Prosimian

Prosimians are a group of primates that includes all living and extinct strepsirrhines (lemurs, lorisoids, and adapiforms),^[5] as well as the haplorhine tarsiers and their extinct relatives, the omomyiforms, i.e. all primates excluding the simians. They are considered to have characteristics that are more "primitive" (ancestral or plesiomorphic) than those of simians (monkeys, apes, and humans).^[5]

Prosimian Temporal range: Early Eocene–Present PreꞒ Ꞓ O S D C P T J K Pg N
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
Strepsirrhini[b] Tarsiiformes
Cladistically included but traditionally excluded taxa
Simiiformes

Simians emerged within the Prosimians as sister group of the haplorhine tarsiers, and therefore cladistically 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 prosimians paraphyletic. 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 to Madagascar, but are also found throughout Africa and in Asia.

Characteristics

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.^[5] 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^[6]).

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.^[7] 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.^[8]

All prosimians possess two laterally flattened toilet claws, used for grooming. These are 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.^[9]

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.^[10]

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.^[11] 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.^[12]

Classification

Primate phylogeny[13]

Primates   Strepsirrhini   Adapiformes  †Adapiforms  Lemuriformes  Lemurs Lorisoids  Haplorhini   Omomyiformes  †Omomyiforms  Tarsiiformes  Tarsiers  Simiiformes   Platyrrhini  New World monkeys  Catarrhini  Old World monkeys Apes & humans prosimians simians

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 descendants (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,^[14] although it is used to emphasize similarities between strepsirrhines, tarsiers, and the early primates.^[15]

• Order Primates
  • Suborder Strepsirrhini: non-tarsier prosimians
    • Infraorder †Adapiformes: extinct "lemur-like" primates
    • Infraorder Lemuriformes: lemurs, lorises, and bushbabies^[b]
  • Suborder Haplorrhini: tarsiers, monkeys and apes
    • Infraorder †Omomyiformes: extinct "tarsier-like" primates
    • Infraorder Tarsiiformes: tarsiers
    • Infraorder Simiiformes: New World monkeys, Old World monkeys, apes, and humans

See also

• Evolution of mammals
• List of primates

Notes

1. The division of the order Primates into two evolutionary grades, Prosimii ("lower primates") and Anthropoidea ("higher primates") is sometimes used, but has been shown through morphological and genetic evidence to be incorrect. Alternatively, a three-way split in the order Primates—Prosimii, Tarsiiformes, and Anthropoidea—has also been suggested.^[1]
2. Although the monophyletic relationship between lemurs and lorisoids is widely accepted, their clade name is not. The term "lemuriform" is used here because it derives from one popular taxonomy that clumps the clade of toothcombed primates into one infraorder and the extinct, non-toothcombed adapiforms into another, both within the suborder Strepsirrhini.^[2][3] However, another popular alternative taxonomy places the lorisoids in their own infraorder, Lorisiformes.^[4]

References

1. Rose 2006, p. 166.
2. Szalay & Delson 1980, p. 149.
3. Cartmill 2010, p. 15.
4. Hartwig 2011, pp. 20–21.
5. Whitten, P. L.; Brockman, D. K. (2001). "Chapter 14: Strepsirrhine reproductive ecology". In Ellison, P. T (ed.). Reproductive Ecology and Human Evolution. Transaction Publishers. pp. 321–350. ISBN 978-0-202-30658-2.
6. Cawthon Lang KA. 2005 July 18. Primate Factsheets: Owl monkey (Aotus) Taxonomy, Morphology, & Ecology. Accessed 2012 July 25.
7. Ali, Mohamed Ather; Klyne, M.A. (1985). Vision in Vertebrates. New York: Plenum Press. pp. 174–175. ISBN 978-0-306-42065-8.
8. 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. S2CID 53156761.
9. 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.
10. Nowak, Ronald M. (1999). Walker's primates of the world. Baltimore: Johns Hopkins University Press. p. 25. ISBN 978-0801862519. prosimians uterus placenta.
11. 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. S2CID 3905636.
12. Reader, S. M.; Hager, Y.; Laland, K. N. (2011-04-12). "The evolution of primate general and cultural intelligence" (PDF). Philosophical Transactions of the Royal Society B: Biological Sciences. 366 (1567): 1017–1027. doi:10.1098/rstb.2010.0342. PMC 3049098. PMID 21357224. Archived from the original (PDF) on 2011-10-03. Retrieved 2011-07-04.
13. Rose 2006.
14. Groves, C. P. (1998). "Systematics of tarsiers and lorises". Primates. 39 (1): 13–27. doi:10.1007/BF02557740. S2CID 10869981.
15. Hartwig 2011, p. 28.

Literature cited

• Cartmill, M. (2010). "Chapter 2: Primate Classification and Diversity". In Platt, M.; Ghazanfar, A (eds.). Primate Neuroethology. Oxford University Press. pp. 10–30. ISBN 978-0-19-532659-8.
• Hartwig, W. (2011). "Chapter 3: Primate evolution". In Campbell, C. J.; Fuentes, A.; MacKinnon, K. C.; Bearder, S. K.; Stumpf, R. M (eds.). Primates in Perspective (2nd ed.). Oxford University Press. pp. 19–31. ISBN 978-0-19-539043-8.
• Rose, K. D. (2006). The Beginning of the Age of Mammals. Johns Hopkins University Press. ISBN 978-0-8018-8472-6.
• Szalay, F.S.; Delson, E. (1980). Evolutionary History of the Primates. Academic Press. ISBN 978-0126801507. OCLC 893740473.