Prosimian

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Tarsiers are prosimian primates, but more closely related to monkeys, apes, and humans (simians) than to other prosimians.

Prosimians are a type of primate that includes lemurs, lorises, bushbabies, and tarsiers, but not simians, e.g., monkeys and apes (including humans). They are considered to have characteristics that are more "primitive" than those of monkeys and apes.[1] Prosimians are the only primates native to Madagascar, but are also found throughout Africa and in Asia. With the exception of tarsiers, all extant prosimians are in the suborder Strepsirrhini. Because simians (including all monkeys and apes) are not included in the prosimian group even though they also descend from the prosimian most recent common ancestor, prosimians are a paraphyletic group and not a clade.

The adapiforms are an extinct grouping that were both prosimians and strepsirrhines.[1] The omomyiforms are another extinct group of prosimians, but they are believed to be haplorhines, closely related to the tarsiers, but an outgroup to the rest of the haplorhines.

The term "prosimian" is no longer used in official taxonomy, but is still used to illustrate the behavioral ecology of tarsiers relative to the other primates.

Traits[edit]

The tapetum lucidum of a galago, typical of prosimians, reflects the light of the photographer's flash.

Being an evolutionary grade rather than a clade, 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.[1] All prosimians outside Madagascar are nocturnal, meaning that no prosimian competes directly with simian primates (the only nocturnal simians are New World monkeys of genus Aotus[2]).

Related to their frequently nocturnal lifestyle, prosimians lack the colour vision of higher primates. Like most placental mammals, they are in effect red–green colour blind. This allows for more rod cells in the retina, which may enhance vision under low-light conditions.[3] Except in tarsiers, the nocturnal vision is further augmented by a reflective tapetum lucidum behind the retina, similar to that found in other nocturnal mammals. This layer reflects the light that passes through the retina, increasing the photoreceptors exposure to the light. It is however not well developed in diurnal forms like many lemurs.[4]

All prosimians possess two laterally flattened toilet claws, used for grooming. These can be found on the second toe in lemurs and lorises, and the second and third in tarsiers. Aye-ayes have functional claws on all other digits except the hallux, including a toilet claw on the second toe. Clawlike nails are however also found in the small-bodied callitrichids, a group of New World monkeys, though none of them have a toilet claw.[5]

The prosimians have retained the primitive mammalian condition of a bicornuate 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.[6] They also have multiple sets of nipples, at least two pairs.

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.[7] 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.[8]

Classification[edit]

Primate phylogeny[9]
 Primates 
 Haplorhini 
 Simiiformes 
 Catarrhini 

 Apes & humans 



 Old World monkeys 



 Platyrrhini 

 New World monkeys 



 Tarsiiformes 

 Tarsiers 


 Omomyiformes 

 †Omomyiforms 



 Strepsirrhini 
 Adapiformes 

 †Adapiforms 


 Lemuriformes 

 Lemurs 



 Lorisoids 





simians
prosimians
Prosimians (in green brackets) are a paraphyletic group by including the tarsiers and omomyiforms to the exclusion of the simians (in red brackets).

The prosimians were once a group considered a suborder of the primate order (suborder Prosimii - Gr. pro, before, + Latin simius/simia, ape), which was named in 1811 by Johann 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 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 infraorder level. The term "prosimian" is considered taxonomically obsolete,[10] although it is used to emphasize similarities between strepsirrhines, tarsiers, and the early primates.[11]

See also[edit]

References[edit]

  1. ^ a b c Whitten, P. L.; Brockman, D. K. (2001). "Chapter 14: Strepsirrhine reproductive ecology". In Ellison, P. T. Reproductive Ecology and Human Evolution. Transaction Publishers. pp. 321–350. ISBN 978-0-202-30658-2. 
  2. ^ Cawthon Lang KA. 2005 July 18. Primate Factsheets: Owl monkey (Aotus) Taxonomy, Morphology, & Ecology. Accessed 2012 July 25.
  3. ^ Ali, Mohamed Ather; Klyne, M.A. (1985). Vision in Vertebrates. New York: Plenum Press. pp. 174–175. ISBN 0-306-42065-1. 
  4. ^ Pariente, GF (1976). "[Different aspects of the limit of the tapetum lucidum in prosimians]". Vision research 16 (4): 387–91. doi:10.1016/0042-6989(76)90201-7. PMID 821249. 
  5. ^ Soligo, C., Müller, A.E. (1999). "Nails and claws in primate evolution". Journal of Human Evolution 36 (1): 97–114. doi:10.1006/jhev.1998.0263. PMID 9924135. 
  6. ^ Mittermeier, Ronald M. Nowak ; introduction by Russell A.; Rylands,, Anthony B.; Konstant, William R. (1999). Walker's primates of the world. Baltimore: Johns Hopkins University Press. p. 25. ISBN 0801862515. 
  7. ^ Rosenberger, Alfred L. (16 October 2010). "The Skull of Tarsius: Functional Morphology, Eyeballs, and the Nonpursuit Predatory Lifestyle". International Journal of Primatology 31 (6): 1032–1054. doi:10.1007/s10764-010-9447-x. 
  8. ^ Reader, S. M.; Hager, Y.; Laland, K. N. (2011-04-12). "The evolution of primate general and cultural intelligence". Philosophical Transactions of the Royal Society B: Biological Sciences 366 (1567): 1017–1027. doi:10.1098/rstb.2010.0342. Retrieved 2011-07-04. 
  9. ^ Rose, K. D. (2006). The Beginning of the Age of Mammals. Johns Hopkins University Press. ISBN 978-0-8018-8472-6. 
  10. ^ Groves, C. P. (1998). "Systematics of tarsiers and lorises". Primates 39 (1): 13–27. doi:10.1007/BF02557740.  edit
  11. ^ Hartwig, W. (2011). "Chapter 3: Primate evolution". pp. 19–31.  Missing or empty |title= (help)