The rodents from La Cantera and the early evolution of caviomorphs in South America

VUCETICH M.G.,; VIEYTES, EMMA; PÉREZ, ME; CARLINI AA.

The Paleontology of Gran Barranca: Evolution and Environmental Change through the Middle Cenozoic of Patagonia”, Madden, R.H., Carlini, A.A., Vucetich, M.g. and Kay R.F. (eds).

CAMBRIDGE UNIVERSITY PRESS

Lugar: Cambridge; Año: 2010; p. 193 - 205

Here we describe the oldest rodents from Patagonia, found in the La Cantera level at Gran Barranca, intermediate in age between Tinguirirican and Deseadan South American Land Mammal Age (SALMA). The represented taxa are the Octodontoidea Draconomys verai gen. et sp. nov., Vallehermosomys mazzonii gen. et sp. nov., and Vallehermosomys? merlinae sp. nov., the Cavioidea cf. Eobranisamys, Dasyproctidae gen. et sp. indet., and Chinchillooidea? gen. et sp. indet. Isolated teeth, P4 and Dp4? that cannot be referred to any superfamily, are also described. The rodents from La Cantera are essentially brachyodont; only one single fragment of an upper molar referred to Chinchilloidea? gen. et sp. indet. has conspicuous unilateral hypsodonty. The enamel microstructure of incisors agrees with that of other caviomorph taxa, only multiserial Hunter–Schreger bands with interprismatic matrix in acute angle and with an intermediate subtype between acute and rectangular has been found. The absence of rodents in fossiliferous levels immediately below (called the La Cancha fauna) referable to the Tinguirirican SALMA suggests that the arrival of rodents to the latitude of Gran Barranca occurred during the early Oligocene. The arrival to the continent was not much before the early Oligocene. The geographic and temporal distribution of the oldest caviomorphs suggests a north–south dispersion route within South America. This route agrees with the hypothesis of the arrival of rodents via a transatlantic crossing from Africa.