Colhuehuapian rodents from Gran Barranca and other Patagonian localities: the state of the art

VUCETICH, KRAMARZ, CANDELA

The Paleontology of Gran Barranca: Evolution and Environmental Change through the Middle Cenozoic of Patagonia

Cambridge Uiniv. Press

Año: 2010; p. 193 - 219

Almost 20 years of fieldwork in the Early Miocene of Patagonia reveals that the various faunas assigned to the Colhuehuapian SALMA share numerous rodent taxa, but they do not share them with faunas of SALMAs immediately younger or older. This supports assignment to a single biochronologic unit. Taxonomical differences especially between the classical localities of Bryn Gwyn and Gran Barranca are scarce and would result mainly from environmental variations. New finds resulted in a dramatic increase of the estimates of diversity for this time, and therefore, the Colhuehuapian caviomorphs currently constitute the most diverse Cenozoic rodent fauna of South America. This high taxonomic diversity could result from the coexistence of old Patagonian lineages together with others of probable northern origin that would have entered Patagonia in a post Deseadan event or events. This diversity also is reflected in various degrees of hypsodonty, an important diversity of occlusal designs and a relatively wide size range, showing that Colhuehuapian caviomorphs had already developed a large variety of adaptive types and strategies in the use of food resources. Colhuehuapian rodent faunas are characterized by the richness of small octodontoids with a mosaic of derived and primitive characters, and the great diversity of erethizontids that have their acme at this time. Most of the Colhuehuapian rodents belong to lineages not recorded in post Middle Miocene faunas; only eocardiids and chinchillids are certainly closely related to extant representatives. After the Colhuehuapian there occurred an impoverishment in taxonomic diversity, variety of occlusal designs, and degree of hypsodonty, suggesting a reduction of adaptive types.