A new fossil rodent assemblage from the Solimões Formation (upper Miocene), Acre, Brazil

Abstract

International audienceCaviomorpha is a South American hystricognath clade with great taxonomic and phenotypic diversity. Their stratigraphic distribution ranges from the middle Eocene to the present times. In the Solimões Formation, northern Brazil, a rich Neogene fossil record has been documented over the last years. Here, we report preliminary data about a new fossiliferous assemblage recovered in recent fieldwork in the Envira River, State of Acre, Brazil. The specimens were recovered in 2010 and 2019 from Neogene sedimentary strata exposed in this river. The fossils were found using a screen-washing method with an aqueous hydrogen peroxide solution and subsequent screening in a stereoscopic magnifying glass. After these procedures, the specimens are being scanned with a micro-CT. The preliminary analysis identified a mandible with premolar and molars and many isolated molariform teeth. Our results suggest the presence of Octodontoidea (including Acarechimys-like), Erethizontoidea, Chinchilloidea (Scleromys-like dinomyids and a potamarchine; and Neoepiblemidae), and Cavioidea (Hydrochoerinae). Based on previous records of Solimões Formation, the presence of potamarchines, neoepiblemids, and hydrochoerines is in accordance with a late Miocene age for these strata (typical Acre fauna). Although fossils have not yet been identified at a less inclusive level, it is possible to observe that this is the most diverse assemblage of Neogene rodents from the Brazilian Amazon