New insights on Diaphorocetus poucheti: a Physeteroidea (Cetacea, Odontoceti) from the early Miocene of Patagonia (Argentina)

PAOLUCCI, FLORENCIA; BUONO, MÓNICA R.; FERNÁNDEZ, MARTA S.

Congreso; 5th International Palaeontological Congress; 2018

The Pan-Physeteroidea represent one of the earliest diverging lineages of odontocetes with extant representatives. The extant diversity of the group - three species distributed in two genera - contrasts with the past diversity, as depicted by the rich Miocene fossil record ? approximately 20 species divided in 16 genera. Most Miocene physeteroids were recovered from the North Atlantic (USA), North Pacific (USA and Japan), Mediterranean and North Sea (e.g. Italy, Belgium), Southeast Pacific (Peru), and Southwest Atlantic (Argentina). Among southwestern Atlantic collections, the most complete and diverse records are from Patagonia (Argentina), from which four species were named: Diaphorocetus poucheti and Idiorophus patagonicus (Gaiman Formation, Early Miocene, Chubut), Preaulophyseter gualichensis (Gran Bajo del Gualicho Formation, Late Miocene, Río Negro), and ?Aulophyseter? rionegrensis (Barranca Final Formation,Late Miocene, Río Negro). These taxa were de cribed from wellpreserved cranial materials and have not been restudied since their original descriptions. Miocene physeteroids from Patagonia are particularly relevant given that Diaphorocetus and Idiorophus are some of the oldest physeteroids known, being keytaxa to assist in resolving the physeteroid phylogenetic relation ships. Thus, a detailed review of the Miocene Patagonian physeteroids is necessary to evaluate their primary diversity and analyze their phylogenetic relationships in the context of a modern phylogenetic analysis of Odontoceti. In particular, theanatomical study of Diaphorocetus resulted in an exhaustive description of the skull and the modification of several characters. In the brief original description of Diaphorocetus, illustrations showed regions of theskull that are not present nowadays. It was a very important point to review the phylogenetic relationships of Diaphorocetus and analyze its phylogenetic position, incorporating the new anatomic information. As a result, Diaphorocetus is recovered in a more basal position than in recent analyses, in a basal polytomy within crown Physeteroidea. Anatomic and taxonomic revisions of the other Miocene physeteroids from Patagonia are currently in progress. Future studies evaluating the ecomorphological disparity of the group will contribute to having a more accurate knowledge of the Miocene radiation of Physeteroidea.