Slow Loris - Evolutionary History

Evolutionary History

Slow lorises (genus Nycticebus) are strepsirrhine primates and are related to other living lorisiforms, such as slender lorises (Loris), pottos (Perodicticus), false pottos (Pseudopotto), angwantibos (Arctocebus), and galagos (family Galagidae), and to the lemurs of Madagascar. They are generally considered to be most closely related to the slender lorises of South Asia, followed by the angwantibos, pottos and false pottos of Central and West Africa, although some researchers favor a closer relationship between the slow lorises and the similarly robust pottos on the one hand and the more gracile angwantibos and slender lorises on the other. Lorisiforms are thought to have evolved in Africa, where most living species occur; later, one group may have migrated to Asia and evolved into the slender and slow lorises of today.

Lorises first appear in the Asian fossil record in the Miocene, with records in Thailand around 18 million years ago (mya) and in Pakistan 16 mya. The Thai record is based on a single tooth that most closely resembles living slow lorises and that is tentatively classified as a species of Nycticebus. The species is named ? Nycticebus linglom, using open nomenclature (the preceding "?") to indicate the tentative nature of the assignment. Several lorises are found in the Siwalik deposits of Pakistan, dating to 16 to 8 mya, including Nycticeboides and Microloris. Most are small, but an unnamed form dating to 15–16 mya is comparable in size to the largest living slow lorises. Molecular clock analysis suggests that slow lorises may have started evolving into distinct species about 10 mya. They are thought to have reached the islands of Sundaland when the Sunda Shelf was exposed at times of low sea level, creating a land bridge between the mainland and islands off the coast of Southeast Asia.