Prosimians are the most primitive extant primates; they represent forms that were ancestral to monkeys, apes and humans. Prosimians are the only primates native to Madagascar, and are also found in Southeast Asia. With the exception of the tarsiers, all of the prosimians are in the suborder Strepsirrhini.

The adapids are an extinct grouping that were most certainly prosimians and closely related to the strepsirhines. The omomyids are another extinct group of prosmians but they are believed to be haplorhines, closely related to the tarsiers, but an outgroup to the rest of the haplorrhines.

Classification

Although the prosimians were once considered a suborder of the Primate order (suborder Prosimii), they have been shown to be polyphyletic - that is, the smallest clade of related species that includes all of the prosimians also includes all of the primates. This relationship is shown by the bolded ranks in the list below of the current Primate classification between the order and family level.

• ORDER PRIMATES
  • Suborder Strepsirrhini: non-tarsier prosimians
    • Infraorder Lemuriformes
      • Superfamily Cheirogaleoidea: dwarf and mouse lemurs
      • Superfamily Lemuroidea : lemurs
    • Infraorder Chiromyiformes: Aye-aye
    • Infraorder Loriformes : lorises, etc.
  • Suborder Haplorrhini: tarsiers, monkeys and apes
    • Infraorder Tarsiiformes: tarsiers
    • Infraorder Simiiformes
      • Platyrrhini: New World monkeys
      • Catarrhini: apes and Old World monkeys