The genus Thomasomys, a key genus within the Thomasomyini tribe of the Sigmodontinae subfamily, is a focal point for understanding the phylogeny, biogeography, and ecological adaptation of Andean rodents. As the most diverse genus within the Sigmodontinae, Thomasomys includes 51 valid species and numerous undescribed ones, predominantly inhabiting Neotropical montane forests and paramos. Its distribution, however, excludes regions like the Guiana Shield, lowland tropical forests, deserts, and oceanic islands. Conflictive findings between early molecular phylogenetic analyses and morphological studies highlight the necessity for an integrated approach encompassing genetic, molecular, and morphological research. This research delves into Thomasomys complex taxonomic background, phylogenetic relationships, species diversity, and morphological adaptations, shedding light on its evolutionary ...