Late middle Miocene caviomorph rodents from Tarapoto, Peruvian Amazonia

Abstract

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.

Late middle Miocene Metatheria (Mammalia: Didelphimorphia and Paucituberculata) from Juan Guerra, San Martín Department, Peruvian Amazonia

“…The fossil-bearing layer is a microconglomerate lens 10 to 15 cm-thick, which was completely mined out, assigned to the lower member of the Ipururo Formation (Fm.) (Figure 2; Marivaux et al, 2020;Boivin et al, 2021). Fossil specimens documenting a wide array of organisms have been recovered from this locality, such as seeds, silicified wood, amber clasts (with no organic inclusions so far), decapod crustaceans, fishes (Chondrichthyes and Actinopterygii), anurans, turtles, crocodylomorphs, an unidentified bird, and several mammal orders.…”

“…Among those mammals, the cebid primate Neosairimi cf. fieldsi, nine rodent taxa, including the octodontoid Ricardomys longidens, the chinchilloids Microscleromys paradoxalis and M. cribriphilus, and the erethizontoid Nuyuyomys chinqaska (Marivaux et al, 2020;Boivin et al, 2021) have already been described in detail. Additionally, the interatheriine notoungulate Miocochilius sp., the didolodontid litoptern Megadolodus sp., as well as chiropterans, sirenians and xenarthrans have been preliminarily identified.…”

“…Additionally, the interatheriine notoungulate Miocochilius sp., the didolodontid litoptern Megadolodus sp., as well as chiropterans, sirenians and xenarthrans have been preliminarily identified. Based on its fauna, TAR-31 was dated as late middle Miocene in age (Laventan; Marivaux et al, 2020;Boivin et al, 2021) (Figure 2). TAR-31 is further situated stratigraphically ~110 m above another vertebrate locality in the same section (TAR-16, Fig.…”

“…Only a few Miocene fossil mammal-bearing localities are known to depict Miocene faunas at tropical latitudes of South America. These include the Castillo, Querales, Socorro, and Urumaco formations in Venezuela (various localities, early, middle and late Miocene in age; Quiroz and Jaramillo, 2010;Sánchez-Villagra et al, 2010;Rincón et al, 2014;Moreno et al, 2015); Acre basin in Brazil (various localities, late Miocene in age; Negri et al, 2010;Bissaro-Júnior et al, 2019); Madre de Dios (MD-67 locality, early middle Miocene in age; Antoine et al, 2013), Fitzcarrald local fauna (various localities, late middle Miocene in age; Tejada-Lara et al, 2015), Tamshiyacu (late middle Miocene; Salas-Gismondi et al, 2015), Contamana (various localities spanning the early-early late Miocene; Antoine et al, 2016), and Juan Guerra area (locality of TAR-31; Marivaux et al, 2020;Boivin et al, 2021) in Peru; as well as in Colombia with the Castilletes Formation and the outstanding La Venta fauna Suárez et al, 2016). The best studied of these fossil communities is La Venta, which is represented by dozens of fossil-bearing localities of the Honda Group at the Magdalena Valley, spanning 13.5-11.6 Ma (e.g., Montes et al, 2021).…”

“…The present study aims at reporting fossil metatherians recovered from the locality of TAR-31, in Peruvian Amazonia, dated as late middle Miocene (Laventan) in age by mammalian biostratigraphy (Marivaux et al, 2020;Boivin et al, 2021), in order to i) part address the regional gap of knowledge regarding metatherians, ii) depict local paleoenvironments, and iii) provide paleobiogeographic insights in northern South America during the middle Miocene. Additionally, U-Pb on zircon grains ages were obtained to independently constrain the age and further reveal the provenance of the concerned sediments at a Panamazonian scale.…”