55-34 million years ago
Ancestral anthropoid primates evolved new skeletal features shared among modern anthropoids.
In anthropoid primates, the orbits are more forward-facing, the braincase
is larger, and the sphenoid and ethmoid contribute to the enclosing of
the orbit with bone. Eocene primates developed a more grasping foot. Anthropoid
primates developed a shorter face and the two dentary bones fused to form
one solid lower jaw. Catopithecus possessed several prosimian characteristics
but is thought to be near the base of the anthropoids. Its upper central
incisors are larger than the lateral incisors as in anthropoid primates.
Although the lower central incisors are smaller than the lateral incisors
(this is an adapid characteristic; see illustration below); the incisors
are similar to those of anthropoids rather than prosimians (such as Arsinea).