The large spiny mouse Neacomys spinosus (Thomas, 1882) has been considered the widest ranging species of the genus, occurring in southern Colombia, eastern Peru, western Brazil and northern Bolivia. The morphological variation between subspecies and populations of N. spinosus has been noted; nonetheless, this variation has not been assessed in a morphological or molecular context. Here, we present a taxonomic revision of Neacomys spinosus s.l. using qualitative and quantitative morphological analyses. These analyses were complemented with molecular analysis to reconstruct the phylogenetic relationships among species of Neacomys, based on sequences of the cytochrome b gene. Our results reveal that N. spinosus s.l. is a monophyletic group, and morphological and molecular evidence to differentiate three taxa: N. spinosus s.s., an endemic species from mountain cloud forests in Peru; N. amoenus s.l. from the Cerrado between Bolivia and Brazil to the Amazonia between Ecuador and northern Peru, and Neacomys sp. nov. from mountain cloud forests from southern Peru to Bolivia. Also, our molecular results indicate that Neacomys is still far from being completely known. For instance, there are three candidate species pending of taxonomic revision. Finally, we propose three species groups within Neacomys: "paracou", "tenuipes" and "spinosus", and discuss biogeographical scenarios of the genus within South America.

A previous study showed that Dromiciops gliroides has deep phylogeographic structure, with 3 allopatric and highly differentiated groups. Here, we constructed on that study by assessing the morphologic variation of D. gliroides. Our results show that along its distribution Dromiciops is morphologically highly variable and that the geographic pattern of morphologic variation matches the phylogeographic pattern. Taken together, morphological and molecular data indicate the existence of 2 unrecognized and unnamed species of monito del monte, which are here named and described. Cranial and dental features can easily distinguish species of Dromiciops. One of the new species is endemic of Chile, and the other new species occurs in Argentina and Chile. D. gliroides s.s. is restricted to the southern part of the genus distribution including Chiloé Island. We comment on the conservation significance of our findings and on the need of continuing with field- and collection-based research in order to characterize the richness of the Chilean mammal assemblage. Un estudio previo mostró que Dromiciops gliroides tiene una marcada estructura filogeográfica con 3 grupos alopátridos bien diferenciados. Dado esos resultados, en el presente estudio analizamos la variación morfológica de D. gliroides. Nuestros resultados indican que D. gliroides es, a través de su distribución, altamente variable y que el patrón geográfico de la variación morfológica es congruente con el patrón filogeografico. Considerada en conjunto, la evidencia morfológica y molecular indica la existencia de dos especies de monito del monte que no han sido reconocidas, las que son aca descritas y nominadas. Las tres especies de Dromiciops se pueden distinguir fácilmente por características craneales y dentales. Una de las nuevas especies es endémica de Chile y la otra se distribuye en Argentina y Chile. D. gliroides s.s. se restringe a la porción sur del área distribucional del género, incluyendo la Isla de Chiloé. Cerramos el trabajo comentado sobre la necesidad de continuar realizando colectas y trabajo basado en colecciones con el fin de caracterizar la diversidad del ensamble de mamíferos de Chile.

The genus Oligoryzomys, distributed from southern South America to southern North America, is the most diverse of the tribe Oryzomyini of sigmodontine rodents. Even when 22 species are currently recognized, species boundaries are unclear for several forms. The species Oligoryzomys destructor is one of the least studied species of the genus and is the one with the largest distribution along the Andes (from southern Colombia to northern Bolivia). The species was described without the selection of a holotype and indication of its type locality. In addition, several taxa are regarded as synonyms of O. destructor. These facts are relevant because previous analysis of DNA sequences has shown that O. destructor represents a species complex. Herein, in addition to test the phylogenetic position of O. destructor within the genus Oligoryzomys, we assess patterns of morphological and molecular variation of O. destructor and its associated nominal forms aimed to assess the boundaries of the species. As part of the study, we selected neotypes for Hesperomys destructor and H. melanostoma. At the light of our results, we recognized O. destructor as a species with two subspecies, O. d. destructor and O. d. spodiurus. Also, we discuss the role of Andean rivers, and their different permeability, as allopatric barriers molding the structure of O. destructor.

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Oligoryzomys, as currently understood is formed by 25 living species, is the most diverse genus of the tribe Oryzomyini of the New World subfamily Sigmodontinae of cricetid rodents. Nonetheless, the species richness of Oligoryzomys seems to be an underestimate, given some species complex has been proposed in previous studies, at the time that large geographic areas remain to be sampled, and several taxonomic forms have not been assessed with contemporary approaches. In this study, we present a new assessment of the species diversity of Oligoryzomys based on multiple unilocus species delimitation methods (ABGD, BPP, PTP, GMYC and b GMYC), using 665 cytb gene sequences as evidence (532 gathered from Genbank and 133 obtained in this study). We sampled representatives of almost all currently known species of Oligoryzomys, at the time that extending the geographic coverage to the Central Andes, a large area that was largely unrepresented in previous studies. Phylogenetic relationships, based on a non‐redundant alignment, were inferred via maximum likelihood and Bayesian inference; an ultrametric tree, used in species delimitation analyses, was obtained using multiple secondary calibration points. Results of species delimitation methods are discussed at the light of previous knowledge (e.g., taxonomic history and geographic provenance of samples in relation to type localities) and the morphological assessments of some specimens. Results of the distinct delimitation methods are mostly congruent, being BPP and PTP the most sensible to estimate species delimitation, allowing us to suggest that Oligoryzomys is composed of 30 lineages of species level. Of these, 22 correspond to forms currently considered species; some of these include in their synonymy some forms currently considered valid species (e.g., yatesi would be a synonym of longicaudatus). The remaining eight lineages are candidate species that need to be further evaluated. This study, by advancing taxonomic hypothesis that should be further tested in future studies, constitutes a stepping‐stone for upcoming taxonomic and biogeographic studies centred on Oligoryzomys.

Andean long-tailed mice of the genus Oligoryzomys have a complex and instable taxonomic history. Recent studies, in addition to circumscribe O. destructor to populations from southern Peru up to the north, and O. brendae to those from Argentina and southern Bolivia, have identified a candidate species in northern Bolivia. Herein, we assessed the status of the mentioned candidate species by morphologically comparing it with O. brendae, its sister group; with O. destructor, which is morphologically similar and distributed parapatrically; and with O. flavescens occidentalis, which is geographically codistributed. Additionally, we compared it with Oryzomys chaparensis, a poorly known form, currently placed in the synonymy of O. microtis, whose type locality is near the known distribution of the Bolivian candidate species. Results show that the assessed form is morphologically diagnosable. This fact together with its phylogenetic distinction allows us to hypothesize that it represents a new species that is named and described here.

Aim Tropical South America, in particular Amazonia, has been identified as the area of the basal diversification of several large mammal clades. Whether this scenario also holds for younger and widely distributed clades remains unclear. Here, we assessed the historical biogeography of a young but diverse and widely distributed mammal clade. Location The Neotropics. Taxon Long‐tailed mice of the genus Oligoryzomys. Methods We estimated a dated species tree by sampling five genes (one mitochondrial and four nuclear) from 30 of the 32 living species of the genus. We inferred the distribution of the most recent common ancestors (MRCAs) of distinct species groups, using a 13 ecoregion scheme and fitting three biogeographical models, to simulate dispersal events under the selected model. Results The DEC model best explained the diversification of Oligoryzomys. The MRCA of the genus had an age of ~2.64 Mya and its ancestral area was inferred as a large region encompassing Boreal and Southern Amazonia, Chaco and Tropical Andes. Subsequent vicariance events, followed by dispersal events towards the present, account for its diversification and wide distribution. Main conclusion The biogeographical history of Oligoryzomys is complex. It originated in the northern half of South America; and then after a series of vicariant events, a series of dispersion events allowed it to colonize southern South America, the Andes and closer to the present Central and North America. This radiation, which constitutes one of the fastest and largest Pleistocene diversifications of Neotropical mammals, involves events previously suggested for other groups (e.g. Andean diversification), others that are novel for rodents and for the most part for South American mammals (e.g. the identification of the Chaco as a centre of diversification).

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