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

VUCETICH, M.G.; KRAMARZ, A.; CANDELA, A.

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

Cambridge University Press

Lugar: Cambridge; Año: 2010; p. 206 - 219

Almost 20 years of fieldwork in the early Miocene ofPatagonia reveals that the various faunas assigned to theColhuehuapian SALMA share numerous rodent taxa, butthey do not share most of them with faunas of SALMAsimmediately younger or older. This supports assignmentto a single biochronologic unit. Taxonomic differencesespecially between the classical localities of Bryn Gwynand Gran Barranca are uncommon and may result largelyfrom environmental variation. New finds result in a dramaticincrease of the estimates of diversity for this time.Indeed, the Colhuehuapian caviomorphs currently constitutethe most diverse Cenozoic rodent fauna of SouthAmerica. This high taxonomic diversity could result fromthe coexistence of old Patagonian lineages together withothers of probable northern origin that entered Patagoniain a post-Deseadan event or events. This diversityexpresses itself in varying degrees of hypsodonty, a varietyof occlusal designs, and a relatively great size range,showing that Colhuehuapian caviomorphs had alreadydeveloped considerable dietary niche breadth. Colhuehuapianrodent faunas are characterized by the richness ofsmall octodontoids with a mosaic of derived and primitivecharacters, and the great diversity of erethizontids thathave their acme at this time. Most of the Colhuehuapianrodents belong to lineages not recorded in post middleMiocene faunas; only eocardiids and chinchillids are certainlyclosely related to extant representatives. After theColhuehuapian there occurred a decline in taxonomicdiversity, variety of occlusal designs, and degree ofhypsodonty, suggesting a reduction of adaptive types.