CONICET | Buscador de Institutos y Recursos Humanos

Elasmosauridae is a clade of long-necked plesiosaurs that radiated during the Late Cretaceous. Although they have been considered an extremelyconservative group, recent discoveries indicate a previously unknown diversity in their anatomy. Here we present a new elasmosaurid specimen (IAAPV 443), from levels of the López de Bertodano Formation (Unit 9, upper Maastrichtian of the Seymour Island=Marambio), James RossArchipelago, Antarctica, represented by a partial and severely eroded skeleton. Despite its bad preservation, IAA PV 443 preserves someinformative cranial and postcranial elements which allow considering it a non aristonectine elasmosaurid (e.g., presence of elongated cervicalcentra). The preserved cervical vertebrae are more elongated (maximum vertebral length elongation~ 120) than the recorded for Vegasaurusmolyi (maxi-mum VLI ~110), the only well known non aristonectine elasmosaurid from Antarctica. The PV 443 shows three symphyseal alveoli,differing from other Weddellian non-aristonectines: Kawanectes lafquenianum, upper Campanian-Maastrichtian of North Patagonia(2.5 symphyseal alveoli) and Tuarangisaurus keyesi, upper Campanian-lower Maastrichtian of New Zealand (4 symphyseal alveoli). Howeverthe PV 443 shows a humerus with aligned epipodial facets and long posterior expansion, features shared with the weddellonectians Vegasaurusmolyi; Kawanectes lafquenianum; Morenosaurus stocki and Kaiwhekea katiki. Therefore the IAA PV 443 adds new combination offeatures in both cranial and postcranial anatomy, indicating that Weddellian Maastrichtian elasmosaurids were more diverse than previously though.