Acre River Research Articles

MINERALOGIA E GEOQUÍMICA DOS SEDIMENTOS DE PRAIAS (BARRAS EM PONTAL) E BARRANCOS DO RIO ACRE E SUA RELAÇÃO COM A FERTILIDADE AGRONÔMICA

The State of Acre is situated in the southwestern portion of the Amazon region and occupies 3.16% of its area. Two systems of drainage cross it: Juruá and Purus rivers. During the dry season, some beaches (point bars) are formed in the concave parts of the meanders. An example of this is observed on the Acre River, tributary of the Purus River. Incidentally, this area is of great historical importance for the region, as it was the site of a battle between Brazil and Bolivia for ownership of the State of Acre. Those beaches, which occur on the edges of the main rivers of the Acre, are intensely used for agriculture of subsistence of short cycle (beans (Vigna unguiculata (l) Walp), maize (Zea- Mays) and watermelon (Citrullus Lanatus) by the local peasants. These cultures occupy small areas, up to 2 hectares, on these beaches. Such situation is different from those on beaches from other regions of the Amazonia and Brazil. With the purpose of understanding the source of these sediments and the origin of this fertility, the present work was developed.The main unity of the State Acre is Solimões Formation, that occupies more than 80% of its surface (SEHA, 2000). It is formed mainly by argilites with carbonized organic matter (Radambrasil, 1976), and some fossils fragments of vertebrates and invertebrates. Locally, argillaceous siltites, calcareous rocks, ferruginous arenites and polimithics conglomerates are found (Radambrasil, 1976). On this Formation it was deposited holocenic sediments which constitute in part unstable abrupt declivities and, currently, beaches in both the edges of the rivers.The beach sediments, mainly in the cultivated areas, are predominantly siltics with unimodal distribution. The grains are angular to sub-angular and are constituted mainly of quartz, followed by smectite, illite, kaolinite and feldspar. The chemical composition shows high values of SiO2 (84,0 ± 4,7%, n = 10), and moderate to low values of the oxides (1 to 6%): Al2O3 (6,1 ± 1,7%, n = 10), Fe2O3 (2,7 ± 0,6%, n = 10), K2O (1,3 ± 0,2%, n = 10); Na2O (0,43 ± 0,12%, n = 10), CaO (0,28 ± 0,08%, n = 10) and MgO (0,4 ± 0,15%, n = 10), compatible with the mineralogical assembly identified, and therefore very different from those of other fluvial beaches, which are very poor in these components. Mineral constituents, such as feldspar and smectite and the angular form of the grains beach sediments, indicate immature evolution being Solimões Formation the source of these sediments.The fertility show that these sediments are comparable the eutrofic cambissols, with high capacity of exchange of cations (~ 11.01 Cmolc/Kg) and percentage of saturation of bases (v) above 90, indicating that they are in fact appropriate for agriculture. This fertility is related to clay minerals (smectite and illite) and its siltic and loosely bound grains.

OS MINERAIS PESADOS E IDADES DE ZIRCÕES DOS SEDIMENTOS DE PRAIAS (BARRAS EM PONTAL) DOS RIOS PURUS E ACRE NO ESTADO DO ACRE (BRASIL)

The Purus River and its largest tributary, the Acre River, originate in Peru and constitute the main drainage system for the northeast and southeast portions of the State of Acre. These rivers and their smaller tributaries develop their beds over the Solimões Formation (Miocene to Pliocene-Late) and form a broad dendritic drainage pattern. During the rainy season, due to the high rainfall in the region and the low resistance of the drained rocks, these rivers mobilize a large volume of sediment, which is deposited mainly during the dry season, forming beaches (pointed bars), predominantly composed of fine sand, silt and clay. To investigate the probable primary sources of these sediments and their possible geographic locations, a mineralogical and morphological study of their heavy minerals and a geochronological analysis of their detrital zircons were used. Heavy minerals were extracted from fractions between 0.062-0.125 and 0.125-0.250. The transparent ones were investigated using a petrographic microscope and the opaque non-magnetic ones, together with the lithic fragments using a Scanning Electron Microscope (SEM/SED). In descending order, the main transparent heavy minerals of the Purus River are epidote (19%), kyanite (17%), zircon (14.5%), andalusite (8%), tourmaline (7.4%) and sillimanite (5 .5%), in addition to these, in amounts less than 5%, staurolite, garnet, apatite, amphibole, chlorite, muscovite, biotite, anatase, pyroxene and cassiterite occur. With similar content and different proportions, the assemblage of heavy minerals from the Acre River consists of andalusite (22.5%), kyanite (22.5%), zircon (12%), epidote (8%), sillimanite (5%) and tourmaline (5%), its accessories are: garnet muscovite, chlorite, apatite, amphibole, biotite, staurolite, titanite, anatase, serpentine and rutile. The non-magnetic opaque minerals of both rivers were shown to be predominantly formed by ilmenite, and the ages obtained in the zircons varied from 180 Ma to 3000 Ma, with great frequency in the intervals between 200-400 Ma and 900-1200 Ma.

Estimación de la erosión en un área de deforestación en la cuenca amazónica del bajo río Acre

The Lower Acre River Basin is located in an area of deforestation with the implementation of pastures for beef cattle ranching in soils susceptible to erosion and equatorial climate. The existence of slaughterhouses and beef cattle in the municipality of Boca do Acre, in the state of Amazonas, is one of the problems linked to deforestation in the Brazilian Amazon. Given this scenario, an estimate of soil losses was presented with the application of the Universal Equation in a geographic information system. In the methodology, a database was elaborated with vectorized information for the extraction of the areas of the types of soils and land cover, including the spatial analysis of slopes extracted from the digital elevation model. Due to the analysis of the areas by geoprocessing occurring by vectorization, the calculations of the erosion plots were obtained through tables with the parameters adopted by the scientific references. It was found that 60% of the soil loss occurs in the area of agriculture in 11% of the territory of the watershed, being predominantly in areas of rural settlements of the state of Acre. As a result of the estimate, soil loss in the Lower Acre River Basin was 386,422 t/ha/year, with a production of 46 million tons of sediment per year.

New fossil anhingids from the upper Acre River (Late Miocene of southwestern Amazon).

Four extant species of anhingids are found worldwide, all belonging to a single genus (Anhinga). However, the fossil record reveals a much greater diversity of this group in the past. The oldest known anhingids date back to the upper Oligocene period in Australia, but during the Miocene epoch in South America, they achieved their most remarkable diversity. This study describes newly discovered anhingid fossils from the Late Miocene period in South America. These fossils were extracted from the Acre conglomerate member, part of the Upper Miocene deposits in the southwestern Amazon region. The described fossils consist of two fragments of pelvic girdles, two femora, and two vertebrae belonging to a giant anhingid (Macranhinga sp.), as well as a vertebra from Anhinga minuta, the smallest of all darters. The examination of these fossils suggests the presence of potentially three distinct anhingid taxa within the same locality. The environment in which the conglomerate deposits were formed was ecologically complex. It is likely that these three species coexisted within the same ecosystem but avoided direct competition for food and reproductive sites by not fully exploiting their fundamental niche.

Inundation mapping using hydraulic modeling with high-resolution remote sensed data: a case study in the Acre River Basin, Brazil

Inundation mapping using hydraulic modeling with high-resolution remote sensed data: a case study in the Acre River Basin, Brazil

Diametric distribution of forestry species in riparian forest in the southern part of the Amazon

The expansion and changes in land use and land cover in the Southwest Amazon are mainly related to the activities of logging without management rules, agriculture and cattle production, which resulted in the conversion of natural forests, especially along water courses. This study aimed to verify the diametric distribution of forestry species with higher importance value index in the riparian forest of the Acre River (Acre, Brazil). The forestry inventory was performed at eight municipalities crossed by the Acre River, using two stage sample units (conglomerates) and applying stratified random sampling techniques at the river bank. Twenty-seven primary plots were installed, within which another four secondary plots were implanted. It was fitted Weibull’s probability density functions with 2 and 3 parameters to species diametric distribution, provided by the maximum likelihood method. Graphic analysis verified that 86% of the species analyzed presented a distribution trend with positive asymmetry. The distribution of the Weibull function with two parameters presented better the best estimative of the frequency of species by diameter class of the natural forest evaluated. Considering the heterogeneity of the species, further studies to verify whether the distribution behavior follows the same trend is recommended.

Men, Women, and Children in the Occupation of the Purus and Acre River Valleys: Social Aspects in Southwestern Amazonia from 1889 to 1904

RESUMO O artigo discute o panorama social dos homens, mulheres e crianças que ocuparam os vales dos rios Purus e Acre no início do século XX, abordando temas relativos à idade, raça e meios de resistência. A base documental é proveniente das fichas deixadas por esses trabalhadores junto ao Instituto Histórico e Geográfico do Acre, que estão sob a guarda da Universidade Federal do Acre. O método de exposição apresenta os dados seriais com narrativas de casos, aliando uma perspectiva micro-histórica para discutir os temas investigados. Assim, espera-se, como pano de fundo, enfrentar alguns silêncios da historiografia amazônica a respeito da expansão dos seringais nessa parte do Brasil, principalmente no uso insuficiente das fontes primárias para tratar desse assunto.

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

Currently, 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).

IMPACTS OF URBAN DEVELOPMENT ON AN OXBOW LAKE IN THE AMAZON REGION: LANDSCAPE AND GEOCHEMICAL EVIDENCE

Amapá Lake is an abandoned meander of the Acre River, the margins of which are occupied by agricultural settlements, smallholdings, fish farms and dirt roads. This paper discusses the impact of this occupation on the lake area based on field data and physical-chemical and elementary chemical analyses of the lake and river waters. The strong physical changes in the lake landscape have impacted the quality of its water. During the dry season (low water), when the temperature of the water reaches 30-34ºC, there is a proliferation of green algae and in the area affected by fish farms and smallholdings there is an increase in total dissolved solids, electrical conductivity, and transparency, while turbidity and total suspended solids become more concentrated during the flood season. The anthropogenic impact is also indicated by the higher levels of ammonia, chlorides, bromides, and phosphates in the water. However, the concentrations of dissolved metal ions are all consistent with those found in the Acre River, and other muddy water lakes and rivers in the Amazon basin, reflecting the mineralogy of the suspended material. The concentrations of most heavy metals (Pb, Cu, (Zn), Cd and Hg) are below 0.01 mg L-1, while that of Hg (0.006 mg L-1) is above the recommended limits for human consumption. Overall, the results of the study indicate that Amapá Lake is suffering ongoing impacts (physical and chemical) from urban development, which are mitigated by the periodic flooding of the river. Key words: Urban expansion, Environmental impacts, Waters, Heavy metals.

Helminth diversity in Pimelodus blochii Valenciennes, 1840 (Osteichthyes: Pimelodidae) in two Amazon Rivers

Structure of the helminth community and analyses of helminth population parameters of Pimelodus blochii collected in the Xapuri River in comparison with those in the Acre River were evaluated. Eight adult helminth species were found parasitizing P. blochii in the Acre River: the nematodes Orientatractis moraveci, Rondonia rondoni, Philometroides acreanensis, Cucullanus (Cucculanus) pinai pinai, Procamallanus (Spirocamallanus) pimelodus, Rhadochona acuminata, and Brasilnema sp., and the trematode Dadaytrema oxycephala. For Xapuri’s fishes, nine helminth species were found: the nematodes O. moraveci, R. rondoni, C. (C.) pinai pinai, Procamallanus (Spirocamallanus) rarus, P. (S.) pimelodus, R. acuminata, Brasilnema sp., and Cystidicolidae gen. sp., and the trematode D. oxycephala. Nematode and Acanthocephala larvae were also reported. Helminth abundance, prevalence, and diversity were influenced by seasonality and locality (river). The helminth parasites from Acre’s fishes formed a subset of the helminth community of the Xapuri’s. The results indicate an influence of the environmental characteristics of the rivers on the helminth community structure and diversity. This is the first study of the parasite community of P. blochii in the Xapuri River. The paretheses of (Spirocamallanus) and (S.) should not be in italics all along the text and tables.

Ichthyofauna of sandy beaches along the Acre river, Brazil

Abstract: Despite increasing efforts in recent years to catalog the fish diversity of Amazonian rivers, many regions are still under-sampled, and sandy beach environments are particularly poorly understood. The present study focused on a 300 km stretch of the Acre river, in the southwestern Amazon basin, where we sampled 30 sandy beaches separated by a mean interval of 10 km. We collected 15,329 fish representing 80 species, 26 families, and nine orders. The Characiformes were the most abundant order, providing 88.24% of the individuals collected, followed by the Siluriformes, with 10.03%, while the Siluriformes had the highest species richness, with 37 species (45.0%), followed by the Characiformes, with 30 (37.5%). The most abundant species were the characiforms Knodus orteguasae and Creagruto barrigai. Reliable data on a region’s biota is fundamental for the evaluation of patterns of biodiversity, and the occurrence and management of threatened species. As fish are directly affected by pollutants and the degradation of aquatic environments, further research in areas that are still poorly sampled will be essential for the elaboration of effective conservation strategies.

Climate variability and hospitalizations due to infectious diarrheal diseases in a municipality of the Western Brazilian Amazon Region.

Morbimortality due to infectious diarrheal diseases still is a serious health issue in Brazil and is highly related to factors such as weather, environment, and people's life conditions. This study aimed to analyze the relationship between hospitalization rates due to infectious diarrheal diseases among the population of the municipality of Rio Branco (AC), Brazil and precipitation, river level, humidity and temperature between 2000 and 2013. Data were retrieved from the Hospital Information System of the SUS (Unified Health System), the National Institute of Meteorology and the National Water Agency. Multiple Poisson and negative binomial regression models were adjusted. Results showed that there is a positive association between hospitalization due to infectious diarrheal diseases and the level of the Acre river (RR: 1.07; CI 95%: 1.04 to 1.1); these hospitalization rates fell 14% between 2000 and 2013 (RR: 0.86; CI 95%: 0.85 to 0.87). The most vulnerable group was the age group of less than 1 year of age. This study showed the vulnerability of an Amazonian city to climate variability and its respective epidemiological influence on the incidence of hospitalizations due to infectious diarrheal diseases.

Metazoan parasites of Calophysus macropterus (Siluriformes: Pimelodidae) in the Acre and Iaco rivers in the western Amazon region of Brazil: diversity, similarity and seasonal variation

ABSTRACTThe diversity, similarity and seasonal variation of metazoan parasite communities in Calophysus macropterus in the Acre and Iaco rivers, in the western Amazon (Brazil), was investigated. Parasites from 13 taxa were collected from C. macropterus in both rivers: four species of monogeneans, four nematodes, two cestodes, one digenean, one crustacean and one pentastomid. In hosts from the Acre river, Cucullanus pinnai predominated; while in hosts in the Iaco river, Monticellia amazonica predominated. The component communities of the parasites among the hosts in the two rivers presented high similarity (100%). Prevalence of Alinema amazonicum was higher in hosts in the Acre river; while the prevalence of C. pinnai was higher in hosts in the Iaco river and the mean prevalence and abundance of M. amazonica were higher in fish from the Iaco river. Regarding C. macropterus from the Acre river, infection levels by A. amazonicum were higher during the rainy season, while Demidospermus pinirampi only occurred in the dry season and Procamallanus (Spirocamallanus) inopinatus only occurred in the rainy season. In hosts from the Iaco river, infections by larvae of Anisakidae gen. sp. were higher during the dry season, while infection by Rudolphiella piracatinga and Sebekia sp. only occurred in the rainy season. However, P. (S.) inopinatus, Ergasilus callophysus, Ameloblastella unapi, Demidospermus luckyi, Demidospermus macropteri and D. pinirampi only occurred in the dry season. High similarity of the component communities of the parasite was observed between the rainy and dry seasons. These results suggest that factors other than location and seasonality were influencing the communities and infracommunities of the parasites found. Lastly, C. macropterus is a new host for almost 50% of the parasite species found. In addition, the results from the present study have expanded the geographical range of these 13 species of parasites to the western Amazon region.

Length–weight relation of the 14 fish species occurring on sandy beaches along a tropical river in the Amazon

We analyzed the length-weight relation (LWRs) of 14 species of fish, sampled in 30 sandy beaches along the Acre river, encompassing approximately 300 km of the river between the municipalities of Brasileia and Rio Branco, Acre state, Brazil, during the draught period in 2017 (August and September). For sampling, we used a picaré type trawl with 9 m of length, 2 m of height and 5 mm mesh between opposing knots, during the day and night periods. New information was made available for eight fish species.

Climatic variables associated with dengue incidence in a city of the Western Brazilian Amazon region

This study aimed to examine the impact of climate variability on the incidence of dengue fever in the city of Rio Branco, Brazil. The association between the monthly incidence of dengue fever and climate variables such as precipitation, temperature, humidity, and the Acre River level was evaluated, using generalized autoregressive moving average models with negative binomial distribution. Multiple no-lag, 1-month lag, and 2-month lag models were tested. The no-lag model showed that the incidence of dengue fever was associated with the monthly averages of the Acre River level (incidence rate ratio [IRR]: 1.09; 95% confidence interval [CI]: 1.02-1.17), compensated temperature (IRR: 1.54; 95% CI: 1.22-1.95), and maximum temperature (IRR: 0.68; 95% CI: 0.58-0.81). The 1-month lag model showed that the incidence of dengue fever was predicted by the monthly averages of total precipitation (IRR: 1.21; 95% CI: 1.06-1.39), minimum temperature (IRR: 1.54; 95% CI: 1.24-1.91), compensated relative humidity (IRR: 0.90; 95% CI: 0.82-0.99), and maximum temperature (IRR: 0.76; 95% CI: 0.59-0.97). The 2-month lag model showed that the incidence of dengue fever was predicted by the number of days with precipitation (IRR: 1.03; 95% CI: 1.00-1.06) and maximum temperature (IRR: 1.23; 95% CI: 1.05-1.44). Considering the impact of global climate change on the region, these findings can help to predict trends in dengue fever incidence.

Fluctuación estacional de Rotifera de un lago tropical en la Amazonia (llanura de inundación del Río Acre, Brasil)

Fluctuación estacional de Rotifera de un lago tropical en la Amazonia (llanura de inundación del Río Acre, Brasil)

Abrasive effects of sediments on impellers of pumps used for catching raw water

ABSTRACT This study presents an analysis of the abrasive effects of sediments from the bed of the Acre River, Brazil, on the wear of three different ferrous materials employed in the manufacture of impellers of centrifuge pumps used to catch raw water. In order to evaluate the abrasive wear and specific wear coefficient (k) as a function of sediment concentration, tests were conducted in samples of SAE 8620 steel, nodular cast iron and gray cast iron by using a rotary-ball abrasion meter. These tests employed abrasive slurry with concentration of 1, 2, 3, 5 and 10 g L-1 of sediments in distilled water. The volume of worn material as a function of the relative velocity of water flow in relation to the impeller blades was mathematically estimated. The experimental results showed that: i) The semi-angular and semi-rounded shapes of the sediments from the Acre River produced evidence of micro-grooving and plastic deformation in the three metallic alloys; ii) SAE 8620 steel showed higher resistance to abrasive wear than samples of gray and nodular cast iron; iii) the increase in the volume of worn material due to increment in sediment concentration and the relative velocity of the mixture (water + sediment) to the rotor pads.

Pollen and seed dispersal of Brazil nut trees in the southwestern Brazilian Amazon

ABSTRACT Pollen and seed dispersal patterns greatly influence the spatial distribution of plant genetic diversity. Microsatellite-based parentage analysis provides accurate estimates of contemporary gene dispersal. Although most tropical trees have been shown to exhibit widespread pollen dispersal, few studies have estimated contemporary gene dispersal after seedling establishment. Bertholletia excelsa (Lecythidaceae) is pollinated by large-bodied bees, while previous seed-tracking experiments suggest their seeds are mainly dispersed across very short distances by scatter-hoarding rodents, who primarily act as seed predators. Here we used parentage analysis to provide contemporary estimates of pollen and seed dispersal in B. excelsa recruits. We examined six 25-ha plots located in two natural stands in the Acre River valley, in the southwestern Brazilian Amazon. We used 11 microsatellite markers to estimate genetic diversity and fixation index parameters in adults, seedlings and saplings. Genetic diversity was moderate and did not differ across size classes or sampling locations. We assigned pollen and seed parents for < 20% of the recruits, indicating that most events of realized gene flow occurred beyond our 25-ha plots. Only 10 parentage assignments were confirmed with 80% confidence. Pollen distance ranged from 33 to 372 m and seed dispersal from 58 to 655 m. Actual seed-dispersal distances were far greater than the estimates obtained in previous seed-tracking experiments. Thus, studies encompassing larger sampling areas are necessary to determine a more representative spatial scale of B. excelsa’s pollen and seed dispersal capacity in natural stands.

Case study: Effects of sediment concentration on the wear of fluvial water pump impellers on Brazil's Acre River

The most important factor causing surface wear in hydraulic systems is the impact produced by abrasive particles suspended in the water flow. The impact conditions, such as mean particle velocity; particle mass; abrasive particle concentration in the liquid flow (number of particles per unit of liquid volume, size distribution of the particles); angle of attack at which the particles collide with the surface; and duration of the effect produced by the particles on the surface contribute to the development of the abrasion process. The wear resistance of the centrifugal pump impellers depends on the characteristics of the materials used in their manufacture and the abrasiveness of the suspended sediments in the pumped water. Despite special care in choosing the material used in its manufacture, abrasive wear is practically impossible to totally avoid. This work analyses the wear of ductile cast iron impeller blades of a centrifugal pump, used at the Fluvial Water Elevation Station (FWES) of the Acre River sedimentary basin in Brazil, due to the sediment concentration variation and the river water level. To determine the wear pattern and the relationship between the material and specific wear coefficient (k) due to increased sediment concentration, a ball-cratering microscale abrasive wear test was performed on samples of ductile cast iron, withdrawn from a used impeller, and abrasive suspensions at concentrations of 1, 2, 3, 5 and 10 g L−1 of river sediment in distilled water. The wear volume to the impeller blades due to the relative velocity of the mixture (water + sediment) and the wear accumulated in an annual hydrological cycle were estimated mathematically. The results showed that: i) the k remains constant regardless of the normal force (FD) applied in the tests in the abrasometer; ii) the wear tests showed the abrasive capacity of the sediments at different concentrations; and iii) the rotational control of the pump speed based on the sediment concentration and the river water level can contribute to a reduction in wear of up to 30% considering the hydrological cycle.

A new rodent (Caviomorpha: Dinomyidae) from the upper Miocene of southwestern Brazilian Amazonia

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-A64879AAFC7Ahttp://www.zoobank.org/NomenclaturalActs/16235A7B-A261-445E-8DD4-940AB21DCB06