Additional morphological evidence for taxonomic diversity in the Pen-tailed Treeshrew (<i>Ptilocercus</i>, Scandentia)

Abstract The Pen-tailed Treeshrew Ptilocercus lowii Gray, 1848 is a small arboreal mammal known from Southeast Asia. Two subspecies are currently recognized, P. l. lowii from Borneo and some nearby offshore islands, and P. l. continentis from the Malay Peninsula, Sumatra, and the surrounding islands of Lingga, Karimunbesar, Bangka, Siberut, and Pini. Previous work demonstrated that these 2 subspecies are distinctive in aspects of their osteology, especially their postcranial morphology, which suggests that they may be distinct species. We sought to further investigate taxonomic boundaries of the Pen-tailed Treeshrew by examining museum specimens for differences in linear dimensions of the manus and pes (methods previously shown to reflect species boundaries among treeshrews), as well as in the geometry of the lower second molar using an automatic landmarking algorithm for geometric morphometrics known as auto3dgm and SAMS. Results of the linear measurements suggest that these 2 subspecies are subtly different from one another, though not consistently so, and that P. l. lowii is slightly larger than P. l. continentis in dimensions of the manus and pes. Results of the geometric morphometric analysis suggest that these 2 taxa are distinctive in their molar morphology. Comparisons of gross molar morphology demonstrate that the lower second molar of P. l. lowii is wider crowned, has more lingually placed cusps, and a buccally inflated cingulid. Our work provides further evidence that these subspecies may represent distinct lineages worthy of species-level recognition. This work highlights the need for additional genomic data and the need to reassess the conservation status of Ptilocercus, particularly in light of global climatic change and local deforestation.