Search

A new genus and species of chinchilloid rodent is described here. It was found in Colhuehuapian levels (early Miocene) of the localities of Bryn Gwyn and Gran Barranca, Chubut Province, Argentina. The new taxon shows a unique combination of characters (e.g., protohypsodont teeth, upper molars trilophodont, m1 and m2 tri- or tetralophodont with the second crest in position of variable development, and m3 trilophodont, cement absent) that make it different from any other known chinchilloids. We performed a phylogenetic analysis to corroborate the relationships of the new taxon within the Chinchilloidea. Our results indicate that the new taxon is best classified as Chinchilloidea incertae sedis, together with Incamys, Garridomys, and Scotamys. These species form the basal stock that leads to the modern lineage Chinchillidae (chinchillas and viscachas). The presence of the new taxon in these localities increases the diversity of chinchilloids during the early Miocene and reduces the dissimilarity between the faunas found in Bryn Gwyn and Gran Barranca. Un nouveau genre et une nouvelle espèce de rongeur chinchilloïde sont ici décrits. Celui-ci a été trouvé dans les niveaux colhuéhuapiens (Miocène inférieur des localités de Bryn Gwyn et de Gran Baranca, province de Chubut, Argentine). Le nouveau taxon montre une combinaison unique de caractères (à savoir, dents protohypsodontes, molaires supérieures trilophodontes, m1 et m2 tri- ou tétralophodontes avec la seconde crête en position de développement variable et m3 trilophodonte, ciment absent) qui le rend différent de tous les autres chinchilloïdes connus. Une analyse phylogénétique a été réalisée pour confirmer les relations du nouveau taxon au sein des Chinchilloidea. Nos résultats montrent que le nouveau taxon se classe au mieux en tant que Chinchilloida incertae sedis, avec Incamys, Garridomys et Scotamys. Ces espèces forment le stock basal qui conduit à la lignée moderne des Chinchillidae (chinchillas et viscachas). La présence du nouveau taxon dans ces localités augmente la diversité des chinchilloïdes pendant le Miocène inférieur et réduit la différence entre les faunes trouvées à Bryn Gwyn et à Gran Barranca. Fil: Busker, Felipe. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; Argentina Fil: Pérez, María E.. Museo Paleontológico Egidio Feruglio; Argentina Fil: Dozo, María T.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; Argentina

The evolution of subterranean and fossorial rodents has been linked to the Neogene climatic shift to xeric conditions leading to open vegetation, like prairies and grasslands; most modern subterranean rodents occur in arid and open areas. Among South American spiny rats (family Echimyidae), the subfamily Euryzygomatomyinae includes both fossorial (Clyomys and Euryzygomatomys) and ambulatorial (Trinomys) genera, some of them endemic to open vegetated areas and other ones restricted to forested regions. The closely related genus Carterodon is also a fossorial rodent endemic to open vegetated areas. If the open environments constitute a determinant factor triggering the evolution of fossoriality in these spiny rats, it is expected that the fossorial lineages evolving since the Miocene in open environments (Carterodon sulcidens and Clyomys laticeps) show morphologies more specialized for digging than those currently restricted to Atlantic Forest habitats (Euryzygomatomys spinosus). Moreover, it is likely that Trinomys species specialized for xeric environments (T. albispinus and T. yonenagae) show incipient adaptations for fossoriality. The appendicular skeleton of three fossorial and five ambulatorial echimyid species were morphometrically analyzed with multivariate statistical approaches in order to test these presuppositions. The analyses showed that the appendicular morphology of T. yonenagae and T. albispinus, in comparison with the Atlantic Forest Trinomys species, and of C. sulcidens and C. laticeps in relation to E. spinosus are more adapted to scratch-digging activities, corroborating the hypothesis that open environments favor the evolution of fossoriality in spiny rats.

The Subfamily Dolichotinae comprises two living species, Dolichotis patagonum, an emblematic component of the Patagonian fauna of Argentina, and Dolichotis salinicola, endemic to the Chaco ecoregion. These two species are also considered as pertaining to different genera, D. patagonum and Pediolagus salinicola. The oldest records of Dolichotis come from the Pliocene–Pleistocene boundary of northeastern and central Argentina, and the late Pleistocene from southern Brazil, and northern and southern Uruguay. Five fossil species were described from the Pleistocene and Holocene in central Argentina (D. minor, D. plathycephala, D. major, D. intermedia, and D. improla). “Orthomyctera” chapalmalense was described on the basis of remains from the coast of Mar del Plata and Chapadmalal, Buenos Aires Province, Chapadmalal Formation (late Pliocene, 3.74–3.04 Ma). A new detailed description of the holotype and its comparison with closely related taxa suggests that this species is more related to the genus Dolichotis, resulting in the new combination D. chapalmalense. The close affinities with Dolichotis revealed by phylogenetic analyses combined with molecular and morphological characters were corroborated in previous analyses. The origin of this lineage extends at least to a million years ago, taking the record back to the middle Pliocene. The evolutionary novelties that appear at least since the Pliocene, marking a key period for the Caviidae, are analyzed. Based on a phylogenetic perspective with the inclusion of the fossil record, our data support the inclusion of the two species (D. patagonum and D. salinicola) in a single genus., Facultad de Ciencias Naturales y Museo

Background The rich rodent assemblages from the Eocene–Oligocene deposits of the Jebel Qatrani Formation (Fayum Depression, Egypt) have important implications for our understanding of the origin and paleobiogeography of Hystricognathi, a diverse clade that is now represented by the Afro-Asiatic Hystricidae, New World Caviomorpha, and African Phiomorpha. Methods Here we present previously undescribed material of the enigmatic hystricognath clade Phiocricetomyinae, from two stratigraphic levels in the lower sequence of the Jebel Qatrani Formation—a new genus and species (Qatranimys safroutus) from the latest Eocene Locality 41 (~34 Ma, the oldest and most productive quarry in the formation) and additional material of Talahphiomys lavocati from that species’ type locality, early Oligocene Quarry E (~31–33.2 Ma). Results The multiple specimens of Qatranimys safroutus from L-41 document almost the entire lower and upper dentition, as well as mandibular fragments and the first cranial remains known for a derived phiocricetomyine. Specimens from Quarry E allow us to expand comparisons with specimens from Libya (late Eocene of Dur at-Talah and early Oligocene of Zallah Oasis) that have been placed in T. lavocati, and we show that the Dur at-Talah and Zallah specimens do not pertain to this species. These observations leave the Fayum Quarry E as the only locality where T. lavocati occurs.

El género Galea (Rodentia, Caviidae) incluye cinco especies vivientes y dos extintas de cávidos terrestres y herbívoros, que ocupan pastizales y matorrales rocosos, tanto en áreas altas como bajas de América del Sur. Algunas muestras fósiles del Pleistoceno-Holoceno del centro-este de Argentina han sido referidas como Galea sp., G. musteloides o G. cf. musteloides y finalmente se describieron como una nueva especie bajo el nombre de G. tixiensis. Sin embargo, estudios recientes basados en series grandes de individuos fallaron en encontrar diferencias morfológicas cualitativas entre G. lecucoblephara y G. tixiensis. Sobre la base de estos hallazgos, en esta contribución revisamos el estatus taxonómico de la especie extinta G. tixiensis. Se examinaron 110 individuos de las tres subespecies actualmente reconocidas de G. leucoblephara (i.e., G. l. demissa, G. l. leucoblephara y G. l. littoralis) de Argentina, Bolivia y Paraguay. Se registraron nueve medidas cráneo-dentarias. Los datos cuantitativos se sometieron a un análisis de componentes principales (PCA) con el fin de identificar la contribución de cada medida a la varianza total. Los caracteres cualitativos se evaluaron a través de las comparaciones de los rasgos supuestamente diagnósticos de G. tixiensis con la variabilidad representada por las muestras recientes. Los espacios multivariados de las tres subespecies estudiadas se superpusieron ampliamente en el PCA, lo que sugiere que estos taxones no difieren significativamente en la figura del cráneo. El holotipo de G. tixiensis se ubicó dentro del morfoespacio correspondiente a muestras recientes de G. l. littoralis. Los caracteres cualitativos supuestamente diagnósticos de G. tixiensis también se verificaron en muestras recientes de G. leucoblephara, en particular de G. l. littoralis. Sobre la base de sus rasgos craneanos cualitativos y cuantitativos se sugiere que G. tixiensis es un sinónimo de G. leucoblephara. Los mayores valores para algunos rasgos craneanos cuantitativos en las muestras fósiles –comparadas con las actuales– son reinterpretados en este trabajo como una respuesta ecofenotipica a las condiciones climáticas más severas durante el Holoceno. The genus Galea (Rodentia, Caviidae) includes five living and two extinct species of terrestrial and herbivorous cavies that inhabit grasslandsand rocky scrub areas at both high and low elevations in South America. Fossil samples from the late Pleistocene-Holocene from central-easternArgentina have been referred to as Galea sp., G musteloides or G. cf. musteloides and finally described as a new species under the name of G. tixiensis. However, recent studies based on large series of individuals fail to find qualitative morphological differences between G. leucoblephara and G.tixiensis. Based on these findings, in this contribution we reviewed the taxonomic status of the fossil species G. tixiensis. A total of 110 individualsof the three currently recognized subspecies of G. leucoblephara (i. e., G. l. demissa, G. l. leucoblephara and G. l. littoralis) from Argentina Boliviaand Paraguay were examined. Nine craniodental measurements were recorded. Quantitative data were subjected to a principal component analysis (PCA) in order to identify the contribution of each measurement to the total variance. Qualitative characters were evaluated through the comparisons of the diagnostic traits of G. tixiensis with the variability derived from the recent samples. PCA showed a high overlap of the multivariate spaces of the three subspecies studied, suggesting that they do not differ significantly in terms of cranial shape. The holotype of G. tixiensis was allocated within the morphospace of the recent G. l. littoralis samples. Qualitative traits diagnostic of G. tixiensis were also recorded in recent samples of G. leucoblephara, in particular of G. l. littoralis. Based on both qualitative and quantitative cranial traits, we suggest that G. tixiensis is a synonym of G. leucoblephara. The morphological traits supposedly unique to G. tixiensis were also recorded in specimens of living populations of G. l. littoralis. The large values of some quantitative cranial traits in fossil samples -compared to living ones- are reinterpreted here as an ecophenotypical response to the more severe climatic conditions of the Holocene. Fil: Teta, Pablo Vicente. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales ; Argentina Fil: Campo, Denise Heliana. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales ; Argentina

South American giant fossil rodents represent a notable example of an extreme evolutionary trend towards size differentiation among caviomorph lineages. Although spectacular, fossil remains of these animals are uncommon and usually highly incomplete. We here describe fully grown adult and juvenile fossil specimens from the rodent family Dinomyidae Alston, 1876, collected from the same location, lithostratigraphical formation and fossiliferous horizon: the coast of the Rio de la Plata of southern Uruguay in pelitic sediments assigned to the late Miocene Camacho Formation. The adult remains consist of an almost complete skull with partial jaw and represent the first published description of associated craneo-mandibular remains of a giant rodent within the subfamily Eumegamyinae. The juvenile specimen is the first to be recognized as such for the entire subfamily, and consists of a complete mandible and a right calcaneus. Based on the homologies observed in the configuration of the teeth, the new specimens a...

Wild cavies from the taxon Cavia aperea–Cavia porcellus are known for their extensive use of acoustic signals for communication including a courtship call that is a rarity in Mammalia. The genus Ca...

Herbivores exhibit specializations at the intestinal level that facilitate the bacterial fermentation. The available information on the digestive physiology of Lagostomus maximus makes this rodent an interesting model to evaluate morpho-functional adaptations to herbivory. The general objective of this work was centered on the study of the morphology and histochemistry of the descending colon and rectum of L. maximus. To do so, a comparative analysis of the morphology, ultrastructure and glycosylation pattern of both anatomical regions was carried out. Histochemical results revealed that in both sectors of the large intestine, there are goblet cells with different glycosylation pattern within a morphologically homogeneous cell population. The main difference between both intestinal segments lay in the fact that the most distal region of the large intestine showed a greater proportion of sialomucins, characterized by being slightly O-acetylated. Further specific differences were revealed by lectin histochemistry. These data allowed to perform a functional interpretation of the cell types and secreted substances, thus contributing to a better understanding of the role of mucins in the intestinal tract functioning. Fil: Tano de la Hoz, María Florencia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentina Fil: Flamini, Mirta Alicia. Universidad Nacional de La Plata. Facultad de Ciencias Veterinarias; Argentina Fil: Portiansky, Enrique Leo. Universidad Nacional de La Plata. Facultad de Ciencias Veterinarias; Argentina Fil: Díaz, Alcira Ofelia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata; Argentina

Cavioids are one of the most eco-morphologically divergent clades among South American caviomorph rodents. In an unique way, they display three mandibular morpho-types which are linked to the relative positions and relations among masseteric muscles. The derived configuration present in Caviidae would be linked to a preponderance of grinding function during mastication. Oppositely, a greater vertical component in the plesiomorphic condition, observed in Dasyprocta and Cuniculus, could be linked to a likely predominant crushing function. These differences also are associated with changes in the direction of mastication; caviids have more propalinal movements of mandible whereas those taxa with the plesiomorphic morphology show more oblique movements. The sister clade of caviids represented by †Guiomys unica and †Prodolichotis pridiana, show relative high values of teeth scars inclination, indicating a slightly oblique mastication. Differences in masseteric configurations and masticatory patterns among cavioids would correspond mainly to variations in the diet, which in turn is related to the environmental conditions where each species lives. Caviids are mostly graminivorous/folivorous while dasyproctids and cuniculids have more frugivorous/folivorous diet. The plesiomorphic condition of the mandibular masseteric configuration is present in the oldest cavioids, from the first records in the Oligocene (about 33 Ma) while the derived condition is recorded from middle late Miocene (11.5 Ma), Based on the phylogenetic mapping of variables representing masseteric muscular structure and masticatory patterns we detected a potential association between the stepwise morphological evolution observed among cavioids with environmental changes occurred during Cenozoic era. Fil: Alvarez, Alicia. 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 Fil: Pérez, María Encarnación. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Museo Paleontológico Egidio Feruglio; Argentina. Field Museum Of Natural History; Estados Unidos

The South American rodents of the genus Ctenomys (Rodentia, Hystricognathi), which use both forelimbs and incisors to dig, show strong, specialized morphological adaptations to living in the underground niche. In these rodents, the effectiveness of a bite − in this case the potential to inflict physical damage − mostly depends on the strength of the incisors (e.g. bending and torsion stresses) and the power of the masseteric muscle of the jaw. Ctenomys australis (the sand dune tuco-tuco) is a highly territorial subterranean rodent that builds large and exclusive burrow systems in coastal sand dunes found continuously along the Atlantic coast of the Buenos Aires province, Argentina. Incisors in this species are used both in agonistic encounters among congeners (i.e. reproductive or territorial intentions) as well as to dig and increase the size of their burrows daily (e.g. acquisition of plant material as food resources). We first characterized sexual dimorphism in cranial traits involved in aggressive interactions between males, analyzing ontogenetic trajectories of both sexes. We also analyzed some remarkable attributes of sexual dimorphism in subadult and adult individuals, the bending and torsion stresses and the bite performance in vivo, hypothesizing that males are able to apply comparatively stronger bite forces at their incisor tips than females, concordant with a broader mandible for the insertion of a powerful adductor musculature. Bite forces were measured in vivo in wild animals of both sexes using a strain gauge load cell force transducer. These individuals were also used to estimate the incisor area (CA), the 2nd moment of inertia of the incisors (I, or the bending strength to external forces), and the torsional strength of the incisor (J), all traits involved in the production of the force that can be withstood at the incisor tips. Ontogeny explained some sexual differences in the cranial traits of adults, expressed as (i) morphological changes related to body size variation, and (ii) morphological changes associated with differences in the slope of ontogenetic trajectories (regardless of body size variation). Recordings of in vivo bite forces were significantly higher in adult males than in females. These differences in bite forces were not associated with the sex itself, but the sexual dimorphism in body size. Although males did not show significantly higher allometric coefficients for I, J and CA than females, males still showed a strong sexual dimorphism in these traits due to body size variation. On the other hand, measurements of mandibular width – an estimator of the relative size of masseteric muscles – in vivo showed strong differences between sexes, suggesting higher force performance at the incisor tips for males. Overall, we observed that many attributes related to bite performance might have been molded by sexual selection, which implies differences in allometric coefficients from some morphological traits throughout ontogeny. Fil: Mora, Matias Sebastian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina Fil: Becerra, Federico. Institut Max Planck for Evolutionary Anthropology; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina Fil: Vassallo, Aldo Iván. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina

‘Cardiomyine’ rodents are extinct large terrestrial Caviidae closely related to capybaras, that inhabited large parts of South America during the middle Miocene and Pliocene. They are mostly preserved as isolated teeth, but also as skull and jaw fragments. Here we revise the taxonomy of this group and describe two new species, each pertaining to one of the two main late Miocene groups, represented by the genera Caviodon and Cardiomys. This suggests that the diversity of ‘cardiomyines’ was higher than previously thought. Among the specimens studied there are two almost complete skulls; one from the Andalhuala Formation, Catamarca, and the other from the Arroyo Chasicó Formation, Buenos Aires. The first, housed in the Field Museum of Natural History, was originally catalogued as Cardiomys ameghinorum, a common species for the late Miocene of north‐western Argentina (NOA), but is here transferred to the genus Caviodon. This is the first mention of the genus for NOA, enlarging its geographical distribution for the late Miocene. The second skull, assigned to Cardiomys sp., is housed in the Museo de La Plata. Furthermore, from the revision of the holotypes of the species of Caviodon (C. multiplicatus, C. bravardi, C. (Lelongia) paranensis, C. angustidens and C. scalai from the Conglomerado osífero of the Ituzaingó Formation; late Miocene, Argentina) we propose their synonymy with the type species C. multiplicatus, decreasing the specific diversity in that locality. Finally, our phylogenetic analysis indicates that the species of ‘cardiomyines’ are paraphyletic, placing them in a basal position among the Hydrochoerinae. Fil: Pérez, María Encarnación. Museo Paleontológico Egidio Feruglio; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Deschamps, Cecilia Marcela. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Paleontología Vertebrados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Vucetich, María Guiomar. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Paleontología Vertebrados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

A capivara é uma espécie altamente social que vive em grupos multi-macho e multi-fêmea hierarquicamente organizados. Um rico repertório de comportamentos, incluindo o acústico, regula as interações sociais e organiza a vida em sociedade. Para investigar o repertório acústico da espécie realizamos o levantamento e a descrição categorizada das vocalizações. Os sinais acústicos foram registrados a partir de uma população de vida livre habitante do campus da USP de Ribeirão Preto e um grupo de capivaras do Bosque e Zoológico Municipal Fábio Barreto, em Ribeirão Preto. Nossos resultados mostram a existência de dez sinais acústicos, alguns deles com 3 a 4 variantes, o uso de um sistema de combinação de notas, e a presença de efeitos não-lineares em sinais relacionados a estados internos alterados como no grito de agonia emitido durante a contenção. Os resultados encontrados apontam para uma riqueza maior e mais variada de chamados já descritos na literatura revelando um repertório acústico comparável com o descrito para o mocó (Kerodon rupestris), o preá (Cavia aperea) e outros caviomorfos. O registro de outros níveis de organização de notas e a presença de elementos não-lineares também enriquecem o sistema de comunicação da espécie e demostram a sua complexidade. Nossos resultados vêm trazer contribuições de forma a complementar a descrição do repertório da espécie que se mostrou maior e mais complexa The capybara is a highly social species that lives in hierarchically organized multi-male/multi-female groups. A rich behavioral repertoire, including acoustic signalization, mediates social interactions and life in society. To investigate the acoustic repertoire of this species we conducted a survey and categorization of calls. The acoustic signals were registered from a population living free local campus of USP in Ribeirão Preto and of a captive group (Bosque e Zoológico Municipal Fábio Barreto) in the municipality of Ribeirão Preto. Our results show the existence of ten different acoustic signals, some of them subdivided in 3 to 4 variant, and the use of note composition from two different types, and non-linearity in distress signals, as those produced by under containment individuals. The results point to a larger and more varied richness of calls already described in the literature showing an acoustic repertoire comparable to that described for the mocó (Kerodon rupestris) , the guinea pig (Cavia aperea) and other caviomorph . The registry of other levels of organization of notes and the presence of non - linear elements also enrich the communication system of the species and demonstrate its complexity. Our results come bring contributions to complement the description of the repertoire of the species that was larger and more complex

The Ctenohystrica is one of the three major lineages of rodents and contains diverse forms related to gundis, porcupines, and guinea pigs. Phylogenetic analyses of this group using mitochondrial and nuclear gene sequences confirm the monophyly of the infraorder Hystricognathi and most of its recognized subclades, including both the Neotropical caviomorphs and the African phiomorphs, which are recovered as sister groups. Molecular timetrees calibrated with 22 securely placed fossils indicate that hystricognath superfamilies originated in the Eocene and Oligocene and most families had appeared by the end of the Oligocene, ∼23 Mya. Divergences leading to hystricognath genera took place in the Miocene and Pliocene, with a single exception. The naked mole-rat (Heterocephalus) diverged from other African mole-rats (Bathyergidae) in the early Oligocene (∼31.2 Mya), when the four caviomorph superfamilies (Erethizonoidea and Cavioidea at 32.4 Mya, Chinchilloidea and Octodontoidea at 32.8 Mya) were first appearing in South America. The extended independent evolution of Heterocephalus suggested by this analysis prompted a closer examination of mole-rat characters. Heterocephalus indeed shares many characters with bathyergids, befitting their joint membership in the parvorder Bathyergomorphi and superfamily Bathyergoidea as well as their shared exploitation of subterranean lifestyles. However, a diverse array of cranial, dental, postcranial, external, and ecological characters distinguishes Heterocephalus from other African mole-rats. These differences equal or exceed those used to diagnose caviomorph families and justify recognizing the naked mole-rat in its own family, Heterocephalidae Landry, 1957. This taxonomic arrangement poses questions for the inter-relationships of fossil and extant mole-rats and brings time equivalence to the ranks assigned to the major clades of hystricognaths. © 2014 The Linnean Society of London

Hydrochoerinae is a clade of caviomorph rodents broadly distributed in South America, which includes the maximum body size recorded among extant rodent taxa. The most basal forms of this group are an assemblage of small to medium body size extinct taxa with a plesiomorphic dentition, traditionally clustered in the group cardiomyines. One of the oldest known cardiomyine is Procardiomys martinoi (Chasicoan South American Land Mammal Age SALMA; early late Miocene), which was known only from the holotype, a fragmentary palate with the left and right molar series. New mandibular remains from the Arroyo Chasicó Formation (Chasicoan SALMA) are described and identified here as belonging to P. martinoi because they share a unique combination of characters (as well matching in size) with the upper dentition of the holotype. These materials help in critically reviewing the taxonomic identification of the mandibular remains previously assigned to Procardiomys and allow testing the phylogenetic affinities of this taxon within Caviidae. P. martinoi is depicted as one of the most basal forms of Hydrochoerinae, placed basally on the lineage leading to extant capybaras after the split between the common ancestor of Kerodon and Hydrochoerus. Fil: Perez, Margarita E.. Museo Paleontológico Egidio Feruglio; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Vucetich, María Guiomar. 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; Argentina Fil: Deschamps, Cecilia Marcela. Universidad Nacional de la Plata. Facultad de Ciencias Naturales y Museo. División Paleontología Vertebrados; Argentina. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas; Argentina

Cavioidea is represented today by Dasyproctidae (agouties), Cuniculidae (pacas), and Caviidae (cavies or “guinea pigs”, maras, mocos, and capybaras). Cavioidea sensu stricto (Cavioidea s.s.) clusters the extant and extinct Caviidae together with a diverse assemblage of extinct taxa grouped in the family Eocardiidae. Recent phylogenetic analyses of this group based on morphological characters corroborated the monophyly of Cavioidea s.s., but retrieved a paraphyletic arrangement of “eocardiids” as successive sister taxa of the crown-group Caviidae. The late Oligocene (Deseadan South American Land Mammal Age, SALMA) record of Cavioidea s.s. is relevant because it represents the oldest occurrence of the group, represented only by very scarce materials of Asteromys punctus and Chubutomys simpsoni . New materials of Deseadan cavioids are of prime importance to understand the early evolution of this group. The locality of Punta Nava (northeastern Santa Cruz Province, Patagonia, Argentina) has yielded a fauna assigned to the Deseadan SALMA, but no rodent remains were known so far. A recent fieldwork in this locality provided the first findings of fossil caviomorphs, including remains of Cavioidea, Octodontoidea, Chinchilloidea, and Erethizontoidea. A new species of Cavioidea s.s. from this locality is here described, and its phylogenetic affinities are evaluated. This new cavioid from the Deseadan SALMA, and the reinterpretation of the morphology of Chubutomys simpsoni , provide new insights into the early diversification of Cavioidea s.s. The new species from the late Oligocene, and the high position of Chubutomys in the phylogeny, draw back the origin of all protohypsodont lineages of Cavioidea s.s. to the Deseadan SALMA. Furthermore, this suggests that the early evolution of Cavioidea s.s. occurred through a major diversification pulse larger than previously proposed.

Blanco R.E., Rinderknecht, A. & Lecuona, G. 2011: The bite force of the largest fossil rodent (Hystricognathi, Caviomorpha, Dinomyidae). Lethaia, Vol. 45, pp. 157–163. An exceptionally well-preserved skull of the largest fossil rodent Josephoartigasia monesi allows the first analysis of the bite mechanics of this group of South American giant rodents. In this study, we reconstructed the main anatomical features of the skull of this Pliocene rodent, relating them to the bite force at incisors. Bite force was estimated using three different techniques. Two methods suggest that bite forces at incisors of around 1000 N were possible for these mammals. However, the incisors seem to be stronger than expected for this bite force implying that the bite forces may have been greater than 3000 N. We consider three hypotheses: allometric effects, teeth digging or defence against predators, to explain our results. □Bite force, Dinomyidae, incisors, largest rodent, Pliocene.

The fossil record of phiomorph hystricognathous rodents from the Afro-Arabian Paleogene is important for understanding the origins and dispersal routes of the early crown hystricognaths. Here, we describe a “new” basal phiomorph genus and species, Acritophiomys bowni, based on complete upper and lower dentitions, mandibular fragments, and partial crania from the terminal late Eocene (~34 Ma) Locality 41 (L-41) in the Fayum Depression of northern Egypt. Acritophiomys bowni is the oldest and largest representative of the family “Phiomyidae”, being more or less the same size as contemporaneous gaudeamurids, and is one of the most abundant hystricognaths at L-41. The genus exhibits a mosaic of primitive and derived features, the former shared with primitive hystricognaths, such as Waslamys and Protophiomys from the earliest late Eocene, and the latter shared with Metaphiomys from early Oligocene (~31–29 Ma) sites in the upper sequence of the Jebel Qatrani Formation. Phylogenetic analysis of craniodental features, scored across a number of different hystricognathous groups, consistently places Acritophiomys bowni and members of the genus Phiomys as basal members of the phiomorph stem lineage, implying that the commonly used family “Phiomyidae” is a paraphyletic assemblage. Among other things, this material shows that basal members of the phiomorph clade consistently replaced dP4/4 with permanent P4/4, and suggests an African origin of stem and crown Phiomorpha.

Cavioidea sensu stricto (Cavioidea s.s.) is one of the most divergent lineages within the South American Hystricognathi, and is currently represented by cavies, maras (Caviidae), and capybaras (Hydrochoeridae). Caviids and hydrochoerids have been interpreted as forming the crown group, whereas the stem group of Cavioidea s.s. is formed by “Eocardiidae”, a paraphyletic group recorded in the late Oligocene to middle Miocene, mainly in Patagonia. One of the most interesting features of Cavioidea s.s. is the record of evolution of hypsodonty, which develops relatively slowly compared to other groups of caviomorphs, enabling this process to be followed in the fossil record. Phanomys is recorded in Patagonia during the late early Miocene, and since its description this genus has been considered close to euhypsodont genera. The objective of this paper is to: (1) report new material of Phanomys; (2) re-describe the two species of the genus; (3) determine the phylogenetic position of Phanomys among Cavioidea s.s. by morphological cladistic analysis; and (4) explore the sequence of appearance of characters related to the origin of euhypsodonty. The new materials assigned to Phanomys mixtus are the first mandibular fragments and palate known, yielding valuable morphological, ontogenetic, and phylogenetic information. Phanomys vetulus is recognized as a valid species, although better material is needed for a more robust definition. The phylogenetic analysis shows that Phanomys is the sister group of euhypsodont Cavioidea s.s. The evolutionary history of Cavioidea s.s. demonstrates that character states previously thought to correlate with the degree of hypsodonty (e.g. absence of fossettes/ids) do not all appear at the same time during the evolution of the group. Although the evolutionary trend in Cavioidea s.s. shows progressively increasing hypsodonty, the morphological changes inferred from this phylogenetic analysis indicate that hypsodonty and other character states were temporally decoupled during the evolution of the group during the Oligocene and early Miocene.

International audience; The long-term isolation of South America during most of the Cenozoic produced a highly peculiar terrestrial vertebrate biota, with a wide array of mammal groups, among which caviomorph rodents and platyrrhine primates are Mid-Cenozoic immigrants. In the absence of indisputable pre-Oligocene South American rodents or primates, the mode, timing and biogeography of these extraordinary dispersals remained debated. Here, we describe South America's oldest known rodents, based on a new diverse caviomorph assemblage from the late Middle Eocene (approx. 41 Ma) of Peru, including five small rodents with three stem caviomorphs. Instead of being tied to the Eocene/Oligocene global cooling and drying episode (approx. 34 Ma), as previously considered, the arrival of caviomorphs and their initial radiation in South America probably occurred under much warmer and wetter conditions, around the Mid-Eocene Climatic Optimum. Our phylogenetic results reaffirm the African origin of South American rodents and support a trans-Atlantic dispersal of these mammals during Middle Eocene times. This discovery further extends the gap (approx. 15 Myr) between first appearances of rodents and primates in South America.

The Hydrochoeridae are caviomorph rodents of medium to large size. They are euhypso- dont and elasmodont, with a peramorphic trend to increase the number of M3 prisms from basal to advanced taxa. The diversity of this family was higher during the Miocene/Pliocene, but today they are represented by a single genus, with two species, Hydrochoerus hydrochaeris (Linnaeus, 1766) and H. isthmius GoLdman, 1912. In this paper we described fossil remains assigned to H. hydro- chaeris from Touro Passo Creek (Touro Passo Formation, upper Pleistocene, Lujanian Age) in west- ern Rio Grande do Sul State, southern Brazil. The main charac ters used to assign these specimens to H. hydrochaeris are: M3 with 13 free prisms, upper diastema shorter than the maxillary cheek teeth, rostral area relatively wide, smaller proportion s than Neochoerus Hay, 1926 and larger than H. isthmius. The presence of H. hydrochaeris suggests that in late Pleistocene of western Rio Grande do Sul State, probably existed environments with permanent water bo dies.

The family Caviidae is represented in modern faunas by cavies and maras, whereas the family Hydrochoeridae is represented by capybaras. The evolutionary origin of these families has been related to a diversity of plesiomorphic fossil forms (recorded from the late Oligocene up to the middle Miocene) traditionally grouped in the family ?Eocardiidae?. These fossil forms were included, together with Caviidae and Hydrochoeridae, within the Cavioidea s.s. (sensu stricto), because they share high crowned cheek teeth, double-hearted occlusal surface, short lower incisors, and moderate hystricognathy. Within Cavioidea s.s., caviids and hydrochoerids were interpreted as forming its crown group, because they have unique craniomandibular and dental features. In this contribution, a new taxon of Cavioidea s.s. from the middleMiocene of central Patagonia, Argentina, is described, and its phylogenetic position is determined on the basis of a morphological cladistic analysis in which ?eocardiids? were included. The study permits the understanding of the sequence of appearance of characters that originated the highly divergent morphology of crown-group cavioids. The analysis of the sequence of appearance of the characters that traditionally diagnosed the crown group indicates that these changes did not occur at the same time. On the contrary, many of these features seem to have appeared at different nodes of the evolutionary history of Cavioidea s.s. The remarkably derived morphology of modern cavioids is the result of a stepwise appearance of a mosaic of evolutionary innovations that originated gradually along the history of Cavioidea during the late-middle Miocene.?Eocardiidae?. These fossil forms were included, together with Caviidae and Hydrochoeridae, within the Cavioidea s.s. (sensu stricto), because they share high crowned cheek teeth, double-hearted occlusal surface, short lower incisors, and moderate hystricognathy. Within Cavioidea s.s., caviids and hydrochoerids were interpreted as forming its crown group, because they have unique craniomandibular and dental features. In this contribution, a new taxon of Cavioidea s.s. from the middleMiocene of central Patagonia, Argentina, is described, and its phylogenetic position is determined on the basis of a morphological cladistic analysis in which ?eocardiids? were included. The study permits the understanding of the sequence of appearance of characters that originated the highly divergent morphology of crown-group cavioids. The analysis of the sequence of appearance of the characters that traditionally diagnosed the crown group indicates that these changes did not occur at the same time. On the contrary, many of these features seem to have appeared at different nodes of the evolutionary history of Cavioidea s.s. The remarkably derived morphology of modern cavioids is the result of a stepwise appearance of a mosaic of evolutionary innovations that originated gradually along the history of Cavioidea during the late-middle Miocene. Fil: Pérez, María Encarnación. Museo Paleontológico Egidio Feruglio; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Vucetich, María Guiomar. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Departamento Científico de Paleontología de Vertebrados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina

The genus Ctenomys of subterranean rodents is one of the most diverse of the mammal radiation. In addition to external and skull morphology, studies of Ctenomys alpha taxonomy have relied in an intense manner on chromosomal variation and several populations of this genus have been characterized only by means of cytogenetic techniques. Ctenomys pearsoni is the most karyotypically variable species of the genus (2n=56-70). The goal of this study was to assess the pattern of geographic variation of the skull morphology in several karyomorphs of Ctenomys pearsoni . Our main results indicate that, with the exception of the Solis karyomorph, the remaining are morphologically indistinguishable. These results also agree with previous morphological and population genetics analyses performed in this species. Taken together the available evidence, we support the point of view that not all fixations of chromosomal rearrangement define independent evolutionary units.

Cavioidea sensu stricto groups three traditionally recognized families that are characterized by hypsodont, double-heart-shaped cheek teeth and moderate hystricognathy: Eocardiidae, Caviidae, and Hydrochoeridae. Eocardiidae was erected to include a diverse assemblage of extinct and plesiomorphic taxa, whereas Caviidae and Hydrochoeridae (the crown group of Cavioidea) include the lineages with extant representatives (cuyes, maras, and capybaras). A new genus and species of Cavioidea sensu stricto, Guiomys unica, is described here from the middle Miocene of west central Patagonia (Argentina). The new taxon is known from mandibular and maxillary fragments with molars, and isolated cheek teeth. A phylogenetic analysis of Cavioidea sensu stricto shows G. unica as the sister taxon of the clade formed by the crown group of Cavioidea sensu stricto ('medialis series'). The new species displays characters states intermediate between eocardiids and the 'medialis series.' The most outstanding character of Guiomys unica is the autapomorphic position of the notch for the insertion of the masseter medialis pars infraorbitalis muscle, isolated from both the masseteric and horizontal crests. This notch is located at the anterior end of the masseteric crest in eocardiids and represents the plesiomorphic state for Cavioidea sensu stricto. In caviids and hydrochoerids, the notch is located at the anterior end of the horizontal crest, the derived state for this character. G. unica allows reinterpretation of the homologies of the mandibular crests in basal cavioids and clarifies the evolutionary origins of crown-group cavioids (Caviidae + Hydrochoeridae). Fil: Pérez, María Encarnación. Museo Paleontológico Egidio Feruglio; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

We redescribe Andrya octodonensis based on new material from Phyllotis xanthopygus from Argentina. Andrya vesicula n. sp. from Phyllotis xanthopygus and Andrya boliviensis n. sp. from Phyllotis osliae are also described and illustrated. The occurrence of these species in South America suggests that cestodes of the genus Andrya were introduced on that continent by sigmodontine rodents from the Nearctic, probably after the formation of the Isthmus of Panama.

As presently recognized, the genus Galea is composed of 3 species, G. musteloides, G. flavidens, and G. spixii. The most widely distributed species is G. musteloides (the common yellow-toothed cavy), ranging from southern Peru to southern Argentina and from sea level to over 4,000 m elevation. Our current taxonomic and systematic understanding of Galea is based primarily on morphological studies that have been limited in both taxonomic and geographic sampling. In this study phylogenetic analyses of sequences from the cytochrome-b gene were used to test hypotheses related to the content, limits, and systematic relationships within G. musteloides. Our data support restricting G. musteloides to the highlands of northwestern Bolivia, southeastern Peru, and extreme northeastern Chile. We elevate G. leucoblephara Burmeister, 1861, for populations occupying the lowlands of Bolivia and Paraguay to central Argentina, and we elevate G. comes Thomas, 1919, for populations from the Andes of southern Bolivia and northern Argentina. Our results also suggest the presence of a previously unrecognized form at midelevations in the southern Bolivian Andes. We find support for treating G. spixii campicola as a junior synonym of G. l. demissa and G. monasteriensis as a junior synonym of G. musteloides boliviensis. Most of the evolution of the taxa within the G. musteloides complex appears to have occurred in the Prepuna biogeographic province, with 2 independent vicariant events culminating in the separation of the G. musteloides, G. comes, and G. leucoblephara clades. Dating estimates suggest a late Miocene divergence between G. spixii and the G. musteloides group, followed by species-level divergence within the G. musteloides group during the Pliocene. DOI: 10.1644/08-MAMM-A-214R1.1.

The first information on the gestation period, maternal behaviour, neonatal development and growth of the subterranean caviomorph rodent Ctenomys mendocinus Philippi, 1869, is reported herein. My hypothesis was that, despite its belonging to a typically precocial suborder, the life history traits of C. mendocinus would favour its altricial condition. Th e off spring of C. mendocinus were categorized as altricial by using two diff erent classifi cation systems. Th is condition was also refl ected in maternal care. Females built large nests (2000 cm 3 ) where, after a long gestation period (95.9 days), they gave birth to litters of blind pups, half-naked, with external ear meatus open and good physical coordination. Th e mothers suckled the off spring in long bouts (19.9 min), retrieved their pups, and these showed no tactics to reduce the suckling bout. Overall, evidence was consistent with the hypothesis analyzed, although particularities found, e.g. some precocial traits, suggest the existence in C. mendocinus of a trade-off between the constraints and advantages related to its subterranean way of life and the phylogenetic inertia typical of caviomorphs. Fil: Camín, Sergio Ramón. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Investigaciones de las Zonas Áridas. Provincia de Mendoza. Instituto Argentino de Investigaciones de las Zonas Áridas. Universidad Nacional de Cuyo. Instituto Argentino de Investigaciones de las Zonas Áridas; Argentina

The Diatomyidae (Rodentia, Mammalia) are a group of medium to large rodents restricted to southern and eastern Asia. The skull, characterized by hystricomorphous musculature, a 4/4 cheek tooth formula, a sciurognathous jaw, and other features, places the Diatomyidae in a phylogenetic position near, but not within, Hystricognathi. Like living Ctenodactylidae, they are a product of the early radiation of Rodentia that includes, ultimately, the hystricognaths. The oldest fossil Diatomyidae occur in Oligocene terrestrial sediments of the Indian subcontinent. Younger sediments in Pakistan near the Oligocene/Miocene boundary produce a quite different diatomyid that presents unique, derived conditions, and demonstrates early diversification of the family. This diatomyid, described here as Marymus dalanae, new genus and species, has cuspate anterior cheek tooth morphology interpreted as specialized, possibly for predation on invertebrates. All early diatomyids are relatively abundant components of their ...

Laonastes aenigmamus is an enigmatic rodent first described in 2005. Molecular and morphological data suggested that it is the sole representative of a new mammalian family, the Laonastidae, and a member of the Hystricognathi. However, the validity of this family is controversial because fossil-based phylogenetic analyses suggest that Laonastes is a surviving member of the Diatomyidae, a family considered to have been extinct for 11 million years. According to these data, Laonastes and Diatomyidae are the sister clade of extant Ctenodactylidae (i.e., gundies) and do not belong to the Hystricognathi. To solve the phylogenetic position of Laonastes , we conducted a large-scale molecular phylogeny of rodents. The analysis includes representatives of all major rodent taxonomic groups and was based on 5.5 kb of sequence data from four nuclear and two mitochondrial genes. To further validate the obtained results, a short interspersed element insertion analysis including 11 informative loci was also performed. Our molecular data based on sequence and short interspersed element analyses unambiguously placed Laonastes as a sister clade of gundies. All alternative hypotheses were significantly rejected based on Shimodaira–Hasegawa tests, supporting the idea that Laonastes does not belong to the Hystricognathi. Molecular dating analysis also supports an ancient divergence, ≈44 Mya ago, between Ctenodactylidae and Laonastes . These combined analyses support the hypothesis that Laonastes is indeed a living fossil. Protection of this surviving species would conserve an ancient mammalian family.

Despite possessing a rather generalised postcranial skeleton, rodents are on average capable of a wide variety of locomotory behaviours, such as swimming, digging and climbing (Nowak, 1999). Particularly, rodents belonging to Ctenohystrica (sensu Huchon et al., 2002, and Fabre et al., 2012: Ctenodactylidae, Diatomyidae and Hystricognathi) display a diversity of locomotory styles and encompass a large range in body mass from approximately 50 g for the naked mole-rat Heterocephalus glaber to around 60 kg for the largest living rodent, the capybara Hydrochoerus hydrochaeris, consequently filling many different ecological niches (e.g. MacDonald, 2009; Wilson and Sanchez-Villagra, 2009, 2010). Moreover, this diversity is greatly expanded by the inclusion of giant extinct members such as Phoberomys, Arazamys and Josephoartigasia that reached body masses at least seven or eight times that of the capybara (Sanchez-Villagra et al., 2003; Rinderknecht and Blanco, 2008; Rinderknecht and Bostelmann, 2011). The adaptive diversity that characterises the evolution of Ctenohystrica, and particularly the Caviomorpha, a group that dispersed from Africa to colonise South America (Poux et al., 2006; Rowe et al., 2010) and evolved on that continent during a period of splendid isolation in the Cenozoic, has been the subject of numerous morpho-functional and evolutionary studies (e.g. Verzi et al., 2010; Wilson et al., 2010; Alvarez et al., 2011a, b; Hautier et al., 2011, 2012; Cox et al., 2012; Geiger et al., 2013; Wilson, 2013). The interplay between form and function has been studied in the postcranial skeleton of a number of mammals (e.g. Kappelman, 19; Anemone, 1990;White, 1993; Vizcaino and Milne, 2002; Kley and Kearney, 2007; Meachen-Samuels, 2010), and studies of Ctenohystrica have, for example, examined individual bones (e.g. Seckel and Janis, 2008; Morgan, 2009; Steiner-Souza et al., 2010; Elissamburu and De Santis, 2011), long bones (Biknevicius, 1993; Elissamburu and Vizcaino, 2004; Samuels and Van Valkenburgh, 2008; Morgan and Alvarez, 2013) and the autopodial skeleton (e.g. Weisbecker and Schmid, 2007; Morgan and Verzi, 2011). These studies have used morphological traits, described as ratios or quantified using biomechanical indices or geometric morphometric descriptors of shape, to identify functional specialisations and instances of adaptive convergence underpinned by shared function and/or ecology.

Echimyidae (spiny rats, tree rats and the coypu) is the most diverse family of extant South American hystricognath rodents (caviomorphs). Today, they live in tropical forests (Amazonian, coastal and Andean forests), occasionally in more open xeric habitats in the Cerrado and Caatinga of northern South America, and open areas across the southern portion of the continent (Myocastor). The Quaternary fossil record of this family remains poorly studied. Here, we describe the fossil echimyids found in karst deposits from southern Tocantins, northern Brazil. The analyzed specimens are assigned to Thrichomys sp., Makalata cf. didelphoides and Proechimys sp. This is the first time that a fossil of Makalata is reported. The Pleistocene record of echimyids from this area is represented by fragmentary remains, which hinders their determination at specific levels. The data reported here contributes to the understanding of the ancient diversity of rodents of this region, evidenced until now in other groups, such as the artiodactyls, cingulates, carnivores, marsupials, and squamate reptiles., Facultad de Ciencias Naturales y Museo

Within South American rodents, the Acaremyidae is an independent fossil lineage of octodontoids represented in the late Oligocene–middle Miocene of Patagonia. Acaremys is represented by six species recorded in the early Miocene, which have not been re-studied since their original description. Morphological and phylogenetic analyses suggest that Acaremys is paraphyletic. Three species are valid, Acaremys murinus, Acaremys major, and Acaremys messor. Acaremys karaikensis is a junior synonym of Acaremys murinus. ‘Acaremys’ tricarinatus is excluded from the genus being closely related to Sciamys. The new species, Pseudoacaremys kramarzi, is closely related to ‘Acaremys’ tricarinatus and Sciamys. ‘Acaremys’ preminutus is excluded from the family being closely related to the early Miocene Protacaremys prior, or living octodontoids. The phylogenetic analysis demonstrated that Acaremyidae includes Platypittamys, Galileomys, Acaremys, Pseudoacaremys and Sciamys. The new acaremyid increases the diversity of extinct octodontoids and added a new evolutionary lineage within Acaremyidae. The evolutionary history of the superfamily suggests that the hypsodonty and the consequently occlusal simplification evolved twice within Octodontoidea: in Acaremyidae and in Octodontidae. In addition, the cladistic analysis confirmed that most character ambiguities are due to missing data, and hence, it is essential to find better remains to elucidate the relationships among acaremyids., Facultad de Ciencias Naturales y Museo

Introduction: Thrichomys is a genus of cursorial rodents of the family Echimyidae that is distributed across open tropical ecoregions in central and eastern South America. The understanding of species boundaries within the genus has changed dramatically during the last decade with the widespread usage of chromosomal and molecular data, resulting in an unstable taxonomy. One of the issues recently raised, on the basis of a study of specimens from south central Brazil (Mato Grosso do Sul State), is the distinctiveness at the species level of T. fosteri (with type locality in Paraguay), usually considered a synonym of T. pachyurus. Here we provide the first morphologic, karyotypic and molecular data for a series of Paraguayan specimens of Thrichomys aimed to resolve this taxonomic conundrum. Methodology: Thirty one specimens collected at five Paraguayan localities were morphologically assessed . Descriptive statistics for 20 cranial measurements were calculated for a subset of specimens considered juveniles and for a subset of specimens considered to be adults. Seven specimens of Thrichomys from three Paraguayan localities were karyotyped using standard chromosome techniques. The genetic (p-distance) and phylogenetic (Bayesian inference) analyses were based on the first 801 base pairs of the cytochrome b gene of 15 Paraguayan specimens collected at one locality and 71 Brazilian specimens of Thrichomys that belong to about eight forms of species level. Results: Paraguayan specimens examined closely match Thomas’s (1903) description of Thrichomys fosteri in size and qualitative characters. All specimens have 2n = 34, FN = 64. The Paraguayan sample used for the genetic analysis shows no variation. Observed genetic variation between the Paraguayan haplotype and haplotypes from other populations ranges from 0.5 % to 8.5 %. The phylogenetic analysis show that Paraguayan haplotype falls within the clade (PP = 1) formed by haplotypes of specimens from Mato Grosso do Sul, Brazil and referred by Nascimento et al. (2013) to Thrichomys fosteri. Discussion and conclusions: Our data indicate that in fact Paraguayan populations of Thrichomys belong, together with those of the neighbouring Brazilian state of Mato Grosso do Sul, to a distinct species of Thrichomys to which the name T. fosteri applies. We expect that these data will contribute to a much needed comprehensive revision of the genus.

Molecular phylogenetic relationships were investigated in 6 species of Chinchillidae (Chinchilla lanigera, C. brevicaudata, Lagidium peruanum, L. viscacia, L. wolffsohni, and Lagostomus maximus), 1 species of Dinomyidae (Dinomys branickii), 1 of Abrocomidae (Abrocoma cinerea), and 1 of Octodontidae (Octodon degus) using the first 548 base pairs of the mitochondrial cytochrome-b gene. Maximum-parsimony and maximumlikelihood analyses consistently showed Chinchillidae as a robust clade and confirmed a close relationship with Dinomyidae. Both Chinchilla species differed at 22 sites, and 3 were nonsilent; average genetic distances were approximately 6%. Sequences from domestic C. lanigeraand wild C. brevicaudatashowed low levels of variation. Although all topologies obtained were congruent with current taxonomy, Lagidium exhibited large genetic distances (range 5.9‐8.9%), suggesting the existence of more than the 3 species currently recognized. Chinchillids are endemic South American rodents (Rodentia, Hystricognathi, Chinchillidae) and occur along the Andes. They include chinchillas (Chinchilla), mountain viscachas (Lagidium), and pampas viscachas (Lagostomus).

Three acaremyid rodents from the Miocene of Patagonia are described. Galileomys antelucanus, gen. et sp. nov. (Colhuehuapian SALMA, early Miocene) is the most plesiomorphic genus within the Acaremyidae. Galileomys? colloncurensis, sp. nov. is the first acaremyid recorded from the Colloncuran SALMA (middle Miocene). The generic referral is tentative because the known material does not display enough characters. Acaremys cf. murinus Ameghino, 1887 represents a second Colhuehuapian acaremyid. Cladistic analyses of dental and mandibular characters do not support previous hypotheses that Sciamys and Acaremys are the ancestors of the Octodontidae. On the contrary, these two genera and Galileomys constitute a monophyletic group united by the presence of a hypoflexus in P4, a well defined anterodorsal limit of mandibular masseteric fossa, and a figure-eight-shaped molar pattern. The inclusion of other genera in the Acaremyidae is not supported by cladistic analysis. A shared figure-eight-shaped dental pa...

Mitochondrial cytochrome-b DNA and karyologic data were used to clarify taxonomic status of genera Coendou and Sphiggurus within the family Erethizontidae (Rodentia: Hystricognathi). Molecular and karyologic data were concordant in demonstrating that Coendou and Sphiggurus represent 2 evolutionary lineages. Comparative analyses showed that species of Coendou are karyotypically conservative, sharing the same diploid and fundamental number, whereas those of the genus Sphiggurus diverge in diploid number despite sharing the same fundamental number. We herein describe the karyotype of Sphiggurus melanura, a species considered a junior synonym of S. insidiosus by some authors. Our karyologic data (2n = 72, fundamental number = 76), however, clearly contradict this hypothesis and suggest that S. melanura is a valid taxon.

In the absence of a comprehensive pre-Oligocene fossil record, the origin and early evolution of hystricognathous rodents have long been the subject of much uncertainty. Baluchimyinae (Rodentia) were initially interpreted as a subfamily of the ctenodactyloid Chappatimyidae (sciurognathous), a group considered to be endemic to the Indian subcontinent and to be closely related to hystricognathous rodents. A newly discovered early Oligocene hystricognathous rodent, Bugtimys zafarullahi gen. n. et sp. n., described herein, from the Bugti Hills (Balochistan, Pakistan) sheds new light on the higher level taxonomy of the previously described Baluchimyinae. As a contribution to the phylogenetic debates regarding the origin of Hystricognathi, we present a cladistic assessment of the dental evidence for the Palaeogene hystricognathous rodent cladogenesis. Our phylogenetic results consistently support the monophyly of the Hystricognathiformes clade (including Tsaganomyidae plus Hystricognathi) of which baluchimyine rodents are clearly members. There is, however, no support for the monophyly of a baluchimyine clade. Nonetheless, ‘baluchimyines’ are for the moment reinterpreted as Hystricognathi incertae sedis. Hystricognathous rodents appear to be well diversified at least since the early Oligocene, both in Africa and South America (phiomorphs and caviomorphs, respectively), and also now in south Asia. Furthermore, our phylogenetic results support close relationships between early hystricognathous and Asian ‘ctenodactyloid’ rodents, which clearly points to an Asian origin for Hystricognathi. In this phylogenetic framework, ‘baluchimyines’ and tsaganomyids are representatives of an initial phase of diversification of hystricognathous rodents in Asia. Oligocene phiomorphs and caviomorphs (sister groups) seem therefore to share a common ‘Asian’ hystricognathous ancestor. This reinforces the possibility that the early dispersal of hystricognathous rodents to South America was not from Africa but from Asia.

Hypsosteiromys is the only New World porcupine that shows a tendency to hypsodonty. It is recorded exclusively from the Colhuehuapian Age (Early Miocene) of central Patagonia (Argentina). In addition to the type species, a second one, Hypsosteiromys nectus (AMEGHINO, 1902) , is recognized, from the southern cliff of Colhuehuapi Lake (Chubut province). It differs from the type species in the lesser development of the anterolabial and posteroflexid notches of the m1-3, shorter p4 and dp4, and more slender incisors. Dental morphology suggests that the species of Hypsosteiromys lived in more open areas than most fossil and living Erethizontidae.

Background Caviomorph rodents, some of the oldest Leishmania spp. hosts, are widely dispersed in Brazil. Despite both experimental and field studies having suggested that these rodents are potential reservoirs of Leishmania parasites, not more than 88 specimens were analyzed in the few studies of natural infection. Our hypothesis was that caviomorph rodents are inserted in the transmission cycles of Leishmania in different regions, more so than is currently recognized. Methodology We investigated the Leishmania infection in spleen fragments of 373 caviomorph rodents from 20 different species collected in five Brazilian biomes in a period of 13 years. PCR reactions targeting kDNA of Leishmania sp. were used to diagnose infection, while Leishmania species identification was performed by DNA sequencing of the amplified products obtained in the HSP70 (234) targeting. Serology by IFAT was performed on the available serum of these rodents. Principal findings In 13 caviomorph rodents, DNA sequencing analyses allowed the identification of 4 species of the subgenus L. (Viannia): L. shawi, L. guyanensis, L. naiffi, and L. braziliensis; and 1 species of the subgenus L. (Leishmania): L. infantum. These include the description of parasite species in areas not previously included in their known distribution: L. shawi in Thrichomys inermis from Northeastern Brazil and L. naiffi in T. fosteri from Western Brazil. From the four other positive rodents, two were positive for HSP70 (234) targeting but did not generate sequences that enabled the species identification, and another two were positive only in kDNA targeting. Conclusions/Significance The infection rate demonstrated by the serology (51.3%) points out that the natural Leishmania infection in caviomorph rodents is much higher than that observed in the molecular diagnosis (4.6%), highlighting that, in terms of the host species responsible for maintaining Leishmania species in the wild, our current knowledge represents only the “tip of the iceberg.”, Author Summary Leishmaniasis is a major public health problem expanding in Brazil and one of the reasons is that we still have poor knowledge of some aspects of the biology and epidemiology of Leishmania species, including the role of wild mammals. Caviomorph rodents, some of the oldest Leishmania spp. hosts, are widely dispersed in Brazil and reported as potential reservoirs of Leishmania parasites. Spleen fragments of 373 brazilian caviomorph rodents from 20 species were investigated for Leishmania infection. The molecular algorithm proposed to diagnose the infection associate the sensitivity of a molecular target with multiple copies with the specificity of another marker with discriminatory taxonomic ability between species. These demonstrated their usefulness in identifying most of the parasite species infecting the rodents, including the description of species in previously unknown hosts and in areas not previously included in their known distribution, such as L. shawi in Thrichomys inermis from Northeastern Brazil and L. naiffi in T. fosteri from Western Brazil. Although the percent of infection by molecular diagnosis was 4.6%, the serology demonstrated that about 51% of them had been exposed to Leishmania parasites pointing that caviomorph rodents are inserted in enzootic cycles of Leishmania, to a higher extent than currently recognized.

We examined the morphology of the wrist (carpal region) skeleton using histological serial sections and cleared and stained forelimbs of representatives of three rodent clades: ‘Hystricomorpha’ (Caviomorpha: Ctenomys opimus, C. talarum, Cuniculus taczanowskii, Erethizon dorsatum, Galea sp., Lagostomus maximus, Spalacopus cyanus; Phiomorpha: Fukomys mechowii, Heliophobius argenteocinereus, Hystrix cristata, H. africaeaustralis; Ctenodactylids (Ctenodactylus gundi)), ‘Myomorpha’ (Arvicola amphibius, Ondatra zibethicus, Meriones unguiculatus, Myodes glareolus, Spalax sp.) and ‘Sciuromorpha’ (Eliomys quercinus, Glis glis, Marmota marmota). We describe the arrangement of the carpal bones and identify several variable traits, some of which represent convergent evolution. One element, the Os posthamatum, lies in the carpal region and has not been recorded before. We interpret this bone as a putative autapomorphy of Hystricognathi but not of ‘Hystricomorpha’.

The order Rodentia includes nearly half of all living mammalian species. Phylogenetic relationships among 22 species of rodents were investigated by use of a 1.2-kb region from exon 1 of the single-copy nuclear gene IRBP. IRBP has been extensively used for study of interordinal phylogeny in mammals, which allowed inclusion of 50 outgroup species, representing every eutherian order plus seven marsupials. Several clades were strongly supported, regardless of analytical method or inclusion/exclusion of data. These include a monophyletic Muroidea, with a clade including Spalax and Rhizomys as the first divergence; a clade uniting Zapus with Dipus, but excluding Sicista; a monophyletic Myodonta (Muroidea plus Dipodidae); and a clade including Aplodontidae as sister to Sciuridae. One bipartition, separating Hystricognathi and Geomyoidea from the remaining rodents, is strongly supported in all analyses that include third-position sites but almost completely absent from analyses that exclude third-position sites. A combination of nonstationary nucleotide composition and branch length effects may be causing all methods examined (including those using the LogDet distance) to support an incorrect conclusion when third-position sites are analyzed together with first- and second-position sites.

Genetic variation and the allozymic relationships of five families comprising 23 species of hystricognath rodents were examined using electrophoretic data from 19 presumptive gene loci. Direct-count heterozygosity ranged from 0% to 13.6%, and polymorphism varied from 0% to 36.8%. Fixed allele differences were instrumental for the segregation of taxa as summarized by the Distance Wagner procedure and by majority-rule consensus trees. The monophyly of the Octodontidae, and the family rank of the Abrocomidae and Ctenomyidae is supported by the data. Monotypic Myocastor coypus is not resolved as a distinct family but appeared within the Caviidae. Within the Octodontidae, paraphyly was detected in polytypic Octodon, whereas a high bootstrap value supported the node containing the desert specialists O. mimax (2n= 56) and Tympanoctomys barreare (2n= 102). The implications of allozymic data as a robust phylogenetic signal that connected biochemical associations to the prediction of tetraploidy in T. barrerae are discussed.

The fossil record of the first genera of each family of South American Hystricognathi rodents is reviewed. On this basis the main events for the radiation of the infraorder on this continent are recognized. Two main events can be identified: the first occurs probably during the Eocene-Oligocene boundary, and the second at the Middle-Late Miocene boundary.

The phylogenetic relationships among 23 individuals representing 14 species of underground hystricognath rodents of the genus Ctenomys were studied by analyzing variation of complete cytochrome b gene sequences. Maximum parsimony, neighbor joining, and maximum likelihood analyses were performed, using the octodontine genera Octodon and Tympanoctomys as outgroups. Our analyses support previous studies based on chromosomes and skull morphology that suggested a clade comprised of Argentinean and Uruguayan populations of C. rionegrensis. This clade is closely related to one comprised of C. flamarioni and the C. mendocinus species complex. Our analyses provide evidence that the symmetric sperm morph, which is common to other South American hystricognath rodents, is the plesiomorphic character state in Ctenomys and in Hystricognathi. Our analyses do not support the hypothesis that the sperm morphs define two major lineages of tuco-tuco species, because species with asymmetric sperm are diphyletic on the basis of cytochrome b sequences, and this morphology appears to have evolved twice in Ctenomys.

The order Rodentia is subdivided into two suborders, the Sciurognathi and the Hystricognathi. Within the Sciurognathi, the shortwave-sensitive (SWS1) class of visual pigments is ultraviolet-sensitive (UVS) amongst the largely nocturnal murine species, whereas violet-sensitive (VS) pigments are thought to be present in diurnal ground and tree squirrels [1,2]. As the ancestral mammalian pigment is most likely UVS [3] and UVS pigments are retained in many rodent species, the evolution of VS pigments must have occurred within the squirrel branch of the Sciurognathi.

Introduction The Laotian rock rat is a relict species in a sister group relationship to hystricognath rodents (Hystricognathi). We asked whether there were similarities in placentation that might reflect this relationship or differences that might cast light on the evolution of Hystricognathi. Methods We examined the reproductive tract of nonpregnant ( n = 5), early ( n = 3) and mid to late gestation ( n = 2) females. Selected characters were mapped to a phylogenetic tree to examine their evolution in rodents. Results The chorionic placenta was discoid and labyrinthine with a spongy zone but without internal lobes. The interhemal region was hemodichorial with syncytiotrophoblast lining maternal blood spaces and an inner layer of vacuolated cytotrophoblast. There was no subplacenta. The yolk sac was well developed with a villous portion that faced the placental disk but no fibrovascular ring. There was a single fetus that very likely would be precocial at birth. Discussion A lobulated labyrinth and the presence of a subplacenta and a fibrovascular ring emerged as synapomorphies for Hystricognathi. Laonastes , Ctenodactylus and stem Hystricognathi all had precocial young, whereas altriciality was the plesiomorphic condition for rodents. A hemomonochorial interhemal region was plesiomorphic for rodents and Hystricognathi, and the hemodichorial condition found in Laonastes , and possibly in Ctenodactylus , was unlike that of any rodent studied to date. Conclusion Similar to Hystricognathi, Laonastes bears precocial young, but this species lacks placental adaptations such as the subplacenta, suggesting they were evolved subsequent to a change in reproductive strategy in the common ancestor of Laonastes and Hystricognathi.

Octodontoidea is the most diverse clade of hystricognath rodents, and is richly recorded in South America since at least the Oligocene. A parsimony-based morphological phylogenetic analysis of a wide range of extant and extinct octodontoids recovered three major clades, here recognised as Echimyidae, Octodontidae, and Abrocomidae. Taxa previously assigned to Echimyidae or Octodontoidea incertae sedis are here interpreted for the first time as early representatives of Ctenomyinae (Octodontidae), Octodontinae or Abrocomidae. Based on our results, we estimate the divergence of octodontoid families and subfamilies to have occurred during the Late Oligocene, which is consistent with molecular estimates, but older than previous inferences based on the fossil record. Contrary to previous suggestions, we show the first appearances of modern members of Abrocomidae, Octodontinae and Ctenomyinae to be distinctly decoupled from the origin of these clades, with different stages in the evolutionary history of octodontoids seemingly following distinct phases of palaeoenvironmental change. Depending on the phylogenetic pattern, fossils from the stage of differentiation bear evolutionary information that may not be provided by crown groups, thus highlighting the unique and important contribution of fossils to our understanding of macroevolutionary patterns.

Phylogenetic relationships among major rodent superfamilies traditionally have been difficult to establish because of the apparent high level of convergence and parallelism seen among morphological characters and/or rapid differentiation of rodent groups in the Paleocene/Eocene. Nucleotide sequence data from the mitochondrial 12S rRNA gene were used to clarify phylogenetic relationships among the major groups of rodents as defined by Brandt (1855) and Tullberg (1899). Based on the approximately 800 bp analyzed for the 12S rRNA gene in 59 mammalian species, including 25 of the 32 extant rodent families, the major rodent groups that could be defined as monophyletic clades were the Hystricognathi, the Muroidea, and the Geomyoidea. In addition, support for superfamilial sister-group relationships was found for Aplodontoidea with Sciuroidea and Dipodoidea with Muroidea.

The karyotype has been studied in 2 species of Rodents, the Redless squirrelFunisciurus anerythrus (Sciurognathi, Sciuridae) and the Cane ratThryonomys swinderianus (Hystricognathi, Thryonomyidae), from crop lands and woodlands of the Republic of Benin (West Africa). Chromosomes were obtained by bone marrow method and stained both by standard Giemsa and NOR banding procedures. T.swinderianus shows a2n = 44 (NF = 86) complement. Chromosomes are all biarmed except for one pair acrocentrics. Nuclear Organising Regions (NORs) are located on one submetacentric pair coinciding with a secondary constriction.F. anerythrus shows a2n = 38 (NF = 62) complement. The karyotype is composed of 7 acrocentric chromosomal pairs and 12 biarmed chromosomal pairs. The karyotype morphology of the species was discussed within the context of Old World Hystricognathi and African Sciuridae comparative cytogenetics.

Caviomorph rodents, the New World Hystricognathi, are one of the most noteworthy groups of mammals in South America. Isolated for more than 30 Ma, they have given rise to several extraordinary rodents including the pacas (Cuniculusspp.), cavies (Caviaspp.), vizcachas (Lagostomusspp.), agouties (Dasyproctaspp.), as well as two giants: Phoberomys, from the late Miocene (6 Ma; mega annum = million years) which probably weighed more than 400 kg (Sanchez Villagra et al. 2003), and Josephoartigasia monesiprobably from the Pleistocene (2.5 Ma), at about 1,000 kg (Rinderknecht and Blanco 2008). Capybaras (Hydrochoerusspp.) are particularly conspicuous because of their size – they are the largest living rodents – and their aggregation in herds (Ojasti 1973; Macdonald 1981; Macdonald et al. 2007). This chapter examines their paleontology and evolution, focusing particularly on another striking feature: their unpaired ever-growing cheek teeth whose very complicated occlusal surface design changes throughout the capybara’s life (Vucetich et al. 2005).