A new species of the endemic Tarsomys clade (Muridae, Rodentia) from eastern Mindanao Island, Philippines.

The article focuses on the discovery and description of a new species of murine rodent, *Tarsomys orientalis* (Kampalili Moss Mouse), from Mt. Kampalili in eastern Mindanao Island, Philippines. This species is the third known member of the genus *Tarsomys*, distinguished from its congeners (*T. apoensis* and *T. echinatus*) by smaller body size, shorter tail, smaller hind feet, darker and softer pelage, and distinct cranial features. Molecular phylogenetic analyses place *T. orientalis* as a sister species to *T. apoensis*, diverging approximately 1.0 to 1.75 million years ago, within the "Tarsomys clade" of the tribe Rattini, a group endemic to Mindanao that includes other genera such as *Limnomys* and *Baletemys*. The discovery highlights Mt. Kampalili as a significant center of mammalian endemism and supports the pattern of within-island diversification as a key driver of small mammal species richness in the Philippines.