A new species of Chubutomys (Rodentia, Hystricognathi) from the late Oligocene of Patagonia.

PÉREZ M. E.; KRAUSE, M.; VUCETICH M. G.

Buenos Aires

Jornada; XXVI Jornadas Argentinas de Paleontología de Vertebrados; 2012

Cavioidea sensu stricto clusters the extant and extinct Caviidae together with a diverse assemblage of extinct taxa grouped in the family Eocardiidae. Recent phylogenetic analyses of this group based on morphological characters corroborated the monophyly of Cavioidea s.s., but retrieved a paraphyletic arrangement of "eocardiids" as successive sister taxa of Caviidae. The late Oligocene (Deseadan SALMA) record of Cavioidea s.s. is relevant because it represents the oldest occurrence of the group, represented only by very scarce materials of Asteromys punctus Ameghino and Chubutomys simpsoni Wood and Patterson. New materials of Deseadan cavioids are of prime importance to understand the early evolution of this group. The locality of Punta Nava (northeastern Santa Cruz Province, Patagonia, Argentina) has yielded a fauna assigned to the Deseadan SALMA, but no rodent remains have been so far known. A recent fieldwork in this locality provided the first findings of fossil caviomorphs, including remains of Cavioidea, Octodontoidea, Chinchilloidea, and Erethizontoidea. A new species of Cavioidea s.s. from this locality is here described, and its phylogenetic affinities are evaluated. This new cavioid from the Deseadan SALMA, and the reinterpretation of the morphology of Chubutomys simpsoni, provide new insights on the early diversification of Cavioidea s.s. The new species from the late Oligocene, and the derived position of Chubutomys in the phylogeny, draw back the origin of all protohypsodont lineages of Cavioidea s.s. to the Deseadan SALMA. Furthermore, this suggests that the early evolution of Cavioidea s.s. occurred through a major diversification pulse, larger than previously proposed.