Prosimians are a grouping of mammals defined as being primates, but not monkeys or apes. They include, among others, lemurs, bushbabies, and tarsiers. They are considered to have characteristics that are more primitive than those of monkeys and apes. Prosimians are the only primates native to Madagascar, and are also found in Africa and Asia. With the exception of the tarsiers, all extant prosimians are in the suborder Strepsirrhini. Because tarsiers, as well as some extinct prosimians, share a more recent common ancestor with monkeys and apes than with other prosimians, they belong to a paraphyletic group and not a clade.
The adapids are an extinct grouping that were most certainly prosimians and closely related to the strepsirrhines. The omomyids are another extinct group of prosimians, but they are believed to be haplorrhines, closely related to the tarsiers, but an outgroup to the rest of the haplorrhines.
The prosimians were once a group considered a suborder of the primate order (suborder Prosimii - Gr. pro, before, + simia, ape). They have been shown, however, to be paraphyletic - that is, their most recent common ancestor was a prosimian but it has some nonprosimian descendents (i.e. monkeys and apes). This relationship is shown by the ranks (prosimians in bold) in the list below of the current primate classification between the order and family level. The classification is used on a more behavioural term nowadays, due to the lack of a unique last common ancestor.