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

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

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

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

Late middle Miocene caviomorph rodents from Tarapoto, Peruvian Amazonia

Miocene deposits of South America have yielded several species-rich assemblages of caviomorph rodents. They are mostly situated at high and mid- latitudes of the continent, except for the exceptional Honda Group of La Venta, Colombia, the faunal composition of which allowed to describe the late middle Miocene Laventan South American Land Mammal Age (SALMA). In this paper, we describe a new caviomorph assemblage from TAR-31 locality, recently discovered near Tarapoto in Peruvian Amazonia (San Martín Department). Based on mammalian biostratigraphy, this single-phased locality is unambiguously considered to fall within the Laventan SALMA. TAR-31 yielded rodent species found in La Venta, such as the octodontoid Ricardomys longidens Walton, 1990 (nom. nud.), the chinchilloids Microscleromys paradoxalis Walton, 1990 (nom. nud.) and M. cribriphilus Walton, 1990 (nom. nud.), or closely-related taxa. Given these strong taxonomic affinities, we further seize the opportunity to review the rodent dental material from La Venta described in the Ph.D. volume of Walton in 1990 but referred to as nomina nuda. Here we validate the recognition of these former taxa and provide their formal description. TAR-31 documents nine distinct rodent species documenting the four extant superfamilies of Caviomorpha, including a new erethizontoid: Nuyuyomys chinqaska gen. et sp. nov. These fossils document the most diverse caviomorph fauna for the middle Miocene interval of Peruvian Amazonia to date. This rodent discovery from Peru extends the geographical ranges of Ricardomys longidens, Microscleromys paradoxalis, and M. cribriphilus, 1,100 km to the south. Only one postcranial element of rodent was unearthed in TAR-31 (astragalus). This tiny tarsal bone most likely documents one of the two species of Microscleromys and its morphology indicates terrestrial generalist adaptations for this minute chinchilloid

New records of marsupials from the Miocene of Western Amazonia, Acre, Brazil

The Amazonian region covers a significant part of the South American continent and harbors outstanding biodiversity. However, much of its history is still unknown. This situation has begun to change with paleontological field efforts over the last decades, which have been proving that fossils can be common in this region. Despite their great current species richness and abundance in the area today, marsupials have a sparse fossil record, restricted to a few specimens from handful Cenozoic Amazonian localities. Here we present new records of fossil marsupial teeth from the Solimões Formation (lower Eocene–Pliocene), on the Juruá and Envira riverbanks (Acre, Northwestern Brazil). The localities investigated yield at least four distinct didelphid didelphimorphians at PRE 06 (Ponto Rio Envira: Marmosini ?Marmosa sp., Didelphis cf. D. solimoensis, Thylamys? colombianus, plus unidentified didelphids), and two paucituberculatans from the Juruá River localities (Ponto Rio Juruá: the palaeothentid Palaeothentinae indet. at PRJ 25 and PRJ 33’, and Abderitidae indet. from PRJ 33). In agreement with the associated mammalian faunas, most of the didelphids, except for Thylamys? colombianus from PRE 06, indicate a (?early) Late Miocene age for this locality. Conversely, the abderitid specimens found in situ at PRJ 33 would match a Middle Miocene age. The palaeothentids found at PRJ 25 and PRJ 33’ localities cannot be considered for biostratigraphic inferences, since they were found outside a stratigraphic context. Nevertheless, these paucituberculatans considerably add to our knowledge, as they are the first ever recorded in Brazilian Amazonia