Plesiosaurs from the Late Cretaceous Deposits of Antarctica

Plesiosaurs were one of the first reptiles found from the Late Cretaceous rocks of Antarctica. However, the identification of specific plesiosaurs has long been problematical. The first plesiosaur identified to lower taxonomic levels is an elasmosaurid that was originally described as Morturneria (originally Turneria); that taxon was synonymized with Aristonectes (Gasparini et al., 2003) described from the Late Cretaceous of Chubut Province of Argentina. A second elasmosaurid is represented by only postcranial elements, and its taxonomic identity has long been questioned. Recently, cooperative expeditions between the United States and Argentina have produced a number of specimens of the second elasmosaurid taxon. In 2005, postcranial skeletons of a juvenile and adult specimen, as well as gastralia of a large adult associated with gastroliths, were discovered from the Late Cretaceous upper Cape Lamb Member of the Snow Hill Island Formation on Vega Island, east of the Antarctic Peninsula. The gastralia had gastroliths aligned along each element, and a hexanchid shark tooth was found associated, suggesting scavenging. The juvenile skeleton exhibits a rounded propodial and raised eminence on the coracoids that is characteristic of Mauisaurus known from the Late Cretaceous of New Zealand. Therefore, the two taxa of known Antarctic plesiosaurs are Aristonectes and Mauisaurus, both of which are restricted to the austral Weddellian Biogeographic Province, indicating endemism of these large marine reptiles. This research was supported in part by the National Science Foundation, Office of Polar Programs.