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In this paper, we study the postcranial morphology (humerus, ulna, innominate, femur, tibia, astragalus, navicular, and metatarsal III) of Neoepiblema, a giant Late Miocene South American rodent, searching for evidence about its paleobiology based on unpublished specimens from Solimoes Formation (Upper Miocene, Brazil). The study includes a morphofunctional analysis of the postcranial bones and a comparison with extant and extinct rodents, especially Phoberomys. The morphofunctional analysis of the postcranial bones suggests that Neoepiblema (as well as Phoberomys) would have a crouched forelimb that was not fully extended, with powerful pectoral and triceps musculature, and able to produce movements of pronation/supination and possibly with a hand able to grasp. The combination of characters of the innominate bone, femur, and tibia indicates a predominance of parasagittal movements and a thigh with powerful musculature used during propulsion. In sum, the analyzed postcranial features are consistent with the limb morphology of ambulatory rodents, but with faculty to dig or swim. The sedimentary evidence of the localities in which fossils of neoepiblemids have been found suggests that these rodents lived in wet and water-related environments (near swamps, lakes, and/or rivers).

The Niterói and Talismã sites comprise two of the most important fossiliferous deposits of the Neogene in Brazil. After 30 years of research, these sites have revealed rich assemblages of vertebrates and provided a glimpse of the Amazonian fauna and environment during the Miocene. Despite this, detailed studies that attempt to explain the genesis of these bonebeds are still scarce and hamper more robust paleoenvironmental and paleoecological reconstructions. Here we provide the first in-depth taphonomic analysis for both locations. Sedimentological and taphonomic evidence suggest that the depositional environments of Niterói and Talismã were similarly represented by shallow and calm waters in lacustrine/swampy contexts. We propose that the accumulation of bones and teeth is the result of attritional (day-to-day) mortality of organisms of the local community in a low sedimentation environment. The thanatocoenosis was exposed to biostratinomic processes for longer periods of time, which explains the high disarticulation, disassociation, fragmentation and loss of skeletal elements. The almost absence of weathering indicates that the aquatic environment slowed down the organic degradation of bioclasts, while the rarity of abrasion shows a limited influence of hydraulic flows in transporting and remobilizing bioclasts. Thus, both sites preserve mostly autochthonous to parautochthonous bioclasts, with a moderate level of time-averaging. Our results corroborate the hypothesis that lentic environments can present remarkable preservational conditions for the formation of attritional accumulations of vertebrate remains. Moreover, we show how the different collecting methods affect the description of preservational features and taphonomic interpretations of both fossil assemblages.

International audience; 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.

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 Rondonia 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 C3-dominated environments from closed canopy forests to wooded savannas, agreeing with paleovegetation reconstitution. Most species were browsers (piC3=100%; Niche breadth, BA=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 C3/C4 generalist Trigodonops lopesi (∼1,900 kg), which foraged in wooded savannas (piC3=70%; BA=0.72), similarly with its relative Toxodon platensis (∼1,800 kg) that had a browse-dominated mixed feeder diet (piC3 ≥ 84%, BA ≤ 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 (piC3=∼69%; BA=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.

The Solimões Formation (Eocene-Pliocene) is a well-known geological unit due to the great diversity of crocodylian species. Here we describe a new species of Melanosuchus, M. latrubessei sp. nov., from the Talismã locality, state of Amazonas, from the Upper Miocene of the Solimões Formation (Solimões Basin, Brazil). A new phylogenetic inference focused on Caimaninae is provided and the different evolutionary scenarios involving this new species are discussed. In addition, quantitative morphology studies are carried out and comments regarding the paleoecology aspects of this new species are made. M. latrubessei represents a medium-sized generalist predator, being proportional to the medium-sized M. niger. This new species inhabited the drainages of the Solimões Formation and was ecologically related to other taxa of crocodylians during the proto-Amazon Miocene. The evolutionary advantages of Melanosuchus genus are discussed to better understand the biogeographical occurrence of M. niger in South America, a species which survives to this day in contrast to several other species that became extinct during the Miocene-Pliocene periods. The extinction of the Miocene-Pliocene crocodylian taxa of the Solimões Formation, including Melanosuchus latrubessei, seems to be directly related with the uplift of the northern portions of the Andes, which generated significantly changes in drainages and Amazon paleoenvironments.

Fossil data collecting is an essential stage of every paleontological undertaking. Although there is a consensus regarding the fundamental importance of sedimentary and stratigraphic context, there is still some debate surrounding the need to record the exact position of a fossil in relation to other elements within the same deposit (provenance). Here we provide a practical guide for the in-field use of the Total Station (TST, electronic equipment for xyz coordinates measurements), a tool that has seen wide application in archaeology but has been largely neglected in paleontology. With the TST, recording the provenance of in situ fossils can be done quickly and with great precision. We also present a configuration tutorial showing how to use the equipment, based on our experience in the Solimoes Formation (upper Miocene, Acre basin, Brazil), highlighting both its advantages and disadvantages for recording fossil provenances.

Several studies have reported Miocene shallow-marine incursions in the Pebas Megawetland system (Western Amazonia) based on paleontological and sedimentological evidence. Only a few publications restricted to Middle and Late Miocene fossils outcropping in the Iquitos (Peru), Benjamin Constant and Eirunepe (Brazil) areas have provided isotopic evidence to test these incursions. In this study, we present new carbon, oxygen, and strontium (87Sr/86Sr ratios) isotopic data of macrofossils (pacu and ray teeth, crab claws and oysters), and microfossils (ostracods and foraminifera) from reported lower to lower upper Miocene sedimentary rocks of Western and Eastern Amazonian (Peru and Brazil), mainly from shallow-marine deposits. It was also analyzed present-day organisms from distinct environments (beach, sea, riverine, and estuary) and compared these results with Miocene fossils. While C and O isotopic compositions indicate that Western Amazonia fossils display an isotopic composition similar to the present-day continental, limnic and riverine, environments (−17‰ to −5.61‰ for δ13C and − 10.14‰ to −1.92‰ for δ18O), Eastern Amazonia fossils display C and O isotopic compositions comparable to those from seawater environments (−2.53‰ to −0.72‰ for δ13C and − 4.85‰ to −1.76‰ for δ18O). We further used the 87Sr/86Sr isotopic composition of the fossils to estimate paleosalinity conditions. The 87Sr/86Sr isotopic compositions indicates that Eastern Amazonian water bodies of the Pirabas Formation (Marajo Basin) varied from mesohaline to marine conditions. In contrast, Early Miocene Western Amazonian water bodies of the Pebas Megawetland System (PMWS) are characterized by freshwater conditions. Nonetheless, in Middle and Early Late Miocene, oligohaline conditions are found in the Peruvian part of the PMWS. Paleosalinity estimates of the Brazilian part of the PMWS are less constrained and might indicate a salinity range between freshwater or oligohaline conditions. Our isotopic data suggest the PMWS was occasionally submitted to oligohaline conditions during Middle and Early Late Miocene shallow-marine incursions. We suggest that Miocene shallow-marine incursions in Western Amazonia at this time were characterized by transitional paleoenvironments, reconciling isotopic, sedimentological and paleontological evidences.

Modifications on the cheek teeth and dentary bone (loss of dental tissues on the extra-alveolar portion of the cheek teeth, and corrosion on the surface of the dentary bone) of fossil specimens of medium to giant South American rodents (mainly neoepiblemids) from the Neogene (Brazil and Argentina) are documented here. These features are similar to those observed in teeth and bones of small hypsodont rodents (recent and Quaternary fossils) that were subjected to digestive process by predators/scavengers. Based on comparisons, we tentatively hypothesize that acid-etching resulting from digestive processes could have caused the modifications in the specimens, providing evidence of a palaeoecological interaction between neoepiblemids (and other rodents), and predators or scavengers.

The rodent Neoepiblema acreensis (Chinchilloidea: Neoepiblemidae) is member of a lineage that reached gigantic dimensions during the Late Miocene of South America-the Neoepiblemidae. In this paper, the cranial anatomy of this rodent is reviewed. Noninvasive imaging is used to reveal internal structures. Our review is based mainly on an almost complete cranium from the Upper Miocene deposits of the western Amazonia of Brazil. The cranium has an elongated rostrum, large frontal sinuses, a deep temporal fossa, well-developed sagittal, nuchal, medial occipital, and secondary crests, and a tympanic fenestra connected to the external acoustic meatus by a thin ventral cleft. Remarkably, the cranium shows the presence of fossae on the posterior region of the frontal and parietal bones, and a "W-shaped" fronto-parietal suture, which are not present in other analyzed chinchilloids. This study contributes to the knowledge of the morphology of this extinct rodent as well as to the phylogenetic relationships and paleobiology of neoepiblemids.

Made available in DSpace on 2019-10-06T15:26:21Z (GMT). No. of bitstreams: 0 Previous issue date: 2019-02-15 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) The fossiliferous beds of the Solimões Formation, western Brazilian Amazon have yielded several vertebrate fossils that are key to understand the evolution of Neotropical biotas. Although this sedimentary unit has been studied for more than two centuries, no absolute dates are available so far, preventing more precise bio/chronostratigraphic interpretations and broader comprehension of the biotic/geological events that affected this northern portion of South America during the Neogene. Here, we present the first Neogene radioisotopic dates for the Brazilian Amazon, via U-Pb dating of detrital zircon from two classical sites. Both samples have small proportions of relatively young zircon grains, the dates from which are the maximum ages of deposition. LA-ICPMS analysis of two grains from the Niterói locality yielded a weighted mean of 8.5 ± 0.5 Ma and CA-TIMS analysis of two grains from the Talismã locality yielded a weighted mean of 10.89 ± 0.13 Ma. These maximum deposition ages are in the Tortonian stage, late Miocene, confirming the age previously inferred based on biochronological data. Universidade de São Paulo–USP Faculdade de Filosofia Ciências e Letras de Ribeirão Preto Universidade Federal de Santa Maria-UFSM CAPPA – Centro de Apoio à Pesquisa Paleontológica da Quarta Colônia Boise State University Department of Geosciences Museu de Ciências Naturais da Fundação Zoobotânica do Rio Grande do Sul Universidade Estadual Paulista–UNESP Departamento de Ciências Biológicas Faculdade de Ciências Universidade Federal do Acre–UFAC Departamento de Ciências da Natureza, Campus Universitário Universidade Federal do Acre–UFAC Campus Floresta Universidade Estadual Paulista–UNESP Departamento de Ciências Biológicas Faculdade de Ciências FAPESP: 2011/14080-0 FAPESP: 2014/02206-9 FAPESP: 2016/00476-3 CNPq: 309434/2015-7

The fossil-bearing stratigraphic sections of the Solimoes Formation (southwestern Brazilian Amazonia) are exposed mainly along the Jurua, Purus, and Acre rivers, and in road cuts. These deposits have provided fossils of the four main lineages of Caviomorpha – Cavioidea, Erethizontoidea, Octodontoidea, and Chinchilloidea, contributing to the understanding on the evolution of tropical Neogene rodents. Herein, our knowledge about fossil rodents from this region is reviewed. New specimens are recorded, including taxa mentioned for this region for the first time, such as basal cavioids, Dolichotinae, Caviodon (Hydrochoeridae), and Drytomomys (Dinomyidae). Unfortunately, the deposits have no absolute ages, and based on palynological data and the biochronology of several taxa (mainly mammals), the encompassed fauna has been constrained to the late Miocene. However, some rodent lineages recorded here seem to be more related to older faunas, from the middle Miocene and Paleogene. Regarding the biogeographic and paleoenvironmental affinities, most of the Neogene rodents from the Acre region show more similarities to those from the Entre Rios, Argentina, and Urumaco, Venezuela, where wet environments were present during Neogene times. An increase in prospecting along southwestern Amazonian rivers looking for rodents (among other vertebrates) associated with methods to better constrain the ages of these faunal assemblages will contribute to a better understanding of the evolution of the tropical rodents as well as the stratigraphy and age of that portion of the basin.

The ecomorphological diversity of caviomorph rodents in South America included giant forms, such as the chinchilloid Neoepiblema acreensis from the Upper Miocene of Brazil. The evolution of the brain anatomy and size of these animals can be now studied with non-invasive imaging techniques and exceptional fossils. Caviomorphs show diversity in the traits of the olfactory bulbs, cerebrum, cerebellum, cranial nerves, and blood vessels. Neoepiblema acreensis had a gyrencephalic brain, with an expansion of the frontal lobe, lacking an evident paraflocculus. Compared to the predictions based on extant taxa, even when considering taphonomical effects, N. acreensis , a rodent that weighted almost 80 kg, had a very low encephalization quotient compared to other rodents. The adaptive value of a low energetic cost and other ecological factors could explain the presence of a small brain in this giant rodent––a pattern we also hypothesize for other Neogene giant rodents.

Le Paléogène d’Amazonie péruvienne a livré les plus anciennes communautés de rongeurs caviomorphes d’Amérique du Sud, lesquelles sont le résultat des premières phases de diversification de ce groupe. Ce travail présente l’étude de restes dentaires inédits de rongeurs fossiles issus de deux nouvelles sections situées à proximité des villes de Juanjui et de Balsayacu (Département de San Martín, Amazonie péruvienne). Les analyses de la morphologie occlusale des dents jugales et de la microstructure de l’émail des incisives indiquent la présence de taxons basaux tels que les genres Cachiyacuy Antoine, Marivaux, Croft, Billet, Ganerød, Jaramillo, Martin, Orliac, Tejada, Altamirano, Duranthon, Fanjat, Rousse & Salas Gismondi, 2012, Canaanimys Antoine, Marivaux, Croft, Billet, Ganerød, Jaramillo, Martin, Orliac, Tejada, Altamirano, Duranthon, Fanjat, Rousse & Salas Gismondi, 2012, et Eoespina Frailey & Campbell, 2004, dans les niveaux inférieurs de la série sédimentaire, auxquels succèdent des taxons plus dérivés, comme Eoincamys Frailey & Campbell, 2004, dans des niveaux plus récents. Ces taxons témoignent d’une morphologie intermédiaire entre ceux documentés en Amazonie péruvienne dans les localités éocènes de Contamana (fin de l’Éocène moyen) et ceux des localités oligocènes de Tarapoto/Shapaja et Santa Rosa (?Éocène supérieur/Oligocène inférieur). Ces fossiles apportent ainsi une documentation inédite en Amazonie, en ce que les secteurs de Juanjui et de Balsayacu présentent des dépôts sédimentaires couvrant vraisemblablement la fin de l’Éocène moyen, une partie de l’Éocène supérieur et la base de l’Oligocène. Enfin, la continuité stratigraphique de la longue section de Juanjui permet de démontrer l’existence d’un hiatus temporel significatif entre les assemblages à Canaanimys-Cachiyacuy-Potamotrygon ucayalensis (Contamana, Formation Pozo ; base de la section de Juanjui ; Balsayacu) et ceux à Eoincamys (Santa Rosa ; Tarapoto/ Shapaja ; sommet de la section de Juanjui). Paleogene deposits of Peruvian Amazonia have yielded the oldest caviomorph rodent communities from South America, and the clues that their early diversification had occurred in this area. Here we report fossil dental remains of rodents from two new sections located in the vicinity of Juanjui and Balsayacu (San Martín Department, Peruvian Amazonia). Analyses of the occlusal morphology of cheek teeth and of the incisor enamel microstructure indicate the occurrence of basal caviomorphs (such as Cachiyacuy Antoine, Marivaux, Croft, Billet, Ganerød, Jaramillo, Martin, Orliac, Tejada, Altamirano, Duranthon, Fanjat, Rousse & Salas Gismondi, 2012, Canaanimys Antoine, Marivaux, Croft, Billet, Ganerød, Jaramillo, Martin, Orliac, Tejada, Altamirano, Duranthon, Fanjat, Rousse & Salas Gismondi, 2012, and Eoespina Frailey & Campbell, 2004, genera so far known from late middle Eocene deposits of Contamana, Peruvian Amazonia) in levels situated in the lower part of the studied stratigraphic section. More derived taxa (such as Eoincamys Frailey & Campbell, 2004), known from early Oligocene deposits of Tarapoto/Shapaja and Santa Rosa, Peruvian Amazonia) occur only in upper levels of the section. Based on these considerations, the rodent-bearing localities of the Juanjui/Balsayacu area seem to be intermediate in age between the Contamana Eocene localities and the Tarapoto/Shapaja Oligocene ones and the Santa Rosa ?Eocene/Oligocene one. These new data document a poorly known period in Western Amazonia, in providing a sedimentological record most likely documenting the late middle Eocene, the late Eocene and the earliest Oligocene interval. Furthermore, the existence of a long temporal hiatus between Canaanimys-Cachiyacuy-Potamotrygon ucayalensis assemblages (Contamana, Pozo Formation; Balsayacu; lower levels at Juanjui) and Eoincamys-yielding faunas (Santa Rosa; Tarapoto/Shapaja; uppermost levels at Juanjui) is demonstrated in a single continuous and long-ranging stratigraphic section at Juanjui. Fil: Assemat, Alexandre Rémi Jean Pierre. Université Montpellier II; Francia Fil: Boivin, Myriam. Universidad Nacional de Jujuy. Instituto de Ecorregiones Andinas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Ecorregiones Andinas; Argentina. Université Montpellier II; Francia Fil: Marivaux, Laurent. Université Montpellier II; Francia Fil: Pujos, François Roger Francis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentina Fil: Benites Palomino, Aldo. Museo de Historia Natural de Lima; Perú. Universidad Nacional Mayor de San Marcos; Perú Fil: Salas Gismondi, Rodolfo. Museo de Historia Natural de Lima; Perú. Universidad Nacional Mayor de San Marcos; Perú Fil: Tejada Lara, Julia Victoria. Museo de Historia Natural de Lima; Perú. Universidad Nacional Mayor de San Marcos; Perú. Columbia University; Estados Unidos Fil: Varas Malca, Rafael M.. Museo de Historia Natural de Lima; Perú. Universidad Nacional Mayor de San Marcos; Perú Fil: Negri, Francisco Ricardo. Universidade Federal do Acre; Brasil Fil: Ribeiro, Ana Maria. Museu de Ciências Naturais, Fundação Zoobotânica Do Rio Grande do Sul; Brasil Fil: Antoine, Pierre Olivier. Université Montpellier II; Francia. Centre National de la Recherche Scientifique; Francia

Recently, the fossil record of rodents from southwestern Brazilian Amazonia has been reviewed with regards to its diversity as well as its ecological relationships. In the reviews, the necessity to report new specimens collected with stratigraphic control was stated. Here, a new dinomyid specimen collected during a 2015 expedition to the Niterói locality, Acre River, is reported. The material is a fragment of skull with the right P4–M1 and the left P4–M2 preserved. The cheek teeth are protohypsodont, a characteristic employed to differentiate Potamarchinae dinomyids from the euhypsodont dinomyids Eumegamyinae and Tetrastylinae. The occlusal surface of the cheek teeth is composed of lophs with interruptions, showing little wear, which suggests that the specimen is not fully ontogenetically developed. The specimen has a unique combination of characters (protohypsodont and pentalophodont cheek teeth, with the leading edges of similar thickness to the trailing edges, and presence of a groove on the bottom of the infraorbital foramen) not present in other known dinomyids, which led us to erect a new taxon. The abundant and diverse fossil record of protohypsodont dinomyids suggests that an important radiative event may have occurred during the middle–late Miocene of northern South America. http://zoobank.org/urn:lsid:zoobank.org:pub:E082C3C6-47B6-4D83-9009-A64879AAFC7A http://www.zoobank.org/NomenclaturalActs/16235A7B-A261-445E-8DD4-940AB21DCB06

Neoepiblemidae (Caviomorpha) includes South American hystricognath rodents that together with Chinchillidae and Dinomyidae compose the clade Chinchilloidea. Despite the considerable advance...

The Miocene deposits of South America are notable for their diverse crocodyliform fauna, of which the giant caimanine Purussaurus is a well-known example. This contribution describes a new caimanin...

The Amazonian rainforest is arguably the most species-rich terrestrial ecosystem in the world, yet the timing of the origin and evolutionary causes of this diversity are a matter of debate. We review the geologic and phylogenetic evidence from Amazonia and compare it with uplift records from the Andes. This uplift and its effect on regional climate fundamentally changed the Amazonian landscape by reconfiguring drainage patterns and creating a vast influx of sediments into the basin. On this >Andean> substrate, a region-wide edaphic mosaic developed that became extremely rich in species, particularly in Western Amazonia. We show that Andean uplift was crucial for the evolution of Amazonian landscapes and ecosystems, and that current biodiversity patterns are rooted deep in the pre-Quaternary.

New genera of characoid fossil fishes are described on the basis of remains from the Maastrichtian El Molino Formation and the early late Paleocene Santa Lucia Formation of Bolivia, and the Mio-Pliocene Solimoes Formation of Brazil. Comparisons with the Hepsetidae, Erythrinidae, Ctenoluciidae, Acestrorhynchidae, and the characid Hydrocynus allow the following conclusions to be made: the new Bolivian genus lacks some erythrinid synapomorphies but shows notable resemblance to the Acestrorhynchidae, particularly in the pattern of the replacement teeth. The Brazilian genus is included in the erythrinids.

The fossil rodents from the southwestern Amazonia of Brazil have been studied since the first half of the 20th century. Several caviomorph rodents were reported for the Neogene of this region, mainly neoepiblemids and dinomyids. Until recently, the record of dinomyids in the Solimoes Formation (Late Miocene) was predominantly based on a few isolated teeth, which made it difficult to make more accurate taxonomic identifications due to the scarcity of diagnostic characters. Here, new remains, more complete than those previously reported, of potamarchine dinomyids from the Neogene of Brazil are described. A new species of Potamarchus and a new genus and species of a Potamarchinae are erected. In addition, new material of Potamarchus murinus and Potamarchus sp. is identified. These data suggest a higher diversity of dinomyids in in the western Amazonia than previously supposed.

2 páginas.-- El documento en word es la versión del autor del artículo aceptado.-- et al.

Late Miocene tidal sediments of Acre, Brazilian Amazonia, were deposited in an embayment or interior seaway located in the sub-Andean zone. This late Tertiary embayment system may once have connected the Caribbean with the South Atlantic. The tidal coasts of the embayment-seaway have provided an avenue for the earliest waif (over water) dispersal phases of the great American biotic interchange in the late Miocene. The subsequent change from semimarine to terrestrial environments is of value in assessing the importance of earlier hypotheses on the evolution of the westem Amazonian landscape and gives insight into the formation of several observed biogeographic patterns, especially of aquatic biota.