A RECENT DISCOVERY SHEDS LIGHT ON THE PRESENCE OF CROCODILES IN THE EOCENE OF WEST ANTARCTICA

BONA, P.; PEREYRA, M. ; GELFO J. N.; ACOSTA HOSPITALECHE, CAROLINA; GARCÍA-LÓPEZ, D. A.; IRAZOQUI, F.; REGUERO, M.A.,

Salta

Otro; REUNIÓN DE COMUNICACIONES DE LA ASOCIACIÓN PALEONTOLÓGICA ARGENTINA; 2022

Asociación Paleontológica Argentina

Among archosaurs, the clade Avemetatarsalia is well documented in the Antarctic fossilrecord. However, the presence of crocodyliforms was mentioned but never accuratelysupported. Herein we describe by first time a partial osteoderm coming from the LaMeseta Formation (Ypresian), at Marambio/Seymour Island. It is a half huge dermalplate (anteroposterior length: 58 mm, maximum thickness: 17 mm) which preserves theinterdigitated latero-medial contact between axial osteoderms. Its highly eroded dorsalsurface is typically ornamented by small and large cells delimited by thin, sharp, andanastomosed ridges. The longitudinal section of the plate is exposed by fracture,spindle-shaped and ventrally concave. Microstructurally is observed a deep regioncomposed by poorly vascularized lamellar bone with many growth marks, a coreformed by large resorption spaces and compacted coarse cancellous bone, and asuperficial region composed of highly vascularized woven bone tissue. Traces ofSharpey's fibers are abundant, mainly in the superficial region and on the laterals of thedermal plate. The combination of these anatomical features allows us to identify thismaterial as a dorsal osteoderm of a crocodyliform with an osteohistological patternsimilar to that of extant and extinct crocodylians. The clade Crocodylia is known sincethe Late Cretaceous to the present in all continents except Antarctica. This apparentabsence was traditionally explained by the latitudinal position of the continent, due tothe Antarctic polar-night and the restrictions imposed by the presumed ectothermy ofthe group. This new finding situates crocodiles in southernmost Gondwanan Paleogenelandscapes and raises new questions related to their physiological plasticity.