The primate lineage is thought go back to at least 65 mya, even though the oldest known primate from the fossil record is Plesiadapis (c. 55–58 mya) from the Late Paleocene. Other studies, including molecular clock studies, have estimated the origin of the primate branch to have been in the mid-Cretaceous period, around 85 mya.
In modern cladistic reckonings, the Primates order is monophyletic. The suborder Strepsirrhini, the "wet-nosed" primates, is generally thought to have split off from the primitive primate line about 63 mya (million years ago), although earlier dates are also supported. The seven strepsirhine families are the four related lemur families and the three remaining families that include the Aye-aye, the lorids, and the galagos. Older classification schemes wrap the Lepilemuridae into the Lemuridae and the Galagidae into the Lorisidae, yielding a three-two family split instead of the four-three split as presented here. During the Eocene, most of the northern continents were dominated by two groups, the adapids and the omomyids.The former is considered a member of Strepsirrhini, but it does not have a toothcomb like modern lemurs. The latter was related closely to tarsiers, monkeys, and apes. It is unclear exactly how these two groups relate to extant primates. Omomyids perished about 30 mya, while Adapids survived until about 10 mya.