Oligoocene Epoch

33-23 million years ago


Ancestral catarrhines evolved a number of modifications of their nervous systems, including color vision and a loss of olfactory ability.

The size of the facial, hypoglossal, and trigeminal (motor portion) nerves increased in catarrhine primates relative to more primitive primates, and increased further in the great ape lineage. Apes and Old World monkeys possess a sulcus occipitalis superior and sulcus postcentralis inferior.
In prosimians and New World monkeys, the cervical and brachial plexuses are separated by a greater distance than they are in Old World monkeys and apes due to a cranial migration of the brachial plexus in the latter group. The contribution of the second thoracic nerve to the brachial plexus in Old World monkeys occasionally occurs in humans and apes.
Ancestral catarrhine primates lost their accessory olfactory bulbs and the vomeronasal organs were much reduced in adults. A large number of the olfactory receptor genes became pseudogenes (about 27% of those in Old World monkeys; 60-70% in humans, and virtually none in New World monkeys). A mutation in the TRP2 gene caused the entire vomeronasal system to become nonfunctional. The genes involved in this system (such as those of the receptors) began to become pseudogenes.
Ancestral catarrhines developed the ability to taste the protein thaumatin (from African berries) as sweet; which other primates don't taste. The ear developed a long, bony auditory meatus. Catarrhine primates improved their ability to see in color. A duplication of long/middle opsin produced green cone pigment giving catarrhine primates the ability to distinguish between green and red, unlike most mammals.