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By Sarah Cover
Geographic Range
Common marmosets are New World primates. Their original range was limited to north eastern Brazil, but habitat destruction in that area is widespread. Wild populations of the common marmoset are now located in south eastern Brazilian coastal rainforest. (Parker, 1990)
Biogeographic Regions:
neotropical 
(native ).
Habitat
Common marmosets can be found around the edges of the forest as opposed to deep within it. They live in many forest types, including plantations. (Parker)
Terrestrial Biomes:
rainforest .
Physical Description
(10.56 to 12.67 oz; avg. 11.62 oz)
The common marmoset has a body length of about 12 - 15 cm, with a tail length of 29.5 - 35 cm. Distinguishing characteristics of common marmosets include white ear tufts, and a white blaze on the forehead. Their head fur is usually dark brown, while their back fur is a greyish brown color with light transverse striping. They also have very pronounced transverse tail stripes.
(Parker, 1990)
Some key physical features:
endothermic ; bilateral symmetry .
Reproduction
It was originally thought that common marmosets were monogamous creatures, forming pair bonds and raising their offspring as a team. This was believed because captive marmosets only bred successfully in a pair situation. However, it has recently been discovered that the common marmoset, along with other species of marmosets and tamarins, is actually polyandrous (one female mates with multiple males). In the wild, groups of two males and a female form in order to mate and rear offspring. The female mates nearly equally with both males while in estrus.
Mating systems:
polyandrous ; cooperative breeder .
After gestating for approximately 148 days, the female gives birth to the offspring, usually twins (Smuts et al., 1987).
Key reproductive features:
iteroparous ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; viviparous .
The twins combined can equal up to 40% of the female's body weight. The males assist the female in carrying the infants, and it is generally thought that polyandry in this species is due to the large size of these babies and the energy needed to raise them.
Parental investment:
pre-fertilization (provisioning, protecting: female, female); pre-hatching/birth (provisioning: female, female, protecting: female, female); pre-weaning/fledging (provisioning: female, female, protecting: male, female, male, female); pre-independence (protecting: male, female, male, female).
Behavior
Common marmosets are diurnal, and generally live in groups of 2-13 individuals which may include mated polyandrous groups and their offspring. The most outstanding feature of common marmoset behavior is nonmaternal infant care (also found in other callitrichid primates). Males and siblings are quick to assist mother common marmosets with infant care, and indeed, it seems that this help is necessary for infant survival. (Smuts et al., 1987)
Food Habits
While the common marmoset generally feeds on tree sap, this species has also been found to eat insects, spiders, fruit, flowers, and nectar. Less frequently, they have been observed feeding on small lizards, bird's eggs, nestlings, and frogs.
(Parker, 1990)
Primary Diet:
herbivore (eats sap or other plant foods).
Animal Foods:
birds; amphibians; reptiles; eggs; insects; terrestrial non-insect arthropods.
Plant Foods:
fruit; nectar; flowers.
Economic Importance for Humans: Negative
Because they have adapted to life on the edge of the forests of south eastern Brazil, common marmosets have also learned to take advantages of the plantations in the area. In greater numbers, they may become pests to human farmers. (Smuts et al., 1987)
Economic Importance for Humans: Positive
When zoos are able to obtain these tiny creatures, they are very popular attractions.
Conservation Status
Common marmosets are one of the most endangered callitrichid species. The complete destruction of their habitat in north eastern Brazil has severely threatened the species, but their numbers in reserves in south eastern Brazil seem to be growing.
(Smuts et al., 1987)
Other Comments
It is only very recently that humans have been able to obtain any information about this species at all. Because of their rarity and size, they are difficult to study in the wild, and comparisons between captive and field studies have proved that their behavior varies between the two. (Evans, 1986)
Contributors
Sarah Cover (author), University of Michigan.
Phil Myers (editor), Museum of Zoology, University of Michigan.
