The fraternal squirrel is a tree squirrel endemic to Indonesia's Mentawai Islands. Research reports island differences in coat and records of both ground and tree use.
The tail tapers toward its tip and is thickest at the base. Ventral fur is grizzled in most island populations; Siberut is reported as an exception.
A field account cited in the study reports extensive ground use. When climbing, the squirrels preferred heights up to about 5 m and avoided the upper canopy.
An extinction-risk assessment has not been added yet.