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Verreaux's Sifaka

Verreaux's Sifaka
(Propithecus verreauxi)
Scientific classification
E. Geoffroy, 1812

Daubentoniidae (Aye-aye)

The Strepsirrhini clade is one of the two suborders of primates. One of their most distinguishing characteristic of these 82 species is that they have wet noses and it is this feature which the grouping is named for. Madagascar's only primates are strepsirrhines, although others can be found in southeast Asia.

The suborder is composed of seven families split into two groups. The first group contains the infraorder Lemuriformes, four families of creatures typically called lemurs. The other three families include all of the lorises, plus the galagos, the Aye-aye, and the pottos. However, the Aye-aye is considered an outgroup in this clade and is given its own infraorder (Chiromyiformes), although alternatively it is seen as a sister to all of the other strepsirrhines. The remaining two families make up the infraorder Lorisiformes.

Strepsirrhines are considered to have more primitive features and adaptations than their haplorrhine ("dry-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 have 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 is generally very different than haplorrhine. Instead of a 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.

Classification and evolution

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 (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 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.


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