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The Neogene strata of the Solimões Formation (northern Brazil) have revealed an astonishing diversity of extinct caviomorph rodents. The main exposures of this formation are found along the Juruá, Acre, and Purus rivers, and some road cuts in the State of Acre. In this paper, we reported a new locality containing a rodent assemblage. The outcrop (Coqueiro locality) is located in the Envira River, central region of State of Acre, Brazil. During fieldwork in 2010 and 2019, several isolated cheek teeth and bones of mammals were recovered in conglomeratic levels from this locality. Here, we described specimens assigned to Cardiatherium sp. (Caviidae: Hydrochoerinae), Potamarchus sp. and cf. Pseudopotamarchus (Dinomyidae: Potamarchinae), and Neoepiblema sp. (Neoepiblemidae). The locality is not yet dated by radiometric methods but based on the biostratigraphic information of the taxa here reported, we suggest that the fossil-bearing levels of this locality were deposited during the Late Miocene. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Recently, the fossil record of rodents from southwestern Brazilian Amazonia has been reviewed with regards to its diversity as well as its ecological relationships. In the reviews, the necessity to report new specimens collected with stratigraphic control was stated. Here, a new dinomyid specimen collected during a 2015 expedition to the Niterói locality, Acre River, is reported. The material is a fragment of skull with the right P4-M1 and the left P4-M2 preserved. The cheek teeth are protohypsodont, a characteristic employed to differentiate Potamarchinae dinomyids from the euhypsodont dinomyids Eumegamyinae and Tetrastylinae. The occlusal surface of the cheek teeth is composed of lophs with interruptions, showing little wear, which suggests that the specimen is not fully ontogenetically developed. The specimen has a unique combination of characters (protohypsodont and pentalophodont cheek teeth, with the leading edges of similar thickness to the trailing edges, and presence of a groove on the bottom of the infraorbital foramen) not present in other known dinomyids, which led us to erect a new taxon. The abundant and diverse fossil record of protohypsodont dinomyids suggests that an important radiative event may have occurred during the middle-late Miocene of northern South America. http://zoobank.org/urn:lsid:zoobank.org:pub:E082C3C6-47B6-4D83-9009-A64879AAFC7Ahttp://www.zoobank.org/NomenclaturalActs/16235A7B-A261-445E-8DD4-940AB21DCB06 [ABSTRACT FROM AUTHOR]

The fossil rodents from the southwestern Amazonia of Brazil have been studied since the first half of the 20th century. Several caviomorph rodents were reported for the Neogene of this region, mainly neoepiblemids and dinomyids. Until recently, the record of dinomyids in the Solimões Formation (Late Miocene) was predominantly based on a few isolated teeth, which made it difficult to make more accurate taxonomic identifications due to the scarcity of diagnostic characters. Here, new remains, more complete than those previously reported, of potamarchine dinomyids from the Neogene of Brazil are described. A new species of Potamarchus and a new genus and species of a Potamarchinae are erected. In addition, new material of Potamarchus murinus and Potamarchus sp. is identified. These data suggest a higher diversity of dinomyids in in the western Amazonia than previously supposed. [ABSTRACT FROM AUTHOR]

A rich assemblage of fossil sloths is recognized in the southwestern Brazilian Amazon, Upper Solimões Formation (Acre Basin), and represents some of the most diverse Folivora fauna from the Late Miocene of tropical South America. Here, we have used a multiproxy approach using carbon (δ 13C sc) and oxygen (δ 18O sc) isotope compositions of bioapatite structural carbonate, stereomicrowear, ecomorphological indices (relative muzzle width, RMW and occlusal surface area, OSA), and body mass estimates in order to suggest the habitats and diet of the mylodontids (Octodontobradys puruensis, Urumacotherium campbelli , Pseudoprepotherium venezuelanum and Mylodontinae gen. et. sp. nov.) and the nothrotheriid (cf. Mionothropus) ground sloths from localities along the banks at the Purus and Acre rivers in Amazonas and Acre states. The isotopic results (δ 13C sc = −13.2 ± 1.2 ‰; δ 18O sc = +24.7 ± 0.8 ‰) indicated a consistently C 3 plant diet in open-canopy woodland and closed-canopy forest habitats during warm conditions across the Tortonian ages (∼10 and 8.5 Myr). U. campbelli (Urumacotherium sp., bm: 605 kg; Niterói Site) and cf. Mionothropus (bm: 163 kg; Acre 5 Site) possibly had specialized browsing habits (folivorous/frugivorous), due to the few coarse scars in relatively polished tooth surfaces and elongate skull with narrow muzzle, respectively. Both taxa, as also P. venezuelanum (bm: 733 kg; Niterói Site), showed a low OSA values suggesting limited oral food processing offset by higher fermentation capacity and/or lower metabolic requirements. Efficient capacity for oral food processing and a generalized browsing habit with consumption of high intrinsic toughness and abrasiveness items were inferred for O. puruensis (bm: 526 kg; Talismã Site), resembling the pattern observed for the Pleistocene megathere Eremotherium laurillardi from the southwestern Amazon (Acre State). A non-selective browser diet was also supported for the Mylodontinae gen. et. sp. nov. specimen from Cavalcante Site; its similar dentary morphology to the bulk-feeder taxa implies that this individual could occasionally eat C 3 herbaceous/grasses. • Amazonian ground sloths had C 3 diet in woodland/forest habitats during warm conditions in the Tortonian age; • Folivorous/frugivorous diets were estimated for U. campbelli and cf. Mionothropus ; • Specialist taxa had limited oral food processing offset by higher fermentation capacity and lower metabolic requirements; • Efficient capacity for oral food processing and a diet composed of high abrasiveness items were estimated for O. puruensis ; • A non-selective browser diet with occasional consumption of C 3 herbs was supported for Mylodontinae gen. et. sp. nov. [ABSTRACT FROM AUTHOR]

Caviomorphs are the neotropical hystricognathous rodents (Ctenohystrica: Hystricognathi: Caviomorpha). Octodontoidea are today the richest and most speciose clade of caviomorphs. Their fossil record also reveals a wide array of extinct species, including Acarechimys, a taxon with a widespread South American distribution and extensive temporal range. This genus comprises at least five species documented in deposits ranging from the late Oligocene to the Middle Miocene. Here, we report the discovery of a new species of Acarechimys from Upper Miocene deposits of the Envira River (PRE06 outcrop), situated in the Acre State, western Brazilian Amazonia. The new species differs from the other species of the genus in having lower molars with a strong posterior arm of the metaconid, the presence of a mesostylid (usually prominent) and a neomesolophid forwardly directed and connected to the metalophulid I on m1 but not on m2–3, and the absence of posterior arm of the protoconid. This taxon represents the youngest known species of the Acarechimys lineage to date. Its occurrence in Western Amazonia strengthens support for the hypothesis that South American rodent lineages survived longer during the Neogene at low latitudes than in the southern regions of the continent. [ABSTRACT FROM AUTHOR]

Much of what we know about late Miocene vertebrates from the Brazilian Amazonia is based on the fossil record from several sites in the Solimões Formation. The Talismã site, one of the most important for vertebrate fossils in the formation, has produced an abundant and diverse fauna dominated by crocodylians, mammals, and turtles, but small vertebrates are still underrepresented. We report some isolated bones recovered from this site, providing the first Neogene records of anurans in Brazil. Two taxa are recognized, a distinct species of Pipa, and an unidentified species of the Rhinella clade, both of which are members of the extant Amazonian batrachofauna. These new fossils expand our knowledge of the late Miocene anuran assemblages from the region and contribute to the paleoenvironmental reconstruction of the site. [ABSTRACT FROM AUTHOR]

Abstract The fossiliferous beds of the Solimões Formation, western Brazilian Amazon have yielded several vertebrate fossils that are key to understand the evolution of Neotropical biotas. Although this sedimentary unit has been studied for more than two centuries, no absolute dates are available so far, preventing more precise bio/chronostratigraphic interpretations and broader comprehension of the biotic/geological events that affected this northern portion of South America during the Neogene. Here, we present the first Neogene radioisotopic dates for the Brazilian Amazon, via U-Pb dating of detrital zircon from two classical sites. Both samples have small proportions of relatively young zircon grains, the dates from which are the maximum ages of deposition. LA-ICPMS analysis of two grains from the Niterói locality yielded a weighted mean of 8.5 ± 0.5 Ma and CA-TIMS analysis of two grains from the Talismã locality yielded a weighted mean of 10.89 ± 0.13 Ma. These maximum deposition ages are in the Tortonian stage, late Miocene, confirming the age previously inferred based on biochronological data. Graphical abstract Unlabelled Image Highlights • First detrital zircon U-Pb data of Upper Miocene sedimentary rocks in the Acre basin, Solimões Fm., Brazil. • Zircon U-Pb age from fossil bearing localities indicates a c. 8.5 Ma and a c. 10.89 Ma as the maximum ages of deposition. • The age constraints shed new lights on the faunal composition and the temporal resolution of Solimões Fm. [ABSTRACT FROM AUTHOR]

Several studies have reported Miocene shallow-marine incursions in the Pebas Megawetland system (Western Amazonia) based on paleontological and sedimentological evidence. Only a few publications restricted to Middle and Late Miocene fossils outcropping in the Iquitos (Peru), Benjamin Constant and Eirunepé (Brazil) areas have provided isotopic evidence to test these incursions. In this study, we present new carbon, oxygen, and strontium (87Sr/86Sr ratios) isotopic data of macrofossils (pacu and ray teeth, crab claws and oysters), and microfossils (ostracods and foraminifera) from reported lower to lower upper Miocene sedimentary rocks of Western and Eastern Amazonian (Peru and Brazil), mainly from shallow-marine deposits. It was also analyzed present-day organisms from distinct environments (beach, sea, riverine, and estuary) and compared these results with Miocene fossils. While C and O isotopic compositions indicate that Western Amazonia fossils display an isotopic composition similar to the present-day continental, limnic and riverine, environments (−17‰ to −5.61‰ for δ13C and − 10.14‰ to −1.92‰ for δ18O), Eastern Amazonia fossils display C and O isotopic compositions comparable to those from seawater environments (−2.53‰ to −0.72‰ for δ13C and − 4.85‰ to −1.76‰ for δ18O). We further used the 87Sr/86Sr isotopic composition of the fossils to estimate paleosalinity conditions. The 87Sr/86Sr isotopic compositions indicates that Eastern Amazonian water bodies of the Pirabas Formation (Marajó Basin) varied from mesohaline to marine conditions. In contrast, Early Miocene Western Amazonian water bodies of the Pebas Megawetland System (PMWS) are characterized by freshwater conditions. Nonetheless, in Middle and Early Late Miocene, oligohaline conditions are found in the Peruvian part of the PMWS. Paleosalinity estimates of the Brazilian part of the PMWS are less constrained and might indicate a salinity range between freshwater or oligohaline conditions. Our isotopic data suggest the PMWS was occasionally submitted to oligohaline conditions during Middle and Early Late Miocene shallow-marine incursions. We suggest that Miocene shallow-marine incursions in Western Amazonia at this time were characterized by transitional paleoenvironments, reconciling isotopic, sedimentological and paleontological evidences. • 374 Miocene Amazonian fossils attributed to shallow marine intervals analyzed. • Isotopic analyses of lower Miocene fossils from Eastern Amazonia indicate mesohaline to seawater conditions. • Isotopic data of middle and lower upper Miocene fossils from Peru yields oligohaline conditions in the Pebas Megawetland. • Marine incursions in Western Amazonia studied here occurred in transitional paleoenvironments with low seawater contribution. [ABSTRACT FROM AUTHOR]