La paleontología de los vertebrados en Argentina desde la segunda mitad del siglo XX hasta nuestros días: un estudio cuali-cuantitativo basado en Ameghiniana

The aim of this paper is to analyze the evolution of vertebrate paleontology in Argentina based on the journal Ameghiniana. Using all documents on vertebrate paleontology published in this journal during 1957-2014, items such as the number of paper published, the number of signatures (total and by paper), the percentage of man and woman authorships, first authors place of residence, the geographic and stratigraphic origin of fossils, and topics considered were analyzed. A total of 668 documents were included in the study. The results show an increasing trend in the number of documents and signatures per document along the span considered (the latter mainly from the ´80s to present day). Also, there is an increase in the number of man and woman authorships, in an even masculinized discipline but showing a promising trend towards gender parity/equality. There is a predominance of single and double authorships, and most contributions have Argentinian paleontologists as first authors (especially from La Plata). Regarding the stratigraphic origin, most papers are devoted to Cenozoic, and to the Neogene within it.  When main topics are considered, taxonomy papers predominate. Mammals (especially rodents and xenarthrans) followed by reptiles (particularly dinosaurs) are the most studied taxa. Fossils studied come mainly from Argentina (especially, from Patagonia, followed by those of the Pampean region). The results obtained are explained in the historical context in which the discipline has developed in Argentina.El objetivo de este trabajo es analizar la evolución de la Paleontología de Vertebrados en Argentina, tomando como fuente la revista Ameghiniana. Utilizando todos los documentos sobre Paleontología de Vertebrados publicados en dicha revista en el período 1957-2014, se cuantificaron aspectos como el número de trabajos publicados, el número de firmas (totales y por trabajo), los porcentajes de autores hombres y mujeres, la procedencia del primer autor, la procedencia geográfica de los fósiles, la representación de los grandes intervalos temporales (eras y períodos) y los temas considerados. Se analizaron un total de 668 documentos. Los resultados muestran a lo largo del periodo un incremento en el número de trabajos y en el número de autores por trabajo (esto último, fundamentalmente a partir de los ’80). Asimismo, se observa un incremento en la cantidad de autorías masculinas y femeninas, en una disciplina aun masculinizada pero que muestra una promisoria tendencia hacia la paridad/equidad de géneros. Predominan las autorías únicas y dobles. La mayoría de los documentos tienen investigadores argentinos como primeros autores (especialmente de La Plata). En relación con la representación de los grandes intervalos temporales, predominan los trabajos sobre el Cenozoico y, dentro de esta Era, del Neógeno. En cuanto a los temas principales, predominan los trabajos taxonómicos. Los taxones más estudiados son los mamíferos (fundamentalmente roedores y xenartros) y los reptiles (dinosaurios). Los fósiles considerados provienen principalmente de Argentina (especialmente de Patagonia, seguidos por los de la región Pampeana). Los resultados obtenidos son explicados en el contexto histórico en el que se ha desarrollado la disciplina en la Argentina

La paleontología de los vertebrados en Argentina desde la segunda mitad del siglo XX hasta nuestros días: un estudio cuali-cuantitativo basado en Ameghiniana

The aim of this paper is to analyze the evolution of vertebrate paleontology in Argentina based on the journal Ameghiniana. Using all documents on vertebrate paleontology published in this journal during 1957-2014, items such as the number of paper published, the number of signatures (total and by paper), the percentage of man and woman authorships, first authors place of residence, the geographic and stratigraphic origin of fossils, and topics considered were analyzed. A total of 668 documents were included in the study. The results show an increasing trend in the number of documents and signatures per document along the span considered (the latter mainly from the ´80s to present day). Also, there is an increase in the number of man and woman authorships, in an even masculinized discipline but showing a promising trend towards gender parity/equality. There is a predominance of single and double authorships, and most contributions have Argentinian paleontologists as first authors (especially from La Plata). Regarding the stratigraphic origin, most papers are devoted to Cenozoic, and to the Neogene within it.  When main topics are considered, taxonomy papers predominate. Mammals (especially rodents and xenarthrans) followed by reptiles (particularly dinosaurs) are the most studied taxa. Fossils studied come mainly from Argentina (especially, from Patagonia, followed by those of the Pampean region). The results obtained are explained in the historical context in which the discipline has developed in Argentina.El objetivo de este trabajo es analizar la evolución de la Paleontología de Vertebrados en Argentina, tomando como fuente la revista Ameghiniana. Utilizando todos los documentos sobre Paleontología de Vertebrados publicados en dicha revista en el período 1957-2014, se cuantificaron aspectos como el número de trabajos publicados, el número de firmas (totales y por trabajo), los porcentajes de autores hombres y mujeres, la procedencia del primer autor, la procedencia geográfica de los fósiles, la representación de los grandes intervalos temporales (eras y períodos) y los temas considerados. Se analizaron un total de 668 documentos. Los resultados muestran a lo largo del periodo un incremento en el número de trabajos y en el número de autores por trabajo (esto último, fundamentalmente a partir de los ’80). Asimismo, se observa un incremento en la cantidad de autorías masculinas y femeninas, en una disciplina aun masculinizada pero que muestra una promisoria tendencia hacia la paridad/equidad de géneros. Predominan las autorías únicas y dobles. La mayoría de los documentos tienen investigadores argentinos como primeros autores (especialmente de La Plata). En relación con la representación de los grandes intervalos temporales, predominan los trabajos sobre el Cenozoico y, dentro de esta Era, del Neógeno. En cuanto a los temas principales, predominan los trabajos taxonómicos. Los taxones más estudiados son los mamíferos (fundamentalmente roedores y xenartros) y los reptiles (dinosaurios). Los fósiles considerados provienen principalmente de Argentina (especialmente de Patagonia, seguidos por los de la región Pampeana). Los resultados obtenidos son explicados en el contexto histórico en el que se ha desarrollado la disciplina en la Argentina

A unique, Late Oligocene shrew-like marsupial from western Argentina and the evolution of dental morphology

<div><p>We describe a new metatherian mammal, <i>Fieratherium sorex</i> gen. et sp. nov., found in western Argentina (Quebrada Fiera locality, southern Mendoza Province), in Late Oligocene deposits (Agua de la Piedra Formation, Deseadan age). The only known specimen is a juvenile with fragments of both dentaries, the right maxilla and a fragment of the left premaxilla with dentition. The loci and the number teeth preserved suggest a dental formula of I?3/i3, C1/c1, P3/p3, M?3/m?3. <i>Fieratherium sorex</i> has a convergent shrew-like appearance and a unique combination of features among metatherians and other South American mammals of Palaeogene age, including the well-known faunas of Patagonia. An analysis of its phylogenetic affinities suggests that <i>Fieratherium</i> is the sister-group of the Paucituberculata. As already described by other authors for several mammalian taxa, the mainly Patagonian South American Palaeogene fossil record offers little information to understanding the evolution of northern lineages. <i>Fieratherium</i> may represent a taxon belonging to a lineage that had its origin in Neotropical regions, so far unrecorded in the southern region of South America.</p><p><a href="http://zoobank.org/urn:lsid:zoobank.org:pub:5F6D3A50-6345-4E66-BE3E-7FEF6CC66A9B" target="_blank">http://zoobank.org/urn:lsid:zoobank.org:pub:5F6D3A50-6345-4E66-BE3E-7FEF6CC66A9B</a></p></div

Biotic community and landscape changes around the Eocene–Oligocene transition at Shapaja, Peruvian Amazonia: Regional or global drivers?

Since 2012, we have investigated a stratigraphic section encompassing the late Eocene–earliest Oligocene interval at Shapaja (Tarapoto area, Peruvian Amazonia, ca. 7°S), through paleontological and geological fieldwork. The measured sedimentary series (120 m-thick [West] plus 90 m-thick [East]), assigned to the upper member of the Pozo Formation, records fluvial micro-conglomeratic lenses intercalated with floodplain and evaporite-rich fine red deposits, estuarine/coastal-plain tidally-influenced fine sandstones, and oxbow lake nodule-rich blue clays. This sedimentary shift coincides locally with the demise of the large Eocene coastal-plain wetland known as Pozo System. The late Eocene–early Oligocene Shapaja section was extensively sampled for chemostratigraphy (δ13C on dispersed organic matter and pedogenic carbonate nodules), which in turn allowed for refining the location of the Eocene-Oligocene Transition (EOT) and other climatic events recognized at a global scale (i.e., Oi-1 and Oi-1a). The section has yielded nine fossil localities with plant remains (leaves, wood, charophytes, and palynomorphs), mollusks, decapods, and/or vertebrates (selachians, actinopterygians, lungfishes, amphibians, sauropsids, and mammals), documenting ~130 distinct taxa. Four localities of the upper member of the Pozo Formation at Shapaja predate the EOT, one is clearly within the EOT, while four are earliest/early Oligocene in age. The small leaf impressions found along the Shapaja section could be indicative of dry and/or seasonal conditions for this region throughout and after the EOT. Monkeys, indicative of tropical rainforest environments, are only recorded in a latest Eocene locality (TAR-21). Two biotic turnovers are perceptible in the selachian, metatherian, and rodent communities, well before the EOT [~35–36 Ma] and a few hundred thousand years after the EOT [~33 Ma]. The latter turnover seems to be primarily related to a global sea-level drop (ichthyofauna: marine-littoral elements replaced by obligate freshwater taxa) and/or the onset of a drier and more seasonal climate in early Oligocene times (terrestrial components). Changes in the structure of the Shapaja paleocommunities were mostly driven by the flexural subsidence during the late Eocene, and then globally driven by the earliest Oligocene climatic deterioration

Late Miocene mammals from the Calchaquí Valley (Palo Pintado Formation, northwestern Argentina): Biogeographic and paleoenvironmental implications for the southern central Andes

With noteworthy outcrops in the Angastaco Basin (Salta Province), the Palo Pintado Formation is perhaps one of the most intensely studied late Miocene stratigraphical unit of northwestern Argentina from geological, paleoecological, and paleobotanical approaches. In contrast, the mammals from this unit are scarcely known, most of them lacking a precise stratigraphical and geochronological adjustment. In this contribution, we report new caviomorph rodents from the Palo Pintado Fm, exposed at Calchaquí Valley (Eastern Cordillera, Angastaco Basin). The stratigraphical and geochronological control of the new specimens indicate a time window ranging from ∼9.3 Ma to ∼6.1 Ma. The first records of brachydont mammals of the Palo Pintado Fm, represented by the caviomorph Erethizontidae (Erethizontidae sp. nov. cf. Microsteiromys sp.) and Echimyidae (cf. “Eumysops” parodii, and cf. Thrichomys sp.), are described. Dinomyidae (cf. Ferigolomys sp.), small Caviidae (gen. and sp. indet. A and B), and the abrocomid Protabrocoma paranensis are also identified. Caviomorphs from the Palo Pintado Fm (containing the oldest and more recent taxa of different Neotropical linages) allow us to suggest Angastaco Basin as “museum” and “cradle” of biodiversity during the Tortonian and Messinian ages. Our analysis indicates that the late Miocene mammals of the Palo Pintado Fm are compatible with the occurrence of forested environments developed under humid and warm conditions, in agreement with independent paleoenvironmental and paleoclimatic proxies. A close biogeographic relationship between the area of the Calchaquí Valley, the Brazilian Acre, and the Argentinian Mesopotamia during the late Miocene is also suggested.Fil: Candela, Adriana Magdalena. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Paleontología Vertebrados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; ArgentinaFil: Galli, Claudia Inés. Universidad Nacional de Jujuy. Instituto de Ecorregiones Andinas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Ecorregiones Andinas; ArgentinaFil: Rasia, Luciano Luis. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Paleontología Vertebrados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; ArgentinaFil: Voglino, Damián. Museo de Ciencias Naturales “Rvdo. P. Antonio Scasso”; ArgentinaFil: Abello, María Alejandra. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Laboratorio de Sistemática y Biología Evolutiva; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; ArgentinaFil: García Esponda, Cesar M.. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo; ArgentinaFil: Zurita, Alfredo Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Centro de Ecología Aplicada del Litoral. Universidad Nacional del Nordeste. Centro de Ecología Aplicada del Litoral; Argentin

The megatherioid sloth "Xyophorus" villarroeli from the late Miocene of Achiri (Bolivia)

International audienceMiocene vertebrate localities are uncommon in central South America. In Bolivia, the best known mammalian faunas ofthis period come from Quebrada Honda (late middle Miocene, Tarija Department) and Cerdas (early middle Miocene, PotosíDepartment). The Achiri locality (La Paz Department) was reported first by Hoffstetter in 1972. Subsequently, campaignswere conducted in this locality by several paleontologists, including Villarroel, Anaya, Saint-André, and by our team over thelast decade. Recently, we have obtained two precise absolute dates (40Ar/39Ar) on feldspar contained in ashes intercalatedbetween fossiliferous levels and confirmed a late Miocene age (10.35±0.07 Ma and 10.42±0.09 Ma, late Mayoan–earlyChasicoan South American Land Mammal Ages) as suggested by Marshall and colleagues in 1983. Almost all the specimenscome from the Cerros Virgen Pata and Jiska/Jacha Pisakeri localities, the latter located 3–4 km southeast of Achiri village.In the past, discoveries of numerous spectacular specimens have allowed the identification of new mammalian speciessuch as the notoungulates Plesiotypotherium achirense and Hoffstetterius imperator, the sparassodontan Borhyaenidiumaltiplanicum, and the xenarthrans Trachycalyptoides achirense and Xyophorus villarroeli. Xyophorus was erected by Ameghinoin 1887 on the basis of a dentary fragment from the lower Miocene Santa Cruz Formation (Argentina). This taxon is generallyconsidered to be a nothrotheriid sloth (although has never been formally included in a phylogenetic analysis based onosteological characters). Six species are recognized in Argentina. This genus is also recorded in Achiri through the endemicspecies X. villarroeli, and also in Cerdas and Quebrada Honda through X. cf. bondesioi. Unfortunately, all the specimensreferred to Xyophorus are extremely fragmentary. Here we present a partial skull (MNHN-Bol-V 12690, National Museumof Natural History, La Paz, Bolivia) discovered in Achiri, belonging to an adult, and referred as “Xyophorus” villarroeli. Itconsists of a right posterolateral portion of the skull, including parts of squamosal, parietal, basioccipital, exoccipital, andits complete ear region with ectotympanic, entotympanic, and petrosal. Preliminary observations of this new specimenreveal the presence of at least seven autapomorphies, including a very rugose external surface of ectotympanic, a clearcontact between styliform process of ectotympanic and pterygoid, and a reduced or absent subarcuate fossa. Thismegatherioid sloth shares several synapomorphies with nothrotheriids, including a dorsoventrally elongated ectotympanicand an ovate stylohyal fossa. It exhibits also transitional features between basal megatherioids and nothrotheriids, like aventral portion of the ectotympanic that is expanded transversely in ventral view (more than Hapalops and less thanNothrotheriidae) and deeper in lateral view than that of Hapalops, although similar in proportions to Pronothrotherium andMionothropus. This specimen thus suggests that “Xyophorus” villarroeli could be an early-diverging nothrothere, withaffinities to Hapalops and also early Nothrotheriidae, and probably distinct from Xyophorus of more austral localities. Acomprehensive phylogenetic analysis of the Megatherioidea including this form from Achiri, Aymaratherium from the earlyPliocene of Pomata-Ayte, and Lakukullus and Hiskatherium from Quebrada Honda, should allow for a better understandingof the relationships among Patagonian and Andean Megatherioidea

Neotropical metatherian diversity around the Eocene-Oligocene Transition: the Shapaja section, Peruvian Amazonia

International audienceMetatheria (Mammalia) were remarkable faunal components of South American Cenozoic history. Now represented solelyby the marsupials (e.g., opossums, kangaroos), metatherians evolved multiple adaptive types with greater past diversity andabundance than today. One important chapter of this history is the Eocene–Oligocene transition, a period of considerablechanges worldwide, with marked extinctions, diversity changes, and drastic climatic processes (i.e., transition from the earlyCenozoic “Greenhouse World” to the post-Eocene “Icehouse World”). For Metatheria, the Eocene-Oligocene transition isconsidered the major turnover point in their evolutionary history in South America, an assumption mainly based on thefossil record from Argentinian Patagonia. However, the Eocene–Oligocene transition is scarcely known at tropical latitudesof South America, like other time intervals, since this region is still poorly understood from a paleontological and geologicalstandpoint. This study aims at partly filling this knowledge gap, by reporting preliminary identifications of metatherians fromthe late Eocene–early Oligocene Shapaja section, near Tarapoto, Peruvian Amazonia. Nine fossiliferous localities of thePozo Formation were dated by chemostratigraphy and explored through wet screening (1–2 mm meshes), which allowedrecovering small-sized fossils (plants, mollusks, decapods, fishes, amphibians, reptiles, and many mammals). Metatherianswere found in most localities and, according to their taxonomic composition, three assemblages could be recognizedthroughout the section, a pattern also observed in rodents and fishes. The oldest assemblage (TAR-74, early late Eocene)is composed of only one new prepidolopid polydolopimorphian. The second assemblage (TAR-20, 72, 21), latest Eocene,encompasses scarce and fragmentary remains of another probable prepidolopid, numerous remains of a small gerbil-likeargyrolagid, and teeth of palaeothentoids, an extinct clade of paucituberculatans, with two basal forms plus twopalaeothentines. These records represent the oldest occurrences of Palaeothentinae and Argyrolagidae, and thenorthernmost record of the latter clade. The earliest Oligocene localities yielded none (TAR-22) or few fragmentedmetatherian remains (TAR-13), possibly due to taphonomic biases, being considered transitional. Finally, the thirdassemblage (TAR-01, early Oligocene) includes one larger, rarer argyrolagid and several palaeothentoids (three basal taxa,three palaeothentids, and one abderitid). Thus, the Shapaja section does not attest to a smaller diversity around theEocene–Oligocene transition. However, the changes in the taxonomic composition of the assemblages, along with othergeological and paleontological data, point to two biotic turnovers. The first one, during the late Eocene, has probably beendriven by regional processes related to the Andean orogeny, which led to an episodic marine incursion in this area. Thelater biotic turnover, by contrast, seems to be related to the Eocene–Oligocene transition global processes, namely thegreat drop in sea level and the onset of drier and cooler climates worldwide, with decreased precipitation and increasedseasonality. Indeed, fossil plants from Shapaja indicate the occurrence of multi-stratified rainforests during the latestEocene and more open, deciduous forests in the earliest Oligocene. Finally, the Shapaja section highlights the importanceof fieldwork and research efforts in northern South America, to get better correlations with middle and high latitudeslocalities, and thus a refined paleobiodiversity picture in the whole continen

Los roedores caviomorphos (Rodentia, Hystricognathi) del Mioceno tardío de Achiri (Bolivia)

International audienceEl conocimiento de los mamíferos neógenos de Bolivia se ha centrado principalmente en unos pocos yacimientos del Mioceno temprano (Cerdas, Nazareno) y el Mioceno medio (Quebrada Honda). En la última década, se han incrementado los esfuerzos de exploración, dando como resultado un mejor conocimiento de la fauna de la localidad de Achiri (Prov. de Pacajes) del Mioceno tardío (~10,42–9,42 Ma; Formación Mauri). Dentro de esta fauna, los especímenes de caviomorfos, depositados en la Unidad de Paleontología del Museo Nacional de Historia Natural de La Paz, son abundantes y consisten en restos cráneo-mandibulares y post-craneanos, y dientes aislados. El estudio preliminar indica la presencia de Prodolichotis prisca, Cardiomys sp. (Cavioidea), Tetrastylus sp., Lagostomus sp. (Chinchilloidea) y un octodontoideo indet. Prodolichotis abarca el 80% de la diversidad, con cráneos excepcionalmente preservados (varios asociados a mandíbulas). Los otros taxones están representados por especímenes que, aunque escasos y fragmentarios, permiten una asignación genérica clara (excepto el octodontoideo por su mala preservación). Prodolichotis prisca es el dolicotino más antiguo, registrado en el Mioceno tardío–Plioceno temprano del noroeste de Argentina. Cardiomys, Tetrastylus y Lagostomus se encuentran ampliamente distribuidos en niveles del Neógeno tardío de Argentina. Además, Tetrastylus se registra en el Mioceno tardío de Brasil, Uruguay y Venezuela. Aunque es necesario un análisis profundo de la taxonomía de los roedores de Achiri, los mismos indican mayor afinidad con las faunas de edad Chasiquense-Huayqueriense de Argentina. El estudio de esta asociación permitirá aumentar el conocimiento biogeográfico del Neógeno tardío de América del Sur

New data on the glyptodontid Trachycalyptoides from the late Miocene Bolivian locality of Achiri

International audienceAmong armored xenarthrans, Glyptodontidae appears as one of the most peculiar and also characteristic groups of SouthAmerican mammals that inhabited this continent since at least the early Eocene until the end of the Pleistocene. Theirevolutionary history is particularly well documented in Patagonia, Central and North America, but less so in the tropics andcentral South America. In Bolivia during the Miocene epoch, this family is only recorded at the Laventan locality of QuebradaHonda, represented by cf. “Asterostemma”, “Propalaehoplophorus” andinus, and two sclerocalyptine species, the ?Colloncuranlocality of Nazareno represented by “Propalaehoplophorus” and ?Neothoracophorus, occurring in Choquecota, and the lateMayoan–early Chasicoan localities of Chokorasi and Achiri by a single species, Trachycalyptoides achirense. The late Miocenevertebrate locality of Achiri discovered in the early 70’s by the French paleontologist Hoffstetter, was explored by severalteams during the subsequent decades. Its mammalian fauna is particularly diverse with more than 20 taxa, includingmetatherians (i.e., Borhyaenidium), notoungulates (e.g., Hoffstetterius), litopterns, rodents (e.g., Prolagostomus), as well asxenarthrans sloths (e.g., “Xyophorus”) and cingulates (e.g., Trachycalyptoides). Trachycalyptoides was erected by Saint-Andréin 1996 on the basis on two dermal armors and caudal tubes, an incomplete skull, and a hemimandible. The abundantmaterial collected by our team during recent fieldwork, and the preliminary revision of the material housed in the museumsof La Paz and Paris, has allowed us to gather new information, specifically on the dentition, dorsal carapace, and caudal tubeon this peculiar glyptodontid. In Trachycalyptoides the presence of three lobes is well marked on certain upper and lowermolariforms, especially on the most posterior teeth (fourth to eighth molariforms), whereas their presence is doubtful onthe third teeth, and absent on the first and second teeth. The general structure of the osteoderms corresponds to apentagonal or hexagonal polygon with a “rosette” pattern (a central figure surrounded by peripheral figures) on the exposedsurface. The central and peripheral figures are elevated and separated by a sulcus. The subcircular central figure is slightlyconcave in the center. The peripheral figures are small and in a variable number according to region (ranging from 3–4 to12–15), with foramina at the intersection with the sulcus of the central figure. The caudal tube is conical and elongated andits apex is relatively acute. The ventral face is slightly convex and the dorsal face is flat. The distal portion of the tube isformed by two large right and left osteoderms. The latter are roughly quadrangular, rectangular proximally and quadratedistally. The osteoderms of the caudal tube lack peripheral figures. The molariforms, dorsal carapace, and caudal tube ofTrachycalyptoides show affinities with glyptodonts that have a simplified trilobate pattern in the anteriormost molariforms,a dorsal carapace formed by osteoderms with a “rosette” pattern, and a caudal tube formed by osteoderms withoutperipheral figures like Cochlops, Palaehoplophorus, Trachycalyptus, and Lomaphorus

Late middle Miocene Metatheria (Mammalia: Didelphimorphia and Paucituberculata) from Juan Guerra, San Martín Department, Peruvian Amazonia

International audienceCurrently, marsupials (modern members of the Metatheria clade) are widely distributed in tropical and subtropical areas of South America, but poorly represented in the fossil record of these regions. Except for the species-rich fossiliferous localities of La Venta in Colombia, additional Miocene metatherians from tropical, equatorial South America are sparsely reported in Bolivia, Brazil, Peru, and Venezuela. Here, we introduce new metatherian remains recovered from the late middle Miocene locality of TAR-31, San Martín Department, Peru, which has been assigned to the Laventan South American Land Mammal Age (~13 Ma) by mammalian biostratigraphy. Three metatherian taxa are recognized at TAR-31: the didelphid didelphimorph ‘Thylamys’ cf. ‘T.’ colombianus, and the paucituberculatans aff. Palaeothentes and Pitheculites ipururensis sp. nov. This assemblage and the presence of a cebid primate at TAR-31 suggests predominantly humid and warm tropical conditions, with the occurrence of both forests and drier habitats in the surroundings. Comparisons with other Miocene metatherian assemblages at low and mid latitudes of South America clearly confirm close relationships between TAR-31 and La Venta (agreeing with observations based on monkeys and rodents), as well as, to a lesser extent, with Acre River local faunas and Madre de Dios (MD-67) in Brazil and Peru, respectively. The current results support the hypothesis that Western Amazonia was a single and consistent biogeographical region for land mammals over middle Miocene times, at the western edge of the Pebas Mega-Wetland System, and highlight the role of the Amazonian region concerning marsupial Neogene radiation. U-Pb analysis made on detrital zircon grains from TAR-31 gave a maximum depositional age of 17.4 ± 0.12 Ma (i.e., 4 Ma older than the biostratigraphical age), with a mixed detrital source likely comprising Precambrian (Western Amazon Craton), Neoproterozoic (Neoproterozoic mobile belts), and Phanerozoic rocks (Andes)