Strepsirrhini

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Strepsirrhines Fossil range: Early Eocene - Recent
Verreaux's Sifaka (Propithecus verreauxi)
Scientific classification
Kingdom: Animalia Phylum: Chordata Class: Mammalia Order: Primates Suborder: Strepsirrhini E. Geoffroy, 1812
Families
Cheirogaleidae Lemuridae Lepilemuridae Indriidae Daubentoniidae (Aye-aye) Lorisidae Galagidae

The Strepsirrhini clade is one of the two suborders of primates. One of the most distinguishing characteristic of these 111 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.

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.

With the exception of the Aye-aye, all strepsirrhines have a dental comb—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.

[edit] Classification and evolution

The Strepsirrhini suborder is composed of seven families split into three groups. The first group is the Lemuriformes infraorder, four families of creatures typically called lemurs. The other three families are split with the lorises, pottos and the galagos in the Lorisiformes infraorder, 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.

Early classification scheme 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. Other classifications split Strepsirrhini directly into four superfamilies: Daubentonioidea, Lemuroidea, Loroidea (including Cheirogaleidae) and Indroidea. However, significant evidence suggests that Cheirogaleidae is not related to the lorises, and that Indridae is sister-group to Lemuridae.

If the Aye-aye represents a form that is ancestral to all the rest of Strepsirrhini, then it evolved away from the strepsirrhine line between 63 million years ago (mya) (when the strepsirrhines split from the primitive primate line) and 50 mya (the lemur/loris split). If Chiromyiformes is to be considered as the sister only to the lemurs, then it must have evolved after the lemur/loris split 50 mya.

The strepsirrhine phylogeny has also been elucidated by Retrotransposon presence/absence data.

The adapids are an extinct polyphyletic grouping that were most certainly prosimians and closely related to the strepsirhines. The omomyids are another extinct group of prosmians but they are believed to be haplorrhines, closely related to the tarsiers, but an outgroup to the rest of the haplorrhines.

• ORDER PRIMATES
  • Suborder Strepsirrhini: non-tarsier prosimians
    • Infraorder Lemuriformes
      • Superfamily Cheirogaleoidea
        • Family Cheirogaleidae: dwarf and mouse lemurs (30 species)
      • Superfamily Lemuroidea
        • Family Lemuridae: lemurs (19 species)
        • Family Lepilemuridae: sportive lemurs (22 species)
        • Family Indriidae: woolly lemurs and allies (14 species)
    • Infraorder Chiromyiformes
      • Family Daubentoniidae: Aye-aye (1 species)
    • Infraorder Lorisiformes
      • Family Lorisidae: lorises, pottos and allies (9 species)
      • Family Galagidae: galagos (19 species)
  • Suborder Haplorrhini: tarsiers, monkeys and apes

[edit] References

• Roos C, Schmitz J, Zischler H (2004) Primate jumping genes elucidate strepsirrhine phylogeny. Proc Natl Acad Sci U S A 101: 10650–10654.
• Primate Taxonomy (Smithsonian Institute Press, 2001), Colin Groves (ISBN 1-56098-872-X)
• Primates in Question (Smithsonian Institute Press, 2003), Robert W. Shumaker & Benjamin B. Beck (ISBN 1-58834-176-3)
• Groves, Colin (16 November 2005). in Wilson, D. E., and Reeder, D. M. (eds): Mammal Species of the World, 3rd edition, Johns Hopkins University Press, 111-127. ISBN 0-801-88221-4. 

Extant primate families by suborder
Strepsirrhini: Cheirogaleidae · Lemuridae · Lepilemuridae · Indriidae · Daubentoniidae · Lorisidae · Galagidae Haplorrhini: Tarsiidae · Cebidae · Aotidae · Pitheciidae · Atelidae · Cercopithecidae · Hylobatidae · Hominidae