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Thomasomys cinereus is the type species of Thomasomys, type genus of the sigmodontine tribe Thomasomyini. As currently recognized, Thomasomys includes 48 species, all of which are endemic to humid montane or premontane forests in the tropical Andes. Although it has been suggested that T. cinereus is a species complex, this hypothesis has yet to be critically evaluated. Herein we provide a revision of the species based on a qualitative assessment of external, craniodental, and soft morphological traits; morphometric analyses; a phylogenetic analysis based on cytochrome b gene sequences; species delimitation methods; and first-hand examination of type material. Our analyses of genetic data recovered four distinct clades within T. cinereus, one corresponding to T. cinereus sensu stricto (restricted to the montane forests delimited by the Río Marañón, Río Huancabamba, and Río Tablachaca in Cajamarca department, Peru) and three new species: Thomasomys lojapiuranus, sp. nov., from the montane forests of Piura department, Peru, and Loja province, Ecuador; T. shallqukucha, sp. nov., restricted to the Kañaris montane forests in the Peruvian department of Lambayeque; and T. pagaibambensis, sp. nov., restricted to the montane forests of Pagaibamba in Cajamarca department, Peru. These species can be distinguished by several discrete morphological traits of the skull, dentition, mandible, stomach, palatal rugae, and glans penis. Genetic distances among these taxa range from 5.06%–7.65% at the cytochrome b locus, and delimitation analyses based on cytochrome b sequence data support their recognition as distinct species. Our results suggest the existence of previously unsuspected dispersal barriers in the Andes of northern Peru, and they confirm that the Río Marañón is a formidable barrier that limits the distribution of species of Thomasomys as well as other sigmodontine rodents. [ABSTRACT FROM AUTHOR]

Monodelphis ronaldi is a short-tailed opossum currently known only by the holotype captured in Madre de Dios, Peru. The relationships of this species with other congeners are unknown, although it has been hypothesized to belong to the subgenus Mygalodelphys. Here, we report six additional specimens of M. ronaldi from the Alto Purús, Ucayali department, Peru, extend the range of the species about 240 km eastward, examine ontogenetic variation, and analyze its phylogenetic relationships using sequences of the mitochondrial Cytochrome-b gene. Our analyses recovered M. ronaldi as the sister species of M. handleyi, confirming its position within the subgenus Mygalodelphys. The genetic distance between them was almost 6%, besides several morphological traits differentiating both species. However, some morphological traits previously proposed as diagnostic were found to vary with age, so an emended diagnosis for M. ronaldi is provided. Additionally, we include new information about the habitat, geographic range, and natural history of this elusive species. [ABSTRACT FROM AUTHOR]

Herein, based on molecular and morphological evidence, we report the first record of Eumops bonariensis (Peters 1874) and Pteronotus fuscus (Allen 1911) for Peru, representing a range extension of at least 1580 km (to Ucayali department) and 1860 km (to San Martín department) from the nearest records, respectively; and confirm that Pteronotus rubiginosus (Wagner 1843) is absent in Peru. We also provide comments on the taxonomy, distribution, and natural history of these species. This study highlights the importance of exploring unsampled localities and doing detailed morphological studies and extensive use of molecular methods. [ABSTRACT FROM AUTHOR]

Nephelomys albigularis is a sigmodontine rodent of the tribe Oryzomyini distributed in the Andean forests from central Ecuador to central Peru. Although several studies recognize this species as monotypic, significant morphological variation has been reported in Peruvian populations that were not properly assessed by direct comparisons with the type series from central Ecuador. We present a preliminary review of N. albigularis with an integrative approach and emphasis on Peruvian populations. We analyzed specimens using morphological and morphometric methods, complemented with phylogenetic analyses and species delimitation using sequence data from the cytochrome-b gene. Our results reveal that N. albigularis (sensu lato) comprises two taxa: N. albigularis s.s., from the montane forests in central and southern Ecuador and northwestern Peru, and Nephelomys sp. nov. from montane forest east of the Maran River. These taxa are morphologically distinct and are separated by a genetic distance of 5.90 1.01%. Nephelomys sp. nov. differs from N. albigularis s.s. by longer rump hairs, narrow hypothenar pads, faintly bicolor tail; absent interorbital ridges, low zygomatic plates, smoothly squared posterior margin of the hard palate or with a small median postpalatal process, smoothly edged ventral margin of the external auditory meatus, and slightly angular mandibular sigmoid notches. In this work, we present a diagnosis and description of the new species of Nephelomys and discuss the role of the Maran River as a potential driver for speciation in the genus Nephelomys.