Unlocking Andean sigmodontine diversity: five new species of Chilomys (Rodentia: Cricetidae) from the montane forests of Ecuador

The Andean cloud forests of Ecuador are home to several endemic mammals. Members of the Thomasomyini rodents are well represented in the Andes, with Thomasomys being the largest genus (47 species) of the subfamily Sigmodontinae. Within this tribe, however, there are genera that have escaped a taxonomic revision, and Chilomys Thomas, 1897, constitutes a paradigmatic example of these forgotten Andean cricetids. Described more than a century ago, current knowledge of this externally unmistakable montane rodent is very limited, and doubts persist as to whether or not it is monotypic. After several years of field efforts in Ecuador, a considerable quantity of specimens of Chilomys were collected from various localities representing both Andean chains. Based on an extensive genetic survey of the obtained material, we can demonstrate that what is currently treated as C. instans in Ecuador is a complex comprising at least five new species which are described in this paper. In addition, based on these noteworthy new evidence, we amend the generic diagnosis in detail, adding several key craniodental traits such as incisor procumbency and microdonty. These results indicate that Chilomys probably has a hidden additional diversity in large parts of the Colombian and Peruvian territories, inviting a necessary revision of the entire genus.

Automated summary

The Andean cloud forests in Ecuador are home to many unique mammals, and the Thomasomyini rodents, with Thomasomys being the largest genus, are well represented in the Andes. However, there are still genera within this group that have not been taxonomically revised, and Chilomys Thomas, 1897, is an example of these overlooked Andean cricetids. After years of field work in Ecuador, a large number of Chilomys specimens were collected, indicating that what is currently considered C. instans in Ecuador is actually a complex comprising of at least five new species. This discovery suggests that Chilomys likely has additional hidden diversity in other parts of Colombia and Peru, and calls for a revision of the entire genus.