Mountains of diversity: a systematic revision of the Andean rodent genus <i>Oreoryzomys</i> (Cricetidae: Sigmodontinae)

The until recently monotypic cricetid genus <i>Oreoryzomys</i> inhabits piedmont and cloud forests, primarily in eastern Ecuador and northwestern Peru. Erected following the taxonomic revision of a polytypic <i>Oryzomys</i> complex two decades ago, <i>Oreoryzomys</i> has remained poorly understood, with most references limited to the original descriptions of its type species (<i>O. balneator</i>) and a subspecies (<i>O. b. hesperus</i>). Here, we present an integrative taxonomic revision of the genus, based on new field collections and comprehensive museum-based analyses. Phylogenetic reconstructions from mitochondrial and nuclear gene sequences, combined with morphometric and qualitative morphological data, support the recognition of three species: (1) a redescribed <i>O. balneator</i> from central-eastern Ecuador; (2) <i>O. hesperus</i>, elevated to full species rank based on topotypic material; and (3) a new species from populations of the Quijos River Valley, northeastern Ecuador. This revision triples the known species diversity of <i>Oreoryzomys</i> and highlights the genus as a notable radiation of small-bodied oryzomyines adapted to Andean environments. Our findings emphasize the need for systematic revisions of other poorly known Andean rodents to better reveal the hidden diversity of cricetids and the role of the Andes in shaping Neotropical biodiversity.