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The genus Ctenomys of subterranean rodents is one of the most species-rich genera of Mammalia, with 66 living species currently recognized. However, the taxonomy of the genus is dynamic with several new species and new synonymies proposed during the last decade. One of the species groups that have undergone more changes in contents in the last years is the Ctenomys mendocinus species group. Here, based on phylogenetic analysis of mitochondrial DNA sequences and qualitative and quantitative morphological evidence, we conducted an appraisal of the species richness of tuco-tucos of the C. mendocinus species group, describing two new species from west-central Argentina. The new taxa are morphometrically distinctive when compared with other geographically or phylogenetically close species of the genus, showing qualitative differences in their craniodental anatomy. One of the new species is known from the eastern Andean slopes of La Rioja and San Juan provinces, occurring on montane grasslands and shrublands above 3,500 m a.s.l., while the other is endemic of southwestern Mendoza province, occurring on montane grasslands and shrublands between 2,400–2,700 m a.s.l. In addition, we include for the first time the nominal forms C. fochi and C. validus in a phylogenetic analysis of the genus Ctenomys, showing that both correspond to the C. mendocinus species group, being the second a junior synonym of C. mendocinus. Finally, we made some comments about other candidate species within this species group as well as highlight issues that need to be addressed to gain a robust picture of the specific richness of Ctenomys.

The subterranean rodent Ctenomys is the most polytypic South American mammal genus and one of the most speciose and rapidly diversifying mammal genera in the world. Its systematics is unstable due to the underlying accelerated diversification processes that give rise to evolutionary lineages at different stages of differentiation and to remarkable morphological homogeneity even among long-differentiated species. As a result, species boundaries are often difficult to define. Diversity of this genus in the coastal area of central Argentina has been extensively studied, with two independent lineages currently recognized while a distinct third population had not been previously detected. Through a phylogenetic analysis based on combined morphological and molecular evidence, Bayesian estimates of divergence times, and morphometric and morphological assessments, we recognize this third population as an independently evolving lineage. The new species, Ctenomys pulcersp. nov., is here described for both the living fauna and the fossil record of the Pampean region of central Argentina. According to phylogenetic results, Ctenomys pulcersp. nov. belongs to the essentially Patagonian magellanicus clade, and would have diverged from its sister species, Ctenomys bidaui, during the middle Pleistocene (ca. 0.4 Ma). Its current distribution in the fixed and semifixed dunes of the coastal Pampean region is assumed to represent a relict of a wider and continuous distribution of potentially suitable environments during the late Pleistocene. Ctenomys pulcersp. nov. occurs in a particularly fragile natural system subjected to profound disturbances caused by diverse anthropic actions and therefore measures for the conservation of its habitat will be indispensable.

The greater cane rat (Thryonomys swinderianus) is an African rodent with a wide Sub-Saharan distribution range. This species is viewed as an important protein source in many African countries. These rodents are also regularly viewed as a pest species who frequently raid croplands in agricultural settings. No phylogenetic work has to date been published on T. swinderianus from southern Africa. This paper therefore reports the first phylogenetic assessment on the species across the South African distribution range. Thirty samples were sourced from local museum collections, with one direct submission by a member of the public who found a rodent carcass identified as T. swinderianus west of its known distribution range in the Eastern Cape Province of South Africa. Two mitochondrial loci previously used in West African studies of this species were used in the current study to asses T. swinderianus population genetic diversity and phylogenetic structure across the South African distribution. A comparison to sequence data from West Africa was also performed. A divergence time estimation was conducted to further investigate the evolutionary history of the South African sub-population. Similar genetic diversity estimates were observed for the South African sub-population when compared to the West African datasets. Specimens from the eastern parts of South Africa showed higher genetic diversity estimates, possibly indicative of an initial colonisation site from eastern Africa. Two distinct phylogenetic clades were identified by Bayesian inference, forming distinct West African and South African groups. The divergence estimates showed similar ages for the T. swinderianus most recent common ancestor (MRCA) as previously reported. The MRCA estimates for the South African group identified a possible middle to late Pleistocene migratory event from eastern African into southern Africa. Further fine scale sampling across the African distribution range is however needed to provide more accurate assessments for future conservation management planning for the different sub-populations, as needed.

Abstract Nasal anatomy in rodents is well-studied, but most current knowledge is based on small-bodied muroid species. Nasal anatomy and histology of hystricognaths, the largest living rodents, remains poorly understood. Here, we describe the nasal cavity of agoutis (Dasyprocta spp.), the first large-bodied South American rodents to be studied histologically throughout the nasal cavity. Two adult agoutis were studied using microcomputed tomography, and in one of these, half the snout was serially sectioned and stained for microscopic study. Certain features are notable in Dasyprocta. The frontal recess has five turbinals within it, the most in this space compared to other rodents that have been studied. The nasoturbinal is particularly large in dorsoventral and rostrocaudal dimensions and is entirely non-olfactory in function, in apparent contrast to known muroids. Whether this relates solely to body size scaling or perhaps also relates to directing airflow or conditioning inspired air requires further study. In addition, olfactory epithelium appears more restricted to the olfactory and frontal recesses compared to muroids. At the same time, the rostral tips of the olfactory turbinals bear at least some non-olfactory epithelium. The findings of this study support the hypothesis that turbinals are multifunctional structures, indicating investigators should use caution when categorizing turbinals as specialized for one function (e.g., olfaction or respiratory air-conditioning). Caution may be especially appropriate in the case of large-bodied mammals, in which the different scaling characteristics of respiratory and olfactory mucosa result in relative more of the former type as body size increases.

This study reports the histochemistry and the distribution of glycoconjugates (GCs) in the zona pellucida (ZP) of preantral, secondary, tertiary, polyovulatory and atretic follicles of ovaries from non-pregnant (NPr) and pregnant (Pr) females of Lagostomus maximus. GCs were studied using histochemical and lectin histochemical methods. The viscacha ZP was positive to all the histochemical techniques. In addition, it was observed that the intensity of staining of the ZP was constant in the different follicular stages between both female groups. The lectin histochemical study revealed that ZP was positive for certain lectins (WGA, RCA-I and CON-A) and that the labelling did not vary between the different follicular stages, but between the two groups of females. By using both histochemical techniques, it was established that the GCs present in the ZP label the complexity of the area. These results allow us to increase our knowledge on the biology of the viscacha's ovary, particularly contributing to the study of polyovulation. Fil: Acuña, Francisco. Universidad Nacional de La Plata. Facultad de Ciencias Veterinarias; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina 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: Díaz, Alcira Ofelia. 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: Portiansky, Enrique Leo. Universidad Nacional de La Plata. Facultad de Ciencias Veterinarias; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina Fil: Barbeito, Claudio Gustavo. Universidad Nacional de La Plata. Facultad de Ciencias Veterinarias; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina Fil: Flamini, Mirta Alicia. Universidad Nacional de La Plata. Facultad de Ciencias Veterinarias; Argentina

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.

Very scarce information is available about the extinct Neogene communities of the Subandean valleys of Jujuy province, Northwestern Argentina. A new vertebrate fossiliferous locality (Los Alisos), and the first mammalian assemblage from Guanaco Formation, is described. The taxa recorded include mainly caviomorph rodents (Hystricognathi)represented by Orthomyctera sp., Lagostomus sp., and an Octodontoidea and cingulates (Xenarthra)represented by the armadillos aff. Stenotatus, Dasypus sp. nov., two Euphractinae, and a Glyptodontidae. A single remain of a turtle (Testudines)is also described. The composition of the faunistic record has similitude with Andalhuala, Chiquimil and Salicas formations, but some taxa differ from all other late Miocene Northwestern Argentina localities. The most outstanding feature of Los Alisos paleocommunity is the presence of Dasypus, which confirms the existence of the genus in times as old as the late Miocene. The presence of a tuff with known age (5.9–6.4 Ma)immediately below to the fossiliferous level gives a lower temporal constraint for the association, and this absolute age as well as the biochrons of the identified taxa are compatible with an Huayquerian stage. The integrative analysis of the mammals of Los Alisos allowed preliminary paleoecological and paleoenvironmental inferences for Guanaco Formation, indicating a landscape composed by open areas, whether extensive or arranged in patches, including grasslands, under warm and seasonal climatic conditions. Fil: Ercoli, Marcos Darío. 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. Universidad Nacional de Jujuy. Instituto de Geología Minera; Argentina 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. Universidad Nacional de Jujuy. Instituto de Geología Minera; Argentina Fil: Santamans, Carla Daniela. 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. Universidad Nacional de Jujuy. Instituto de Geología Minera; Argentina Fil: González Patagua, Sonia A.. Universidad Nacional de Jujuy. Instituto de Geología Minera; Argentina Fil: Villalba Ulberich, Juan Pablo. 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. Universidad Nacional de Jujuy. Instituto de Geología Minera; Argentina Fil: Constantini, Ornela Estefania. 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. Universidad Nacional de Jujuy. Instituto de Geología Minera; Argentina

The objective of this study focused on the comparative morphological and histochemical analysis of the duodenum of fetuses, juveniles and adult coypu (Myocastor coypus bonariensis), the major socioeconomic wildlife resource of Argentina. Histological and histochemical procedures for in situ characterization of glycoconjugates (GCs) were used. This study evidenced that fetal mucins differ histochemically in many respects from their adult counterparts. Only in fetuses from 90 days-post coitus (dpc) glycogen-rich sites were observed throughout the duodenal epithelium. The goblet cells appeared from 105 dpc and their secretory content varied considerably after birth. Duodenal glands presented scanty neutral and sulphated GCs in the 30-day juveniles; in adults the proportion of these GCs increased, and carboxylated and sialylated GCs were also observed. The results obtained in this work may be used in future studies to evaluate the effects of diet and intestinal pathologies in the glycosylation pattern of GCs. Also, knowledge of the normal glycoprofile of the duodenum of M. coypus bonariensis during its ontogenetic development may constitute a basis for the study of this organ in other Hystricognathi rodents.

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

The ascending colon of most rodent species shows a longitudinal colonic groove that works as a retrograde transport pathway for a mixture of bacteria and mucus toward the cecum. We describe the morphology and glycosylation pattern of the colonic groove of Lagostomus maximus to analyze the role of mucins in this anatomical feature. We also studied the distribution pattern of the interstitial cells of Cajal (ICC) to evaluate their regulatory influence on gut motility. The groove originated near the cecocolic junction and extended along the mesenteric side of the ascending colon, limited at both ends by nonpapillated ridges. These ridges divided the lumen of the ascending colon into two compartments: a narrow channel and a large channel, called the groove lumen and the main lumen, respectively. The histochemical analysis showed differences in the glycosylation pattern of the goblet cells inside and outside the groove. Unlike the mucosa lining the main lumen of the colon, the groove was rich in goblet cells that secrete sulfomucins. The PA/Bh/KOH/ PAS technique evidenced an abrupt change in the histochemical profile of goblet cells, which presented a negative reaction in the groove and a strongly positive one in the rest of the colonic mucosa. The anti-c-kit immunohistochemical analysis showed different ICC subpopulations in the ascending colon of L. maximus. Of all types identified, the ICC-SM were the only cells located solely within the colonic groove., Facultad de Ciencias Veterinarias

A new caviomorph rodent, Dudumus ruigomezi, gen. et sp. nov., is described from the Sarmiento Formation, Trelew Member (early Miocene), of the Argentinian Patagonia. This new taxon is represented by upper and lower cheek teeth, mandible, and maxillary remains. It is characterized by retention of deciduous premolar, and low-crowned and terraced lower and upper cheek teeth with well-differentiated cusps, as in Caviocricetus lucasi; upper molariforms with the mesolophule and metacone fused with the posterior-most crest, as in C. lucasi; lower molars with lingual cusp enlarged and metalophulid II longer in m2 than in m1and m3, as in Prospaniomys priscus; and dp4 with metalophulid I separated from the metaconid and a spur projecting posterolingually from the posterior wall of metalophulid I, between the protoconid and anteroconid. The incisor enamel microstructure is derived, with the interprismatic matrix perpendicular (at a right angle) to the prisms, as in other octodontoids. A cladistic analysis corroborates that D. ruigomezi represents an octodontoid rodent with unusual tooth morphology. This analysis demonstrates that the early evolutionary history of Octodontoidea was characterized by the differentiation of successive lineages that survived until the early or middle Miocene, with no direct relationships with modern Octodontidae and Echimyidae. This analysis also suggests that fossil taxa previously classified as octodontoids are instead more closely related to the other caviomorph rodents. Fil: Arnal, Michelle. 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; Argentina Fil: Kramarz, Alejandro Gustavo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; 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; Argentina Fil: Vieytes, Emma Carolina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Zoología de Vertebrados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

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.

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.

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

Phylogenetic relationships and divergence times are important pieces of information for evolutionary biologists, given that they provide a framework for understanding the evolution of phenotypes. There are now statistical methods that estimate divergence times without assuming that all lineages evolve at the same rate (Huelsenbeck et al., 2000; Sanderson, 1997; Thorne et al., 1998). Here I apply these methods to the neotropical hystricomorph rodents. The hystricomorph rodents are highly diverse in terms of life history traits, body sizes, and overall reproductive strategies (Begall et al., 1999; ScharV et al., 1999). This diversity in life history strategies and body size is accompanied by considerable heterogeneity in rates of molecular evolution (Honeycutt et al., 2003; Huchon et al., 2000; Huchon and Douzery, 2001; Rowe and Honeycutt, 2002). The faster rate of molecular evolution of rodents compared to other mammals has been attributed to the shorter generation times of rodents (Gu and Li, 1993). However, the rate heterogeneity observed among hystricognath rodents suggests that the causes of rate heterogeneity may be more complex than previously thought (Gu and Li, 1993). Huchon and Douzery (2001) have addressed the problem of divergence times among major clades of hystricomorph rodents. Others have estimated divergence times using more complex taxonomic sampling for speciWc groups such as the caviomorph rodents (neotropical hystricomorph rodents) (Galewski et al., 2005; Honeycutt et al., 2003). Among these rodents, the superfamily Octo

Hystricomorph rodents are a group of species that belong to the suborder Hystricognathi. They mainly inhabit South American (caviomorph) and African (phiomorph) habitats. This group of rodents has a divergent insulin structure. For example, insulin in this group of rodents exhibits only 1-10% of biological activity in comparison to other mammals. Therefore, hystricomorph rodents may hypothetically be unable to regulate blood glucose concentration as non-hystricomorph mammals. In this work we evaluated blood glucose concentration in nine species of caviomorph rodents, with emphasis on species belonging to the families Abrocomidae, Ctenomyidae and Octodontidae. Specifically we: (1) measured glucose concentrations after a fasting period; and (2) conducted a glucose tolerance test. In the latter assay we used Octodon degus as a representative species of the genus Octodon. Results showed that blood glucose concentration values after fasting, and in the glucose tolerance test, were within the expected range for mammals. We postulate that this group of rodents has compensatory traits that may permit the maintenance of standard values of plasma glucose.

The aim of this paper is to reconstruct the evolution of chorioallantoic placental characters in Rodentia. The analysis is based on pre-existing hypotheses of rodent relationships and the tracing of character evolution. Data on 64 rodent species of 49 genera are derived from the literature. New results refer to the hystricognath species Petromus typicus A. Smith, 1831 and Octodon degus (Molina, 1782). This comprehensive analysis confirms that the stem species pattern of Rodentia is characterised by a haemochorial placenta which is divided horizontally. Inside the placental labyrinth, fetal vessels and their trophoblastic external border build up a network through which the maternal blood flows. The trophoblastic tissue is one-layered, syncytial and possess a considerable surface extension. Within Rodentia, evolutionary transformations occurred on the macroscopic as well as the fine structural level. The results suggest that the stem species of Hystricognathi underwent transformations only on the macroscopic level, i.e., forming a ring-shaped arrangement of placental regions with centrally situated maternal arteries and the acquisition of a subplacenta. By contrast, in Muridae the chorioallantoic placenta shows derived features only in regard to the fine structure of the labyrinth, i.e. the interhaemal membrane is modified in composition, and the fetal capillary endothelium is fenestrated. Geomyoidea underwent transformations on both levels. Macroscopically, their placenta is modified into a hillock shape. Microscopically, the interhaemal membrane is formed by the cytotrophoblast. In addition to the mentioned transformations, some aspects of other fetal membrane differentiation in Rodentia are briefly discussed.

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.

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.

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.

The South American hystricognath rodents are one of the most diverse mammalian clades considering their occupied habitats, locomotor modes and body sizes. This might have been partly evolved by diversification of their masticatory apparatus' structure and its ecological commitment, for example, chisel-tooth digging. In this phylogeny-based comparative study, we test the relationship between ecological behavior and mechanical features of their incisors and molariforms. In 33 species of nine families of caviomorph rodents, we analyze incisor attributes related to structural stress re- sistance and molar features related with grinding capacity, for example, second moment of inertia and enamel index (EI) (enamel band length/occlusal surface area), respectively. Most of these variables scaled isomet- rically to body mass, with a strong phylogenetic effect. A principal component analysis discrimination on the EI clustered the species according to their geographic dis- tribution. We presume that selective pressures in Andean-Patagonian regions, on particular feeding hab- its and chisel-tooth digging behaviors, have modeled the morphological characteristics of the teeth. Subterranean/ burrower ctenomyids, coruros, and plains viscachas showed the highest bending/torsion strength and an- chorage values for incisors; a simplified enamel pattern in molariforms would be associated with a better grind- ing of the more abrasive vegetation present in more open and drier biomes. J. Morphol. 273:1150-1162

The rodent superfamily Octodontoidea comprises 6 families, 38 genera, and 193 living species of spiny rats, tuco-tucos, degus, hutias, and their relatives. All are endemic to the Neotropical Region where they represent roughly three-quarters of extant caviomorphs. Although caviomorph monophyly is well established and phylogenetic hypotheses exist for several families, understanding of octodontoid relationships is clouded by sparse taxon sampling and single-gene analyses. We examined sequence variation in one mitochondrial (12S rRNA) and three nuclear genes (vWF, GHR, and RAG1) across all caviomorph families (including 47 octodontoid species), all phiomorph families, and the sole remaining hystricognath family, using the gundi ( Ctenodactylus ) and springhaas ( Pedetes ) as outgroups. Our analyses support the monophyly of Phiomorpha, Caviomorpha, and the caviomorph superfamilies Cavioidea (Dasyproctidae, Cuniculidae, and Caviidae, the latter including Hydrochoerus ), Erethizontoidea, Chinchilloidea (including Dinomyidae), and Octodontoidea. Cavioids and erethizontoids are strongly supported as sisters, whereas chinchilloids appear to be sister to octodontoids. Among octodontoids, Abrocomidae is consistently recovered as the basal element, sister to a pair of strongly supported clades; one includes Octodontidae and Ctenomyidae as reciprocally monophyletic lineages, whereas the other includes taxa currently allocated to Echimyidae, Capromyidae and Myocastoridae. Capromys appears near the base of this clade, in keeping with current classification, but Myocastor is nested securely inside a clade of Echimyidae that also contains eumysopines, echimyines and dactylomyines. Another, more weakly supported clade of Echimyidae contains fossorial and scansorial taxa from the Chaco–Cerrado–Caatinga and the Atlantic Forest. Biogeographic analyses robustly recover the Patagonia–Southern Andes complex as ancestral for the Octodontoidea, with three component lineages emerging by the Oligocene–Miocene boundary (∼23 Ma): (1) stem abrocomids in the Central and Southern Andes; (2) a lineage leading to octodontids plus ctenomyids in Patagonia, later dispersing into the Chaco–Cerrado–Caatinga; and (3) a lineage leading to echimyids, capromyids, and myocastorids that subsequently radiated in more mesic biomes, including Amazonia, Atlantic Forest, and the Antilles. This reconstruction refutes earlier ideas that the diverse, generalized, mainly lowland family Echimyidae, which appears early in the fossil record, gave rise to the Andean lineages of octodontoids—instead, the reverse derivation appears to be true. We recommend formal synonymy of Myocastoridae with Echimyidae but defer a similar treatment of Capromyidae until additional hutia taxa and sequences can be analyzed.

The Palaeogene fossil record of rodents in Africa is very poor compared to that of North America or Eurasia. Despite this, Africa has long appeared to be a centre of adaptive radiation for two distinct groups of Rodentia: Hystricognathi and Anomaluroidea. The >45-million-year-old enigmatic Zegdoumyidae is the oldest and only rodent family known of this age from Africa (Algeria and Tunisia). Zegdoumyids have been tentatively regarded as a possible early African stem group for Anomaluridae, a link that has never been clearly established because of the highly fragmentary nature of zegdoumyid fossils, as well as the major temporal and morphological gaps between zegdoumyids and the first true anomaluroids from the Late Eocene. About 200 rodent teeth have been sorted after acid treatment of indurated sediments from several new localities in the Gour Lazib of western Algeria dating from the late Early or early Middle Eocene. These new fossils allow us to better describe the morphology of the Zegdoumyidae (especially Glibia and Zegdoumys) and to identify a new taxon, Lazibemys zegdouensis gen. et sp. nov. With this material, we investigated the phylogenetic position of the Zegdoumyidae in a high-level rodent phylogeny with cladistic assessment of the dental evidence. Our analyses have yielded six equally most-parsimonious trees in which zegdoumyids represent the earliest offshoots (pectinately arranged) of a large clade that embraces Eocene anomaluroids plus stem and crown Anomaluridae. This phylogenetic assumption underscores the great antiquity of the Anomaluroidea clade in Africa, as expected given the high morphological divergence of the Late Eocene African anomaluroids. Zegdoumyids exhibit a variety of dental morphologies and provide some suggestions on evolutionary trends within the Anomaluroidea (early stages of pentalophodonty, incisor enamel microstructure transitional from the pauciserial to the uniserial condition). The source of Zegdoumyidae is still unclear inasmuch as there is no well-identified sister group among early Palaeogene rodents. Zegdoumyids seem to share a common ancestry with both stem Myodonta and North American Sciuravidae. Given the high degree of dental specialization of zegdoumyids, we cannot exclude the possibility that zegdoumyids are rooted in a more primitive, as yet unknown, African rodent lineage older than the Early-Middle Eocene. Journal of Systematic Palaeontology, ISSN : 1477-2019, DOI : 10.1080/14772019.2011.562555, Issue : 4, Volume : 9, pp. 563-588, 2011.

We tested the applicability of Allen ' s rule in 47 species and 32 unnamed forms (populations that are probably good species or undefined taxa within a superspecies or species group) of the South American subterranean Hystricomorph rodents of the genus Ctenomys (tuco-tucos) (Rodentia: Ctenomyidae) by analyzing tail length in relation with head and body length, and body mass. Tail length allometry was analyzed by Reduced Major Axis regression while the possible correlation of relative tail length with temperature, precipitation and evapotranspiration variables was explored through Simultaneous Autoregression to account for spatial autocorrelations. Our results indicate that tuco-tucos do not follow Allen ' s rule but its converse, tail proportion relative to body mass increasing with latitude while body size decreases in the same direction (the trend is similar for tail length relative to head and body length but not statistically significant). Regarding climatic variables, the main predictors of relative tail length were temperature and evapotranspiration variables with trends confirming the positive (non-Allenian) correlation of relative tail length with latitude. We conclude that tuco-tucos, being almost fully subterranean, thermoregulate behaviorally by maintaining constant temperatures within their burrows independent of geographic location. The former confirms previous results that indicated that Ctenomys follows the converse to Bergmann ' s rule. Relative tail length variation would be a result of simple allometric growth. © 2011 by Walter de Gruyter. Fil:Bidau, C.J. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.

International audience; A new African species of hystricognathous rodent, Gaudeamus lavocati sp. nov., is described herein from the early Oligocene deposits of Zallah locality (Sirt basin, Central Libya). The dental morphology of this species is very close to that of some earliest South American caviomorphs. It allows a reinterpretation of molar crest homologies among earliest caviomorphs, pentalophodonty being confirmed as the plesiomorphic molar condition in Caviomorpha. This morphological resemblance argues for close affinities between Gaudeamus and earliest South American hystricognaths. Cladistic analysis supports Gaudeamus lavocati sp. nov. as the first known African representative of Caviomorpha, implying that its ancestors were part of the African phiomyid group that crossed the South Atlantic by a direct immigration route. Alternatively, the series of derived dental features of Gaudeamus could also be interpreted as evolutionary synchronous convergences of an African hystricognath lineage towards the specialized pattern of some caviomorphs. However, the high level of similarities concerning teeth morphology and enamel microstructure and the similar age of fossiliferous strata on both continents make this interpretation less probable. The phylogenetic position of this taxon is of considerable importance because it represents an enigmatic component of the phiomorph-caviomorph radiation in Africa and appears as a new clue toward the understanding of caviomorph origins.

The early evolutionary and paleobiogeographic history of the diverse rodent clade Hystricognathi, which contains Hystricidae (Old World porcupines), Caviomorpha (the endemic South American rodents), and African Phiomorpha (cane rats, dassie rats, and blesmols) is of great interest to students of mammalian evolution, but remains poorly understood because of a poor early fossil record. Here we describe the oldest well-dated hystricognathous rodents from an earliest late Eocene (approximately 37 Ma) fossil locality in the Fayum Depression of northern Egypt. These taxa exhibit a combination of primitive and derived features, the former shared with Asian "baluchimyine" rodents, and the latter shared with Oligocene phiomorphs and caviomorphs. Phylogenetic analysis incorporating morphological, temporal, geographic, and molecular information places the new taxa as successive sister groups of crown Hystricognathi, and supports an Asian origin for stem Hystricognathi and an Afro-Arabian origin for crown Hystricognathi, stem Hystricidae, and stem Caviomorpha. Molecular dating of early divergences within Hystricognathi, using a Bayesian "relaxed clock" approach and multiple fossil calibrations, suggests that the split between Hystricidae and the phiomorph-caviomorph clade occurred approximately 39 Ma, and that phiomorphs and caviomorphs diverged approximately 36 Ma. These results are remarkably congruent with our phylogenetic results and the fossil record of hystricognathous rodent evolution in Afro-Arabia and South America.

Sutures, joints that allow one bone to articulate with another through intervening fibrous connective tissue, serve as major sites of bone expansion during postnatal craniofacial growth in the vertebrate skull and represent an aspect of cranial ontogeny which may exhibit functional and phylogenetic correlates. Suture evolution among hystricognath rodents, an ecologically diverse group represented here by 26 species, is examined using sequence heterochrony methods, i.e. event pairing and PARSIMOV. Although minor nuances in suture closure sequence exist between species, the overall sequence was found to be conserved both across the hystricognath group and, to an increasing degree, within selected clades. At species level, suture closure pattern exhibited a significant positive correlation with patterns previously reported for hominoids. Patterns for most clades revealed the first sutures to close are those contacting the exoccipital, interparietal, and palatine bones. Heterochronic shifts were found along 19 of 35 branches within the hystricognath phylogeny. The number of shifts per node ranged from one to seven events and, overall, involved 21 of 34 suture sites. The topology generated by parsimony analyses of the event pair matrix yielded only one grouping that was congruent with the evolutionary relationships, compiled from morphological and molecular studies, taken as framework. Sutures contacting the exoccipital displayed the highest levels of most complete closure across all species. Level of suture closure is negatively correlated with cranial length (P < 0.05). Differing life history and locomotory strategies are coupled in part with differing suture closure patterns among several species.

The discovery of an exceptionally well-preserved skull permits the description of the new South American fossil species of the rodent,Josephoartigasia monesisp. nov. (family: Dinomyidae; Rodentia: Hystricognathi: Caviomorpha). This species with estimated body mass of nearly 1000 kg is the largest yet recorded. The skull sheds new light on the anatomy of the extinct giant rodents of the Dinomyidae, which are known mostly from isolated teeth and incomplete mandible remains. The fossil derives from San José Formation, Uruguay, usually assigned to the Pliocene–Pleistocene (4–2 Myr ago), and the proposed palaeoenvironment where this rodent lived was characterized as an estuarine or deltaic system with forest communities.

Platyrrhine primates and caviomorph rodents are clades of mammals that colonized South America during its period of isolation from the other continents, between 100 and 3 million years ago (Mya). Until now, no molecular study investigated the timing of the South American colonization by these two lineages with the same molecular data set. Using sequences from three nuclear genes (ADRA2B, vWF, and IRBP, both separate and combined) from 60 species, and eight fossil calibration constraints, we estimated the times of origin and diversification of platyrrhines and caviomorphs via a Bayesian relaxed molecular clock approach. To account for the possible effect of an accelerated rate of evolution of the IRBP gene along the branch leading to the anthropoids, we performed the datings with and without IRBP (3768 sites and 2469 sites, respectively). The time window for the colonization of South America by primates and by rodents is demarcated by the dates of origin (upper bound) and radiation (lower bound) of platyrrhines and caviomorphs. According to this approach, platyrrhine primates colonized South America between 37.0 +/- 3.0 Mya (or 38.9 +/- 4.0 Mya without IRBP) and 16.8 +/- 2.3 (or 20.1 +/- 3.3) Mya, and caviomorph rodents between 45.4 +/- 4.1 (or 43.7 +/- 4.8) Mya and 36.7 +/- 3.7 (or 35.8 +/- 4.3) Mya. Considering both the fossil record and these molecular datings, the favored scenarios are a trans-Atlantic migration of primates from Africa at the end of the Eocene or beginning of the Oligocene, and a colonization of South America by rodents during the Middle or Late Eocene. Based on our nuclear DNA data, we cannot rule out the possibility of a concomitant arrival of primates and rodents in South America. The caviomorphs radiated soon after their arrival, before the Oligocene glaciations, and these early caviomorph lineages persisted until the present. By contrast, few platyrrhine fossils are known in the Oligocene, and the present-day taxa are the result of a quite recent, Early Miocene diversification.

Insulin is a conservative molecule among mammals, maintaining both its structure and function. Rodents that belong to the Suborder Hystricognathi represent an exception, having a very divergent molecule with unusual physiological properties. In this work, we analyzed the evolutionary pattern of the insulin gene in caviomorph rodents (South American hystricomorph rodents). We found that these rodents have higher rates of nonsynonymous:synonymous substitutions (d(N)/d(S)) than nonhystricomorph rodents and that values are heterogeneous inside the group. We estimated codons under positive selection, specifically the second binding site (A13 and B17) and others related with hexamerization (B18, B20, and B22). In the monomer structure, all selected sites formed a single patch around the second binding site. In the hexamer structure, these amino acids were grouped into three major patches. In this structure, contacts between B chains involved all selected sites (except B18), and between faces in the center of the molecule, all contacts were among selected sites. While there is no clear hypothesis regarding the cause of this drastic change, experimental evidence does show that this group of rodents has some peculiarities in growth function, and, whether coincidental or not, these changes appeared together with important changes in life-history traits.

Major crown-groups of rodents were well established in the early Tertiary, and fossils provide an invaluable window into their evolutionary history. The main focus of this project was to perform a cladistic assessment of the dental evidence for early Tertiary rodent cladogenesis – the masticatory apparatus and teeth are the most frequently preserved anatomical features in the fossil record. We focused on groups that existed in a period corresponding to their early history, combining fossils belonging to extinct lineages and to stem-groups leading to modern lineages. While the monophyly of some groups is not systematically explored, our results have important implications for high-level rodent relationships and systematics. These results are consistent with those of recent molecular phylogenies and reliably congruent with the stratigraphic record, thus enhancing the pertinence of dental characters for phylogenetic inference. Our approach provides evidence of a fundamental dichotomy in early rodent history. Two major clades have been identified: (1) the earliest ‘ctenodactyloid’ (Ctenodactylidae, Chapattimyidae, Yuomyidae, Diatomyidae) and hystricognathous (Tsaganomyidae, Baluchimyinae, ‘phiomorphs’, ‘caviomorphs’) rodents, and (2) the earliest ‘ischyromyoid’ rodents with their closest relatives (Muroidea + Dipodoidea + Geomyoidea + Anomaluroidea + Castoroidea + Sciuravidae + Gliroidea, and Sciuroidea + Aplodontoidea + Theridomorpha). This topology has led us to endorse Ctenohystrica as the first clade and propose a new taxon, Ischyromyiformes, for the second. Although minimized in our working hypothesis, the homoplasy in dental characters remains significant. However, a number of homoplasic characters reveal structuring in their internal distribution, allowing us to discern evolutionary morphological patterns, notably the pentalophodonty of molars, zygomasseteric complex and incisor enamel microstructure. © 2004 The Linnean Society of London, Zoological Journal of the Linnean Society, 2004, 142, 105–134.

The phylogeny of South American spiny rats (Rodentia; Echimyidae) was studied using the exon 28 of the von Willebrand Factor nuclear gene (vWF). Sequences were analysed separately and in combination with a mitochondrial dataset (cyt b, 12S and 16S rRNAs) used in previous publications. The basal polytomy of echimyids was partially resolved and unexpected intergeneric clades were recovered. Thus, the intimate nested position of Myocastor within echimyids is evidenced. A well-supported clade is identified, including all the arboreal genera, and a group formed by Myocastor, Thrichomys, and Proechimys + Hoplomys. The clustering of Euryzygomatomys + Clyomys with Trinomys is also suggested. On the opposite, the phylogenetic position of Capromys as well as the relationships among arboreal genera remain unclear. Molecular divergence times were estimated using a Bayesian relaxed molecular clock and suggest a Middle Miocene origin for most of modern genera. The ecomorphological diversification of echimyids is discussed in the light of these new results and past environmental modifications in South America.

A total of 30 animals of the genus Dasyprocta were cytogenetically studied. They belong to the following species: D. prymnolopha (N=20), D. leporina (N=6), D. fuliginosa (N=1) and Dasyprocta sp. (N=3) (Dasyproctidae, Hystricognathi). Cell suspensions were obtained by peripheral blood culture, besides bone marrow and spleen cells, from D. prymnolopha and D. leporina. The diploid number was 64/65 for all samples. The karyotypes showed similarity, and chromosomal polymorphism was not detected by Giemsa conventional staining and G banding. The constitutive heterochromatin distribution at the pericentromeric region of all the chromosomes was similar in all species. D. prymnolopha, D. leporina and Dasyprocta sp. presented variation in the heterochromatical block size at one of the homologues of the A18 pair. D. fuliginosa presented the heterochromatin uniformly distributed in all chromosomes. There was not variation in the NORs pattern in the species studied.Foram estudados citogeneticamente um total de 30 animais das espécies D. prymnolopha (N=20), D. leporina (N=6), D. fuliginosa (N=1) e Dasyprocta sp. (N=3) (Dasyproctidae, Histricognathi). As preparações cromossômicas foram obtidas do cultivo de sangue periférico, além de medula óssea e baço em D. prymnolopha e D. leporina. O número diplóide foi de 64/65 em todos os exemplares. O cariótipo mostrou similaridade, não sendo detectado, através de coloração convencional de giemsa e de banda G, polimorfismo cromossômico em qualquer uma das espécies estudadas. A distribuição da heterocromatina constitutiva na região pericentromérica de todos os cromossomos foi similar nas quatro espécies. D. prymnolopha, D. leporina e Dasyprocta sp. apresentaram variação no tamanho do bloco heterocromático em um dos homólogos do par A18. D. fuliginosa apresentou a heterocromatina uniformemente distribuída em todos os cromossomos. Não houve variação no padrão das RONs entre as esp��cies estudadas.

Rodentia is the largest order of placental mammals, with approximately 2,050 species divided into 28 families. It is also one of the most controversial with respect to its monophyly, relationships between families, and divergence dates. Here, we have analyzed and compared the performance of three nuclear genes (von Willebrand Factor, interphotoreceptor retinoid-binding protein, and Alpha 2B adrenergic receptor) for a large taxonomic sampling, covering the whole rodent and placental diversity. The phylogenetic results significantly support rodent monophyly, the association of Rodentia with Lagomorpha (the Glires clade), and a Glires + Euarchonta (Primates, Dermoptera, and Scandentia) clade. The resolution of relationships among rodents is also greatly improved. The currently recognized families are divided here into seven well-defined clades (Anomaluromorpha, Castoridae, Ctenohystrica, Geomyoidea, Gliridae, Myodonta, and Sciuroidea) that can be grouped into three major clades: Ctenohystrica, Gliridae + Sciuroidea, and a mouse-related clade (Anomaluromorpha, Castoridae + Geomyoidea, and Myodonta). Molecular datings based on these three genes suggest that the rodent radiation took place at the transition between Paleocene and Eocene. The divergence between rodents and lagomorphs is placed just at the K-T boundary and the first splits among placentals in the Late Cretaceous. Our results thus tend to reconcile molecular and morphological-paleontological insights.

Nucleotide sequence data from the mitochondrial 12S rRNA and cytochrome b genes were used to analyze phylogenetic relationships among sciurognath rodents. Our sample taxa included representatives of 11 sciurognath and 3 hystricognath families with two marsupial species, Didelphis virginiana and Macropus robustus, as outgroups. The dataset was analyzed using both maximum-parsimony (weighted and unweighted) and likelihood methods. Three suprafamilial groupings are strongly supported: Geomyidae + Heteromyidae (Geomyoidea), Sciuridae + Aplodontidae (Sciuroidea), and Pedetidae + Anomaluridae (Anomaluroidea). Although moderately supported, two sister group relationships were identified between Gliridae and Sciuroidea and between Castor and Geomyoidea. In contrast to previous nuclear DNA evidence, the evolutionary affinities between Ctenodactylidae and Hystricognathi (Ctenohystrica) and between Muridae and Dipodidae (Myodonta) are not supported by the mitochondrial data. Molecular divergence dates based on the combined data were estimated for suprafamilial groupings and are discussed in the light of current morphological and paleontological interpretations of rodent phylogeny.

Hystricognath rodents include Old World Phiomorpha and New World Caviomorpha. These two groups have an enigmatic biogeographical history. Using a nuclear marker, the exon 28 of the von Willebrand Factor gene (vWF), we reconstructed the phylogenetic relationships among 23 Hystricognathi species. These taxa encompass the complete familial diversity of the Hystricognathi. Our results indicate a basal trifurcation of hystricognaths leading to Hystricidae, Phiomorpha s.s. (Bathyergidae, Thryonomyidae, and Petromuridae), and Caviomorpha. The monophyly of caviomorphs is robustly supported, confirming a single colonization event of South America by hystricognaths. Caviomorpha are divided into four lineages: Cavioidea, Erethizontoidea, Chinchilloidea, and Octodontoidea. Furthermore, we suggest that (1) Chinchillidae and Dinomyidae are sister clades, (2) Abrocomidae is a true Octodontoidea, and (3) Capromyidae, Echimyidae, and Myocastoridae cluster together. Surprisingly, Erethizontidae does not appear to be the most diverged caviomorph lineage. The molecular results are discussed in the light of previous paleontological and morphological observations. Local molecular clocks are used to estimate divergence dates among hystricognath lineages. An Asian origin is suggested for Caviomorpha, and a colonization route through Australia and Antarctica is indicated as an alternative to the hypothesis of a transatlantic migration of Caviomorpha from Africa to South America.

The order Rodentia contains half of all extant mammal species, and from an evolutionary standpoint, there are persistent controversies surrounding the monophyly of the order, divergence dates for major lineages, and relationships among families. Exons of growth hormone receptor (GHR) and breast cancer susceptibility (BRCA1) genes were sequenced for a wide diversity of rodents and other mammals and combined with sequences of the mitochondrial 12S rRNA gene and previously published sequences of von Willebrand factor (vWF). Rodents exhibit rates of amino acid replacement twice those observed for nonrodents, and this rapid rate of evolution influences estimates of divergence dates. Based on GHR sequences, monophyly is supported, with the estimated divergence between hystricognaths and most sciurognaths dating to about 75 MYA. Most estimated dates of divergence are consistent with the fossil record, including a date of 23 MYA for Mus-Rattus divergence. These dates are considerably later than those derived from some other molecular studies. Among combined and separate analyses of the various gene sequences, moderate to strong support was found for several clades. GHR appears to have greater resolving power than do 12S or vWF. Despite its complete unresponsiveness to growth hormone, Cavia (and other hystricognaths) exhibits a conservative rate of change in the intracellular domain of GHR.