Abstract
Metatheria probably originated in the Jurassic in today’s Asia–North America. In the Late Cretaceous, metatherians dispersed from North America to South America, with their earliest record in early Paleocene of Argentina. The phylogenetic relationships of Metatheria remain a problematic. The crown-group Marsupialia is divided into: Australidelphia, with the extant orders Dasyuromorphia, Peramelemorphia, Diprotodontia and Notoryctemorphia and a fossil order from Australasia, plus the South American order Microbiotheria and the Polydolopimorphia (extinct); and "Ameridelphia," a polyphyletic taxon containing the orders Didelphimorphia and Paucituberculata inhabiting South America. Furthermore, South America had a remarkable past diversity of metatherians, currently extinct. The Cenozoic evolutionary history of metatherians in South America is marked by periods of diversification and extinctions, recorded in some exceptional sites, especially in the south of the continent. However, there are large gaps in the fossil record of Metatheria in South America, mainly for the northern portion of the continent, where they are reported for some Eocene–Miocene deposits from Peru, Brazil, Venezuela and Colombia. Thus, the present thesis aimed to identify fossil remains of Metatheria from Brazilian (Upper Juruá and Envira Rivers, Solimões Formation, Acre Basin) and Peruvian (Contamana, Huallaga and Atalaya Basin) localities of the Amazon region, Eocene–Miocene interval, to contribute to the knowledge of Metatheria systematics and evolutionary history. At the TAR-31 locality, Peru, Middle Miocene (Laventan, ~13 Ma), 3 metatheria taxa were identified: the didelphid 'Thylamys' cf. 'T.' colombianus, and the Paucituberculata aff. Palaeothentes and Pitheculites ipururensis sp. nov. In the Acre localities 4 taxa of didelphids were found at the locality PRE 06, Envira River: Marmosini cf. Marmosa, Didelphis cf. D. solimoensis, 'Thylamys' colombianus. In the Upper Juruá River localities, 2 taxa of Paucituberculata were identified: Palaeothentidae Palaeothentinae indet. (PRJ 25 and PRJ 33', both out of stratigraphic context) and the Abderiditae Abderites sp. (PRJ 33, in situ. The didelphids from PRE 06 indicate a Late Miocene age for this outcrop. Abderites sp. suggests a Middle Miocene age for PRJ 33. Comparisons of these associations with temporally correlated Amazonian faunas indicate great similarity between TAR-31 and Acre, as well as with La Venta, confirming that western Amazonia was a unique biogeographic region for terrestrial mammals during the Middle Miocene, on the western margin of the Pebas Mega-Wetland System. Concerning the Paleogene localities studied, only members of the order Polydolopimorphia were studied, with the identification of 15 taxa, of the suborder Bonapartheriiformes, with Bonapartherioidea Prepidolopidae and Argyrolagoidea Argyrolagidae, plus the genus Wamradolops. The results obtained, in comparison with the literature, indicate that major turnovers occurred during the Eocene–Miocene in the Amazonian metatherian communities. Middle Eocene metatherian associations were predominantly composed of polydolopimorphians, with high diversity and abundance. A first turnover occurred around the Eocene–Oligocene transition, with a decrease in the abundance and diversity of polydolopimorphians (disappearance of Prepidolopidae and only the Argyrolagidae remaining) offset by an increase in paucituberculatans, represented only by the Palaeothentoidea, with great diversity and abundance during the Oligocene. In the early Miocene, the first Didelphimorphia are recorded and in the Late Miocene the second turnover occurs. The metatherian communities are then almost entirely composed of didelphids, which are represented by derived taxa very similar to the current groups. These results highlight the significant role of the Amazon region regarding the evolutionary history and paleobiogeography of metatherians during the Paleogene and Neogene.