# Mountains of diversity: a systematic revision of the Andean rodent genus Oreoryzomys (Cricetidae: Sigmodontinae)

## TL;DR

This study triples the known species in the Andean rodent genus Oreoryzomys through a detailed taxonomic revision using genetic and morphological data.

## Contribution

The study identifies and describes a new species and elevates a subspecies to species rank in the Oreoryzomys genus.

## Key findings

- Phylogenetic and morphological analyses support three distinct Oreoryzomys species.
- A new species was discovered in the Quijos River Valley of northeastern Ecuador.
- The revision highlights the Andes' role in shaping Neotropical biodiversity through rodent diversification.

## Abstract

The until recently monotypic cricetid genus Oreoryzomys inhabits piedmont and cloud forests, primarily in eastern Ecuador and northwestern Peru. Erected following the taxonomic revision of a polytypic Oryzomys complex two decades ago, Oreoryzomys has remained poorly understood, with most references limited to the original descriptions of its type species (O. balneator) and a subspecies (O. b. hesperus). 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 O. balneator from central-eastern Ecuador; (2) O. hesperus, 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 Oreoryzomys 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.