. 2002, PP. 1 — 41 that developed on the extended carbonate plat- forms lining the northern and southern shores of the developing southern branch of the Neotethys. Among the placodonts, the Cyamodontoidea are a far more diverse and more widespread group than the Placodontoidea. However, a better un- derstanding of the phylogeny and historical bio- geography of the Cyamodontoidea remains ham- pered by an incomplete understanding of their taxonomic diversity and phylogenetic interrela- tionships. The reasons for this are partly to be sought in the nature of the material. Articulated cyamodontoid specimens that preserve the skull in association with dermal armor are rare. As a result, some cyamodontoid genera and species are based on skull material (e.g., Cyamodus rostratus, Cyamodus kuhnschnyderi), while others are based on fragments of the dorsal armor only (e.g., Pse- phosaurus suevicus). The dermal armor of cy- amodontoids has received little attention so far, the only recent and comprehensive studies being those of Westphal (1975, 1976). Very little is known about the variability of the dermal armor both within and between species, and nothing is known about the use of the dermal armor for tax- onomic purposes, other than that its usefulness has been disputed (Westphal, 1976). The purpose of this paper is to review the anatomy of the cy- amodontoid dermal armor and its potential use for taxonomic purposes. Material Following is a list of material included in the present study. Institutional abbreviations are: bsp, Bayerische Staatssammlung fiir Palaontologie und historische Geologie, Munich; fafi, Magayar Al- lami Foldtani Intezet (Geological Institute of Hun- gary, Budapest); fmnh, Field Museum of Natural History; HUJ-Pal., Paleontological Collections, Department of Evolution, Systematics and Ecol- ogy, The Hebrew University, Jerusalem; msnb, Museo Civico di Scienze Naturali "E. Caffi," Bergamo; msnm, Museo Civico di Storia Naturale di Milano; pimuz, Palaontologisches Institut und Museum der Universitat Zurich; smns, Staatliches Museum fiir Naturkunde, Stuttgart. Caretta caretta (L.), fmnh 51676, Cuba. Cyamodus hildegardis Peyer, 1931: msnm V458 (complete specimen, ventral view); pimuz T4763 (holotype); pimuz T58. Cyamodus cf. C. kuhnschnyderi Nosotti and Pinna, 1993: smns 81600 (carapace fragment); smns 15891 (carapace fragment). Placochelys placodonta Jaekel, 1902: fafi Ob/ 2323/Vt.3. (holotype). Psephoderma alpinum Meyer, 1858: bsp As I 8 (holotype); msnb 4614 (carapace fragment); msnb 4884a and b (juvenile specimen); msnb 8358 (complete carapace); msnb 8359 (pelvic region and tail); msnm V527 (complete specimen, ventral view). Psephoderma sculptata n. sp.: HUJ-Pal. TR. 198 (holotype, partial carapace); HUJ-Pal. T.R.207 (iso- lated osteoderms), HUJ-Pal. T.R.929 (small cara- pace fragment, original of Haas, 1975, PI. I, Fig. 8). cf. Psephoderma sp.: HUJ-Pal. TR.3189 (almost complete carapace, original of Haas, 1969); T.R.I 044 (carapace fragment and isolated osteo- derm). Psephosauriscus mosis (Brotzen, 1957): HUJ- Pal. C.F.247 (holotype, fragments of carapace and plastron); HUJ-Pal. uncatalogued, fragments from Makhtesh Ramon. Psephosauriscus ramonensis n. sp.: HUJ-Pal. T.R.2751 (holotype, carapace fragment); HUJ-Pal. uncatalogued, fragments from Makhtesh Ramon. cf. Psephosauriscus rhombifer: HUJ-Pal. TR.3676, TR.2492. Psephosauriscus sinaiticus (Haas, 1959): HUJ- Pal. TR.3421 (holotype, carapace fragment, spec- imen A of Haas, 1959); HUJ-Pal. T.R.966, TR.1097, TR.3061, TR.3422, TR.3636, TR.3673 (carapace fragments from Makhtesh Ramon). Psephosaurus suevicus Fraas, 1896: smns 6693 (holotype); smns 7180 (isolated osteoderm); smns 54710 (isolated osteoderm, original of Fraas, 1896, Fig. 7d); smns 17790 (isolated osteoderm, original of Huene, 1936, Fig. 29c). The General Structure of the Cyamodontoid Dermal Armor If completely developed, the dermal armor of cyamodontoids comprises a dorsal shield, the car- apace, and a ventral shield, the plastron (the terms carapace and plastron as used in this paper do not imply homology with the convergent dermal ar- mor of turtles; see the discussion below). Whereas all cyamodontoids develop a carapace (but see comments on Cyamodus below), the plastron is variably developed, or may be absent. Where pre- sent, it is linked to the carapace by a "lateral FIELDIANA: GEOLOGY wall" (Haas, 1959, 1969) that covers the flanks of the body between the anterior and posterior limbs (Fig. 1). The carapace has rounded contours except for an anterior (nuchal) excavation (concavity). It may be developed as a single shield covering the dorsal side of the trunk of the animal (Henodus, Placochelys) or as a dual structure, with a large dorsal shield and a smaller posterior shield cov- ering the posterior pelvic and proximal caudal re- gion {Cyamodus hildegardis, Psephoderma). The basic morphogenetic unit of the carapace is a hex- agonal osteoderm (Fig. 2) with a variable thick- ness that may, or may not, exceed its diameter (Westphal, 1975, 1976). These osteoderms meet in smooth or interdigitating sutures and may dis- play a variety of surface ornamentations. In the case of interdigitating interfaces, interdigitation may be less expressed superficially than at the base of the osteoderms, such that osteoderm con- tours are more regularly delineated on the super- ficial (dorsal) surface of the carapace than on its internal (ventral) surface. Osteoderm size, shape, and ornamentation may vary between species and also in different parts of the carapace of a single species. Prominent is the development of longi- tudinal ridges by the alignment of crested osteo- derms (Psephoderma), or the strengthening of the lateral margins of the carapace by enlarged, tu- bercular osteoderms. A regular geometrical rela- tionship of carapacial osteoderms and underlying endoskeletal elements (vertebrae and ribs) could so far be established for Henodus only (Westphal, 1975, 1976). Haas (1959) described mineralized fibrous connective tissue underlying carapacial osteoderms (see also Westphal, 1975). Well-pre- served specimens show superficial impressions of epidermal scute margins on the carapace and plas- tron, which may or may not coincide in their out- lines with the circumference of underlying osteo- derms. A plastron is absent in Cyamodus (based on Cyamodus hildegardis: Pinna, 1992; see further comments below) and Psephoderma (Pinna & Nosotti, 1989). A plastron is present in Henodus, yet its detailed structure remains poorly known (Huene, 1936; Westphal, 1975), and very little is known about the plastron of Placochelys (Jaekel, 1907; Westphal, 1975; see further comments be- low). The plastron is best known in specimens from the Middle Triassic of Araif en Naqua, Sinai Peninsula (Haas, 1959), and from Makhtesh Ra- mon, Israel (Haas, 1969, 1975), where it is com- posed of osteoderms of distinctly different (su- perficial) shape than those of the carapace. The plastral osteoderms tend to be thinner than their carapacial counterparts, and on the inner (dorsal) surface of the plastron (i.e., at their base) appear as rhomboidal or trapezoidal elements that meet each other in interdigitating sutures. In contrast to carapacial osteoderms (of the same specimens), the plastral osteoderms are aligned in regular, obliquely trending transverse rows. In one well- preserved specimen (Figs. 3, 4), the osteoderms are aligned with gastral ribs (Haas, 1959; West- phal, 1975, Fig. 6). The superficial appearance of the plastral osteoderms (i.e., their ventral surface or "crown") assumes a more or less regular cy- cloid shape congruent with the overlying epider- mal scute area. The apex of these scutes points anteriorly, their convex base posteriorly. Where a plastron in present, it is linked to the carapace by a lateral wall that extends between the anterior and posterior limb. Osteoderm struc- ture in the lateral wall may resemble plastral or carapacial osteoderms respectively in different species. The transition of the lateral wall into the carapace and plastron respectively may be strengthened by the development of enlarged and keeled osteoderms that form dorsolateral and ven- trolateral body ridges. If a lateral wall is present, the distal tips of the dorsal ribs, or of the trans- verse processes of the dorsal vertebrae (if fused with the dorsal ribs), abut the medial surface of its osteoderms (Cyamodontoidea indet., HUJ-Pal. TR.3673). Ontogeny and Phylogeny of the Cyamodontoid Dermal Armor Osteoderms are absent in the placodontoid ge- nus Paraplacodus broilii (Rieppel, 2000a). They are present in the enigmatic genus Saurosphargis volzi from the lower Muschelkalk of Upper Silesia (Huene, 1936; the holotype and only known spec- imen is now lost), which shows overlapping un- cinate processes on the dorsal ribs, as does Para- placodus. The presence of osteoderms in Sauro- sphargis may cast doubt on its previously pro- posed synonymy with Paraplacodus (Rieppel, 1995), or it may indicate that the two specimens represent different species within the genus Par- aplacodus. In Placodus, a single row of osteo- derms is aligned along the midline of the body on top of the neural spines (Drevermann, 1933). It is conceivable that the dermal armor of cy- RIEPPEL: THE DERMAL ARMOR OF CYAMODONTOID PLACODONTS FIELDIANA: GEOLOGY amodontoids originated by coalescence of origi- nally separate osteoderms covering the body sur- face. A juvenile specimen of Cyamodus hildegar- dis was described as showing an immature stage of development of the carapace (Fig. 5), with in- complete coalescence of irregularly shaped osteo- derms (msnm V458: Westphal, 1975; Pinna, 1992; and personal observation). The development and coalescence of osteoderms appears to proceed in an anteroposterior gradient, as osteoderms are more densely packed in the anterior trunk region of msnm V458 (Pinna, 1992, Fig. 2). Similar observations of an ontogenetic consol- idation of the carapace have been reported for Psephoderma alpinum, where the ossification of the caudal shield lags somewhat behind the ossi- fication of the carapace (Pinna & Nosotti, 1989), again indicating an anteroposterior gradient in the development of the dermal armor. One remarkable juvenile specimen (msnb 4884a and b) from the Norian of northern Italy shows a skull length of only 28 mm and a total body length of approxi- mately 150 mm. Approximately 90 mm of the vertebral column is preserved, including the very long and slender tail, and weak ossifications of the four limbs can be identified, but there is no trace of a carapace or of separate osteoderms (Fig. 6). It seems to represent an ontogenetic stage at which dermal ossification has not yet started. This conclusion contrasts with a small cyamodontoid from the Ladinian Muschelkalk of Mont-ral-Al- cover in northeastern Spain with a total length (from the tip of the snout to the tip of the tail as preserved) of 120 mm and a skull length of 24.5 mm. Due to taphonomic peculiarities at this lo- cality (Hemleben & Freels, 1977), bone substance is not preserved, but the body contours are distinct and indicate the presence of a bipartite dorsal ar- mor comprising a carapace and a tail shield (Riep- pel & Hagdorn, 1997, Fig. 2). The carapace does not show the three longitudinal ridges otherwise typical of Psephoderma, which renders the gener- ic identification of the specimen impossible. But with a well-developed dorsal armor at this small size, the specimen either represents a separate miniature cyamodontoid species, or raises ques- tions as to the proper identification of supposedly juvenile Cyamodus and Psephoderma specimens Fig. 2. Carapace fragment and isolated osteoderm of cf. Psephoderma (HUJ-Pal. T.R.I 044) from the Middle Triassic of Makhtesh Ramon, Negev. with what appears to be an absent or incompletely ossified dermal armor. Indeed, knowledge of the ontogeny of the der- mal armor of cyamodontoid placodonts must re- main incomplete until the discovery of new ma- terial. Aside from documenting the presence of dissociated osteoderms which indicate ontogenet- ic fusion in the formation of the carapace, speci- men msnm V458 of Cyamodus hildegardis poses some special problems. The osteoderms come in all sizes and shapes in that specimen, without reg- ularity to their appearance. This irregularity of ap- pearance, together with the fact that the osteo- derms "thin out" toward their margins, may in- dicate their as yet incomplete ossification in a ju- venile animal. But, as already noted by Pinna (1980), some osteoderms lie outside the dorsal rib cage, as they should and as is particularly clear on the right side of the body. Other osteoderms, however, lie inside the body cavity, overlapping the flat ventral surface of the broad transverse pro- cesses of the dorsal vertebrae. And whereas most osteoderms lie in between the transverse process- es of the dorsal vertebrae and in between the gas- tral ribs, not infrequently osteoderms overlap the ventral surface of gastral ribs. Pinna (1980, PI. 4, Fig. 4) even postulated an occasional fusion of osteoderms with the ventral surface of gastral ribs, Fig. 1 . Life reconstruction of a hypothetical cyamodontoid placodont showing the characteristics of the dermal armor (artwork by Marlene Donnelly, the Field Museum). RIEPPEL: THE DERMAL ARMOR OF CYAMODONTOID PLACODONTS Fig. 3. Plastron fragment of Psephosauriscus sinai- ticus Haas (HUJ-Pal. uncatalogued, part of the now bro- ken specimen D of Haas, 1959, PI. V) from the Middle Triassic of Makhtesh Ramon, Negev. A, ventral view; B, dorsal view. which might indicate the presence of an incom- plete plastron. By comparison, the specimen pimuz T58 of Cy- amodus hildegardis clearly displays, on its right side, the hexagonal suture pattern between osteo- derms exposed in ventral view. In other parts of the body, ill-defined dermal bone appears to have been squeezed in between the transverse process- es of the dorsal vertebrae, and bone may even have been squeezed across the ventral surface of the transverse processes. There must also have been some dislocation of skeletal elements in the decaying animal. For example, a gastral rib lies on top of (i.e., morphologically ventral to) the (right) transverse process of the 7th preserved dorsal vertebra. But as the intact yet dislocated gastral rib extends anteriorly, it passes below (i.e., morphologically dorsal to) the (right) transverse process of the 6th preserved dorsal vertebra. De- posited in a supposedly anoxic intraplatform ba- sin, fossilization of vertebrates was generally as- sumed to be undisturbed. However, Tintori (1992) noticed isoorientation and some degree of disar- ticulation in vertebrates (mostly fishes) from the Formazione di Besano (equivalent to the Grenz- bitumen horizon), which he attributed to light bio- turbation (in a disaerobic environment) and cur- rents at the bottom of the basin. The same factors, together with pressure originating from the com- paction of sediment, apparently did have an im- pact on the carapace of Cyamodus and may be responsible for some of the disarticulation and dislocation of the osteoderms. Systematic Paleontology Sauropterygia Owen, 1860 Placodontia Zittel, 1887-1890 Cyamodontoidea Peyer and Kuhn-Schnyder, 1955 Genus Cyamodus Meyer, 1863 Type Species — Cyamodus rostratus (Munster, 1839). Diagnosis— See Rieppel (2000b, 2001) for a diagnosis and discussion of the genus. Distribution — Middle Triassic (Anisian, Ladi- nian); Germanic basin and southern Alps. Description — The genus was erected by Meyer (1863) for Cyamodus rostratus (Munster, 1839) from the upper Muschelkalk (upper Anisian) of southeastern Germany (Bayreuth). Other species from the same age and locality are Cyamodus muensteri (Agassiz, 1833-45) and Cyamodus la- ticeps (Owen, 1858), the latter most probably a junior synonym of Cyamodus muensteri (Rieppel, 2000b, 2001). Cyamodus kuhnschnyderi Nosotti and Pinna, 1993, is from the upper Muschelkalk of southwestern Germany (Crailsheim; lower Ladinian); and Cyamodus hildegardis Peyer, 1931, is from the Grenzbitumen horizon (Anisian- FIELDIANA: GEOLOGY Fig. 4. Plastron fragment of Psephosauriscus sinaiticus Haas (HUJ-Pal. uncatalogued, part of the now broken specimen D of Haas, 1959, PI. V) from the Middle Triassic of Makhtesh Ramon. Negev. A, ventral view; B, dorsal view. Ladinian boundary) of Monte San Giorgio (south- ern Alps). The holotype and only known speci- men of Cyamodus tarnowitzensis Giirich, 1884, from the Karchowice Beds (lower Muschelkalk, lower Anisian) of Tarnowiskie, Poland, was lost during World War II. Among this material, only Cyamodus hildegar- dis is known from articulated specimens. Cyamo- dontoids from the Germanic Triassic are known from skulls collected at three different localities (Upper Silesia, Bayreuth, and Crailsheim), all of which have yielded abundant additional saurop- terygian material, but virtually no osteoderms. and exceedingly rare coherent dermal armor frag- Fig. 5. Detad of carapace of Cyamodus hildegardis Peyer (msnm V458), with incomplete coalescence of ir- regularly shaped osteoderms. ments. This is in stark contrast to other localities (such as Makhtesh Ramon in the Negev: Haas, 1969, 1975; see below), where cyamodontoid os- teoderms and armor fragments, if present, are the most frequently found fossil remains. Only three isolated armor fragments are known from the Ger- manic Muschelkalk (upper Muschelkalk [mo2] of Crailsheim, lower Ladinian), and for stratigraphic reasons they have been referred to Cyamodus kuhnschnyderi (Nosotti & Pinna, 1996, Fig. 14); no armor fragments have been reported from the Muschelkalk of Bayreuth (upper Muschelkalk. mol, upper Anisian) and of Upper Silesia (lower Muschelkalk, lower Anisian). All Cyamodus skulls from the Germanic Triassic show tubercular osteoderms secondarily fused to the temporal re- gion of the skull, demonstrating the developmen- tal capacity to grow osteoderms. which raises the question of why dermal armor remains are so rare in the Germanic Muschelkalk. The most complete dermal armor fragment from the upper Muschelkalk of Crailsheim (smns 81600; Nosotti & Pinna, 1996, Fig. 14C) is 213 mm long. It represents part of a rectangular dor- solateral ridge with the lateral wall still attached to it (Figs. 7, 8). The dorsolateral ridge is formed by enlarged and distinctly keeled osteoderms that slightly interlock with each other in a peg-and- socket fashion. Their circumference is irregularly octagonal, with a length that varies from 37 mm RIEPPEL: THE DERMAL ARMOR OF CYAMODONTOID PLACODONTS Fig. 6. A juvenile specimen of Psephoderma alpinum H. v. Meyer (msnb 4884a) showing the absence of dermal armor. Fig. 7. Carapace fragment from the upper Muschelkalk (lower Ladinian) of Crailsheim (Germany) referred to Cyamodus kuhnschnyderi Nosotti and Pinna (smns 81600). A, dorsal view; B, lateral view. FIELDIANA: GEOLOGY A.1 Fig. 8. Carapace fragments from the upper Muschelkalk (lower Ladinian) of Crailsheim (Germany) referred to Cyamodus kuhnschnyderi Nosotti and Pinna. A, specimen smns 81600 in dorsal view: B, specimen smns 816(H) in lateral view; C, specimen smns 15891c in lateral view. to 39 mm and a width that ranges from 43 mm to 45 mm. The medial ridge is raised into a low, blunt apex at the anterior margin of the osteo- derm. It divides the osteoderm into a medial and a lateral part, which together define an angle of 90°. Medial to the dorsolateral ridge a row of dis- tinctly smaller, triangular osteoderms separates the latter from what appears to be another row of large, irregularly octagonal and keeled osteo- derms. The lateral wall is composed of the verti- cally descending lateral part of the dorsolateral ridge osteoderms, flanked ventral ly by a row of distinctly pentagonal osteoderms. The latter vary in size. Larger osteoderms (width: 24 mm to 26 mm; height: 22 mm to 25 mm) bridge the gaps between adjacent dorsolateral ridge osteoderms. Between these larger elements, at the middle of the dorsolateral ridge osteoderms, are located smaller yet again pentagonal osteoderms (width: 17 mm to 20 mm; height: 17 mm to 18 mm). RIEPPEL: THE DERMAL ARMOR OF CYAMODONTOID PLACODONTS Fig. 9. Carapace fragment from the upper Muschelkalk (lower Ladinian) of Crailsheim (Germany) referred to Cyamodus kuhnschnyderi Nosotti and Pinna (smns 15891c) in lateral view. Collectively, these polygonal osteoderms define a straight ventral margin of the lateral wall, which shows a limited depth and does not appear to have been connected to a plastron. The latter may have been absent. A second dermal armor fragment (smns 15891) of 150 mm total length comprises four very prom- inent tubercular osteoderms, of which the two middle ones are complete and have a width of 44 mm and 46 mm respectively (Figs. 8B, 9). These are of an irregular pyramidal shape with a blunt apex. On one side of the specimen, much smaller, triangular osteoderms bridge the gaps between the larger elements. Collectively, the osteoderms are very reminiscent of the anterolateral peripherals of Proganochelys (Gaffney, 1990), but whereas the latter are solid (E. S. Gaffney, pers. comm.), the cyamodontoid osteoderms are deeply hollow and rather thin-walled, and may have formed a lateral ridge along the margin of the carapace. As such, specimen smns 15891 more closely resem- bles the enlarged tubercular osteoderms lining the lateral margin of the carapace in Cyamodus hilde- gardis than specimen smns 81600, which pre- serves a vertical lateral wall that is absent in Cy- amodus hildegardis. The carapace of Cyamodus hildegardis (see also comments above) is composed of a dorsal shield and a separate tail shield (Fig. 10). A lateral wall, as well as a plastron, is absent. Distinctly enlarged, tubercular or pyramidal osteoderms line the circumference (nuchal region not known) of both the dorsal and the tail shield (pimuz T4763; Fig. 11); similarly enlarged marginal osteoderms are absent in a juvenile specimen (msnm V458). The surface of the osteoderms is pitted, but the carapace does not form longitudinal ridges as are known in Psephoderma. Three rows of osteo- derms cover the dorsal surface of the tail behind the tail shield, of which the two lateral ones are again enlarged and of tubercular shape (pimuz T4763: Pinna, 1992, Fig. 3; T58: Pinna, 1992, Fig. 1; and personal observation). Genus Henodus Huene, 1936 Type Species — Henodus chelyops Huene, 1 936. Diagnosis— See Rieppel (2000b, 2001) for a diagnosis and discussion of the genus. Distribution — Upper Gipskeuper (lower Car- nian, Upper Triassic); southern Germany. Description — The dermal armor of Henodus has been studied in detail and illustrated by Huene (1935, 1958), Reiff (1942), and Westphal (1975, 1976). It may represent the most highly derived dermal armor among cyamodontoid placodonts, as carapacial osteoderms are arranged in a complex yet highly constrained geometrical pattern that re- lates in a well-defined geometry to the underlying endoskeleton. A dorsomedial row of hexagonal os- teoderms is associated with the underlying neural arches of the dorsal vertebrae, whereas a marginal row of smaller hexagonal osteoderms is closely as- sociated with the underlying ribs. It should be not- ed, however, that due to the poor preservation of Henodus, some controversy surrounds the nature of the articulation of the ribs with the transverse processes of the dorsal vertebrae. The discussion as to whether the dorsal vertebrae of Henodus car- ry elongate transverse processes as are known from other cyamodontoids (Huene, 1936) or only very short ones (Reiff, 1942) has been resolved by the removal of part of the carapace in specimen VIII 10 FIELDIANA: GEOLOGY Fig. 10. The dermal armor of Cyamodus hildegardis Peyer (holotype, pimuz T4763. dorsal view). (Huene, 1958). This exposed the characteristically elongated transverse processes, which articulate with free ribs. The association of the marginal plates with the endoskeleton is located at the level of a distal expansion of the ribs, i.e., lateral to the transverse processes. The contours of the epidermal scutes are not congruent with the contours of the underlying osteoderms but are indicated by distinct grooves on the surface of the carapace (Reiff, 1942). The carapace of Henodus is shorter than wide. distinctly excavated both anteriorly and posteriorly, and linked by a lateral wall to the plastron. Because of the poor preservation, the structure of the plas- tron remains incompletely known, but it appears to have been composed of a row of very broad yet short bony lamellae underlying the gastral ribs (Westphal, 1975). Among all cyamodontoids, Hen- odus certainly has the most turtle-like dermal ar- mor (Reiff, 1942), which was identified by Greg- ory (1946) as a case of striking convergence. Fig. 1 1 . Enlarged marginal osteoderms of the cara- pace of Cyamodus hildegardis Peyer (holotype. PIMUZ T4763, dorsal view). Genus Placochelys Jaekel, 1902 Type Species — Placochelys placodonta Jaekel, 1902. Diagnosis— See Rieppel (2000b. 2001) for a diagnosis and discussion of the genus. Distribution — Upper Triassic; central Europe. Description — The dermal armor of Placoche- lys placodonta Jaekel. 1902. is much less well known than is suggested by Jaekel's (1907) mono- graph (Westphal, 1975). Some of the original ma- terial described by Jaekel (1907) was lost during World War II. most notably limb bones and parts of the dorsal armor. The carapace of Placochelys is composed of osteoderms of variable size, with a hexagonal base meeting its neighbors in an interdigitating interface and a distinctly ridged, tubercular or py- RIEPPEL: THE DERMAL ARMOR OF CYAMODONTOID PLACODONTS 11 Fig. 12. Carapace fragment of Placochelys placodonta Jaekel (holotype, fafi Ob/2323/Vt.3) in dorsolateral view. ramidal "crown" (Fig. 12). Enlarged tubercles were aligned along the lateral margins of the car- apace and apparently irregularly interspersed among smaller osteoderms throughout the dorsal shield. The lateral wall is composed of osteo- derms with a cycloid superficial appearance, their blunt apex pointing dorsally, the convex base pointing ventrally (Jaekel, 1907, PI. IX, Fig. 3). The large tubercular or pyramidal osteoderms are solid, but isolated specimens show a ventrally concave base (Jaekel, 1907, PI. IX, Fig. 5b). Nothing is known about the presence of a separate tail shield, and very little is known of the plastron. Among the material still available of Placoche- lys are fragments of bone, identified by Jaekel (1907, PI. VI, Fig. 1) as dorsal ribs; unquestionable parts of slender gastral ribs (Jaekel, 1907, PI. VI, Fig. 2 [lateral element]; Fig. 3 [medioventral ele- ment]); and very peculiar elements that look like rib or gastral rib fragments fully or partially fused with irregular patches of accessory bone. These lat- ter elements were identified as ventral rib frag- ments fused with gastral ribs by Jaekel (1907), or as broadened gastral ribs fused with osteoderms by Westphal (1975). The dorsal vertebrae of cyamo- dontoids are characterized by very broad transverse processes that articulate with rather short dorsal ribs located in the body wall (Cyamodus hildegar- dis: Pinna, 1992) or are completely fused with the dorsal ribs (Psephoderma alpinum: Pinna & No- sotti, 1989). Only one, incompletely preserved dor- sal vertebra is known for Placochelys, with indi- cations of a broad transverse process (Jaekel, 1 907, PI. VII, Fig. 10). It is possible that the fragments identified as dorsal ribs by Jaekel (1907) represent broken parts of dorsal ribs that may or may not have been fused to the transverse processes of dor- sal vertebrae. The ventral rib fragments of Jaekel (1907) show a distinct surface ornamentation of ridges and grooves, which suggests a dermal rather than endochondral origin (Fig. 13). Some frag- ments are elongate and slightly curved (Jaekel, 1907, PI. VI, Figs. 6, 7) and seem to represent segments of distinctly broadened gastral ribs, com- parable to the broadened lateral gastral elements seen in Henodus (Huene, 1958). One specimen is distinctly broadened and angulated (Jaekel, 1907, PI. VI, Fig. 9) and might represent a fragment of a broadened medioventral gastral rib with acces- sory bone wrapped around it (Fig. 13 A). Huene (1958) interpreted this fragment as a ventrolateral part of a dorsal rib carrying an uncinate process, which would form a ventrolateral body ridge com- parable to Henodus. Westphal (1975) showed, however, that the broadening of the distal part of the dorsal ribs underlies the dorsolateral carapacial ridge in Henodus, which in Placochelys carries large, pyramidal osteoderms. Henodus thus appears to be a poor model for the reconstruction of the plastron in Placochelys. The accessory bone has a smooth surface and may wrap around the thickened gastral ribs (Jae- 12 FIELDIANA: GEOLOGY _~ 1 ,0 v y\ "| 20 mm A.2 . ■gijf , iF^^BlpJ J|P ^^ % *" ^H % 4/ * A mm : 1 «i>*" Sj m pi p -i 20 mm 4 -'' # ;' ' "\ . %SB 1 BJP1 -4- B.3 1 ' * '■!'■.•'/.': | Fig. 13. Gastral rib and plastron fragments of Placochelys placodonta Jaekcl (holotype, far Ob/2323/Vt.3). kel, 1907, PI. VI, Figs. 6, 9), or it fills the space between adjacent gastral ribs (Fig. 13B). The gas- tral ribs receive the patches of accessory bone in distinctly concave anterior and posterior margins (Jaekel, 1907, PI. VI, Fig. 7). A foramen piercing the patches of accessory bone in two specimens (Fig. 13B) indicates that these structures were not exposed superficially but were surrounded by vas- cularized tissue (Westphal, 1975, 1976). Given their irregular shape, it seems unlikely that the patches of accessory bone would have combined to form a solid plastron. Still, to the degree that a plastron was developed, it incorporated the gas- tral ribs, unlike the plastron of Psephosauriscus, RIEPPEL: THE DERMAL ARMOR OF CYAMODONTOID PLACODONTS 13 Fig. 14. The left lateral margin of the carapace of Psephoderma alpinum H. v. Meyer (holotype, bsp As I 8) in dorsal view. which is composed of discrete osteoderms lying ventral to the gastral ribs (for a description, see below). Genus Psephoderma Meyer, 1858a,b Type Species — Psephoderma alpinum Meyer, 1858a,b. Diagnosis— See Rieppel (2000b, 2001) for a diagnosis and discussion of the genus based on skull structure. The genus is further diagnosed by a carapace carrying three longitudinal ridges, a dorsomedial one and two dorsolateral ones, which are composed of enlarged and distinctly keeled or tuberculiform osteoderms. Distribution — Upper Triassic; northern and southern Alps, and northern Gondwanan shelf (Middle East). Comments — The holotype of Psephoderma al- pinum is represented by a carapace fragment from the Rhaetian Koessen-Formation of the Bavarian Alps (Winkelmoos Alpe), which was first de- scribed by Meyer (1858a,b). Meyer (1858a) did not provide a formal diagnosis of the taxon, but salient characteristics of the new genus and spe- cies are easily gleaned from his description of the specimen: the carapace is of rounded contours, its width slightly exceeding its length; the rather flat dorsal shield of the carapace meets the lateral wall at an angle of 90°; in addition to the marginal keels, three longitudinal keels are distinct on the dorsal surface of the carapace, the medial one marking the dorsal midline; the osteoderms form- ing the dorsal keels are larger than the intervening elements, and all osteoderms are of a fairly reg- ular hexagonal shape. New and more completely preserved specimens from the southern Alpine Triassic (Pinna, 1978; Pinna & Nosotti, 1989; Re- nesto & Tintori, 1995) added greatly to our un- derstanding of the genus, and hence to the preci- sion of its diagnosis (Pinna, 1999), which can now be based on autapomorphic characters of skull structure (Rieppel, 2000b, 2001). The second species in the genus, Psephoderma anglicum Meyer, 1864, remains very incompletely known. C. J. Duffin considers the latter species a subjective junior synonym of Psephoderma alpi- num (quoted in Rieppel, 2000b: 38), while Storrs (1994) treated the isolated osteoderms referred to Psephoderma anglicum as not diagnostic. Description — The holotype of Psephoderma alpinum Meyer, 1858a,b, is represented by a car- apace fragment with a total length of 375 mm and a total width of 425 mm. Its circumference is al- most circular; the nuchal concavity is distinct, the posterior margin is incomplete. The carapace is composed of regularly shaped hexagonal osteo- derms that meet in slightly interdigitating sutures (Fig. 14). The surface of the osteoderms is flat or elevated into a weakly expressed, blunt apex, sur- rounded by a circular zone of slight depression. The osteoderms are pitted, the pits radiating from the centrally located center of ossification toward 14 FIELDIANA: GEOLOGY Fig. 15. The dermal armor of Psephoderma alpinum H. v. Meyer (msnb 8358) in dorsal view. the margins. The average osteoderm is 34 mm to 36 mm long and 30 mm to 34 mm broad. Frac- tures in the middle of the carapace indicate a thickness of the osteoderms that does not exceed 5 mm (contra Westphal, 1975). The epidermal scute areas are indicated by shallow grooves that coincide with the circumference of the osteo- derms. Diagnostic for the genus are three longitudinal ridges on the carapace, a dorsomedial one and two dorsolateral ones. These are composed of slightly enlarged and distinctly keeled osteoderms with a length of 36 mm to 4 1 mm and a width of 45 mm to 48 mm. The keel is elevated into a low, blunt apex at the center of the osteoderm. The dorso- medial keel is separated on either side from the dorsolateral keels by two rows of intermediate, regular osteoderms, with the rare intercalation of a distinctly smaller third element. The dorsolateral ridge is separated from the lateral margin of the carapace by three rows of regular osteoderms. The lateral margin of the carapace itself is again formed by enlarged osteoderms of 40 mm to 43 mm length, which are of hexagonal circum- ference and distinctly keeled and which define a sharp and rectangular angle between the dorsal surface and the lateral wall of the carapace. These marginal osteoderms meet each other but do not interlock in a peg-and-socket fashion. The lateral wall of the carapace is of limited depth and con- sists of a single row of regularly shaped pentag- onal elements. The apex of each of these elements interlocks with the lateral ridge osteoderms, while the broad base contributes to the formation of a smooth ventral edge. There is no indication that the lateral wall would have connected to a plas- tron, which in fact seems to have been absent (Westphal, 1975). New and beautifully preserved material has come from the upper Norian (Calcare di Zorzino) of the southern Alps (Pinna & Nosotti, 1989: specimens msnm V527, msnb 4614, 8358; Renesto & Tintori, 1995: specimen ST82003). Collective- ly, this material documents that the dorsal armor of Psephoderma is bipartite, including a carapace and a tail shield (Fig. 15); a plastron is again ab- sent in these specimens (Pinna & Nosotti, 1989, Pis. 25, 29). The carapace and the tail shield are composed of very regularly shaped hexagonal os- teoderms that meet each other in slightly interdig- itating (Figs. 16A, 17A) or noninterdigitating (msnb 4614) sutures (Figs. 16B, 17B). As in the holotype, three longitudinal rows of enlarged and keeled osteoderms form a dorsomedial keel and RIEPPEL: THE DERMAL ARMOR OF CYAMODONTOID PLACODONTS 15 Fig. 16. Osteoderm shape and structure in the carapace of Psephoderma alpinum H. v. Meyer (dorsal view). A, specimen msnb 8358; B, specimen msnb 4614. two dorsolateral keels on the carapace; the dor- solateral keels, but not the dorsomedial keel, con- tinue on to the tail shield. As in "Cyamodus" hildegardis, loose osteoderm covering continues on the dorsal surface of the tail behind the tail shield (Renesto & Tintori, 1995). The same ma- terial also documents some variability in the der- mal armor in Psephosaurus. msnb 8358 is a complete specimen from the Norian (Calcare di Zorzino) of Endenna near Ber- gamo (Fig. 15). It is somewhat smaller than the holotype, yet shows a fully developed dorsal ar- mor. The carapace is 210 mm long and 253 cm wide; the tail shield is 49 mm long and 1 1 3 mm wide. Dividing the length of the carapace (dorsal shield) by its width yields a quotient of 0.88 for the holotype and 0.83 for the specimen msnb 8358. The osteoderms meet each other in distinct- ly interdigitating sutures (Figs. 16 A, 17 A). The osteoderm surface is elevated into a low apex sur- rounded by a circular zone of slight depression and is ornamented by a pattern of radiating grooves and ridges, rather than pits as in the ho- lotype. The osteoderms are of a regular hexagonal (occasionally pentagonal) outline with an average diameter of 18 mm to 22 mm. The nuchal area is distinctly concave and has a width of six to seven osteoderms. Along the lateral margins of the dor- sal shield, there are 12 somewhat enlarged osteo- derms (of a length of 23 mm to 25 mm) that form a distinct lateral ridge; their number compares closely with the holotype. The dorsomedial and the two dorsolateral ridges are again composed of enlarged (length: 20 mm; width: 27 mm to 27 mm) and distinctly keeled osteoderms, nine to ten in each row (ten in the right dorsolateral ridge of the holotype). The dorsomedial and dorsolateral ridges are separated from one another by three rows of intervening osteoderms anteriorly but by only two rows posteriorly. The tail shield is three rows of osteoderms long and eight rows of osteo- derms broad. The specimen of Psephoderma published by Renesto & Tintori (1995, specimen ST82003) is larger than any other specimen of its genus found so far. Although its morphology remains to be de- scribed in detail, it can be seen from Figure 2 in Renesto and Tintori (1995) that the carapace is again somewhat wider than it is long, as is also the case for the holotype of Psephoderma alpinum and for specimen msnb 8358. This contrasts with specimen msnm V527, from the upper Norian of Endenna (Pinna & Nosotti, 1989), which is pre- pared in ventral view but which still shows the contours of the carapace. With a length of 275 mm and a width of 240 mm, the dorsal shield is longer than broad, which contrasts with the other specimens of Psephoderma alpinum, including the holotype. At this time it remains unknown whether this difference represents a taphonomic artifact resulting from the strong dorsoventral compression of the fossils or whether some tax- onomic variation is implied (Nosotti & Rieppel, work in progress). The Rhaetian (Calcare di Zu) of Monte Rena near Bergamo has yielded carapace fragments that compare to the holotype of Psephoderma in os- teoderm size, msnb 4614 (Pinna, 1978, PI. 74) is a specimen that shows the osteoderms to meet su- perficially in a smooth rather than interdigitating contact (Figs. 16B, 17B). And whereas the osteo- derms of Psephoderma show a weakly expressed 16 FIELDIANA: GEOLOGY Fig. 17. Osteoderm shape and structure in the carapace of Psephoderma alpinum H. v. Meyer (dorsal view). A.l, specimen msnb 8358, left posterolateral margin; A.2, specimen msnb 8358, right anterolateral margin; B, specimen msnb 4614, left dorsolateral ridge. apex, those of msnb 4614 show a weakly ex- pressed keel, and no circular zone of slight de- pression. The surface of the osteoderms is orna- mented with a pattern of vermiculate radiating ridges and grooves, similar to those seen in other Psephoderma from the Alpine Triassic. The frag- ment msnb 4614 comprises parts of at least two rows of enlarged and distinctly keeled osteoderms that appear to converge on each other. Originally identified (as indicated by the museum label) as Placochelyanus stoppanii (new combination: Pin- na, 1976), a species described by Osswald (1930; who referred it to the genus Placochelys), Pinna (1978) referred it to Psephoderma alpinum. The specimen does indicate some variation in details of carapace structure, but it is too incomplete to allow the identification of taxic diversity within the genus Psephoderma (for comments on cara- pace proportions, see above). The dermal armor appears to be completely ab- sent in a juvenile specimen of Psephoderma (msnb 4884a and b) of approximately 145 mm total length (Fig. 6). B 8359 is an incomplete specimen from the Norian (Calcare di Zorzino) of Endenna near Bergamo comprising the pelvic re- gion and tail (Pinna & Nosotti, 1989, PI. 31). The tail, which comprises 44 to 45 vertebrae (exposed behind the tail shield), measures 268 mm in length and shows no osteoderms associated with it, although the tail shield is ossified and partially RIEPPEL: THE DERMAL ARMOR OF CYAMODONTOID PLACODONTS 17 •%> 1 BJ° mm Fig. 18. Carapace of Psephoderma sculptata n. sp. (holotype, T.R.929, original of Haas, 1975, PI. I, Fig. overview; B, close-up view of enlarged dorsomedial ridge osteoderms. 8). A, covers the pelvic region. A larger specimen from the same locality (msnm V527) shows a tail length of 432 mm, and osteoderms associated with it up to the 9th caudal vertebra. The specimen de- scribed by Renesto and Tintori (1995, Fig. 2) shows rows of associated osteoderms up to at least the 12th caudal vertebra. Collectively, these specimens indicate variability in the ossification of the dermal armor along the tail. Possible tax- onomic implications of these observations must await a comprehensive revision of the genus Pse- phoderma. Psephoderma sculptata n. sp. Holotype — HUJ-Pal. T.R.I 98, carapace frag- ment (original of Haas, 1975, Fig. 14). Stratum and Locus Typicus — Lower Member of the Saharonim Formation of late Anisian (mid- dle and late Illyrian) or early Ladinian (Fassanian) age, Middle Triassic, Makhtesh Ramon, Negev, Israel. Referred Material — HUJ-Pal. T.R.207, isolat- ed osteoderms; T.R.929, small carapace fragment (original of Haas, 1975, PI. I, Fig. 8). Diagnosis — A cyamodontoid placodont with a triple-keeled dorsal shield (carapace); keels com- posed of much enlarged, hexagonal and tubercu- liform osteoderms with a posteriorly inclined apex; dorsomedial keel separated from dorsolat- eral keels by a single row of distinctly smaller, hexagonal or polygonal osteoderms. Comments — The carapace from the Middle Tri- assic of Makhtesh Ramon, which is here referred to a new species of Psephoderma, is again rather incompletely preserved (Fig. 18). It remains un- known whether this carapace was linked to a lat- eral wall, or whether this taxon differentiated a plastron, as it is known to occur in other cyamo- dontoids from Makhtesh Ramon (see below), but which is absent in Psephoderma (Pinna & Nosot- ti, 1989). However, as in Psephoderma alpinum, the carapace of the Makhtesh Ramon cyamodon- toid is composed of hexagonal osteoderms, and it shows clear indications of three longitudinal keels on its dorsal surface formed by enlarged osteo- derms (Haas, 1975). Among the Cyamodontoidea, FIELDIANA: GEOLOGY 20 mm Fig. 19. Isolated osteoderms from the carapace of Psephodertnu sculptata n. sp. (referred specimens, HUJ-Pal. T.R.207). this character is so far known only for Psephod- erma, which is the reason why the new taxon from Makhtesh Ramon is referred to that genus. Distribution — Middle Triassic (Anisian, lower Ladinian), Middle East (Makhtesh Ramon, Ne- gev, Israel). Description — The carapace fragment of Pse- phoderma sculptata n. sp. (original of Haas, 1975, PI. 2, Fig. 14) comprises the middle section of the dorsal shield. As preserved, the fragment is 262 mm wide and 332 mm long. Neither the marginal zones nor any part of the lateral walls (if present) are preserved. The sculpturing of the carapace surface is more distinctly expressed than is the case in Psephoderma alpinum, which is a function of relative osteoderm size. Osteoderm structure is again basically hexago- nal in specimen HUJ-pal. T.R.I 98 (holotype of Psephoderma sculptata, Fig. 18), but the osteo- derms forming the dorsomedial and dorsolateral keels are dramatically increased by comparison to the intervening osteoderms. A typical osteoderm of the dorsomedial keel is between 59 mm and 67 mm wide and between 59 mm and 62 mm long. As a function of their dimensions, these osteo- derms may assume an almost circular circumfer- ence (Fig. 19). The osteoderms again meet in slightly interdigitating sutures. The dorsomedial keel is again somewhat less prominent than the dorsolateral keels, but the sculpturing of the car- apace is generally much more prominently devel- oped than in Psephoderma alpinum. The individ- ual osteoderms contributing to the formation of the dorsal keels are of a tuberculiform shape, the keel developing a tall apex (abraded in the holo- type, but well-preserved in HUJ-Pal. T.R.207, Fig. 19) with distinctly ridged flanks. The apex is slightly asymmetrical, as it is positioned some- what more closely to the posterior margin of the osteoderm. In Psephoderma sculptata, the dorsomedial keel is separated from the dorsolateral keels by a single row of much smaller osteoderms of hex- agonal circumference. One well-preserved and well-delineated intervening osteoderm has a width of 27 mm and a length of 28 mm. Its surface is ornamented by a pattern of radiating ridges. How- ever, the intervening osteoderms vary quite sub- stantially in size and shape in order to fit into the space between the much enlarged osteoderms of the dorsomedial and dorsolateral keels. With its prominently sculptured dorsal surface and the large size discrepancy between the osteo- derms that form the three longitudinal dorsal ridg- es and the intervening osteoderms, specimen huj- Pal. T.R.198 is sufficiently different from any specimen of Psephoderma alpinum known from the Alpine Triassic, or from any other cyamodon- toid, in order to warrant the description, and di- agnosis, of a separate species. RIEPPEL: THE DERMAL ARMOR OF CYAMODONTOID PLACODONTS 19 cf. Psephoderma sp. Haas (1969) published a comparatively well- preserved cyamodontoid carapace (HUJ-Pal. T.R.3189) from the upper Ceratites beds (layer D2 of Brotzen, 1957) of Makhtesh Ramon (see also Haas, 1975, PI. 2, Fig. 11, HUJ-Pal. T.R.I 843). The osteoderm structure seen in this carapace matches that of many fragmentary pieces or isolated os- teoderms from the same locality (Fig. 2). These osteoderms differ from those of Psephosauriscus by their columnar proportions, their height ex- ceeding their diameter. Midcarapacial osteoderms have a fairly regular hexagonal structure. Their diameter averages approximately 15 mm, their thickness 20 to 25 mm. The surface of the osteo- derms shows a distinct central depression. There are no distinct impressions of overlying epidermal scales. The osteoderms meet in smooth or faintly in- terdigitating sutures, which is the reason for their easy dissociation from one another during fossil- ization. It is not uncommon to find small frag- ments composed of only a few osteoderms, or sin- gle elements, in the Muschelkalk of Makhtesh Ra- mon. The cohesion of the osteoderms in the car- apace of the live animal was mediated by calcified bundles of connective tissue ("calcified decussat- ing connective tissue bundles" of Haas, 1969, PI. 1, Fig. c; "mineralized connective fibers" of Westphal, 1976, Fig. 3 A; see also Westphal, 1975, Figs. 3c-e). Laterally, the rather flat carapace merges into a ventrally descending lateral wall. The transition from the dorsal surface of the carapace to the lat- eral wall describes a gentle curve (Haas, 1969, PI. 1, Fig. B) which is capped by somewhat enlarged osteoderms that retain a smooth surface, however. A distinct dorsolateral ridge is not differentiated. There is also no differentiation of distinct longi- tudinal ridges on the dorsal surface of the cara- pace in a manner comparable to Psephoderma. However, the central part of the carapacial surface is slightly depressed (concave), and so is the mar- ginal zone of the carapace. This results in the for- mation of two very shallow and smooth, dorso- lateral and slightly curved ridges (Westphal, 1975, Fig. 2), vaguely reminiscent of the much more strongly differentiated dorsal ridges seen on the carapace of Psephoderma. The carapace HUJ-Pal. T.R.3189 was found in association with its steinkern filling. No remains of the postcranial skeleton or any part of a plas- tron were recovered. It remains unknown whether a plastron was present (Haas, 1959), although the tapering ventral edge of the lateral wall (Haas, 1969, PI. lb) suggests its absence. A plastron is present in Psephosauriscus but absent in Pse- phoderma. Given the characteristics of this carapace, there is no doubt that it represents a separate cyamo- dontoid taxon from Makhtesh Ramon. Since it re- mains unknown whether a plastron was present or absent, there is no basis for the inclusion of this taxon in the genus Psephosauriscus. The osteo- derm structure of this unidentified cyamodontoid from Makhtesh Ramon is also strikingly different from the osteoderms known from Placochelys or Psephosaurus (see above). The faint differentia- tion of longitudinal ridges on the carapace, as well as the tapering ventral edge of the lateral wall, might be taken as an indication for some affinity of this taxon with the genus Psephoderma. But whatever its ultimate generic affinities might turn out to be should more completely preserved ma- terial become available, this taxon adds to the spe- cies diversity of cyamodontoids known from Makhtesh Ramon. Genus Psephosaurus Fraas, 1896 Type Species — Psephosaurus suevicus Fraas, 1896. Diagnosis— See Rieppel (2000b, 2001) for a diagnosis and discussion of the genus. Distribution — Upper Ladinian (Middle Trias- sic); southern Germany. Description — Psephosaurus suevicus Fraas, 1 896, was based on an incomplete carapace from the Lower Keuper (upper Ladinian) of south- western Germany (Hoheneck near Stuttgart; Fraas, 1896). Also available are isolated osteo- derms. Today the carapace is represented by six fragments (Figs. 20, 21) that can no longer be fitted together to reconstruct the carapace outline. Preservation is rather poor, and the delineation of individual osteoderms is difficult. As noted by Fraas (1896), two different types of osteoderms can be distinguished. Large osteo- derms of irregular polygonal or even rounded contours typically have a diameter of 25 mm to 28 mm. The center of these osteoderms is elevat- ed into an apex, which, owing to compression, is weakly expressed. The surface of the osteoderms is ornamented by a pattern of very delicate grooves and ridges that radiate from the center toward the margins. The enlarged osteoderms are 20 FIELDIANA: GEOLOGY separated from one another by smaller, mostly pentagonal or hexagonal but occasionally irregu- lar polygonal osteoderms with a diameter that may vary from 15 mm to 25 mm. The surface of these osteoderms is fiat or slightly depressed and again ornamented with a pattern of delicate yet numerous radiating grooves and ridges. It seems that the epidermal scute area coincides with the osteoderm outline. In one fragment (smns 7113; Fig. 21A.1) the sutures between osteoderms run in shallow grooves, which indicate the congruent circumference of the overlying epidermal scutes. In superficial view, the sutures between osteo- derms are slightly interdigitating; in internal (ven- tral view), suture lines may even appear to be smooth (Fig. 21 A. 2). The osteoderms did not dis- sociate during fossilization, however. Incomplete preservation renders it difficult to establish regu- larity of the arrangement of the larger osteoderms within the smaller ones. On the largest of all the carapace fragments, the enlarged osteoderms can be seen to be aligned in a row, separated from one another by intervening smaller osteoderms. Other enlarged osteoderms appear to be randomly distributed among the smaller elements. Some isolated osteoderms, corresponding to the enlarged elements interspersed between smaller ones, better preserve their three-dimensional shape. All have a concave base and a crown pro- truding into an apex (Figs. 21B-D). This apex may be distinctly keeled (smns 17790; diameter: 27 mm), elongated (smns 7180; diameter: 28.5 mm), or symmetrical (smns 54710; diameter: 27.5 mm). Genus Psephosauriscus n. gen. Type Species — Psephosauriscus mosis (Brotz- en, 1957). Diagnosis — Dermal armor comprising a solid carapace and plastron; carapace composed of hex- agonal osteoderms with smooth or interdigitating interfaces; osteoderm thickness does not exceed their diameter; carapace linked to plastron by a vertically oriented or curved lateral wall; dorso- lateral ridge may (with vertically oriented lateral wall) or may not (with curved lateral wall) be differentiated; ventrolateral ridge always present; plastron composed of osteoderms with trapezoidal to rhomboidal base and cycloid crown. Plastral osteoderms arranged in regular transverse rows, aligned along and partially fused with gastral ribs. Distribution — Lower Anisian to lower Ladi- nian. Middle East. Comments — The Middle Triassic Muschelkalk of Makhtesh Ramon, Negev (Brotzen, 1957, Haas, 1969, 1975), and of Araif en Naqua, Sinai Peninsula (Haas, 1959), has yielded the remains of a variety of cyamodontoid placodonts, all of which have provisionally been referred to the ge- nus Psephosaurus. Unfortunately, the (prepared) material currently comprises the remains of two very incomplete skulls only, and fragments of a lower jaw (Brotzen, 1957; Haas, 1975; Rieppel et al., 1999) from the basal Beneckeia beds (lower Anisian) and younger Ceratites beds (upper Ani- sian, lower Ladinian) of these Muschelkalk de- posits. None of that skull material is diagnostic, and, as noted by Brotzen (1957), there is no char- acter that precludes the best-preserved skull frag- ment from being referred to Cyamodus (no skull is known for Psephosaurus). In contrast to the Germanic Muschelkalk, dermal armor fragments abound in the Middle Eastern deposits and indi- cate a significant taxonomic variety of cyamodon- toids at least at the species level within one genus (or perhaps several genera) distinct from Psepho- saurus. The diversity of dermal armor remains in the Middle East has led to considerable taxonomic confusion at the level of species names. In his original description of cyamodontoids from Makhtesh Ramon, Brotzen (1957) recog- nized two distinct species, viz. "Psephosaurus" mosis from the Beneckeia beds and "P." picardi from the Ceratites beds. In his study of the cy- amodontoids from the Sinai Peninsula, Haas (1959) noted that the presumed carapace of the holotype of "Psephosaurus" mosis (HUJ-Pal. C.F.247) really consists of two carapacial frag- ments and a fragmentary plastron (confirmed by personal observation). A full description of "Pse- phosaurus" picardi, promised by Brotzen (1957), was never published; the original material is rep- resented by a natural mold of the internal side of a carapace (not diagnostic). The taxon is here treated as a nomen duhium for reasons discussed below. In his description of the material from the Sinai Peninsula, Haas (1959) described two additional species, "Psephosaurus" sinaiticus (holotype HUJ-Pal. 3421) and "Psephosaurus" rhomhifer (the holotype cannot be located at present). Com- paring the diagnoses and illustrations provided by Haas (1959), the validity of "P." rhomhifer as a separate taxon is difficult to evaluate (see discus- sion of cf. Psephosauriscus rhomhifer below). If RIEPPEL: THE DERMAL ARMOR OF CYAMODONTOID PLACODONTS 21 Fig. 20. Carapace fragment of Psephosaurus suevicus Fraas (holotype, smns 6693, dorsal view). P. rhombifer is not, indeed, a separate taxon, it would have to be a subjective junior synonym of "P." sinaiticus (by page priority of the latter; see further discussion below). Such a conclusion would conflict with that of Haas (1975), who con- sidered "P." sinaiticus a possible junior synonym of "P." mosis, and "P." picardi a separate spe- cies. The species name ramonensis was intro- duced by Haas (1975: 455) with no description and no illustration (nomen nudum), but apparently with reference to a taxon from Makhtesh Ramon which is close to, or even synonymous with, " Psephoderma" mosis. In the Paleontological Collections of the Hebrew University, specimen HUJ-Pal. T.R.2751 was found to be labeled "Pse- phoderma" ramonensis without indication of an author. The name was never formally published, but the specimen was figured by Westphal (1975, Fig. 5, top). A review of the material presently available in the Paleontological Collections of the Hebrew University, Jerusalem, allows the diag- nosis of at least four species within this genus. The phylogenetic position of the genus Psepho- sauriscus among the Cyamodontoidea remains currently unresolved. The reason for this is that Psephosauriscus is known exclusively from der- mal armor fragments, whereas phylogenetic re- construction of the Cyamodontoidea is based pri- marily on skull structure (Rieppel, 2000b, 2001). Psephosauriscus mosis (Brotzen, 1957) 1957 Psephosaurus mosis Brotzen, p. 210. 1959 Psephosaurusl mosis Haas, p. 18. 1975 Psephosaurus mosis Haas, p. 453. Holotype — HUJ-Pal. C.F.247, two fragments of a carapace, plus one fragment of a plastron. Stratum and Locus Typicus — Beneckeia beds (lower Anisian), Makhtesh Ramon, Negev, Israel. Diagnosis — Dorsal surface of carapace orna- mented by scale impressions of highly irregular size and shape, imprinted on hexagonal osteo- derms; ventral surface of plastron covered by transverse rows of relatively large cycloid osteo- derms, but osteoderm shape becoming irregular toward the margins of plastron; dorsolateral ridge fortified by enlarged, keeled osteoderms separated from one another by a pair of intervening smaller osteoderms; lateral wall vertically placed, com- posed of hexagonal osteoderms; ventrolateral ridge fortified by enlarged, keeled osteoderms that are in noninterlocking contact with one another. Distribution — Middle Triassic (Anisian, lower Ladinian), Middle East (Negev, Israel). Description — The preserved carapace of Pse- phosauriscus mosis comprises two adjacent frag- ments, the anterior one of which preserves part of the nuchal emargination (Fig. 22). The superficial appearance of the carapace shows a complex pat- tern of grooves delineating areas of epidermal scutes of highly irregular shape and size. This pat- tern of epidermal scute areas is imprinted on os- teoderms of more or less regular hexagonal out- lines, although the sutures between the osteo- derms are identifiable in very localized areas only. The thickness of the carapacial osteoderms does not exceed their diameter of around 1 5 to 20 mm. 22 FIELDIANA: GEOLOGY A.1 _20 mm A.2 Fig. 21. Carapace fragments and isolated osteoderms of Psephosaurus suevicus Fraas. A.1, carapace fragment (smns 7113) in dorsal view, showing grooves delineating epidermal scutes; A.2, carapace fragment (smns 7113) in ventral view; B, isolated osteoderm with longitudinal ridge (smns 17790); C, isolated osteoderm (smns 54701); D, isolated osteoderm with abraded apex (smns 7180); E, carapace fragment from holotype (smns 6693) in dorsal view. Regularity of osteoderm pattern is established along the dorsolateral ridge of the carapace (Fig. 23A.2), characterized by distinctly enlarged (max- imal length of 40 mm, maximal width of 36 mm) osteoderms of an irregular octagonal shape with a projecting posterior tip. These enlarged osteoderms carry a longitudinal keel, raised into a low apex at the center of the osteoderm. These enlarged osteo- derms are regularly separated from one another by an intermediate pair of smaller osteoderms. The lateral wall of the dorsal dermal armor of Psephosauriscus mosis is poorly preserved but shows hexagonal or rhomboidal osteoderms at its anterolateral corner. The plastron of Psephosauriscus mosis (Figs. 23A.3, 23B, 24) is composed of transverse rows of regularly arranged cycloid scales, matching the contours of the crown of the underlying osteo- derms with a transverse diameter of 35 mm and a length of 22 mm. The apex of these scales points anteriorly, their convex base faces posteriorly. Along the ventrolateral ridge of the plastron (very incompletely preserved), the osteoderms are en- larged and of rounded contours, with a diameter of 42 mm. These ventrolateral ridge scales are in non- interlocking contact with one another and carry a longitudinal keel that is raised into a low apex to- ward the center of the scale (Fig. 23A.1). In summary, Psephosauriscus mosis differs from Psephosauriscus sinaiticus by a more pro- RIEPPEL: THE DERMAL ARMOR OF CYAMODONTOID PLACODONTS 23 Fig. 22. Carapace fragments of Psephosauriscus mosis Haas (holotype, HUJ-Pal. C.E247) in dorsal view. A, part 3 of Brotzen, 1957; B, part 2 of Brotzen, 1957. nounced development of both the dorsolateral and ventrolateral ridges at the transition of the lateral wall to the carapace and plastron, respectively, by larger plastral osteoderms, and by a highly irreg- ular epidermal scute pattern distinctly imprinted on the underlying osteoderms. Psephosauriscus mosis differs from Psephosauriscus ramonensis n. sp. by the development of a pronounced dorso- lateral ridge on the dorsal armor and by highly irregular epidermal scute areas distinctly imprint- ed on the underlying osteoderms. Comments — Dermal armor fragments with im- prints of similarly irregular epidermal scutes on hexagonal osteoderms are also found in the Cer- atites layers of Makhtesh Ramon. Remarks — Along with "Psephosaurus" mosis, Brotzen (1957) described a second species from the Muschelkalk (Ceratites beds) of Makhtesh Ramon, "Psephosaurus" picardi. This latter spe- cies is based on a natural cast of the inside of a carapace and on dermal armor fragments from different layers (Brotzen, 1957: 215). Brotzen (1957) designated the cast of the carapace as ho- lotype and indicated that he had deposited it in the Paleozoological Department of the Natural History Museum in Stockholm. However, this specimen can no longer be located. Given the tax- onomic diversity of cyamodontoids from Makh- tesh Ramon, as evidenced by carapace fragments, and the poor documentation of the natural cast of the inside of a carapace (Brotzen, 1957, PI. 7), I concur with Haas (1959: 14) in treating "Psepho- saurus" picardi as a nomen dubium. Psephosauriscus ramonensis n. sp. Holotype — HUJ-Pal. 2751, fragment of cara- pace and plastron (Figs. 25A, 26). 24 FIELDIANA: GEOLOGY g 20 mm Fig. 23. Osteoderm shape and structure in the dermal armor of Psephosauriscus mosis Haas in superficial view. A.l, osteoderms from the ventrolateral ridge (holotype, Ht'J-Pal. C.F247): A.2, osteoderms from the dorsolateral ridge (holotype, HUJ-Pal. C.F.247); A.3, plastron: B, plastron of referred specimen HUJ-Pal. 948. RIEPPEL: THE DERMAL ARMOR OF CYAMODONTOID PLACODONTS 25 Fig. 24. Plastron fragment (HUJ-Pal. 948) referred to Psephosauriscus mosis Haas. Stratum and Locus Typicus — Ceratites beds (upper Anisian-lower Ladinian), Makhtesh Ra- mon, Negev, Israel. Diagnosis — Carapace composed of relatively small hexagonal osteoderms with smooth or only slightly interdigitating interfaces; osteoderm thickness does not exceed their diameter; osteo- derms flat, or with very weakly expressed central elevation; osteoderm surface smooth, or with very weakly expressed pattern of irregular radiating ridges; dorsolateral ridge absent; lateral wall curved, composed of relatively large osteoderms; ventrolateral ridge distinct, formed by enlarged and interlocking osteoderms; plastron composed of enlarged, trapezoidal or cycloid osteoderms with a smooth surface and interdigitating interfac- es. Distribution — Middle Triassic (upper Anisian, lower Ladinian), Middle East (Negev, Israel). Description — The holotype (Figs. 25A, 26) comprises articulated parts of a carapace and plas- tron, representing the middle part of the left side of the carapace. As preserved, the specimen is 250 mm long and 150 mm wide. The carapace is composed of relatively small (12 mm to 17 mm diameter) hexagonal osteoderms (Figs. 25B, 26A.1) whose thickness does not exceed their di- ameter. The basic hexagonal design of the osteo- derms shows a marked variability, individual os- teoderms assuming a pentagonal or even an irreg- ular rounded circumference. The sutural interface between osteoderms is smooth or only very slightly interdigitating, which is why these osteo- derms tend to easily dissociate during fossilization in isolated carapace fragments. As a consequence, the same circumferential outline of the osteo- derms is preserved throughout their height. The superficial surface of the individual osteoderms is either flat or shows a slight central elevation sur- rounded by a zone of slight depression. A dorsolateral ridge is absent in Psephosaur- iscus ramonensis n. sp. As a consequence, the lat- eral margins of the dorsal shield gently turn downward to meet the plastron in a well-defined ventrolateral ridge. The only structural difference observable in this curved lateral wall is a distinct increase in size of the osteoderms (maximal di- ameter of 21 mm), which also assume a more reg- ular and constant hexagonal circumference and meet in distinctly interdigitating sutures (Figs. 25C, 26A.2). Interdigitation between these lateral wall osteoderms is more distinctly expressed in transversely oriented sutures than in longitudinal- ly oriented sutures. The ventrolateral ridge (Figs. 26A.3, 27) is composed of distinctly enlarged irregularly octag- onal osteoderms with a diameter of up to 43 mm. These osteoderms carry a longitudinal keel that is elevated into a low apex in the center of the ele- ment, and a somewhat thickened and projecting posterior tip that is directly interlocking with a concavity on the anterior margin of the succeed- ing osteoderm. The plastron (Figs. 26A.3, 27) is composed of relatively large osteoderms with a trapezoidal or cycloid superficial appearance and interdigitating interfaces. The largest ventral osteoderms are 36.5 mm broad and 25 mm long; smaller, more mar- ginally located elements are 24 mm broad and 18 mm long. The trapezoidal rather than cycloid ap- pearance of the larger, more medially located el- ements may be due to some superficial abrasion, because grooves delineating epidermal scute areas are not distinct. These grooves become distinct in more marginal areas; filled with sediment, they account for the appearance of what Westphal (1975) described as a tendency of the plastron to disintegrate. In summary, Psephosauriscus ramonensis n. sp. differs from the other two species in its genus by the absence of a vertically oriented lateral wall and of a dorsolateral ridge, as well as by the smooth or only slightly interdigitating interface between relatively small dorsal carapacial osteo- derms. It differs from Psephosauriscus mosis by the trapezoidal shape of the medial plastral osteo- 26 FIELDIANA: GEOLOGY 4H A 50 mm ■ B CI Fig. 25. The carapace of Psephosauriscus ramonensis n. sp. (holotype, HUJ-Pal. T.R.2751). A, overview of whole specimen; B, dorsal osteoderms; C, dorsolateral osteoderms. derms and by the interlocking relationship of os- teoderms forming the ventrolateral ridge. It differs from Psephosauriscus sinaiticus by larger plastral osteoderms and by a more pronounced enlarge- ment and differentiation of the osteoderms of the ventrolateral ridge. Psephosauriscus sinaiticus (Haas, 1959) 1959 Psephosauriscus^! sinaiticus Haas, p. 17 1975 Psephosaurusl sinaiticus Haas, p. 453. Holotype— HUJ-Pal. T.R.3421 (Fig. 28; speci- men A of Haas, 1959). Stratum and Locus Typicus — Muschelkalk (Middle Triassic), Araif en Naqa, Sinai Peninsula. Referred Material — HUJ-Pal. T.R.966; T.R.I 097; T.R.3061; T.R.3422 (specimen B of Haas, 1959); T.R.3636 (specimen D of Haas. 1959; this specimen is now broken); TR.3673. Other specimens figured by Haas (1959) can no longer be located today. Diagnosis — Carapace composed of hexagonal osteoderms with more or less interdigitating inter- faces; osteoderms with a weak central elevation surrounded by a shallow circular zone of depres- sion; osteoderm surface ornamented with a pattern of radiating ridges; impressions of overlying epi- dermal scales absent, or coinciding with osteoderm circumference; dorsolateral and ventrolateral ridges defined by elongate yet narrow, keeled osteoderms that are in direct contact with one another; lateral wall vertically oriented, formed by four longitudi- nal rows of cycloid or rhomboidal osteoderms; plastron composed of relatively small and regularly shaped osteoderms with a cycloid superficial ap- pearance and a rhomboidal basal outline. RIEPPEL: THE DERMAL ARMOR OF CYAMODONTOID PLACODONTS 27 B 20 mm Fig. 26. Osteoderm shape and structure in the dermal armor of Psephosauriscus ramonensis n. sp. (A: holotype, HUJ-Pal. T.R.2751; B: referred specimen). A.l, dorsal osteoderms; A.2, dorsolateral osteoderms; A.3, left ventrolateral margin of plastron. B, referred carapace fragment (HUJ-Pal., uncatalogued). 28 FIELDIANA: GEOLOGY Fig. 27. The plastron of Psephosauriscus ramonensis n. sp. (holotype, HUJ-Pal. T.R.2751). Distribution — Middle Triassic (Anisian, lower Ladinian), Middle East (Araif en Naqa, Sinai Pen- insula, and Makhtesh Ramon, Negev, Israel). Description — The taxon is represented by sev- eral fragments of dermal armor, the most com- plete of which is specimen A of Haas (1959; huj- Pal. 3421). It is a piece of the carapace and plas- tron joined by the lateral wall (Fig. 28). The carapace is composed of relatively small, more or less regularly shaped osteoderms of hex- agonal circumference that meet each other in an interdigitating suture. The diameter of the osteo- derms is around 20 mm. Their thickness does not exceed their diameter. The superficial surface of the osteoderms shows a slight central elevation surrounded by a slightly depressed zone. Al- though the interdigitation between the osteoderms may in some specimens be weakly expressed on the surface of the carapace, it becomes more dis- tinctly expressed, and the outlines of the osteo- derms more irregularly shaped, toward deeper layers and on the inner (ventral) surface of the carapace. Strongly eroded pieces of dermal armor, showing rather deep interdigitation between ad- joining osteoderms, may consequently appear rather different from less eroded pieces. Impressions of overlying epidermal scales are absent, or they may coincide with the circumfer- ence of the osteoderms. Haas (1959) noted one area in the carapace of the holotype where impres- sions of epidermal scales deviated from the cir- cumference of the underlying osteoderms. Re- newed preparation using acid did not confirm this observation. Instead, impressions of overlying epi- dermal scales are absent in Psephoderma sinaiti- cus, unless they coincide with the circumference of the osteoderms. Especially in the holotype. there is some depression of the suture between adjacent os- teoderms, but this depression may also be the result of partial separation of the osteoderms. The lateral wall is vertically oriented. Carapace and lateral wall therefore meet each other at a we 11 -ex pressed angle defining the dorsolateral body ridge. Narrow yet somewhat elongated and keeled osteoderms are aligned along the dorsolat- eral ridge, joining the lateral wall to the carapace. The ventrolateral ridge is a mirror image of its dorsolateral counterpart, with elongated yet nar- row and keeled osteoderms joining the lateral wall to the plastron in a well-defined angle. Better pre- served than their dorsolateral counterparts, the ventrolateral ridge osteoderms show a maximal length of 32 mm and a maximal width of 13 mm. The lateral wall shows a pattern of cycloid scales. The plastron again shows cycloid scales of 28 mm width and 22.5 mm length. More marginal elements are smaller, with a width of 20 mm and a length of 16 mm. The epidermal scute areas match the superficial crown of the osteoderms. The apex of the cycloid scales points forward. RIEPPEL: THE DERMAL ARMOR OF CYAMODONTOID PLACODONTS 29 Fig. 28. The dermal armor of Psephosauriscus sinaiticus Haas (holotype. HUJ-Pal. T.R.3421). A, dorsal view; B, ventral view. their convex base faces backward. The osteo- derms are aligned in regular transverse rows. The internal (dorsal) surface of the plastron displays the rhomboidal outline of the base of the osteo- derms, which meet at interdigitating interfaces. Specimen HUJ-Pal. T.R.3673 preserves part of the plastron and associated gastrals and part of the lateral wall and associated dorsal ribs or trans- verse processes, but only fragments of the cara- pace. Unfortunately, the specimen does not allow determining whether the dorsal transverse pro- cesses extend laterally to the lateral wall, or whether these elements are the dorsal ribs, which would have articulated with the transverse pro- cesses at a more proximal level that is not pre- served. The ribs, or distal parts of the transverse processes, are hollow and squarely abut the me- dial surface of lateral wall osteoderms with their slightly expanded distal ends. The gastral ribs are composed of five elements, a medioventral element and two collateral elements on either side, which show broad overlap with each other in specimen D of Haas (1959, specimen huj- Pal. T.R.3636; see also Westphal, 1975, Fig. 6, and specimen HUJ-Pal. T.R.3673). The gastral ribs are partially fused to the osteoderms and aligned such as to underlie the transverse suture line separating the transverse rows of osteoderms from one anoth- er. Their arrangement is thus strikingly different from that observed in Placochelys, where plastral ossifications are located between, rather than ven- tral to, the gastral ribs. In summary, Psephosauriscus sinaiticus differs from Psephosauriscus mosis by the absence of distinct impressions of irregular epidermal scute areas on the carapace, by the shape and arrange- ment of osteoderms along the dorsolateral and ventrolateral ridges, and by smaller ventral cy- cloid scutes in the plastron. Psephosauriscus sin- aiticus differs from Psephosauriscus ramonensis 30 FIELDIANA: GEOLOGY Fig. 29. Carapace fragments from the Middle Triassic of Makhtesh Ramon, Negev, referred to Psephosawiscus sinaiticus Haas. A, HUJ-Pal. T.R.966; B, HUj-Pal. T.R.1097; C, HUJ-Pal. T.R.3061 (abraded specimen). by the presence of a vertical lateral wall and of a dorsolateral ridge, by distinct interdigitation at the sutural interface between the osteoderms, and by smaller cycloid scutes on the plastron. Comments — Dermal armor fragments referable to Psephosauriscus sinaiticus are also known from the Ceratites layers of Makhtesh Ramon, Is- rael (HUJ-Pal. T.R.966 [Fig. 29A], T.R.1097 [Fig. 29B], and T.R.3061 [Fig. 29C]). cf. Psephosauriscus rhombifer The holotype of "Psephosaurus" (Psephosaur- iscus) rhombifer (Haas, 1959, specimen G) can no longer be located today. Comparing Haas's (1959, PI. 8, Figs. 30, 31) illustrations of P. rhombifer with those of P. sinaiticus (Haas. 1959, PI. 6, Fig. 23; PI. 7, Fig. 25) shows a closely similar pattern of osteoderm structure and arrangement. The only difference noted by Haas (1959) was that putative impressions from overlying epidermal scales could be identified on the single specimen of P. rhombifer that was available. These scales appear to have been of a strictly rhomboidal shape, with their corners located on the centers of four adja- cent osteoderms. As can be seen from the illus- tration of Haas (1959, PI. 8, Fig. 31), these im- pressions of epidermal scutes are rather vague, however, unlike those in other cyamodontoids RIEPPEL: THE DERMAL ARMOR OF CYAMODONTOID 'LACODONTS 31 Fig. 30. Carapace fragment from the Middle Triassic of Makhtesh Ramon, Negev, referred to cf. Psephosaur- iscus rhombifer Haas (HUJ-Pal. T.R.3676). {Psephosauriscus mosis). However, Haas (1959, PI. 4, Fig. 16; PI. 8, Fig. 29; HUJ-Pal. T.R.3676) figured a carapace fragment from another cyamo- dontoid from Makhtesh Ramon, which deserves a more detailed discussion, as it does represent a separate taxon of a cyamodontoid from Makhtesh Ramon that might be comparable to Psephosaur- iscus rhombifer. Specimen HUJ-Pal. T.R.3676 (Fig. 30) compris- es three carapace fragments, one of which was illustrated by Haas (1959, PI. 4, Fig. 16; PI. 8, Fig. 29). Their morphology recalls that described for Psephosauriscus sinaiticus. The osteoderm surface of the latter taxon was characterized above by the presence of a weak central elevation surrounded by a shallow circular zone of depres- sion. The osteoderms are of a more or less regu- larly hexagonal shape, they meet in interdigitating sutures, and their surface is ornamented by a pat- tern of radiating ridges. By contrast, specimen HUJ-Pal. T.R.3676 shows osteoderms of more ir- regular contours, meeting in more deeply inter- digitating sutures, and with a distinctly more sculptured surface. Their diameter ranges from 1 5 to 20 mm. Their height does not exceed their di- ameter. Unlike Psephosauriscus sinaiticus, the surface of the carapace is very uneven, as the cen- tral part of the individual osteoderm is more or less deeply excavated. A central elevation may rise from the bottom of the excavated area. In contrast to Psephosauriscus sinaiticus, the impressions of overlying epidermal scales are dis- tinct in specimens HUJ-Pal. TR.2492 as well as T.R.3676, and they are not congruent with the hexagonal contours of the osteoderms. This adds significantly to the unevenness of the surface of the carapace. Although a one-to-one relationship is preserved between the number of osteoderms and the number of epidermal scales, the margins of the latter are shifted obliquely out of phase rel- ative to the sutures between the osteoderms by about one-fifth of the diameter of the osteoderms. The epidermal scales still approach a hexagonal shape, which more frequently is modified to a rhomboidal shape, however, or their shape even approaches the cycloid fish-scale pattern other- wise characteristic of the crown of plastral osteo- derms. As the epidermal scute margins are obliquely shifted out of phase relative to the contours of the osteoderms by about one-fifth of the osteoderm diameter, the corners of the epidermal scales do not come to lie on the centers of four adjacent osteoderms as was described by Haas (1959) for "Psephosaurus" rhombifer. Allowing for the in- distinctiveness of the epidermal scale margins in the holotype of "Psephosaurus" rhombifer (Haas, 1959, PI. 8, Figs. 30, 31), and allowing for some variation (regional variation?) in the pattern of overlap between epidermal scales and underlying osteoderms, it might very well be that specimens HUJ-Pal. T.R.3676 and 2492 might be referable to "P." rhombifer. In the absence of the holotype for the latter species, and in the absence of more and better preserved material, it seems prudent at this time to register specimens HUJ-Pal. T.R.3676 and TR.2492 as different cyamodontoids from Makhtesh Ramon, without formalizing taxonomic conclusions by the erection of a neotype or the description of a separate species. A Comparison of the Dermal Armor in Cyamodontoid Placodonts and Turtles Among reptiles, cyamodontoid placodonts and turtles are the only two groups that develop a complete dermal armor covering the dorsal and ventral surface of the body as well as the flanks. In both groups, the pectoral girdle (scapula) shifts 32 FIELDIANA: GEOLOGY Fig. 31. The pectoral girdle of He nodus chelyops (partially reconstructed on the basis of specimen II of Huene. 1936). to a morphological position deep (ventral) to the ribs as a consequence of the development of a carapace (the position of the scapula relative to the ribs is known only in Henodus among the cy- amodontoids). After a detailed comparison of the dermal armor in turtles and cyamodontoids, Greg- ory (1946) concluded that these structures evolved convergently in the two clades. Lee (1995, 1996, 1997) believed the carapace of tur- tles to have evolved by fusion of originally sep- arate osteoderms overlying broadened ribs (of pareiasaurs), and that the pectoral girdle assumed its peculiar position inside the rib cage by a back- ward shift from its ancestral location relative to the axial skeleton. Lee's (1996) scenario of "cor- related progression" does not account for the morphological complexity of the turtle body plan (Rieppel & Reisz, 1999), but instead almost per- fectly captures the evolution of the carapace in cyamodontoids, as is suggested by its ontogeny and by outgroup comparison. Closer anatomical scrutiny reveals that the development of dermal armor is convergent in the two groups, the cara- pace and plastron of turtles being autapomorphic for that clade. The turtle carapace is referred to as a compos- ite, or "duplex," structure, as it involves deeper thecal and superficial epithecal ossifications (Hay, 1898; Kaelin, 1945; Volker, 1913; Zangerl, 1939). The thecal ossifications are arranged in a very regular, strictly defined geometry that is closely comparable throughout turtles. A central longitu- dinal row of neural plates overlies and co-ossifies with the neural arches of the dorsal vertebrae; a lateral row of costal plates is closely associated with the dorsal ribs; a marginal row of marginal plates, an anterior nuchal plate, and one or two posterior pygal plates complete the carapace. In addition, some fossil turtles, such as Proganoche- lys (Gaffney, 1990), show supramarginal scutes. Epithecal ossifications are osteoderms that devel- op superficial to the thecal ossifications. Their ap- pearance and arrangement vary among turtles. In some fossil marine turtles they are superimposed on the neural shields; in dermochelyids, they are interdigitating osteoderms of polygonal (hexago- nal) shape superimposed on the reduced theca; and in trionychids, they occur in a mosaic resem- bling thecal ossifications (Zangerl, 1939. 1969). Earlier authors (Hay, 1898; Oguschi, 191 1 ) had claimed that epithecal ossifications are primitive for turtles and covered the body of the ancestral turtle prior to the development of a deeper theca. Volker (1913) drew attention to the large tuber- cular osteoderms that form longitudinal keels in Dermochelys, and homologi/.ed the marginal keels of Dermochelys with the marginal plates of other turtles, while Versluys (1914) homologi/.ed the lateral keels of Dermochelys with the marginal and supramarginal (submarginal, in his terminol- ogy) plates of Progcmochelys (see also Vallen. 1942, for similar arguments). The discussion sur- rounding the osteoderms and their arrangement in Dermochelys recalls the longitudinal rows of en- larged osteoderms in the carapace of some cy- amodontoids, which may be particularly pro- RIEPPEL: THE DERMAL ARMOR OF CYAMODONTOID PLACODONTS 33 nounced along the dorsolateral and ventrolateral margins of the dermal armor. A striking similarity also exists between the dermal armor fragment of smns 15891 referred to Cyamodus and the antero- lateral peripherals of Proganochelys, as discussed above. Earlier authors visualized the "ancestral" turtle to be covered with longitudinal rows of epi- thecal ossifications (osteoderms). Below these, the neural and costal plates would subsequently de- velop by broadening of the neural arches and ribs. This scenario for the evolution of the turtle shell almost perfectly fits Lee's (1996) hypothesis of "correlated progression" (Versluys, 1914, Fig. 10), but it could just as well account, in morpho- logical terms, for the evolution of a carapace in cyamodontoid placodonts. However, given our modern understanding of turtle interrelationships, epithecal ossifications cannot be claimed to be primitive for turtles. Epi- thecal elements ossify later than thecal compo- nents of the carapace during the ontogeny of ex- tant turtles, and mapping the occurrence of epi- thecal ossifications on a cladogram of Testudines unequivocally indicates their derived nature (Zan- gerl, 1939, 1969; Kaelin, 1945). By contrast, the earliest known turtle, Proganochelys (Gaffney, 1990), shows a full complement of thecal ossifi- cations, including neural and costal plates asso- ciated with the underlying endoskeleton (verte- brae and ribs). And whereas the genuinely dermal nature of the marginal, supramarginal, nuchal, and pygal plates is generally accepted (Vallen, 1942; Kaelin, 1945), the nature of the neural and costal plates is still in dispute. These are at the same time the components of the turtle carapace that cannot be compared to any elements in the dorsal dermal armor of cyamodontoids. The theca of turtles develops within a thickened dermal-epidermal carapacial disc (Burke, 1989; Gilbert et al., 2001). Early during development, growth of the ribs is "deflected" to a dorsal po- sition (Ruckes, 1929) under the inductive influ- ence of the carapacial ridge, which redirects the migration of those somitic cells that will eventu- ally form the ribs (Burke, 1989; Gilbert et al., 2001). That way, the ribs chondrify dorsal to the scapula, but within the dermal carapacial disc. Perichondral ossification of the ribs is initiated in their proximal part — that is, at the point of their entry into the dermis — and from there progresses distally. Completion of the perichondral ossifica- tion of the ribs shows that these are not expanded in turtles at the cartilaginous stage (e.g., Goette, 1899, Pis. 27, 28; Kaelin, 1945, Figs. 4-11). Once the rib is fully encased in bone, ossification of the costal plates proceeds by the formation of trabec- ular bone in continuity with the periost and spreading anteriorly and posteriorly from the rib (Goette, 1899; Vallen, 1942; Kaelin, 1945; Gilbert et al., 2001). The cartilage of the rib itself degen- erates without undergoing concomitant endochon- dral ossification; its space is eventually filled by trabecular bone that develops from haematopoi- etic elements invading the lumen left by the de- generated cartilage (Suzuki, 1963). The fact that the ribs as well as the tips of the neural arches pierce the dermal carapacial disc renders the identification of neurals and costals as endoskeletal versus exoskeletal elements difficult. On the one hand, the neurals and costals ossify from the periosteum of the underlying endoskel- etal elements, which would make them part of the endoskeleton, but this whole process occurs with- in the dermis, which would make them dermal ossifications (Gilbert et al., 2001, distinguish be- tween "primary" and "secondary" dermal bone). Both Patterson (1977) and Starck (1979) stressed that the endo- and exoskeleton cannot be defined on the basis of histogenesis but must be defined with reference to a phylogenetic framework. Exo- skeletal are those elements that are homologous with structures which in the ancestral condition combine bone, dentine, and enamel, i.e., develop at the ectoderm-mesoderm interface. Endoskele- tal are those elements that in the ancestral con- dition are preformed in cartilage, while the carti- laginous stage may be deleted in the descendant (membrane bone). The extension of the ribs into the dermis at a level lateral (dorsal) to the scapula is unique for turtles, yet the ribs as well as the neural arches are endoskeletal components of the carapace (Goette, 1 899). The neural and costal plates ossify from, and in continuity with, the periosteum of their endoskeletal component, and osteogenetic activity is initially most intensive at the deepest layer of the dermis, i.e., at the level of entry of the rib into the dermis. Neurals and costals, there- fore, are, in part, composed of bone that matches the definition of Zuwachsknochen as given by Starck (1979: 13), or bone growing from peri- chondrally ossified elements of the endoskeleton without itself having been preformed in cartilage. As such, neurals and costals are endoskeletal components of the turtle carapace and cannot be compared to osteoderms fused into a carapace in cyamodontoid placodonts. The latter are exoskel- etal elements, as are epithecal ossifications of tur- 34 FIELDIANA: GEOLOGY TESTUDINES CYAMODONTOIDEA Cara pace Duplex structure, may be composed of thecal and epithecal osteoderms Simplex structure, always only composed of osteoderms Well-defined, geometrical arrangement of elements Geometrical arrangement of elements, not as well defined Laterodorsal ridge absent Laterodorsal ridge present Ribs incorporated in endoskeletal costal plates Ribs underlying osteoderms Tip of neural arch incorporated in neural plate Neural arch underlying osteoderms Plastron Relatively small number of ossifications Relatively large number of ossifications Incorporates clavicle and interclavicle Underlies clavicle and interclavicle Incorporates gastral ribs Underlies gastral ribs Chart 1. Morphological differences in the dermal armor of Testudines and Cyamodontoidea. ties, i.e., elements that are homologous to struc- tures that in the ancestral condition develop at the mesoderm-ectoderm interface. The endoskeleton underlying the carapace like- wise differs in the two groups. The dorsal verte- brae of turtles have lost the transverse processes, and the ribs are elongate. In cyamodontoids, the dorsal vertebrae carry very pronounced, elongated and curved transverse processes that articulate with relatively short dorsal ribs (Cyamodus hilde- gardis: Pinna, 1992) or that completely fuse with the dorsal ribs {Psephoderma alpinum: Pinna & Nosotti, 1989). Hollow ribs (or transverse pro- cesses) as observed in Psephosauriscus have nev- er been reported for turtles. It is nevertheless in- teresting to recall in this context that the ribs of turtles likewise do not undergo typical endochon- dral ossification (Suzuki, 1963). Some cyamodontoids develop a plastron, but this structure is again convergent to the plastron of turtles, because it does not include dermal el- ements of the pectoral girdle as does the plastron of turtles (the epiplastra corresponding to the clavicles, the entoplastron corresponding to the interclavicle: Zangerl, 1939, 1969). Zangerl (1939) believed that the ontogeny of the remain- ing plastral elements of turtles betrays their phy- logenetic derivation from gastral ribs (see also Gilbert et al., 2001 ). In cyamodontoids. the gastral ribs remain distinct as separate elements, posi- tioned either dorsal to the plastral osteoderms (Psephosauriscus sinaiticus) or embedded in the dermal bone of the plastron (Placochelys placo- donta). In light of our current understanding of turtle and cyamodontoid relationships (Rieppel & Reisz, 1999), and given the different morphology of the carapace and plastron in the two groups (Chart 1 ), the conclusion must be that the extensive dermal armor evolved convergently in cyamodontoids RIEPPEL: THE DERMAL ARMOR OF CYAMODONTOID PLACODONTS 35 and turtles. This also implies, however, that both groups had to solve similar functional problems associated with the development of such extensive dermal armor. Functional Anatomy of the Dermal Armor in Placodonts Little work has been done on the functional anatomy of armored placodonts. Previous studies mostly addressed the function of the dermal armor in terms of protection and hydrodynamics (West- phal, 1975, 1976; Pinna & Nosotti, 1989; Renesto & Tintori, 1995). It is obvious that the develop- ment of a carapace will cause a shift from axial to paraxial locomotion, and those taxa in which a lateral wall links the carapace to a plastron may experience some restriction of the excursion range of the humerus and femur, as do turtles (Walker, 1971, 1973; Zug, 1971). And, as in turtles, the asymmetry of the metatarsus is less pronounced in cyamodontoids (Psephoderma: Renesto & Tin- tori, 1995) than it is in most other terrestrial rep- tiles, which suggests less agility in terrestrial lo- comotion (Walker, 1971, 1973; Zug, 1971). More important, however, turtles have lost the capability of using the ribs in support of locomotion and respiration by fusion of the ribs into the carapace, and cyamodontoids seem to have faced a similar problem. In a generalized tetrapod reptile, body weight is transferred from the limb to the axial skeleton via the muscular suspension of the pectoral girdle (scapula) from the vertebral column. Medially di- rected force components generated by a sprawling gait are absorbed by the clavicular-interclavicular complex. In turtles (terrestrial or aquatic bottom walkers), body weight is transferred from the limbs via the long and rod-shaped scapula to the carapace; medially directed force components are transmitted to the entoplastron via the acromial process of the scapula (Rieppel & Reisz, 1999). Little is known about the exact configuration of the pectoral girdle with respect to the dermal ar- mor in cyamodontoids. The morphology of the scapula of Cyamodus is plesiomorphic relative to other sauropteryians (specimen msnm V458; see also Pinna, 1992). The scapula shows an elongate, broad, almost rectangular dorsal blade that shows no indication of any well-defined contact to the internal side of the carapace. The ventral glenoid portion is distinctly expanded and shows a convex ventral margin. A deep concavity along the pos- terior margin of the scapula marks the transition from the ventral glenoid portion to the dorsal blade. The coracoid is of almost circular outline, and the coracoid foramen appears as an open notch at its margin. Evidently, the scapula and coracoid were in cartilaginous contact with each other, and both elements were embedded in soft tissue below the dermal armor. The only departure from the plesiomorphic (sauropterygian) condi- tion in the pectoral girdle of Cyamodus is seen in the dermal components. The interclavicle is a rather slender, boomerang-shaped element without any indication of a posterior stem. It contacts the clavicles on either side in an interdigitating suture. The clavicles are again slender, gently curved el- ements without any indication of expanded an- terolateral corners. Together, the elements of the dermal pectoral girdle must have formed an up- right U-shaped structure at the anterior end of the carapace. The dorsal tips of the clavicles may have contacted the inside of the carapace, as is known from Henodus. The pectoral girdle of Psephoderma (specimen msnm V527; see also Pinna & Nosotti, 1989) ap- proaches that of Henodus more closely in its mor- phology than that of Cyamodus. The dermal pec- toral girdle is less well exposed in Psephoderma, as it is obscured by the 5th cervical. However, as far as can be determined, it again forms a slender, upright U-shaped structure at the anterior end of the carapace. The interclavicle again lacks a pos- terior stem. The scapula differs from that of Cy- amodus yet resembles that of Henodus in that it is a tall and slender structure. The dorsal blade is a simple dorsal process, while the ventral portion is only moderately expanded. The reconstruction of the scapula given by Pinna and Nosotti (1989, Fig. 9) is a good rendition of the structure. The clavicles are applied against the medial surface of the scapula. As the interclavicular-clavicular complex is positioned at the anterior end of the carapace, the scapula comes to lie at a morpho- logical level deep to and below the transverse pro- cesses of the dorsal ribs. Among cyamodontoids, it is Henodus (Huene, 1936) that most closely resembles turtles in the structure of its pectoral girdle (Fig. 31; see also Huene, 1936, Fig. 15a, and PI. 84, Fig. 2). The clavicles are massive and sturdy L-shaped struc- tures that meet each other in an interdigitating ventromedial suture in front of the interclavicle. Each clavicle has a prominent dorsal process that abuts the ventral surface of the anterior margin of 36 FIELDIANA: GEOLOGY the carapace. The columnar scapula is sutured to the posteromedial surface of the dorsal process of the clavicle. The coracoid remains unknown for Henodus. In functional terms, Henodus retains a sturdy clavicular-interclavicular complex for the absorption of medially directed force components generated by limb movements when walking on the bottom of a water body or on land, while ver- tically directed force components appear to have been transmitted to the carapace via the long and columnar clavicle and scapula. In this respect, the pectoral girdle of Henodus superficially looks al- most identical to that of Proganochelys (Gaffney, 1990), a remarkable case of convergence (Rieppel & Reisz, 1999). The scapular and clavicular com- plex of Henodus further provides a firm anchoring of the pectoral girdle inside the dermal armor, which results in excellent support for the front limbs during swimming action. In a generalized tetrapod reptile, aspiration of air is effected by an expansion of the body cavity through muscular action exerted on the ribs. Ex- halation is effected either by passive recoil of the body walls or by compression of the lungs as a result of active compression of the rib cage. Res- piration in turtles depends on volume changes in the thoracicoperitoneal cavity inside the rigid der- mal armor, which are achieved by altering the po- sition of the limb flanks through the activity of anterior and posterior muscles (Gans & Hughes, 1997). The only author who addressed respiration in armored placodonts was Westphal (1975, 1976), who suggested mobility of the plastron (where present) as a mechanism that would allow volume changes of the thoracicoperitoneal cavity inside the rigid dermal armor. However, carapacial os- teoderms do not fuse with the underlying endo- skeleton in cyamodontoids (Westphal, 1975). If free dorsal ribs are retained in articulation with the (elongated) transverse processes of the dorsal vertebrae, these could therefore have moved in- dependently from the overlying carapace. In Cy- amodus hildegardis, the relatively short dorsal ribs are located in the flanks of the body (Pinna, 1992), and their movement may have laterally and ventrally expanded the volume of the thoracico- peritoneal cavity below the lateral margin of the carapace (a plastron is absent in Cyamodus hilde- gardis). A similar mechanism cannot be proposed for taxa in which a lateral wall links a carapace to a well-developed plastron (Psephosauriscus) or for taxa in which the dorsal ribs are fused to the transverse processes (Psephoderma). Like aquatic turtles (Gaunt & Gans, 1969), cy- amodontoids may have used gravity (in support of inhalation) and hydrostatic pressure (in support of exhalation) for respiration. Expansion and con- traction of the thoracicoperitoneal cavity through gravity and hydrostatic pressure would be en- hanced by the absence of a plastron (as in Pse- phoderma, with fused dorsal ribs), or by mobility within the plastron if present. Westphal (1995. 1996) noted, as did Haas (1959), that the (super- ficially) cycloid plastral osteoderms are arranged in regular oblique rows in cyamodontoids from Makhtesh Ramon, which suggests the potential for some flexion between these rows. As de- scribed above, plastral osteoderms have a cycloid crown, but the thin base (exposed on the internal surface of the plastron) is rhomboidal and meets its neighbors in interdigitating sutures. The gastral ribs are aligned along the transverse sutures. Giv- en a syndesmotic contact between osteoderms, some flexibility might very well have been pos- sible between the transverse rows of osteoderms, given their regular arrangement, while the gastral ribs provided coherence between the rows. Flexibility in the plastron of Henodus may be indicated by its delicate structure and by the ar- rangement of much broadened osteoderms in an anteroposterior series mimicking transverse rows (Huene, 1936; Reiff, 1942; Westphal. 1975, 1976). Flexibility in the plastron of Placochelys is indicated by the nature of the junction of der- mal bone to gastral ribs. As described above, der- mal bone develops between gastral ribs, and if it does not wrap around the latter, it is received in distinctly concave facets on the anterior and pos- terior aspects of the gastral ribs (Fig. 13). This certainly suggests some mobility between the el- ements, as does the fact that dermal bone and gas- tral ribs easily dissociate in the fossilized stage. Whereas the dermal armor certainly provided protection from potential predators, it is worth mentioning, as Renesto & Tintori ( 1995) did. that large predators may be rare or absent in sediments yielding cyamodontoids. Conversely, cyamodon- toid placodonts represent a clade that survived significantly longer than any other sauropterygian lineage of the Triassic. Triassic stem-group Sau- ropterygia (excluding the plesio-. plio-. and elas- mosaurs of the Jurassic and Cretaceous) had all disappeared by the upper Carnian (Bardet. 1995; Rieppel & Dalla Vecchia, 2001), while cyamo- dontoid placodonts extend through the Norian and into the Rhaetian (Pinna. 1990; Pinna & Mazin. 1993). This may well reflect a greater tolerance RIEPPEL: THE DERMAL ARMOR OF CYAMODONTOID PLACODONTS 37 of armored placodonts for salinity changes caused by the transgression-regression cycles character- istic of the Middle and Upper Triassic. Henodus, for example, comes from layers of the upper Gips- keuper (Carnian) situated above the last occur- rence of Nothosaurus in the Germanic Triassic (Rieppel & Wild, 1994). The sediments from which eight skeletons of Henodus have been col- lected have yielded a single Nothosaurus tooth only, and have been deposited in a lagoonal- brackish lake environment subject to cycles of marginal desiccation and rain flooding (Reiff, 1937; Fischer, 1959). Aigner (quoted in Reif & Stein, 1999) characterized the sedimentary facies of the upper Gipskeuper as a playa covered with brackish to hypersaline ponds that dried up sea- sonally. This is the most severe environment ever successfully invaded by sauropterygians, and it may testify to the role of the dermal armor as an osmotic barrier. Like the turtle shell, the dermal armor of cyamodontoids was covered by epider- mal scutes, which, in combination with a well- ossified carapace and plastron, provide a very ef- ficient osmotic barrier in modern turtles. Experi- mental studies have shown a significantly smaller rate of gain of water (in fresh water) or loss of water (in sea water) in a slider turtle {Pseudemys scripta) with a well-ossified carapace and plastron than in a soft-shelled turtle (Apalone spiniferus) or a caiman {Caiman crocodilus) (Bentley, 1976). The function of the dermal armor as an osmotic barrier may also explain the stratigraphic distri- bution of Sauropterygia in the Muschelkalk of Makhtesh Ramon, Negev, Israel. This deposit has yielded a diverse sauropterygian fauna, including cyamodontoid placodonts, from two separate ho- rizons, the Middle Member of the Gevanim For- mation (lower Anisian: Druckman, 1974) and the Lower Member of the Saharonim Formation (straddling the Anisian-Ladinian boundary: Druckman, 1974). Both of these horizons were deposited under normal shallow marine condi- tions, favorable for the occurrence of sauropter- ygians. The two horizons are separated by the Up- per Member of the Gevanim Formation, which was deposited in a marginal tidal flat, and cyamo- dontoid placodonts were the only sauropterygians that continued to inhabit this environment under those conditions (Druckman, 1974). Discussion and Conclusions A review of the dermal armor of cyamodontoid placodonts identifies a number of areas of incom- plete knowledge, in particular with respect to its ontogenetic development. On the other hand, the structure of the dermal armor allows the identifi- cation of a number of characters of potential use in phylogenetic analysis, such as the presence or absence of a caudal shield separate from the dor- sal shield of the carapace; the presence or absence of a plastron; the presence and nature of carapa- cial ornamentation and/or of the dorsolateral and ventrolateral body ridges; size, shape and orna- mentation of the carapacial and plastral osteo- derms; and the nature of their interfaces. An area that requires further investigation concerns the re- lation of epidermal scutes to the underlying os- teoderms. Equally important is the recognition that char- acters of the dermal armor can be used for taxo- nomic purposes at the species level. This is doc- umented by the description above of the abundant dermal armor fragments from the Muschelkalk (Middle Triassic) of the Middle East, which rec- ognizes a new genus with three species. In total, two genera and five, potentially even six, species of cyamodontoids can be recognized from the Middle Triassic of Makhtesh Ramon. This is a taxic diversity of cyamodontoids that so far is not known to be paralleled in other Triassic deposits. At the same time, this high degree of taxic diver- sification indicates a sophisticated degree of hab- itat partitioning among those coexisting cyamo- dontoids. The only area that might hold the po- tential for a similar taxic diversity of cyamodon- toids is the Triassic of southeastern China (Guizhou Province). Other areas with some taxic diversity of cyamodontoids include the southern Alpine Triassic, which yielded Cyamodus, Pse- phoderma, and Protenodontosaurus. However, unlike at Makhtesh Ramon, these genera (and spe- cies) have been reported from different deposits of different stratigraphic position within the Tri- assic of the southern Alps. The same is true for the different species of Cyamodus reported from the German Muschelkalk, with the exception of C. rostratus and C. muensteri, which coexisted in the lower upper Muschelkalk (mol) of Bayreuth. The skull structure of cyamodontoid placodonts in general shows a remarkable diversification in terms of trophic specialization as expressed in rostrum shape and function and in different pat- terns of dentition (Rieppel, 2001). Unfortunately, the cranial remains of cyamodontoid placodonts recovered from the Triassic of Makhtesh Ramon are too rare, too incompletely preserved, or too conservative in structure to be used for taxonomic 38 FIELDIANA: GEOLOGY purposes at the species level or to reflect any di- versification of trophic specialization (Rieppel et al., 1999). The one relatively complete skull frag- ment from Makhtesh Ramon, the holotype of Pse- phosauriscus mosis (Brotzen, 1957), is not diag- nostic even at the genus level. Given its high po- tential for fossilization, an improved knowledge of the structure of the dermal armor of cyamo- dontoid placodonts, and of the nature of its vari- ability, is essential for a better understanding of the taxic diversity of these exotic animals in the intraplatform basin habitats surrounding the de- veloping southern branch of the Neotethys. Knowledge of the functional anatomy of cy- amodontoid placodonts remains incomplete, in particular with respect to the impact of the devel- opment of a carapace and plastron on locomotion and respiration. A comparison with turtles might shed further light on these issues, yet a detailed anatomical comparison reveals that the dermal ar- mor in placodonts and turtles developed conver- gently in the two groups. Acknowledgments I thank Eitan Tchernov, Department of Ecology and Evolution, The Hebrew University, Jerusa- lem, for unlimited access to the collections in his care, and for allowing me to obtain cyamodontoid material on loan for further preparation. This study was made possible by financial support from the U.S. National Science Foundation (grants DEB-94 19675 and DEB-98 15235). Literature Cited Agassiz, L. 1833-45. Recherches sur les Poissons Fos- siles, Vol. II. Imprimerie de Petitpierre, Neuchatel. Bardet, N. 1995. Evolution et extinction des reptiles marins au cours du Mesozoique. Palaeovertebrata, 24: 177-283. Bentley, P. J. 1976. Osmoregulation. In Gans, C, and W. R. Dawson, eds., Biology of the Reptilia, Vol. 5, pp. 365-412. Academic Press, London. Braun, C. W. F. 1862. Uber Placodus gigas Agassiz, und Placodus Andriani Miinster. Programm zum Jahr- esbericht der konigl. Kreis-Landwirtschafts- und Ge- werbeschule zu Bayreuth fur das Schuljahr 1861/62, pp. 1-14. Theodor Burger, Bayreuth. Brotzen, F. 1957. Stratigraphical studies on the Triassic vertebrate fossils from Wadi Ramon, Israel. Arkiv for Mineralogi och Geologi, 2: 191-217. Burke, A. C. 1989. Development of the turtle carapace: Implications for the evolution of a novel bauplan. Journal of Morphology, 199: 363-378. Drevkrmann, Fr. 1933. Die Placodontier. 3. Das Skelctt von Placodus gigas Agassiz im Senckcnberg-Muse- um. Abhandlungen der senckenbergischen naturfor- schenden Gesellschaft, 38: 319-364. Druckman, Y. 1974. The stratigraphy of the Triassic Se- quence in southern Israel. Geological Survey of Israel, Bulletin, 64: 1-93. Fischer, W. 1959. Neue Funde von Henodus chelyops v. Huene im Tubinger Gipskeuper. Neues Jahrbuch fiir Geologie und Palaontologie, Monatshefte, 1959: 241- 247. Fraas, E. 1896. Die Schwabischen Trias-Saurier. E. Schweizerbart, Stuttgart. Gaffney, E. S. 1990. The comparative osteology of the Triassic turtle Proganochelys. Bulletin of the Ameri- can Museum of Natural History, 194: 1-263. Gans, C, and G. M. Hughes. 1997. The mechanism of lung ventilation in the tortoise Testudo graeca Linne. Journal of Experimental Biology, 47: 1-20. Gaunt, A. S., and C. Gans. 1969. Mechanics of respi- ration in the snapping turtle, Chelydra serpentina (Linne). Journal of Morphology, 128: 195-228. Gilbert, S. E, G. A. Loredo, A. Brukman, and A. C. Burke. 2001. Morphogenesis of the turtle shell: The development of a novel structure in tetrapod evolu- tion. Evolution and Development, 3: 47-58. Goette, A. 1899. Uber die Entwicklung des knochernen Riickenschildes (Carapax) der Schildkroten. Zeit- schrift fiir wissenschaftliche Zoologie, 66: 407-434. Gregory, W. K. 1946. Pareiasaurs versus placodonts as near ancestors to turtles. Bulletin of the American Mu- seum of Natural History, 86: 275-326. Gurich, G. J. E. 1884. Uber einige Saurier des ober- schlesischen Muschelkalkes. Zeitschrift der Deutschen Geologischen Gesellschaft, 36: 125-144. Haas, G. 1959. On some fragments of the dermal skel- eton of Placodontia from the Trias of Aari en Naga, Sinai Peninsula. Kunglia Svenska vetenskapsakadc- miensis Handlingar, (4) 7: 1-19. . 1969. The armor of placodonts from the Mus- chelkalk of Wadi Ramon (Israel). Israel Journal of Zo- ology, 18: 135-147. 1975. On the placodonts of the Wadi Ramon area Muschelkalk. Colloque international, Centre Na- tional de la Recherche Scientiliquc, 218: 451-456. Hay, O. P. 1898. On Protostega, the systematic position of Dermochelys, and the morphogeny of the chelonian carapace and plastron. American Naturalist, 32: 929- 948. Hemleben, Ch., and D. Freels. 1977. Fossilfuhrcnde dolomitisierte Plattenkalke aus dcm "Muschelkalk su- perior" bei Montral (Prov. Tarragona, Spanien). Neues Jahrbuch fiir Geologie und Palaontologie, Abhandlung- en, 154: 186-212. Huene, E v. 1936. Henodus chelyops, ein neuer Placo- dontier. Palaeontographica, A. 84: 99-148. . 1958. Nachtrage zur Kenntnis von Henodus chelyops aus dem Tubinger Gipskeuper. Palaeontogra- phica, 110: 165-169. Jaekel, O. 1902. Ueber Placochelys n. g. und ihre Be- RIEPPEL: THE DERMAL ARMOR OF CYAMODONTOID PLACODONTS 39 deutung fur die Stammesgeschichte der Schildkroten. Neues Jahrbuch fiir Mineralogie, Geologie und Pa- laontologie, Abhandlungen, 1: 127-144. -. 1907. Placochelys placodonta aus der Obertrias des Bakony. In Resultate der wissenschaftlichen Er- forschung des Balatonsees, 1. Band. 1. Teil. Palaeon- tologischer Anhang. Victor Homyanszky, K. und K. Hofbuchdruckerei, Budapest. Kaelin, J. 1945. Zur Morphogenese des Panzers bei den Schildkroten. Acta Anatomica, 1: 144-176. Lee, M. S. Y. 1995. Historical burden in systematics and the interrelationships of "parareptiles." Biological Reviews, 70: 459-547. 1996. Correlated progression and the origin of turtles. Nature, 379: 811-815. -. 1997. Pareiasaur phylogeny and the origin of turtles. Zoological Journal of the Linnean Society, 120: 197-280. Meyer, H. v. 1858a. Psephoderma Alpinum aus dem Dachsteinkalke der Alpen. Neues Jahrbuch fiir Mi- neralogie, Geognosie, Geologie und Petrefaktenkunde, 1858: 646-650. . 1858b. Psephoderma alpinum aus dem Dach- steinkalke der Alpen. Palaeontographica, 6: 246-252. 1863. Die Placodonten, eine Familie von Sau- riern der Trias. Palaeontographica, 11: 175-221. 1864. Mittheilung an Professor H.B. Geinitz. Neues Jahrbuch fiir Mineralogie, Geognosie, Geologie und Petrefaktenkunde, 1864: 698-701. Muller, H. 1979. Bayreuth und die Palaontologie. Auf- schluss, 30: 295-305. Munster, G. 1830. Uber einige ausgezeichnete fossile Fischzahne aus dem Muschelkalk bei Bayreuth. F. C. Birner, Bayreuth. . 1839. Beitriige zur Petrefaktenkunde, mit XVIII nach der Natur gezeichneten Tafeln der Herren Her- mann v. Meyer und Professor Rudolph Wagner. Buch- ner'sche Buchhandlung, Bayreuth. Nopcsa, F. 1923. Die Familien der Reptilien. Fortschritte der Geologie und Palaeontologie, 2: 1-210. Nosotti, S., and G. Pinna. 1993. Cyamodus kuhn- schnyderi n. sp., nouvelle espece de Cyamodontidae (Reptilia, Placodontia) du Muschelkalk superieur al- lemand. Comptes Rendues a l'Academie des Sciences, Paris, 317: 847-850. . 1996. Osteology of the skull of Cyamodus kuhnschnyderi Nosotti and Pinna 1993 (Reptilia, Pla- codontia). Paleontologia Lombarda, n.s., 6: 1-42. Oguschi, K. 1911. Anatomische Studien an der japan- ischen dreikralligen Lippenschildkrote (Trionyx ja- panicus). Gegenbaurs Morphologisches Jahrbuch, 43: 1-10. Osswald, K. 1930. Uber einige Ratfossilien aus dem Risserkogelgebiet (siidlich Tegernsee). Jahrbuch der Preussischen Geologischen Landesanstalt zu Berlin, 50: 733-750. Owen, R. 1858. Description of the skull and teeth of the Placodus laticeps OWEN, with indications of other new species of Placodus, and evidence of the saurian nature of that genus. Philosophical Transactions of the Royal Society of London, 148: 169-184. . 1860. Palaeontology. Adam and Charles Black, Edinburgh. Patterson, C. 1977. Cartilage bones, dermal bones and membrane bones, or the exoskeleton versus the en- doskeleton. In Andrews, S. M., R. S. Miles, and A. D. Walker, eds., Problems in Vertebrate Evolution, pp. 77-121. Academic Press, London. Peyer, B. 1931. Die Triasfauna der Tessiner Kalkalpen. III. Placodontia. Abhandlungen der Schweizerischen Palaontologischen Gesellschaft, 51: 1-125. Peyer, B., and E. Kuhn-Schnyder. 1955. Placodontia. In Piveteau, J., ed., Traite de Paleontologie, Vol. 5, pp. 459-486. Masson, Paris. Pinna, G. 1976. Placochelys zitteli, Placochelys stop- panii, Placochelyanus malanchinii: un caso di sino- nimia fra I rettili placodonti retici della famiglia Pla- cochelyidae. Bolletino dell Societa Paleontologica It- alians*, 15: 107-1 10. . 1978. Descrizione di un nuovo esemplare di Placochelyidae del Retico Lombardo (Psephoderma alpinum Meyer, 1858) e discussione sulla sinonimia P sephoderma-Placochelyanus. Atti della Societa It- aliana di Scienze Naturali e del Museo Civico di Sto- ria Naturale di Milano, 119: 341-352. . 1980. Lo scheletro postcraniale di Cyamodus hildegardis Peyer, 1931, descrito su un esemplare del Triassico Medio Lombardo. Atti della Societa Italiana di Scienze Naturali e del Museo Civico di Storia Na- turale di Milano, 121: 275-306. . 1990. Notes on stratigraphy and geological dis- tribution of placodonts. Atti della Societa Italiana di Scienze Naturali e del Museo Civico di Storia Natur- ale di Milano, 131: 145-156. . 1992. Cyamodus hildegardis Peyer, 1931 (Rep- tilia, Placodontia). Memorie della Societa Italiana di Scienze Naturali e del Museo Civico di Storia Natur- ale di Milano, 26: 1-21. . 1999. Placodontia (Reptilia Triadica). In West- phal, F, ed., Fossilium Catalogus Animalia, Pars 136. Backhuys Publ., Leiden. Pinna, G., and J.-M. Mazin. 1993. Stratigraphy and pa- leobiogeography of the Placodontia. Paleontologia Lombarda, n.s., 2: 125-130. Pinna, G., and S. Nosotti. 1989. Anatomie, morfologia funzionale e paleoecologia del rettile placodonte Pse- phoderma alpinum Meyer, 1858. Memorie della So- cieta Italiana di Scienze Naturali e del Museo Civico di Storia Naturale di Milano, 25: 1-50. Reif, W.-E., and F Stein. 1999. Morphology and func- tion of the dentition of Henodus chelyops Huene, 1936 (Placodontia, Triassic). Neues Jahrbuch fiir Geologie und Palaontologie, Monatshefte. 1999: 65-80. Reiff, W. 1937. Ergebnisse der Grabung des Geolo- gisch-Palaontologischen Universitats-Instituts bei Tii- bingen-Lustnau im Oberen Gipskeuper. Neues Jahr- buch fiir Geologie, Mineralogie und Palaontologie, Monatshefte, Abteilung B, 1937: 530-546. . 1942. Ergiinzungen zum Panzerbau von Heno- dus chelyops v. Huene. Palaeontographica, 94: 31-42. Renesto, S., and A. Tintori. 1995. Functional mor- phology and mode of life of the Late Triassic placo- dont Psephoderma alpinum Meyer from the Calcare 40 FIELDIANA: GEOLOGY di Zorzino (Lombardy, N Italy). Rivista Italiana di Pa- leontologia e Stratigrafia, 101: 37-48. Rieppel, O. 1995. Fragmenta Sauropterygiana. Neues Jahrbuch fur Geologie und Paliiontologie. Abhandlung- en, 197: 383-397. . 2000a. Paraplacodus and the phylogeny of the Placodontia (Reptilia: Sauropterygia). Zoological Journal of the Linnean Society, 130: 635-659. 2000b. Sauropterygia: I. Placodontia, Pachy- pleurosauria, Nothosauroidea, Pistosauroidea. In Welln- hofer. P., ed.. Encyclopedia of Paleoherpetology, 12A. Pfeil, Munich. . 2001. The cranial anatomy of Placochelys pla- codonta Jaekel, 1902, and a review of the Cyamodon- toidea (Reptilia, Placodonta). Fieldiana (Geology), n.s., 45: 1-104. Rieppel, O., and F. M. Dalla Vecchia. 2001. Marine reptiles from the Triassic of Tre Venezie, northeastern Italy. Fieldiana (Geology), n.s., 44: 1-25. Rieppel, O., and H. Hagdorn. 1997. Fossil reptiles from the Spanish Muschelkalk (Mont-ral-Alcover, Province Tarragona). Historical Biology. 13: 77-97. Rieppel, O., J.-M. Mazin, and E. Tchernov. 1999. Sau- ropterygia from the Middle Triassic of Makhtesh Ra- mon, Negev, Israel. Fieldiana (Geology), n.s., 40: 1- 85. Rieppel, O., and R. R. Reisz. 1999. The origin and early evolution of turtles. Annual Review of Ecology and Systematics, 30: 1-22. Rieppel, O., and R. Wild. 1994. Nothosaurus edingerae Schultze, 1970: Diagnosis of the species and com- ments on its stratigraphical occurrence. Stuttgarter Beitrage zur Naturkunde, B, 204: 1-13. Rieppel, O., and R. T. Zanon. 1997. The interrelation- ships of Placodontia. Historical Biology, 12: 21 1-227. Ruckes, H. 1929. Studies in chelonian osteology. Part II. The morphological relationships between girdles, ribs and carapace. Annals of the New York Academy of Sciences, 31: 81-120. Starck, D. 1979. Vergleichende Anatomie der Wirbel- tiere auf evolutionsbiologischer Grundlage, Vol 2. Springer Verlag, Berlin. Storrs, G. W. 1994. Fossil vertebrate faunas from the British Rhaetian (latest Triassic). Zoological Journal of the Linnean Society, 112: 217-259. Si /i Ki. H. K. 1963. Studies on the osseous system on the slider turtle. Annals of the New York Academy of Sciences. 109: 351-410. Tintori, A. 1992. Fish taphonomy and Triassic anoxic basins from the Alps: A case history. Rivista Italiana di Paleontologia i Stratigraphia, 97: 393-408. Vallen, E. 1942. Beitrage zur Kenntnis der Ontogenie und der vergleichenden Anatomie des Schildkroten- panzers. Acta Zoologica. Stockholm. 23: 1-127. Versluys, J. 1914. Uber die Phylogenie des Panzers der Schildkroten und Liber die Verwandtschaft der Leder- schildkrote (Dermochelys coriacea). Paliiontologische Zeitschrift, 1: 321-347.' Volker, H. 1913. Uber das Stamm-. Gliedmassen-, und Hautskelett von Dermochelys coriacea L. Zoologische Jahrbucher, Abteilung fiir Anatomie und Ontogenie derTiere, 33: 431-552. Walker, W F 1971. A structural and functional analysis of walking in the turtle, Chrysemis picta marginata. Journal of Morphology, 134: 195-214. . 1973. The locomotor apparatus in turtles. In Gans, C., and T S. Parsons, eds.. Biology of the Rep- tilia, Vol. 4, pp. 1-100. Academic Press, London. Weiss, G. (Ed.). 1983. Bayreuth als Statte alter erdge- schichtlicher Entdeckungen. Druckerei Ellwanger, Bayreuth. Westphal, F. 1975. Bauprinzipien im Panzer der Pla- codonten (Reptilia triadica). Paliiontologische Zeit- schrift, 49: 97-125. . 1 976. The dermal armor of some Triassic pla- codont reptiles. In Bellairs, A. d'A., and C. B. Cox, eds.. Morphology and Biology of Reptiles, pp. 31-41. Academic Press, London. Zangerl, R. 1939. The homology of the shell elements in turtles. Journal of Morphology. 65: 383-406. . 1969. The turtle shell. In Gans. C.. A. d'A. Bellairs, and T. S. Parsons, eds.. Biology of the Rep- tilia, Vol. 1, pp. 31 1-339. Academic Press. London. Zittel, K. A. v. 1 887-90. Handbuch der Palaeontologie. 1. Abtheilung. Palaeozoologie, III. Band. Vertebrata (Pisces, Amphibia, Reptilia, Aves). R. Oldenbourg. Munchen und Leipzig. Zug, G. R. 1971. Buoyancy, locomotion, morphology of the pelvic girdle and hindlimb. and systematics of cryptodiran turtles. Miscellaneous Publications. Mu- seum of Zoology, University of Michigan. 142: 1-98. RIEPPEL: THE DERMAL ARMOR OF CYAMODONTOID PLACODONTS 41 A Selected Listing of Other Fieldiana: Geology Titles Available Osteology of Simosaurus gaillardoti and the Relationships of Stem-Group Sauropterygia. Bj Olivier RieppeL Fieldiana: Geology, n.s.. no. 28, 1994. 85 pages. 71 illus. Publication 1462, $18.00 A Revision of the Genus Nothosaurus (Reptilia: Sauropterygia) from the Germanic Triassic, with Comments on the Status of Conchiosaurus clavatus. By Olivier Rieppel and Rupert Wild. Fieldiana: Geology, n.s.. no. 34. 1996. 82 pages, 66 illus. Publication 1479, $17.00 The Status of the Sauropterygian Genera Ceresiosaums, Lariosaurus, and Silvestrosaurus from the Middle Triassic of Europe. By Olivier Rieppel. Fieldiana: Geology, n.s.. no. 38, 1998. 46 pages. 21 illus. Publication 1490, $15.00 Sauropterygia from the Middle Triassic of Makhtesh Ramon. Negev. Israel. By Olivier Rieppel, Jean- Michel Ma/in. and Eitan Tchernov. Fieldiana: Geology, n.s., no. 40., 1999. 85 pages, 58 illus. Publication 1499, $25.00 Hie Intramandibular Joint in Squamates, and the Phylogenetie Relationships of the Fossil Snake Fachyrhachis problematicus Haas. By Olivier Rieppel and Hassam Zahar. Fieldiana: Geology, n.s.. no. 43. 2000. 69 pages. 17 illus. Publication 1507, $23.00 Marine Reptiles from the Triassic of the Tre Venezie Area, Northeastern Italy. By Olivier Rieppel and Fabio Marco Dalla Vecchia. Fieldiana: Geology, n.s, no. 44, 2001. 25 pages. 29 illus. Publication 1511, $10.00 The Cranial Anatomy of Plaeoehelys placodonta Jaekel. 1902. and a Review of the ( yamodontoidea (Reptilia, Placodonta). By Olivier Rieppel. Fieldiana: Geology, n.s.. no. 45. 2001. 104 pages. 39 illus. Publication 1514, $30.00 To order Fieldiana, please address correspondence to: Peter Fortsas Fortsas Books, Ltd. 5435 No. Lovejoy Chicago, IL 60630 fieldiana^ aol.com Prices and availability may change. UNIVERSITY OF ILLINOIS-URBANA 3 0112 053337637 Field Museum of Natural History 1400 South Lake Shore Drive Chicago, Illinois 60605-2496 Telephone: (312) 665-7055