First articulated elasmosaur (Sauropterygia, Plesiosauria) from the Santa Marta Formation (Santonian-Lower Campanian), James Ross Island, Antarctica

O GORMAN, J; CORIA, R. A.; SALGADO, L.; PAULINA CARABAJAL, A.; MOLY, J.

General Roca

Otro; Reunión anual de Comunicación de la Asociación Paleontológica Argentina; 2012

The Elasmosauridae, one of themost diverse group of Late Cretaceous plesiosaurs, are characterized by theirlong necks with more than 46 cervical vertebrae. Two patterns of neck elongation have been identified among these marine reptiles. The "elongate" group formed by Elasmosaurus Cope, 1869 and SepcosaurusWelles, 1943 is characterized by an average VLI (vertebral length index) higher than 125, in contrast with the "non elongate" group. Interestingly, the "elongate" group appears to have been recorded only during the Santonian-Campanian interval, and are restricted to the Western Interior Sea, USA. Until now, the biogeographical pattern has been tested in only one elasmosaur from that age in the Southern Hemisphere. Here, we report an elasmosaur specimen (MLP 11-II-20-6) collected from the Lower Campanian section of the Santa Marta Fm (Berta Member), James Ross Island, Antarctica. This specimen is the first articulated elsamosaur collected in this formation where the Elasmosauridae were previously represented only by isolated vertebrae.  The new specimen allows testing the biogeographical pattern above mentioned. Only the mid to posterior section of the neck section of MLP 11-II-20-6) has been collected. It consists in an articulated series of eghteen vertebrae. The fusion between the neural arches, cervical ribs and vertebral centra suggest an adult ontogenetic stage. The mean VLI of the cervical section (108.37) and the stardad deviation (4.82) indicate that this specimen belongs to the "non elongate" group, supporting the inference about the restricted geographical distribution of the "elongate" group