Prosimian

The Ring-tailed Lemur (Lemur catta) is a prosimian of the family Lemuridae.

Prosimians are the most primitive extant primates; they have characteristics similar to forms that were ancestral to monkeys, apes and humans. Prosimians are the only primates native to Madagascar, and are also found in Southeast Asia. They include lemurs, the Aye-aye, bushbabies, and tarsiers. With the exception of the tarsiers, all of the prosimians are in the suborder Strepsirrhini. Due to this reason the classification is not phylogenetically 'valid', as they do not share a unique last common ancestor, and anatomical traits.

The adapids are an extinct grouping that were most certainly prosimians and closely related to the strepsirhines. 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.

Overview and description

Early classification schemes broke the Primate order into the suborders Prosimii (prosimians) and Anthropoidea (simians - monkeys and apes). However the prosimian tarsiers have been shown to be more closely related to the simians, and so it has been moved into the Anthropoidea, which is now renamed as Haplorrhini and Prosimii renamed as Strepsirrhini.

Strepsirrhini

The clade Strepsirrhini is one of the two suborders of primates. One of the most distinguishing characteristic of these 118 species is their wet noses, and it is this feature for which the grouping is named. The Greek name means having a curved or bent nose (a terpsimbrotos compound of strepho "bend" and rhis "nose"). Madagascar's only primates (apart from humans) are strepsirrhines, although others can be found in southeast Asia and Africa.

The suborder Strepsirrhini is composed of seven families split into three groups. The first group is the infraorder Lemuriformes, four families of creatures typically called lemurs. The other three families are split with the lorises, pottos and the galagos in the infraorder Lorisiformes, and the Aye-aye alone in its own family. However, the Aye-aye's placement is tentative. It is placed in its own infraorder (Chiromyiformes), and it is uncertain whether this infraorder split off from the ancestral strepsirrhine line before the lemurs and lorises, or after.

Strepsirrhines are considered to have more primitive features and adaptations than their haplorrhine ("dry-nose", in Greek "simple nose") cousins. Their moist nose is connected to the upper lip, which is connected to the gum, giving them a limit to the facial expressions they can manage. Their brain to body ratio tends to be smaller, indicating a lower intelligence. Their brain's olfactory lobes are larger, lending to the notion that they have a stronger reliance on smell. Their snouts are generally elongated giving them a dog-like appearance, although this is true of some monkeys, too. Strepsirrhines also have a post-orbital bar, adding to the primitive nature when compared to the suborder Haplorrhini. The strepsirrhines have also retained the ability to enzymatically manufacture vitamin C, which has been lost by all the haplorrhines, including the tarsidae.

With the exception of the Aye-aye, all strepsirrhines have a toothcomb—tightly clustered incisors and canine teeth—that is used for grooming. Another grooming adaptation is a claw on the second toe of all strepsirrhines, while the big toe is widely separated from the others allowing a vise-like grip for locomotion.

About 75% of species are nocturnal and all of these have a tapetum, a shiny, reflective layer in the back of their eyes, although several diurnal species like the Ring-tailed Lemur have it as well. Many of the nocturnal species also have very sensitive hearing and ears they can move independently to capture sounds even better.

Strepsirrhine reproduction differs greatly from haplorrhine reproduction. Instead of an individual cycle, strepsirrhines have a breeding season. They also have a litter of offspring and the females have a Y-shaped (bicornate) uterus and multiple sets of nipples.

Tarsiers

The haplorrhines, the "dry-nosed" primates (the Greek name means "simple-nosed"), are members of the Haplorrhini clade: the prosimian tarsiers and all of the true simians (the monkeys and the apes, including humans). Haplorrhines are considered to be less primitive than the strepsirrhine "wet-nosed" primates (whose Greek name means "curved nose"), the other suborder of primates. The haplorrhines, including tarsiers, have all lost the function of the terminal enzyme which manufactures vitamin C, while the strepsirrhine prosimians, like most other orders of mammals, have retained this enzyme and the ability to manufacture vitamin C. The haplorrhine upper lip, which has replaced the ancestral rhinarium found in strepsirrhines, is not directly connected to their nose or gum, allowing a large range of facial expressions. Their brain to body ratio is significantly greater than the strepsirrhines, and their primary sense is vision. Unlike the strepsirhines, haplorrhines have a post-orbital plate. Most species are diurnal (the exceptions being the tarsiers and the night monkeys) and have trichromatic color vision. Their hands and feet are more generally adapted, with specialization only for locomotion, such as th

Classification

The prosimians were once considered a suborder of the Primate order (suborder Prosimii)(Gr. pro, before, + simia, ape). They have been shown, however, to be paraphyletic - that is, the smallest clade of related species that includes all of the prosimians also includes other species - in this case all of the primates.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.

• ORDER PRIMATES
  • Suborder Strepsirrhini: non-tarsier prosimians
    • Infraorder Lemuriformes
      • Superfamily Cheirogaleoidea
        • Family Cheirogaleidae: dwarf lemurs and mouse-lemurs
      • Superfamily Lemuroidea
        • Family Lemuridae: lemurs
        • Family Lepilemuridae: sportive lemurs
        • Family Indriidae: woolly lemurs and allies
    • Infraorder Chiromyiformes
      • Family Daubentoniidae: Aye-aye
    • Infraorder Lorisiformes
      • Family Lorisidae: lorises, pottos and allies
      • Family Galagidae: galagos
  • Suborder Haplorrhini: tarsiers, monkeys and apes
    • Infraorder Tarsiiformes
      • Family Tarsiidae: tarsiers
    • Infraorder Simiiformes
      • Parvorder Platyrrhini: New World monkeys (4 families)
      • Parvorder Catarrhini: humans and other Old World primates (3 families)

References

ISBN links support NWE through referral fees

Smithsonian National Zoological Park (SNZP). 2008. http://nationalzoo.si.edu/Animals/Primates/Facts/Primateness/Differences/ Great apes and other primates: Differences among prosimians, monkeys and apes

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