Résumé
Terrestrial vertebrates provide important clues about the late Cenozoic faunal evolution in South America, and particularly the late Neogene history of lowland Amazonia. Many fossil mammals have been recovered from outcrops in the drainage basins of the Jurua, Purus and Acre Rivers, at the convergence of the Brazilian, Peruvian and Bolivian borders. Most of these fossils originate from the Upper Solimoes Formation (Late Miocene) in the Acre and Amazonas States in Brazil, as well as from adjacent regions of Bolivia and Peru. Here we review the terrestrial vertebrate fauna from the Tertiary of western Amazonia, with special emphasis on the Solimoes Formation fauna(s), as presented for more than 20 years by the Federal University of Acre palaeontological team. The inferred age, usually based on faunal assemblage and palynostratigraphy, is still controversial, although generally considered Late Miocene as a whole (Huayquerian-Mesopotamian South America Land Mammal Ages [SALMA]), i.e. 9.0-6.5 Ma, on the basis of mammal remains, such as caviomorph Rodentia, Xenarthra and toxodontid Notoungulata. These herbivore clades dominated the terrestrial environment throughout this period, as emphasized by their unusually large body size as well as their numerical predominance with respect to other mammals. Comparison of the Solimoes Formation fauna with coeval South American vertebrate faunas demonstrated strong taxonomic affinity with those from the Ituzaingo (Mesopotamian - Argentina), Camacho (Uruguay) and Urumaco (Venezuela) formations. Recent studies on evolutionary morphology of terrestrial mammals from Acre Basin (e. g. tardigrade Xenarthra) evidenced some similarities with older South American assemblages, i.e. documenting Laventan (late Middle Miocene - Colombia) and even Santacrucian (late Early Miocene - Argentina) SALMAs. Such similarity maintains the Solimoes Formation age controversy. However, the Neogene of the Solimoes Formation mainly contains diverse assemblages of terrestrial vertebrates that illustrate the evolution of groups from North and South America. Local faunas from the upper Jurua River (Acre State, Brazil) and Fitzcarrald Arch (Ucayali, Peru) testify to the presence of lowland deposits referrable to Laventan SALMA, i.e. older than classic Huayquerian-Mesopotamian Solimoes/Acre faunas. These upper Jurua/Fitzcarrald faunas document another moment in the history of Neogene terrestrial mammals of Amazonia.