Sigmodont rodents (Mammalia; Muroidea; Sigmodontinae) from the Pliocene (early Blancan) Verde Formation, Arizona

Abstract

ABSTRACT Muroid rodents recovered from sediments of the Verde Formation, central Arizona, aged at about 4 Ma, include species belonging to the subfamily Sigmodontinae. These are Calomys (Bensonomys) arizonae (Phyllotini), Sigmodon medius and Prosigmodon holocuspis, new species (Sigmodontini), and Jacobsomys verdensis, new genus and species. The latter genus shares some dental characters with the Oryzomyini and Akodontini, and also with the extant South American genus Zygodontomys. The mid-Pliocene diversity of sigmodont rodents in the Verde Formation gives further evidence of a late Tertiary diversification of cricetids in southwestern North America, and also tends to support the idea that some differentiation of sigmodontines had taken place in North America prior to the establishment of the Panama land bridge between 2.5 and 3.5 Ma. However, the Verde rodents, which lived at 4 Ma, were too late to have been members of a postulated flotilla of cricetids reaching South America at 6 to 7 Ma.