The order Primates contains all the species commonly related to the lemurs, monkeys, and apes, with the latter category including humans. It is divided into four main groupings: strepsirrhines, tarsiers, monkeys of the New World, and monkeys and apes of the Old World. Strepsirrhines make up all of Madagascar's native primates species, but comprise only a quarter of those of Africa, the rest being simians. Madagascar's strepsirrhines occupy both diurnal and nocturnal niches, while all those of Asia and mainland Africa are nocturnal and nearly all simians are diurnal (the only exception being neotropical "Aotus", which lives where strepsirrhines are absent). Madagascar's 15 genera of extant nonhuman primates compares with , , 23 in Africa and 19 in Asia. A number of lemur species larger than any now alive, ranging in size up to that of a gorilla, are believed to have become extinct shortly after the recent arrival of humans.