Searching on the boundary: a rich vertebrate assemblage on the Antarctic uppermost Maastrichtian

O GORMAN, JOSE; BONA, PAULA; CANALE, JUAN IGNACIO; CÁRDENAS, MAGALÍ; REGUERO, MARCELO

La Plata

Congreso; Reunión de Comunicaciones de la Asociación Paleontológica Argentina; 2019

The Maastrichtian-Danian López de Bertodano Formation comprises a thick sequence of marine deposits that is well exposed on Seymour (=Marambio) and Vega islands. The Lopez de Bertodano Formation yielded vertebrates such as chondrichthyans, teleosts, marine reptiles (plesiosaurs and mosasaurs) and dinosaurs (including birds). On the last three Antarctic fieldtrips our paleontological work has been focused on the prospection of the uppermost Cretaceous levels of the López de Bertodano Formation (Unit 8 and Unit 9) with the final objective of determine the faunal composition registered below the K/Pg boundary in that latitudes. The first result is the recovery of an almost complete skeleton of an elasmosauridae (7 meter in length). The extraction spent about a month since, at least half of the specimen, was buried in the frozen soil (permafrost). The specimen IAA-Pv 752, is extremely relevant because it is the first well-preserved elasmosaurid from the López de Bertodano Formation that kept both cranium and postcranium. A preliminary comparison of this specimen indicates the presence of several interesting features such as 1) high coronoid process, 2) circular atlantal cup 3) wide symphyseal mandibular sulcus, 4) atlas-axis complex with low and rounded ventral keel and 5) relative low cervical account (39 cervical vertebrae). Altough IAA-Pv 752 is clearly a non-aristonectine elasmosurid, several features of its axial skeleton (i.e., 2, 3, 4 and 5) are also observed in the aristonectine elasmosaurids indicating that this specimen povides crucial clues to support the idea of a morphological transition between aristonectine and non-aristonectine elasmosaurids.