The suborder Strepsirhini is often referred to as 'Prosimians', which means 'before apes'. The word 'Prosimians' is derived from the suborder Prosimii established by Simpson, 1945, who incorrectly placed lemurs and tarsiers in one suborder. The strepsirhines, compared to the other suborders within the order Primates, have more primitive or plesiomorph characters, which are not found in the anthropoids.
All strepsirhines are characterized by a tarsal rotation mechanism (Szalay and Decker, 1974) and all strepsirhines (as well as a variety of non-primate mammals) have a tapetum lucidum, which lacks in all haplorhines.
Other characteristic features for most strepsirhines are a dental comb in the lower jaw and a toilet claw (a second pedal digit, with enlarged claw), although there are flat nails everywhere else. The dental comb is formed by the lower canines and incisors, accompanied with a sublingual structure for cleaning it (the Aye-aye has derived characters, which makes his classification confusing for many taxonomists).
Furthermore are the strepsirhines distinguished by a naked, moist and glandular rhinarium, enhancing the perception of smell. The nostrils have a crescent-shaped lateral slit. The fusion between the two halves of the mandible is made in midline by cartilage. The postorbital bar separates the orbit and the temporal fossa, so the eye sockets are not closed. Especially the nocturnal strepsirhines have mobile and large eyes. The brows and muzzle are provided with prominent whiskers.
Most strepsirhines are nocturnal, which as a consequence makes smell and hearing more important than sight. Most strepsirhines have specialized scent glands for olfactory communication (most often in the genital-anal region), with which they can mark their territories.
The suborder Strepsirhini contains two infraorders (Suborder Strepsirhini): The infraorder Adapiformes (which are only represented by extinct taxa, which are the earliest of the Strepsirhini and are mostly Eocene in age) and the infraorder Lemuriformes (which contains the superfamily Loroidae (including; family Loridae [Lorises and Pottos] and family Galagonidae [Bush Babies]) and the superfamily Lemuroidea (including; family Cheirogaleidae, family Phaneridae, family Lepilemuridae, family Eulemuridae, family Indriidae, family Daubentoniidae and family Hapalemuridae).
The family Galagonidae (galagos) are from Africa, the family Loridae from Southeast Asia (lorises) and Africa (pottos). The superfamily Lemuroidea can be found at Madagascar and at the Comoros.