Dh. Verzi, The dental evidence on the differentiation of the ctenomyine rodents (Caviomorpha, Octodontidae, Ctenomyinae), ACT THERIOL, 44(3), 1999, pp. 263-282
Primitive species in the differentiation of the subfamily Ctenomyinae are r
evisited, and, on molar evidence, a new interpretation of the evolutionary
pattern of these earliest members of the group is proposed. The octodontid
Phtoramys is rejected as possible ancestor, whereas the genus Chasichimys (
including Pattersomys), previously included in the family Echimyidae, is tr
ansferred to the Octodontidae as a primitive member of the ctenomyine radia
tion. During the Chasicoan and Huayquerian Ages (Late Miocene), an anagenet
ic event represented by an increase of hypsodonty in Chasichimys, may have
led to the differentiation of the primitive euhypsodont ctenomyines of the
genus Xenodontomys. Coeval cladogenetic processes, occurring during the pro
tohypsodont evolutionary stage of the group, would have resulted in the sep
aration of the genus Palaeoctodon from the lineage Chasichimys-Xenodontomys
. These ancient representatives of the subfamily would have differentiated
in central Argentine pampas. The recognition of such evolutionary events an
d concordant evidence from other octodontoid rodents suggest temporal diffe
rences among the outcroppings of the Cerro Azul Formation in central Argent
ina.