Skeletal Variation and Taxonomic Boundaries in the Pen-tailed Treeshrew (Scandentia: Ptilocercidae; Ptilocercus lowii Gray, 1848)

The Pen-tailed Treeshrew, Ptilocercus lowii Gray, 1848, is a small arboreal mammal from Southeast Asia. It is the only extant species of Ptilocercidae and includes two subspecies: P. l. lowii from Borneo and offshore islands, and P. l. continentis from the Malay Peninsula, Sumatra, and smaller islands, including the Batu and Mentawai Islands. Intraspecific taxonomic boundaries in Ptilocercus have yet to be rigorously evaluated using modern morphological methods, so we investigated the morphometric variation between these subspecies using quantitative cranial and postcranial data obtained from museum specimens. Multivariate analyses revealed limited overlap between P. l. lowii and P. l. continentis in cranioskeletal morphospace, indicating some divergence of these two lineages. Future studies should incorporate additional morphological and molecular data to further test whether these lineages represent two distinct species. Recognition of two Ptilocercus species would have conservation implications for both populations, which should be reevaluated across their separate ranges in light of region-specific threats. Additional biological surveys, particularly from undersampled island populations, will be critical in reassessing the distribution and conservation priorities for P. lowii .