squirrel monkey Either of at least two species of small, diurnal, arboreal monkeys of tropical South America; it has thick, dark fur and a long, heavy tail. Saimiri sciureus has a cap of greyish fur; S. oerstedi has a black cap and reddish fur on its back. Both are gregarious and live primarily on fruit. Length: to 40cm (16in); tail: 47cm (19in). Family Cebidae.

squir·rel mon·key • n. a small South American monkey (genus Saimiri, family Cebidae) with a nonprehensile tail, typically moving through trees by leaping.