A NEW MEIOLANIID (TESTUDINATA: MEIOLANIIDAE) FROM THE MIDDLE EOCENE (SARMIENTO FORMATION) OF CENTRAL PATAGONIA (ARGENTINA): DIVERSITY, PHYLOGENY, AND PALEOBIOGEOGRAPHY OF HORNED TURTLES

STERLI, J.; DE LA FUENTE, M. S.; KRAUSE, M.

Berlin

Otro; SVP Annual Meeting 2014; 2014

Society of Vertebrate Paleontology

The objectives of the present work are: 1) to describe a new genus and species of ahorned turtle and its geological setting; 2) to explore its phylogenetic relationships; 3) toanalyze the diversity and evolution of the group in a paleobiogeographical frame; and 4)to compare the evolution of Meiolaniformes and other turtles with the well-recordedevolution of mammals in southern Gondwana. The specimens come from the lowerSarmiento Formation at Cerro Verde (Cañadon Hondo area). The level containing turtlesand crocodyliforms is located at base of the section and is composed of laminated, finetuffs interpreted as shallow ponds. It underlies another fossiliferous level composed oflenticular, massive sandstones bearing skeletal remains of mammals, referred by previousauthors to the Casamayoran SALMA. Geometry and facies are interpreted a as fluvialdepositional system. Cranial and postcranial remains of this new horned turtle have been found and they represent the most complete meiolaniid known from South America. Thisnew species differs from other meiolaniids in the peculiar thick half-moon shaped rimsurrounding the cavum tympani, the presence of three cranial scutes K, an unenclosedcanalis chorda tympani mandibularis, among other characters. The preliminary cladisticanalysis, based on recent analysis of meiolaniforms, suggests this new species belongs toMeiolaniidae. However, due to the presence of few elements in common between thisspecies and other meiolaniids, its phylogenetic position is not stable inside the clade. Thepaleobiogeographic analysis shows that meiolaniids would have originated in the areathat is today represented by Antarctica, however there is no fossil record supporting thishypothesis. The comparison of the evolution of meiolaniforms with other amniotessuggests a common paleobiogeographical history of these clades in southern Gondwana.Furthermore, different proxies highlight that the paleobiogeographical history ofmeiolaniids is also controlled by the major climatic changes occurred during theCenozoic caused mainly by the breakup of southern Gondwana.