Altiatlasius is potentially the oldest known "euprimate" (primate of modern aspect), dating to the Late Paleocene from Morocco. The only species, Altiatlasius koulchii, was described in 1990. Its true taxonomic position remains controversial. It has also been suggested that it should be classified as a plesiadapiform (an extinct group of arboreal mammal thought to be closely related to primates) or that it should be recognized as a euprimate, either as an omomyid (a branch of fossil primates thought to be closely related to tarsiers), an early tarsiiform, or the oldest stem simian (monkeys and apes).