Prosimians are considered the most primitive group of primates. Examples of prosimians include the indri, lemurs, tarsiers, sifakas, and lorises . Prosimians have relatively smaller brains and rely more on the sense of smell. Prosimians have structural differences in their skull and reproductive biology. All lemurs and lemur-like prosimians are endemic to Madagascar.
Some nocturnal prosimians inhabit parts of Africa and Asia.
Callitrichids share much in common with other New World monkeys. While Callitrichids share the above traits, they are also a very diverse group of primates, especially in appearance. Marmosets gain access to exudates from a variety of tree species by gnawing holes in the tree bark. Dependence on tree exudates is very common among marmosets, but is much less so among tamarins. Among marmosets, but not among tamarins, exudates often serve as an important food source when others are limited.