Thomas's Tree Rat

Thomas's tree rat is the largest known member of Chiromyscus, with a head-and-body length of 14.5–18 cm and a 20–23.1 cm tail. Its upperparts are orange-brown, becoming bright orange from the face to behind the ears, and a darker ring around each eye forms a conspicuous facial mask. The heavy skull and strongly developed ridges above the eyes also separate it from the smaller, more gracile Langbian tree rat (Balakirev, Abramov & Rozhnov 2014).

The species was described from an adult male collected in December 2011 near Lung Lo Pass in Son La Province at about 450 m. Confirmed Vietnamese records span Son La and Lao Cai in the north and Nghe An and Kon Tum in central Vietnam; specimens are also known from northern Laos. Reports farther west and north may represent this species, but the authors considered those identifications unresolved because other masked tree rats occur there (Balakirev, Abramov & Rozhnov 2014).