| Prosimian | |
|---|---|
 | |
| Tarsiers are prosimian primates, but more closely related to monkeys and apes (simians) than to other prosimians. | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Primates |
| (unranked): | Prosimii Illiger, 1811[a] |
| Groups included | |
| Cladistically included but traditionally excluded taxa | |
Prosimians are a group ofprimates that includes all living and extinctstrepsirrhines (lemurs,lorisoids, andadapiforms),[5] as well as thehaplorhinetarsiers and their extinct relatives, theomomyiforms, i.e. all primates excluding thesimians. They are considered to have characteristics that are more "primitive" (ancestral orplesiomorphic) than those ofsimians (monkeys, apes, and humans).[5]
Simians emerged within the Prosimians as sister group of thehaplorhinetarsiers, and thereforecladistically belong to this group. Simians are thus distinctly closer related to tarsiers than lemurs are. Strepsirrhines bifurcated some 20 million years earlier than the tarsier - simian bifurcation. However, simians are traditionally excluded, rendering prosimiansparaphyletic. Consequently, the term "prosimian" is no longer widely used in a taxonomic sense, but is still used to illustrate the behavioral ecology of tarsiers relative to the other primates.
Prosimians are the only primates native toMadagascar, but are also found throughout Africa and in Asia.
Being anevolutionary grade rather than aclade, the prosimians are united by being primates with traits otherwise found in non-primate mammals. Their diets typically are less dominated by fruit than those of the simians, and many are active arboreal predators, hunting for insects and other small animals in the trees.[5] All prosimians outside Madagascar arenocturnal, meaning that no prosimian competes directly with simian primates (the only nocturnal simians areNew World monkeys of genusAotus[6]).
Related to their frequently nocturnal lifestyle, prosimians lack the colour vision of higher primates. Like mostplacental mammals, they are in effectred–green colour blind. This allows for morerod cells in theretina, which may enhance vision under low-light conditions.[7] Except in tarsiers, the nocturnal vision is further augmented by a reflectivetapetum lucidum behind the retina, similar to that found in other nocturnal mammals. This layer reflects the light that passes through the retina, increasing thephotoreceptors exposure to the light. It is however not well developed in diurnal forms like many lemurs.[8]
All prosimians possess two laterally flattenedtoilet claws, used for grooming. These are found on the second toe inlemurs andlorises, and the second and third intarsiers.Aye-ayes have functionalclaws on all other digits except the hallux, including a toilet claw on the second toe. Clawlike nails are however also found in the small-bodiedcallitrichids, a group of New World monkeys, though none of them have a toilet claw.[9]
Male strepsirrhine prosimians have relatively largebacula.[10] Male tarsiers do not havebacula.[11] The prosimians have retained the primitive mammalian condition of abicornuate uterus, with two separate uterus chambers. In the simians, the uterus chambers have fused, an otherwise rare condition among mammals. Prosimians usually have litters rather than single offspring, which is the norm in higher primates.[12]
While primates are often thought of as fairly intelligent animals, the prosimians are not very large-brained compared to other placental mammals. Their brain-cases are markedly smaller than those of simians of comparable sizes. In the large-eyed tarsiers, the weight of the brain is about the same as that of a single eye.[13] Prosimians generally show lower cognitive ability and live in simpler social settings than the simians. The prosimians with the most complex social systems are the diurnal lemurs, which may live in social groups of 20 individuals. The nocturnal prosimians are mainly solitary.[14]
| Primate phylogeny[15] | ||||||||||||||||||||||||||||||||||||||||||||
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| Prosimians (ingreen brackets) are aparaphyletic group by including the tarsiers and omomyiforms to the exclusion of the simians (inred brackets). |
The prosimians were once a group considered a suborder of the primateorder (suborderProsimii - Gr.pro, before, + Latinsimius/simia, ape), which was named in 1811 byJohann Karl Wilhelm Illiger. They have been shown, however, to be paraphyletic - that is, their most recent common ancestor was a prosimian but it has some non-prosimian descendants (i.e. monkeys and apes). This relationship is shown by the ranks (prosimians inbold) in the list below of the current primate classification between the order andinfraorder level. The term "prosimian" is considered taxonomically obsolete,[16] although it is used to emphasize similarities between strepsirrhines, tarsiers, and the early primates.[17]
prosimians uterus placenta.