Eumysops marplatensis Olivares and Verzi 2015 (Rodentia, Hystricognathi) from the Plio-Pleistocene of the Northern Pampa in Argentina: Paleoenvironmental and paleobiogeographic implications

The tribe Myocastorini (Caviomorpha, Echimyidae) currently comprises living species inhabiting Central America from Honduras and extending throughout South America to Patagonia, in a wide variety of environments. This clade is well represented in the late Miocene-Pleistocene fossil beds of central and northern Argentina. Its diversification at high latitudes during part of the Cenozoic would be linked to the rise of open and progressively drier environments. Here we report the record of a myocastorine lower deciduous premolar (dp4) from the locality of Casilda, Santa Fe Province, in central Argentina. The Casilda fossiliferous level is correlated with part of the lithostratigraphic sequence from the elevated San Guillermo block in western Santa Fe province and may be assigned to palustrine clays. Based on recent studies of sequential stratigraphy and lateral correlation, neotectonics, and new dating using Optically Stimulated Luminescence performed in the Northern Pampa geomorphological region, the deposits that overlie those clays have been considered to be the Middle Pleistocene in age. According to this interpretation, the fossil-bearing level corresponds to the Pliocene-Early Pleistocene sensu lato and thus, this specimen is the first vertebrate recorded in that age for the Santa Fe Province. Based on an exhaustive comparison with dp4 of different caviomorph species, the specimen is assigned to Eumysops marplatensis. The occurrence of this extreme open-habitat specialist at Casilda supports previous paleoenvironmental interpretations for the Northern Pampa that indicate open or semi-open environments for the PlioPleistocene. Furthermore, the presence of the three modern species of Eumysops, and other vertebrates, in the Northern and Southern Pampas geomorphological regions during the Pliocene-Early Pleistocene suggest a paleobiogeographic connection between both regions.

Automated summary

The study reports the fossil record of a myocastorine lower deciduous premolar (dp4) from central Argentina, confirming the presence of myocastorine species in the late Miocene and Pleistocene in this region. Based on stratigraphic studies and new dating techniques, the specimen is assigned to the Middle Pleistocene age, marking the first vertebrate recorded in that period in Santa Fe Province.