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

Abstract

Department 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 61 51 S and 53 33 W, 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 PALEONTOLOGYREPTILIAA