Search

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]

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]

The geological history of the Amazon River is a complex story driven by geodynamic processes operating in the South American plate. In spite of recent research, the pre-Neogene structure of Amazon paleodrainage is still underconstrained. A recent study has suggested that the western Amazonian paleodrainage system was reversed, cratonic in origin during the Cretaceous. However, the extent and duration of this system are not well-constrained. To add new constraints, we investigated the sources of Cretaceous sedimentary rocks in the Brazilian Acre and Peruvian Madre de Dios basins, based on major and trace element concentrations, Sm–Nd isotopic compositions, and U–Pb detrital zircon dating. The late Cretaceous samples of the Acre Basin have ε Nd (0) values between −21.2 and −8.4 and zircon grains derived from terranes situated in the easternmost part of the Amazonian Craton: Ventuari–Tapajos (2.0–1.82 Ga) and Rio Negro–Juruena (1.82–1.54 Ga). In contrast, the Madre de Dios Basin samples have ε Nd (0) values ranging from −15.2 to −7.1 and a wide range of U–Pb zircon age distributions. The samples from the northern part of the basin (MD234 and MD238) are dominated by zircon ages between 0.9 and 1.3 Ga (Grenville/Sunsás, 30 %–43 %) and 0.5 and 0.7 Ga (Brazilian/Pampean, 26 %–16 %) with felsic provenance. The oldest MD234 sample also shows a dominant contribution from Paleozoic zircon (20 %). On the other hand, the samples from the southern part of the Madre de Dios Basin (samples MD-2019-4A; MD-2019-10; MD-2019-13; MD-2019-11D and MD-2019-12A) have U–Pb age distributions dominated by zircon ages between 0.9 and 1.3 Ga (Grenville/Sunsás, 30 %–45 %) and 1.54 and 1.3 Ga (Rondonia–San Ignácio, 16 %–43 %), pointing to a cratonic origin for these sedimentary rocks. To elucidate the distinction in provenance between the samples from the northern and southern parts of the Madre de Dios Basin, we suggest that a structural barrier (the Madidi Arch (?)) was active during the late Cretaceous. In this scenario, the northern part of the Madre de Dios Basin had similar sedimentary sources as the nearby basins like Huallaga, Bagua, Ucayali, and Marañón, whereas, in the southern part of the basin, sedimentation was influenced by local sources. Together with previously published studies, these data indicate that the continent-wide cratonic drainage developed between the Cenomanian and Maastrichtian in response to the Purus Arch uplift was probably driven by a geodynamic process related to the post-rift opening of the Atlantic Equatorial Ocean. [ABSTRACT FROM AUTHOR]

We report the first radiocarbon datings and carbon (δ13C) and oxygen (δ18O) stable isotopes data to reconstruct the paleoecology of medium to large herbivorous mammals from late Quaternary of southwestern Amazon (Acre and Rondônia states, Brazil). AMS 14C dates for Neochoerus sp. (29,072 - 27,713 Cal yr BP), Notiomastodon platensis (25,454 - 24,884 Cal yr BP) and Eremotherium laurillardi (11,320 - 11,131 Cal yr BP) support the Lujanian ages. All fossils have low δ13C and δ18O isotopic values that suggest C 3 -dominated environments from closed canopy forests to wooded savannas, agreeing with paleovegetation reconstitution. Most species were browsers (pi C 3 =100%; Niche breadth, B A =0), where the key species with the largest body mass, N. platensis (∼6,300 kg) and E. laurillardi (∼3,500 kg), possibly had a more generalized browser diet in closed-canopies to woodlands. Their diet distinguished from the C 3 /C 4 generalist Trigodonops lopesi (∼1,900 kg), which foraged in wooded savannas (p i C 3 =70%; B A =0.72), similarly with its relative Toxodon platensis (∼1,800 kg) that had a browse-dominated mixed feeder diet (p i C 3 ≥ 84%, B A ≤ 0.38) in Peruvian and Bolivian Amazon localities. Palaeolama major (∼280 kg) was possibly a strictly folivorous within forest canopies, whereas Tapirus sp. (∼250 kg) and Mazama sp. (∼40 kg) were browsers in closed-canopies to woodlands. Holmesina rondoniensis (∼120 kg) was a browser but not restricted, where could also feed on herbaceous from understories in woodlands, and Neochoerus sp. (∼200 kg) feeding predominantly herbaceous plants in wooded savannas (pi C 3 =∼69%; B A =0.75). We estimate that the interspecific competition could have been avoid by different feeding strategies, although more investigations are still needed to better understand their ecological interactions in the habitats of the southwestern Amazon during the late Quaternary. • AMS 14C dates support Lujanian ages for the mammal fossils in southwestern Amazon. • δ13C and δ18O data suggest closed canopy forest to wooded savanna habitats. • Most species were browsers feeding on leaves/fruits of wood plants (pi C 3 = 100%). • Trigodonops lopesi and Neochoerus sp. consumed more proportions of herbaceous plants (p i C 4 = ∼30%). • Different feeding strategies and habitat use avoided interspecific competitions. [ABSTRACT FROM AUTHOR]