carcous nodulcs which made the prcparation ... frequent checks were made of the progress. Aftcr the preparation. ...... Oll/ario MW'elllll LiJe Scicllce Divisioll, 52,.
New plesiosaurs from the Upper Cretaceous of Antarctica !'
SANKAR CHAITERJEE & BRYAN J. SMALL The MuseulIl of Texas Tech University, Lubbock, Texas 79409, USA Abstract: Ncw plesiosaur remains from thc Uppcr Crcta ceou s Lopcz dc 13crtodano Formation (laic C lIllpanian- Maastrichtian) of Scymour Island, Antarctic Pcninsula includ c Cryplodididac and Elasmosauridac. The occurrcncc of Cryptodididac is rcportcd from thc Ant:lrctic region for Ihc first time. Thc taxon represcn ts a ncw gcnus and spccies, bascd on a skull and associ:lled cervical vertcbrac . Thc lo ng, sle ndcr and dclicatc teeth may havc formcd a ' Irapping' device that c nablcd cryptodidiLls to fe eLl on small lish and cruslaceans Ih :l t abound in Ihc same deposits . The cryptodidids had a restricted L1i stribUliun, being known so far from thc Middle a nd Latc Jurassic of England, and the Late Cretaceous uf Chilc, Argentina, and Anlarctiea . Olher specimens, represenled by scveral poslcranial skelctons, arc taxonomically indelcrmin:lle, but Ihe), share sumc fcatures wilh olhcr contcmporary elasmosaurid \!,encra such as I1wlrolhcro.HIIII'II." MOI'CIIO.l'alll'llS, Tiltl/a.l'solllccioll, a nd Mallisal/I'I/s. Unlikc Ih c nyplociidids, Ihc c lasmosa urids had a cosmupolilan dislribution during Ihe Jur:lssie and Cre taceous pcriods. Trophic divcrsity wilhin guilds of marinc prcdators is examined in thc Lopcz de 13crtudano palaellcommunities . Threc predator guilds arc rceognizcd on thc basis of toolh morphology :lIld prey pn:fcrcnce . The mosasau rs composed Ihc 'CUI guild' , and werc the prilKipal predators. The elasm(lsaurids constituted the 'Pierce guild', :Ind Ihc cryptodidids formcd Ih c 'Trap guild'. Thcse marinc reptiles exploited the various pelagic rcsourees s uch as sharks, bon)' fi sh, so ft ccphalopods and crustaceans, and survived until thc end of Ihe Crclaecous. The plesiusaurs wcre cxeellcnt swimmcrs, and uscd Iheir hypcrphalangic paddles for subaqueous nighl in Ihc man ncr o f modern sca lions.
Plesiosaurs were among the most diverse and widespread of the Mesozoic marine reptiles which dominated the seas throughout the Jurassic and Cretaceous periods. They werc highly adapted for a marine predaceous existence with their paddle-like. hyperphalangic limbs. which were used for aquatic locomotion. They were the largest of the marine reptiles with some of the Late Cretaceous genera attaining a length of 15m. and necks over 7 m long. Despite extensive knowledge of the crunial anatomy of plesiosaurs, their systematic position has long been subject to dispute because of the structure of the temporal region. There is a single, large uppe r temporal opening, bounded above by the parietal and below by the squamosal and postorbital. The check region below the fenestra is open and was thought to be deri\'ed by the cmargination of a solid cheek like that of ilracoscc/i.l' (Williston InS) . On the bas is of a singlc upper temporal opening. the plesiosaurs ha\'c long been classificd among euryapsids (Romer 11)56, 1%(1: Colbcrt 1l)(,5, 11)61)). Howcver, it is currently believed that plesiosaurs arc more appropriately allied with the diapsid reptiles that paralleled the squamates in the breakdown of the lower tcmporal arcade (Kuhn-Schnyder 1%7; Carroll 11)8 I,
II)~~) .
Clearly this feature evolved independently in many diverse groups, including protorosaurs (Chatterjee 11)86). nothosaurs (Carroll 1981 ). pleurosaurs (Carroll & Gaskill 1985), sphenodontids (Robin son 1973) , millerettids (Gow 11)72) and eosuchuians. (Evans 1980). Traditionally the order Plesiosauria is divided into two superfamilies, the Plesiosauro idea and the Pliosauroidea, on the basis of the relative length of the skull and neck. Plesiosauroids had long, slender necks, small heads , and a short mandibular symphysis. On the other hand , pliosauroids had large heads, a long mandibular sy mphysis, and short necks. Recently, abundant plesiosauroid remains have been recovered from the Late Cretaceous Lopez de Bertodano Formation of Seymour Island. Antarctic Peninsula . They include members of two different families : Elasmosauridae and Cryptoclididae. Elasmosaurids from Seymour Island have been reported previously (del Valle ('/ lIl. 11)77: Chatterjee & Zinsmeister 11)82: Chatterjee cl al. 11)84 : Gasparini c{ lIl. I W'4). Additional elasmosaur material is discussed here. The cryptoc1idid material, reported here for the first time from th e Antarctic region, represents a new taxon. So far no pliosauroid remains have been found in
Frolll Cramc , J. A. (cd . ). I')~I), Origills lIIU/ E"o/llfioll O/ Iltc AIII(/ruic iliola, Gcological Sociel), Speciall'ublicalioll N(I . 47. pp. 1\17- 215.
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S. CIIATIERJEE & n .J. SMALL
Seymour Island. The plesiosaurs described in this paper are important in that they provide new taxa from Antarctica, as well as demonstrating the wider distribution of cryptoclidids (previously known from only England and South America).
Gcological setting Seymour Island contains a remarkably continuous record of Late Cretaceous through Paleocene nearshore marine and coastal/deltaic sediments of a transgressive-regressive cycle. The plesiosaur fossils were recovered from the Lopez de Bertodano Formation, which is exposed in the southern two-thirds of the islund (Fig. 1) . The lithology consists of c. 1200m of loosely consolidated sandy siltstones, intercalated with calcareous concretions. Macellari (1986) subdivided this formation into 10 informal lithological units. The lowermost six units (1-6) are grouped into 'Rolillaria units', characterized by the abundance of the annelid worm tube ROllllaria, but the near absence of macroinvertebrates. The upper 4 units (7-10) arc included in the 'molluscan units', characterized by abundant macro-invertebrates such as ammonites, echinoids, bivalves, gastropods, and arthropods. The age of the Lopez de Bertodano
Formation ranges from late Campanian to Maastrichtian on the basis of palynomorphs, invertebrates, and glauconite datings (Huber 1985). The inferred K-T boundary has been recognized primarily by the last appearance of ammonites. It probahly occurs hetween units 9 and !O of the Lopez de I3ertodano Formation, about 45 m below the base of the overlying Snhral Formation (Macellari 1986). The marine vertebrate material collected from the Lopez de Bertodano Formation is highly varied and includes the remains of teleosts and sharks (Grande & Chatterjee 1987), plesiosaurs and mosasaurs (Chatterjee & Zinsmeister 1982; Chatterjee el al. 1984), and a newly discovered bird skeleton. The sharks, mosasaurs, and elasmosaurids are distrihuted throughout the formation, hut the cryptoclidids, teleosts and bird specimen arc so far restricted to the 'molluscan units'. Some of the plesiosaurs have been recovered from the uppermost Cretaceous section, close to the K-T boundary.
Matcrial and methods Although isolated plesiosaur bones were found scattered throughout the Lopez de Bertodano Formation, only eight partially associated skeletons were collected during the three field
SEYMOUR ISLAND
Quaternary
_
~ La Meseta Fm. ~ Cross Valley Fm. _
SobralFm.
I';·. lIcioll. 212. 1- D. EDIN(;EH. T. 11)21. Uhcr Nothos;lurus II. ZlIr GmllllcIIJ/'{/gc. Senckcnhcrgiana. 3, 1'13-205. EDMUND. A. G . 1%0. Touth replacement phenomena in the lowcr vcrtebrates. COlltributiollS Royal Oll/ario MW'elllll LiJe Scicllce Divisioll, 52, 1-17'1. EVANS. S. E. I'IX(). Thc skull of ;1 new eosuchian reptile rrom the Lower Jurassic ur South Wales. Zoologiwl ./ollrl/al Lif/llelll/ Society. 70. 2OJ-2M. FELDMANN. R. M. 1()~4 . Decapod crustaceans rrom thc Late Cretaceous and the Eocene or Seymour Island. Antarctic Peninsula. AI/tarctic ./ollrnal oJ the Vllitl'd Swtes . A/1I1I1111 Uel·iell·. 19(5).4-5. GASI'AHINI. Z .. Du .. VALLI'. R. & GONI. R. I'IX4 . An elasmosaurus (Reptilia. Plesiosauria) or the Upper Cretaceous in the Ant .. rctic 'I/,\titlllO AII/artica Argcl/til/o COl/tribllcioll. 3US . 1-24. GODrHEY . S. J. I'1X.J. Plesiosaur suhaljueous locomotion : a reappr .. isal. NClles ./"hrl)//ch /iir Geologie IIl1d i'aliiolltologic, MOl/asheJtc. II. (X'11-672. Gow. C. E. 1'172. The osteology anu rclationships or the Millerettidae (Reptili .. : Cotylosauria). ./ollrl/al of the Zoological Society oJ LOlldoll.
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