Monkeys are haplorhine ("dry-nosed") primates, a group generally possessing tails and consisting of about 260 known living species. There are two distinct lineages of monkeys: New World Monkeys and catarrhines. Apes emerged within the catarrhines with the Old World monkeys as a sister group, so cladistically they are monkeys as well. However, traditionally apes are not considered monkeys, rendering this grouping paraphyletic. The equivalent monophyletic clade are the simians. Many monkey species are tree-dwelling (arboreal), although there are species that live primarily on the ground, such as baboons. Most species are also active during the day (diurnal). Monkeys are generally considered to be intelligent, particularly Old World monkeys.