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