Abstract
Rodents, particularly the family Muridae, are exceptionally species-rich, with a global distribution and significant ecological and economic roles. Despite their ubiquity, many murids remain poorly studied, especially members of the subfamily Murinae inhabiting Southeast Asia’s biodiverse island ecosystems. Borneo, a hotspot for arboreal rodent diversity, hosts several endemic murines, including the elusive Emmons’s tree rat ( Pithecheirops otion ), known from only one museum specimen and three sightings documented with photographs. We assess the phylogenetic placement of P. otion by sequencing DNA from the holotype and presumed relatives in the genus Pithecheir . We recovered high-quality mitochondrial genomes and two nuclear genes to estimate the first species-level phylogeny that includes these two genera. Both mitochondrial and nuclear DNA support a sister relationship between Pithecheirops and Pithecheir and provide sufficient evidence to support their placement in the tribe Pithecheirini. Our review of distributional records of Pithecheirini reveals a severe paucity of geographical information, which hinders conservation assessments.