While finger monkey is not a scientific term, and can refer to any monkey small enough to hold in one hand, the most common type of monkey called a finger monkey is a pygmy marmoset. Weighing an average of 3.5 ounces and at 5 inches tall not counting the tail, the pygmy marmoset is the smallest monkey species.
Pygmy marmosets, which have the species name Cebuella pygmaea, are primates. They are members of the Callitrichidae family, which includes all of the marmosets and tamarins. The monkeys inhabit the Amazon rain forest in Colombia, Ecuador, Bolivia, Peru and Brazil.
Though pygmy marmosets are cute, they generally do not make good pets because they have a propensity to bite and throw feces. The market price for a pygmy marmoset is between $2000 and $5000, as of January 2016. Before buying one, it is important to check local laws to ensure that owning a monkey is legal.
The Callitrichidae family is the only primate family that usually gives birth to twins. Many species in the family are endangered due to habitat destruction. Primates in this family eat a diet made up of fruit, nuts, and the sap and gum of trees. The family contains a number of other small monkey species, and its largest member weighs only 1.4 pounds fully grown.