A Land Mammal Tibia from the Eocene of Marambio/Seymour Island, West Antarctica

GELFO J. N.; REGUERO, M.

Davos

Congreso; POLAR 18; 2018

SCAR

Despite Antarctica is the only continent without terrestrial mammals, in the past it played a key role in the evolutionary history of Southern Hemisphere mammalian communities. Sometime between the Late Cretaceous and the latest Paleocene, before the complete break-up of Gondwana, West Antarctica functioned as a land bridge for the dispersal of metatherians and monotremes, from Southern South America to Australia in the first case, and in the other way round in the last. Fossil land mammals in Antarctica are mostlyconstrained to the dental remains from the Eocene of La Meseta and Submeseta Formations in Marambio Island. Here we described and discuss the implications of the first mammalian long bone, represented by an almost complete right tibia (MLP 94-III-15-6). The remain came from the lower conglomeratic shell bed from Cucullaea I Allomember at La Meseta Formation (Telm 4) in the locality DPV 2/84. The minimum length of the tibia is  approximately of 230 mm; the prominent cnemial crest and most of the proximal epiphysis are cracked and with most of its surface were reconstructed. Proximally, the medial condyle is broken as well as most of the tibial malleolus. The distal third of the bone is the best preserved, particularly the astragalar articular surface. The distal moiety of the shaft resembles some Proterotheriidae litopterns for being more trihedral and less oval in section suggesting Sparnotheriodontid affinities.