Marmosets are the smallest platyrrhines or New World monkeys (NWMs). They are closely related to Goeldi’s monkeys, tamarins, and lion tamarins, which together form the subfamily Callithrichinae. Marmosets reside in tropical rain forests in the Amazonian regions of Brazil, Bolivia, Colombia, Ecuador, and Peru. They are a flamboyant group of monkeys, with many species boasting fine-textured, multicolored pelage and adorning manes, moustaches, tufts, fringes, and crests. Unlike some NWMs, marmosets do not have prehensile tails. However, like the tamarins and lion tamarins, marmosets are characterized by the development of claw-like nails (tegulae) located on all digits except the hallux (big toe), the loss of one set of molars, and the regular production of twin offspring.
Three genera of marmosets have been classified: Callithrix, Cebuella, and Mico. Some taxonomists also include Callimico in the marmoset group. Callithrix are found in the Atlantic coastal regions of Brazil, whereas Cebuella and Mico are found in the Amazon basin of Brazil and a few surrounding countries. Callimico are found in Brazil, Bolivia, Peru, and Colombia. Marmosets, excluding Callimico, range in size from 126 to 450 g, with body lengths between 136 and 231 mm.
Cebuella is composed of one species: the pygmy marmoset (C. pygmaea). Pygmy marmosets are the smallest of the NWMs, with an average body weight of 100 g. They generally live in groups consisting of one adult male, one adult female, and offspring.
There is also only one species in the genus Callimico: Goeldi’s monkey (C. goeldii). Goeldi’s monkeys differ from marmosets in that they are slightly larger (400-535 g, 216-232 mm), retain their third molars, and give birth to singletons. This may mean that Goeldi’s monkeys are more ancestral than other marmosets. Many people still debate whether or not Callimico should be placed with the marmosets or be considered a close but separate relative.
Marmosets are diurnal, arboreal, and quadrupedal. They are omnivorous, feeding on exudates (gum and sap), fruits, and insects. Marmosets are distinguished from the closely related tamarins and other NWMs by having large, chisel-like incisors that they use to gouge out holes in tree trunks to stimulate the flow of exudates. Their claw-like nails help them to cling to trees while feeding.
Marmosets live in communal social groups that have variable social organizations. Some live as monogamous pairs, whereas others live in multiple-female and/or multiple-male groups that are composed of extended family members. Marmosets are most often found in groups consisting of one breeding adult female, other adult females, several adult males, and offspring. Females become sexually mature at around 18 months of age. All group members play an active role in helping to raise the dominant female’s twin offspring, carrying the young so that the mother can forage unimpeded. Marmosets have a life expectancy of 12 to 18 years in the wild.
At least 2 of the 14 species of marmoset are considered to be endangered: the buffy tufted-eared marmoset and the buffy-headed marmoset. The cause of the decrease in these populations is deforestation of these species’ already small habitats.
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