Phylogenetic affinities of the late Miocene echimyid †Pampamys and the age of Thrichomys (Rodentia, Hystricognathi)

Phylogenetic affinities of the late Miocene echimyid dagger Pampamys emmonsae Verzi, Vucetich, and Montalvo, 1995 (Huayquerian South American Land Mammal Age, central Argentina), were analyzed. In the most-parsimonious tree obtained, subfamilies of Echimyidae were nonmonophyletic (except for Dactylomyinae). Two major clades were recovered. One of them included the living fossorial Eumysopinae and the extinct dagger Theridomysops. The other clade grouped the terrestrial eumysopines Thrichomys (punare) and Proechimys- Trinomys (spiny rats), and the arboreal eumysopines Mesomys (spiny tree-rats) + Echimyinae-Dactylomyinae. dagger Pampamys was the sister genus of Thrichomys, suggesting the Huayquerian South American Land Mammal Age (>6.0 million years ago [mya] by biochronology) as a minimum age for the origin of the living genus. Both major echimyid clades recognized here are represented by simplified-molared species in the Huayquerian South American Land Mammal Age. This would be related to the expansion of open environments during the late Miocene, and the geographical bias of the fossiliferous Huayquerian deposits exposed mostly in southern South America.