Historical Classification and Species Discovery
The diversity of galago species has historically been grossly underestimated. In 1931, only 5 species were recognized, 4 in the genus Galago and 1 in Euoticus, and only one species that would later be placed in the genus Otolemur. In 1979, the genus Otolemur was separated from Galago. By 1986, eleven species were recognized with revamped systemic classification including Otolemur crassicaudatus and Otolemur garnettii. Additionally, O. crassidautus and O. monteiri were recognized as separate species instead of O. monteiri as a nested subspecies. By 2001, 23 species were recognized. Classification by vocalization has particularly become prevalent and helpful as a tool in understanding of these species. All Otolemur species exhibit trailing advertising calls.