Un nuevo Xenodontomys (Rodentia, Octodontidae) del Mioceno tardío de La Pampa, Argentina. Patrón evolutivo y biocronología

VERZI, D.H.; MONTALVO, C.I.; TIRANTI, S.

AMEGHINIANA

Año: 2003 vol. 40 p. 229 - 238

0002-7014

A new Xenodontomys sample, composed of 220 specimens, from the Cerro Azul Formation (Late Miocene) at Caleufú (La Pampa Province, central Argentina) is described. The new sample can be distinguished from the two species included in the genus (Xenodontomys simpsoni and X. ellipticus) mainly by the greater size, the elongation of the occlusal figure of molariforms (especially DP4-M3), and the greater relative length of  DP4/4. The Caleufú sample reinforces the hypothesis that Xenodontomys represents a phyletic sequence without diversification, with an anagenetic pattern of change in the general size and dental morphology. Although specific names are used, Xenodontomys samples are interpreted as chronomorphs. The new chronomorph is the most derived of the phyletic sequence. This and other faunal evidences indicate that the fossil-bearing sediments outcropping at Caleufú would be younger than the rest of the Cerro Azul Formation. Likewise, the evolutionary pattern of Xenodontomys suggests that the strata of the Irene “Formation” bearing X. ellipticus would be referable to the Late Miocene.