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.

Key words: Mammalia, Metatheria, Didelphimorphia, Paucituberculata, systematics, historical biogeography, Miocene, Brazil.

Narla S. Stutz [narlasstutz@gmail.com; ORCID: https://orcid.org/0000-0002-1937-3902 ], Programa de Pós-Graduação em Geociências, Universidade Federal do Rio Grande do Sul, Av. Bento Gonçalves 9500, 91501-970, Porto Alegre, Rio Grande do Sul, Brazil, and Laboratoire de Paléontologie, Institut des Sciences de l’Évolution de Montpellier (ISE-M, UMR 5554, CNRS/IRD), Université de Montpellier, Place Eugène Bataillon, 34095, Montpellier, France. Patricia Hadler [patricia.hadler@ufsc.br; ORCID: https://orcid.org/0000-0003-4897-3111 ], Laboratório de Paleontologia, Universidade Federal de Santa Catarina, Campus Universitário s/n, 88040-900, Florianópolis, Santa Catarina, Brazil. Francisco R. Negri [frnegriufac@gmail.com; ORCID: https://orcid.org/0000-0001-7396-0334 ], Laboratório de Paleontologia, Campus Floresta, Universidade Federal do Acre, Estrada do Canela Fina Km 12, 69980-000, Cruzeiro do Sul, Acre, Brazil. Laurent Marivaux [laurent.marivaux@umontpellier.fr; ORCID: https://orcid.org/0000-0002-2882-0874 ] and Pierre-Olivier Antoine [pierre-olivier.antoine@umontpellier.fr; ORCID: https://orcid.org/0000-0001-9122-1818 ], Laboratoire de Paléontologie, Institut des Sciences de l’Évolution de Montpellier (ISE-M, UMR 5554, CNRS/IRD), Université de Montpellier, Place Eugène Bataillon, 34095, Montpellier, France. François Pujos [fpujos@mendoza-conicet.gob.ar; ORCID: https://orcid.org/0000-0002-6267-3927 ], Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), and Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales (IANIGLA), CONICET-UNCUYO-Mendoza, Av. Ruiz Leal s/n, Parque Gral. San Martín, 5500, Mendoza, Argentina. Tiago R. Jacó [jaco.tiago@gmail.com; ORCID: https://orcid.org/0000-0002-5903-4673 ], Programa de Pós-Graduação em Sistemática e Conservação da Diversidade Biológica (PPGSCBIO), Secretaria do Meio Ambiente e Infraestrutura do Rio Grande do Sul, Universidade Estadual do Rio Grande do Sul, R. Dr. Salvador França 1427, 90690-000, Porto Alegre, Rio Grande do Sul, Brazil. Emmanuelle M. Fontoura [emmanuelle.fontoura@acad.ufsm.br; ORCID: https://orcid.org/0000-0002-3907-618X ], Programa de Pós-Graduação em Biodiversidade Animal (PPGBA), Universidade Federal de Santa Maria, Av. Roraima 1000, 97105-900, Santa Maria, Rio Grande do Sul, and Centro de Apoio à Pesquisa Paleontológica da Quarta Colônia (CAPPA), Universidade Federal de Santa Maria, R. Maximiliano Vizzotto 598, 97230-000, São João do Polêsine, Rio Grande do Sul, Brazil. Leonardo Kerber [leonardokerber@gmail.com; ORCID: https://orcid.org/0000-0001-8139-1493 ], Centro de Apoio à Pesquisa Paleontológica da Quarta Colônia (CAPPA), Universidade Federal de Santa Maria, R. Maximiliano Vizzotto 598, 97230-000, São João do Polêsine, Rio Grande do Sul, Brazil. Annie S. Hsiou [anniehsiou@ffclrp.usp.br; ORCID: https://orcid.org/0000-0003-2392-6191 ], Laboratório de Paleontologia, Universidade de São Paulo, Av. Bandeirantes 3900, 14040-901, Ribeirão Preto, São Paulo, Brazil. Roberto Ventura Santos [robertoventurasantos@gmail.com; ORCID: https://orcid.org/0000-0001-6071-8100 ] and André M. V. Alvim [andre.mavaal@gmail.com; ORCID: https://orcid.org/0000-0001-5050-4977 ], Laboratório de Geocronologia, Instituto de Geociências, Universidade de Brasília (UnB), Campus Universitário Darcy Ribeiro ICC - Ala Central, 70910-900, Brasília, Distrito Federal, Brazil. Ana Maria Ribeiro [ana-ribeiro@sema.rs.gov.br; ORCID: https://orcid.org/0000-0003-4167-8558 ], Seção de Paleontologia, Museu de Ciências Naturais, Secretaria do Meio Ambiente e Infraestrutura, R. Dr. Salvador França 1427, 90690-000, Porto Alegre, Rio Grande do Sul, and Programa de Pós-Graduação em Geociências, Universidade Federal do Rio Grande do Sul, Av. Bento Gonçalves 9500, 91501-970, Porto Alegre, Rio Grande do Sul, Brazil.