Duck-billed dinosaurs or hadrosaurs are a very common family of dinosaurs in the Late Cretaceous of North America and Eurasia with rare occurrences in South America. Here, we report the first hadrosaur recovered in Antarctica from sandstones of late Maastrichtian age, Vega Island, Antarctic Peninsula (Fig. 1) during a joint U.S.-Argentinian geological and paleontological field expedition to the island. This discovery supports the hypothesis of a dispersal route between southern South America and Antarctica in the Maastrichtian.Fil: Case, Judd A.. Saint Mary’s College of California; Estados UnidosFil: Martin, James E..  South Dakota School of Mines & Technology; Estados UnidosFil: Chaney, Dan S.. National Museum of Natural History; Estados UnidosFil: Reguero, Marcelo Alfredo. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Paleontología Vertebrados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; ArgentinaFil: Marenssi, Sergio Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Ministerio de Relaciones Exteriores, Comercio Interno y Culto. Dirección Nacional del Antártico. Instituto Antártico Argentino; ArgentinaFil: Santillana, Sergio M.. Ministerio de Relaciones Exteriores, Comercio Interno y Culto. Dirección Nacional del Antártico. Instituto Antártico Argentino; ArgentinaFil: Woodburne, Michael O.. University of California; Estados Unido

Case, Judd A.

Chaney, Dan S.

Marenssi, Sergio Alfredo

Martin, James E.

Reguero, Marcelo Alfredo

Santillana, Sergio M.

Woodburne, Michael O.

Journal of Vertebrate Paleontology

CONICET Digital

612Journal of Vertebrate Paleontology 20(3):612–614, September 2000 2000 by the Society of Vertebrate PaleontologyNOTETHE FIRST DUCK-BILLED DINOSAUR (FAMILY HADROSAURIDAE) FROM ANTARCTICAJUDD A. CASE1, JAMES E. MARTIN2, DAN S. CHANEY3, MARCELO REGUERO4, SERGIO A. MARENSSI5, SERGIO M. SANTILLANA5,and MICHAEL O. WOODBURNE6, 1Department of Biology, P.O. Box 4507, Saint Mary’s College of California, Moraga, California 94575;2Museum of Geology, South Dakota School of Mines & Technology, 501 E. St. Joseph Street, Rapid City, South Dakota 57701;3Department ofPaleobiology, MRC-121, National Museum of Natural History, Smithsonian Institution, Washington, D.C. 20560;4Departmento de VertebradoPaleontologico, Museo de La Plata, Paseo del Bosque, 1900 La Plata, Argentina;5I stituto Antarctico Argentino, Cerrito 1248, Buenos Aires,1010, Argentina;6Department of Earth Sciences, University of California, Riverside, California 92521Duck-billed dinosaurs or hadrosaurs are a very common family ofdinosaurs in the Late Cretaceous of North America and Eurasia withrare occurrences in South America. Here, we report the first hadrosaurrecovered in Antarctica from sandstones of late Maastrichtian age, VegaIsland, Antarctic Peninsula (Fig. 1) during a joint U.S.-Argentinian geo-logical and paleontological field expedition to the island. This discoverysupports the hypothesis of a dispersal route between southern SouthAmerica and Antarctica in the Maastrichtian.Dinosaurs are extremely rare in the dominantly marine deposits ofLate Cretaceous age in Antarctica, so the discovery of a single hadro-saur tooth (Fig. 2) by the third author (DSC) was unexpected. Hadro-saurs are not the first dinosaurs from Late Cretaceous deposits in theJames Ross Basin. Theropod, ornithopod, and ankylosaur specimenshad been previously recorded (Gasparini et al., 1987; Hooker et al.,1991; Molnar et al., 1996). However, these dinosaur groups representeither cosmopolitan taxa or native Gondwanan taxa, thus the duck-billeddinosaur represents a new immigrant family of dinosaurs into this south-ernmost continent.The fossil-bearing deposit occurs at 615 S and 5333W, at Sand-wich Bluff on Cape Lamb, Vega Island, Antarctic Peninsula. The ‘‘Rep-tile Horizon,’’ named for the numerous mosasaur and plesiosaur spec-imens recovered from this stratigraphic level, is in the upper third ofthe Sandwich Bluff Member (Crame et al., 1991; Pirrie et al., 1991) orUnit C (Olivero, 1992) of the Lopez de Bertodano Formation. Thismember is a nearshore marine deposit of composed of fine-grained,ferruginous, loosely consolidated sandstones that are latest Maastrich-tian age (approximately 66–68 million years ago), based on correlationsof ammonite and palynological taxa (Crame et al., 1991; Pirrie et al.,1991).In addition to the hadrosaur, at least four different bird species (whichcan be referred to modern avian orders, including charadriiform andgaviid birds, based on the morphology of their respective tarsometatar-sals), have been recovered from this same stratigraphic level. Addition-ally, numerous specimens of plesiosaurs and mosasaurs were collectedfrom this same horizon, as well as the 5-meter horizon immediatelybelow (Martin et al., 1999a, b). At least five taxa of marine reptiles arerepresented on Vega Island, and numerous specimens of juvenile indi-viduals were collected, concentrations of which are relatively rare inthe North American marine reptile record.SYSTEMATIC PALEONTOLOGYREPTILIAARCHOSAURIA Cope, 1869HADROSAURIDAE, Cope, 1869?HADROSAURINAE Lambe, 1918Referred Material—MLP (Museo de La Plata, Argentina) MLP 98-I-10-1, cheek tooth; a cast, SDSM C641, resides at the Museum ofGeology, South Dakota School of Mines and Technology (SDSM).Horizon and Locality—Sandwich Bluff Member, Lopez de Berto-dano Formation; ‘‘Reptile Horizon’’ on the eastern flank of SandwichBluff, Vega Island, Antarctica.DESCRIPTIONThe Antarctic hadrosaur is represented by a single cheek tooth, whichbased upon morphology, was clearly part of a typical hadrosaur dentalbattery (Fig. 2). The tooth is conical with a lozenge-shaped enamel face.A central ridge (medial carina) bisects the enamel face and extendsfrom the crown apex to the crown base. The tooth crown is 20 mm inheight and is hexagonal in cross-section, which can be easily seen asthe root had been broken off. The diameter across the crown base is 10mm in both the anteroposterior and labiolingual directions. The enamelface is slightly asymmetrical, is 10 mm at its greatest width, and nar-rows to 5 mm at the crown base. The medial carina has a maximumheight of 3 mm above the surface of the enamel and is relatively uni-form in width from the apex to the crown base; however, near the baseof the crown, the carina flares. No secondary carinae exist lateral to theprimary medial carina. The outer margin of the enamel face is onlyincipiently ridged around the margin of the enamel face. The marginalridge has well-worn denticles on both the anterior and posterior mar-gins, resulting in a coarsely serrated appearance. The non-enamelledsurface is faintly rugose and bears a broad, vertical facet set just lateralto the transverse plane. This facet represents the interface for an inter-locking adjacent cheek tooth.The tooth from Antarctica is taller than wide, a characteristic thatdistinguishes hadrosaur teeth from those of other ornithopods (Ryan andVickaryous, 1997). The crown of the tooth is relatively diamond-shaped, rather than elongate, a characteristic that separates hadrosauri-nes from lambeosaurines according to Horner (1990). The crown mor-phology of the Antarctic hadrosaur cheek tooth is very reminiscent ofthat of North American hadrosaurs, especially that ofEdmontosaurus.The tooth is relatively symmetrical, somewhat short, has only a singlemedial carina which is nearly straight, and possesses coarse, poorlyformed denticles. Although these features might suggest that the toothbelongs to a hadrosaurine, the root is broken from the Antarctic spec-imen so the crown-root angulation cannot be determined, another char-acteristic which can be used to separate the two hadrosaur subfamilies(Lull and Wright, 1942; Horner, 1990). Therefore, additional specimensmust be obtained before greater taxonomic precision can be obtained;nevertheless, the tooth clearly represents a species of the Hadrosauridaeand probably that of a hadrosaurine.DISCUSSIONHadrosaurs are known from North America, beginning in the latestAlbian to earliest Cenomanian with the first occurrence being dated by40Ar/39Ar method at 98.3 Ma (Cifelli et al., 1997). The family is avery diverse group with at least thirteen genera having been describedwithin two subfamilies, depending upon taxonomic grouping, and hun-dreds of specimens collected along the western margin of the epicon-tinental seaway which lay across the midland of North America. Spec-imens have been collected from New Mexico to Alaska in the Cordil-leran region, and hadrosaurs are known from the Atlantic and Gulfcoastal plains in the east and westerly to California and Baja California(Horner, 1979; Weishampel and Horner, 1990). Hadrosaurs are less di-verse and more rare from the Late Cretaceous deposits of Europe andeastern Asia (Weishampel and Horner, 1990), and in the Late Creta-613NOTESFIGURE 1. Maps of the Cape Lamb area of Vega Island and theimportant fossil vertebrate localities. A, map of Vega Island illustratingits position in relationship to James Ross Island and the Antarctic Pen-insula. The upper inset is a key to the stratigraphical rock units in thearea, whereas the lower inset places the study area in the geographicalcontext of the Antarctic Peninsula. B, Cape Lamb area of Vega Islandwith indications of important vertebrate fossils which were recoveredfrom west of Leal Bluff in Member B and recovered from SandwichBluff in Member C. The hadrosaur tooth was collected from SandwichBluff.FIGURE 2. Hadrosaur tooth, MLP 98-I-10-1 in occlusal view (left)and side view (right). Scale equals 10 mm.ceous of South America, hadrosaur remains are even more rare. A singlespecies of hadrosaur, Kritosaurus australis (Bonaparte et al., 1984) isknown from the Los Alamitos Formation (late Campanian, ca. 75 Ma)of Patagonia and Secernosaurus koerneri, from the Laguna PalaciosFormation (early Campanian), also from Patagonia (Brett-Surman,1979). However, Bonaparte (1996) commented that the ilium of Secer-nosaurus appears to have been deformed during or after preservationand thus is the earliest known specimen of Kritosaurus in South Amer-ica. Specimens of Kritosaurus were previously known from NorthAmerica and have been collected from Alberta to New Mexico (Brown,1919; Parks, 1920; Horner, 1992). The dispersal of hadrosaurs fromNorth America to South America probably occurred during the early tomid-Campanian, in order for K. australis to appear in Patagonia by thelate Campanian. A dispersal event of terrestrial vertebrates (in this case,a species of hadrosaur) between North and South America during theCampanian would coincide with a hypothesis of marsupial mammaldispersal from North America to South America in the late Campanian,as well, so that marsupials could continue their dispersal into Antarcticaand then onto Australia by the end of the Maastrichtian to the earliestTertiary (Woodburne and Case, 1996).Other dinosaurs have been recorded from Late Cretaceous depositson islands along the eastern coast of the Antarctic Peninsula (Fig. 1).A nodosaurid ankylosaur was found in the Santa Marta Formation (San-tonian to Campanian) on James Ross Island only 15 km from the had-rosaur site on Vega Island (Gasparini et al., 1987). This partially com-plete specimen of a single individual included a mandible with teeth,assorted vertebrae, ribs, girdle elements, podials, and dermal armor(Gasparini et al., 1996). Also from James Ross Island, but further tothe north from the nodosaur locality, the distal portion of a theropod(carnosaur) tibia was recovered from older deposits (i.e., the HiddenLake Formation) of Coniacian to Santonian Age (Molnar et al., 1996).A hypsilophodontid was the first dinosaur collected from Vega Island(Hooker et al., 1991). This dinosaur was recovered from the late Cam-panian to early Maastrichtian ‘‘ Gunnarites’’ Zone of the Cape LambMember (Unit B) of the Lopez de Bertodano Formation. This dinosaursite on the eastern slope of Leal Bluff is only three kilometers from thehadrosaur site at Sandwich Bluff.The nodosaurid, theropod and hypsilophodontid belong to groups ofdinosaurs which have a long geological history with origins in the EarlyJurassic to Early Cretaceous and a broad geographical distribution. Thehypsilophodontids are nearly cosmopolitan with species having beendescribed from North America, Europe, Africa, Australia, and of courseAntarctica (Fastovsky and Weishampel, 1996). Nodosaurs are knownfrom the Early Cretaceous in both Europe and North America, whereaslater forms appeared in Australia and Antarctica (Molnar, 1980; Gas-parini et al., 1996). The theropod most closely resembles plesiomorphicallosauroids or megalosaurs, both of which are biogeographically wide-spread (Europe, Africa, and Australia) and may have their origins inthe Early or Middle Jurassic (Hammer and Hickerson, 1994; Molnar etal., 1996). The theropod and nodosaurid should be regarded as part ofthe resident dinosaur fauna existing in Gondwana, and hypsilophodon-tids and nodosaurids were in Australia by the end of the Early Creta-ceous (Molnar, 1980). However, hadrosaurs are a ‘‘ Northern Hemi-sphere group,’’ as their earlier record is North American and Eurasian,with subsequent dispersal to South America. Consequently, the discov-ery of a hadrosaur in the Maastrichtian of Antarctica represents a latedispersal event of the taxon into Antarctica.The dispersal of hadrosaurs into Antarctica from South America, in-fers a connection, either an island chain or an isthmus, between Pata-gonia and the Antarctic Peninsula. Similar geological histories betweenthese two areas on either side of the Drake Passage suggest the existenceof a connection between southern South America and Antarctica fromthe Late Cretaceous to the beginning of the Oligocene (Lawver et al.,1992; Shen, 1995). The dispersal of hadrosaurs into Antarctica by theMaastrichtian may coincide with and provide additional support for apredicted first wave of marsupials from South America to Antarctica(Case et al., 1996; Woodburne and Case, 1996; Goin et al., 1999).Acknowledgments—This work was supported by National Science614 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 20, NO. 3, 2000Foundation, Division of Polar Program grants OPP-9615933 (to J. A.Case), OPP-9615236 (to M. O. Woodburne) and OPP-9815231 (to J. E.Martin). We would like to thank the Instituto Antartico Argentina (IAA)for their logistical support while on Vega Island and the Fuerza AereaArgentina for providing our transport for the 1998–99 field seasons andaccommodation at Base Marambio. Our special thanks to Dr. PedroSkvarca of IAA for all of his assistance in our communications andDra. Andrea Concheyro, Departmento de Geologia, Universidad deBuenos Aires, for her instruction on the biostratigraphy of the CapeLamb area. We would like to thank the personnel of the Museo de LaPlata for many kindnesses, including providing research facilities duringpreparation of the manuscript. J. R. Horner, W. R. Hammer, and a thirdreviewer made valuable review comments, which added greatly to thecontribution. Ms. Barbara Rowe, a paleontology graduate student atSDSM, rendered the fine drawings of Figure 2.LITERATURE CITEDBonaparte, J. F. 1996. Cretaceous tetrapods of Argentina; pp. 73–130in Contributions of Southern South America to Vertebrate Pale-ontology. Munchner Geowissenschaftliche Abhandlungen (A) 30., M. R. Franchi, J. E. Powell, and E. G. Sepulveda. 1984. LaFormacion Los Alamitos (Campaniano-Maastrichtiano) del sudestede Rio Negro, con descripcion de Kritosaurus australis n. sp. (Had-rosauridae). Significado paleogeografico de los vertebrados. Rev.Association Geol. Argentina 39:284–299.Brett-Surman, M. K. 1979. Phylogeny and paleobiogeography of had-rosaurian dinosaurs. Nature 27:560–562.Brown, B. 1910. 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The first duck-billed dinosaur (Family Hadrosauridae) from Antarctica

The first duck-billed dinosaur (Family Hadrosauridae) from Antarctica

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