Neotropical Pygmy Squirrel , Sciurillus pusillus , is a very small squirrel species from South America . It is the only living member of the genus Sciurillus and the subfamily Sciurillinae . The Neotropical pygmy squirrel ( Sciurillus pusillus ) is a very small tree squirrel , being the only living species in the genus Sciurillus and the subfamily Sciurillinae .