The pygmy marmoset is one of the world's smallest primates, and is the smallest true monkey, with a head-body length ranging from 117 to 152 mm (4. 6 to 6. 0 in) and a tail of 172 to 229 mm (6. 8 to 9. 0 in). The average adult body weight is just over 100 grams (3. 5 oz) with the only sexual dimorphism of females being a little heavier. The fur colour is a mixture of brownish-gold, grey, and black on its back and head and yellow, orange, and tawny on its underparts. Its tail has black rings and its face has flecks of white on its cheeks and a white vertical line between its eyes. It has many adaptations for arboreal living including the ability to rotate its head 180 degrees and sharp claw-like nails used to cling to branches and trees. Its dental morphology is adapted to feeding on gum, with specialised incisors that are used to gouge trees and stimulate sap flow. Its cecum is larger than usual to allow for the greater period of time gum takes to break down in the stomach. The pygmy marmoset walks on all four limbs and can leap up to 5 m (16 ft) between branches.