A Tropical Spiny Tree Rat (Rodentia, Echimyini) in the Late Quaternary of Southern South America (Argentina): Paleoenvironmental and Paleogeographic Implications

Abstract

We report the first occurrence of an arboreal spiny rat of the tribe Echimyini in the EarlyHolocene of southern South America. The specimen, a lower deciduous premolar, wasrecovered from fluvial deposits exposed along the right bank of Doll Creek, in northeasternArgentina. Morphological comparisons indicate strong affinities with the extant Amazoniangenus Lonchothrix, although the fossil exhibits distinct traits such as thicker enameland a transverse, short posterior mesofossettid. The available evidence of strong climaticniche conservatism in Echimyini supports its interpretation as an indicator of the transientpresence of humid, Amazonian-like forests in the region around 10,000 years ago. Sedimentologicaland stratigraphic evidence correlates this warming phase with an Early Holocenetransgression in the Paraná Delta. The absence of aff. Lonchothrix in the recent fauna may bethe result of a post-optimum extinction event triggered by a drier phase during the MiddleHolocene. This discovery provides novel evidence for a short-lived biogeographic connectionbetween Amazonia and the southern cone during a climatic window of expansion fortropical biotas. It also highlights the role of the fossil record of Echimyidae as a sensitiveproxy for reconstructing paleoenvironmental changes in temperate South America.