A New fossil phyllotine (Rodentia, Sigmodontinae) from the late Pliocene in the Andes of northern Argentina

ABSTRACT

†Pardinamys humahuaquensis, a new genus and species of Phyllotini (Rodentia, Cricetidae), is described on the basis of 111 cranial, mandibular, and dental remains belonging to at least 29 individuals. The fossils were recovered from a microvertebrate assemblage found in late Pliocene deposits (between 3 and 2.5 Ma ago) from the Uquía Formation, central Jujuy Province, northwestern Argentina. †Pardinamys is morphologically intermediate between the extant genera Eligmodontia and Calomys and can be differentiated from these taxa by the combination of several traits, including short masseteric crest, with upper and lower ramus similarly developed; coronoid process well developed; anteromedian flexus in M1 only present in very young individuals, without any trace of anteromedian style; M1 and M2 with developed second minor fold; large M2 and M3; and metaflexus, paracone, and metacone of M3 well developed. The morphologic characteristics of the new genus and the other sigmodontines found in the Uquian assemblage (at least three extinct genera) suggest an important radiation before the establishment of the modern communities in the central Andean region and indicate the need for a reevaluation of the divergence-age estimates for the group. The recovered taxa indicate the presence of open environments during depositional times, within arid or semiarid conditions, unlike previous reconstructions for this geologic unit. The finding reveals the need for improving the fossil record of sigmodontines in the central Andean region and its importance to understanding the radiation of this group in a more inclusive South American context.

ACKNOWLEDGMENTS

We thank D. García López, P. Alonso, and J. Babot for their constructive discussions on aspects of taphonomy and geology of the Uquía Formation and V. Deraco and C. Madozzo Jaén for capable field assistance. P. Alonso helped in the description of geologic setting of the fossil in the stratigraphic column. We are grateful to D. García López and N. Gianinni for advice on the interpretation of the putative phylogenetic relationships of the new genera. We thank U. Pardiñas, who generously provided material of Eligmodontia and other phyllotines for comparisons, C. Lanzone for photographs of additional material of all species of this genus, S. Mc Laren (Carnegie Museum) for photographs of holotype of Andalgalomys olrogi, and D. García López for technical assistance in some figures. We are also grateful to J. Salazar-Bravo and an anonymous referee for revising previous versions of the manuscript. CIUNT (Consejo de Investigaciones de la Universidad Nacional de Tucumán) grant 26/G434 to P.E.O. and CONICET (Consejo Nacional de Investigaciones Científicas y Tecnológicas) supported this research.

Handling editor: Guillermo Rougier