Four genera of lorises have traditionally been identified: Perodicticus (potto) and Arctocebus (angwantibo) of sub-Saharan Africa, Loris (slender loris) of Sri Lanka (and possibly also India), and Nycticebus (slow loris) of southeastern mainland Asia as well as Borneo and Sumatra. Again traditionally, taxonomists have generally recognized only two species of Nycticebus (N. coucang and N. pygmaeus) while maintaining that the other genera are monotypic. Preliminary morphological and metric studies of skulls and teeth as well as analysis of comparative pelage patterning suggest, however, that what has been attributed to intraspecific variation in both Perodicticus and N. cou-cang is best interpreted as reflecting taxic diversity.
Although lorises differ in robustness (pottos and slow lorises) versus gracility (angwantibos and slender lorises), they all are solitary nocturnal insectivores that are capable of both running quickly and moving extremely slowly and cautiously through vegetation without attracting notice. The latter locomotory behavior is reflected at least in Perodicticus having extensive collateral vascularization of limbs, a configuration that appears to be correlated with elimination of lactic acid that would otherwise accumulate during sustained periods of physical activity. In the wild, where Perodicticus is sympatric with bushbabies, the potto’s diet consists primarily of slow-crawling, noxious insects; in captivity, it selects the bushbabies’ typical prey of faster, more palatable insects.
Lorises are prosimian by virtue of their possession of a grooming claw on the second pedal digit and a toothcomb. As a group within Prosimii, lorises are distinguished, for instance, by having noticeably short tails, reduced second manual digits, stubby tubes that grow laterally from the petrosal auditory bulla, and ovoid lower premolars. The relationships among the lorises are still in flux. Although some molecular data have been interpreted as uniting the African and Asian taxa as respective sister taxa, morphology overwhelmingly unites Perodicticus and Nycticebus (for example, more greatly reduced second manual digits, more rounded gonial regions and deeper mandibles, stouter toothcomb teeth, puffier cusped upper and lower molars, laterally bulging snouts), and Arctocebus and Loris (for example, thin and elongate long bones, deeper lower molar hypoflexid notches, more pronounced and connected upper and lower molar crests, tubular snouts), as respective sister taxa.
Recently, a new genus and species of a loris relative, Pseudopotto martini, was described from material from the Cameroons and was interpreted as the sister taxon of the traditional loris group, being more primitive than the others, for example, in having a much longer tail, more slender ilia of the os coxa, shorter cervical vertebral spines, and an entepicondylar foramen on the distal humerus. It is craniodentally and skeletally different from, as well as much smaller than, the sympatric Perodicticus batesi. To date, P. martini has not been definitively sighted in the wild.
The status of P. martini is complicated by the fact that the type specimen of Perodicticus captured in the Cameroons and identified as “Bosnian’s potto” {P. potto), which was housed in the Muséum National d’Histoire Naturelle in Paris, is now lost. If it turns out that P. martini is a junior synonym of P. potto, it might be simpler to petition the International Code of Zoological Nomenclature to retain P. martini and designate a specimen of another species of Perodicticus as the type of that taxon.
References:
- Alterman, L., Doyle, G. A., & Izard, M. K. (Eds.). (1995). Creatures of the dark The nocturnal prosimians. New York: Plenum.
- Delson, E., Tattersall, I., Van Couvering, J., & Brooks, A. S. (Eds.). (2000). Encyclopedia of human evolution and prehistory (2nd ed.). New York: Garland.
- Fleagle, J. G. (1999). Primate adaptation and evolution (2nd ed.). New York: Academic Press.
