Pygmy marmoset

The pygmy marmoset (Cebuella pygmaea) is a small species of New World monkey native to rainforests of the western Amazon Basin in South America. The species is notable for being the smallest monkey and one of the smallest primates in the world, at just over 100 grams (3.5 oz) (Madame Berthe's mouse lemur is smaller). It is generally found in evergreen and river-edge forests and is a gum-feeding specialist, or a gummivore. About 83% of the pygmy marmoset population lives in stable troops of two to nine individuals, including a dominant male, a breeding female, and up to four successive litters of offspring. The modal size of a standard stable troop would be six individuals. Although most groups consist of family members, some may also include one or two additional adult members. Members of the group communicate using a complex system including vocal, chemical, and visual signals. Three main calling signals depend on the distance the call needs to travel. These monkeys may also make visual displays when threatened or to show dominance. Chemical signaling using secretions from glands on the chest and genital area allow the female to indicate to the male when she is able to reproduce. The female gives birth to twins twice a year and the parental care is shared between the group. The pygmy marmoset has been viewed as somewhat different from typical marmosets, most of which are classified in the genera Callithrix and Mico, and thus is accorded its own genus, Cebuella, within the family Callitrichidae. It is listed as Least Concern by the International Union for Conservation of Nature as it is common across its wide range and not at immediate risk of widespread decline. The biggest threats to the species are habitat loss and the pet trade. There has been debate among primatologists concerning the proper genus in which to place the pygmy marmoset. An examination of the interstitial retinol binding protein nuclear gene (IRBP) in three marmoset species showed that Callithrix as constructed in the 1990s also needed to include C. pygmaea to be monophyletic, and that the times of separation of pygmaea and the argentata and jacchus species groups from one another are less than 5 million years ago, as might be expected for species of the same genus. However, subsequent separation of the argentata and jacchus species groups into different genera (the argentata group having been moved to Mico) justifies maintaining a separate genus for the pygmy marmoset, as Callithrix is no longer paraphyletic. There are two subspecies described by Colin Groves of the pygmy marmoset: There are few morphological differences between these subspecies, as they may only differ slightly in color, and they are only separated by geographical barriers, including large rivers in Central and South America. The evolution of this species diverged in terms of body-mass from typical primates, with a high rate of body-mass reduction. This involves large decreases in pre-natal and post-natal growth rates, furthering the thought that pro-genesis played a role in the evolution of this animal. The pygmy marmoset is one of the world's smallest primates, being 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.