A new fossil Phyllotine (Rodentia : Muridae) from northwestern Argentina and relationships of the Reithrodon group

We describe an extinct murid, assigned to the tribe Phyllotini, from the la te Pleistocene (Tafi del Valle Formation) of La Angostura (26 degrees 55'30 " S, 65 degrees 41'50 " W; 1,900 m elevation) in northwestern Tucuman Prov ince, Argentina. The new genus is characterized by very hypsodont molars wi th flat crowns and simplified occlusal structure, upper incisors with a med iolateral groove, a straight premaxillary-maxillary suture, and high zygoma tic plate with a small spine on its anterodorsal edge. Phylogenetic analyse s including fossil and living members of the Reithrodon group show that the new genus is the sister taxon to the Reithrodon-Neotomys-Euneomys clade. T he paleoenvironmental and paleogeographic significance of the new genus is discussed within the context of the climatic changes that occurred during t he late Pleistocene in southern South America. The new phyllotine would hav e Lived in high-elevation grasslands, which today occur >1,000 m higher und er cold and dry climatic conditions than those of the last glacial maximum.