Oligoocene Epoch

33-23 million years ago


Ancestral catarrhine primates evolved a number of features which modern catarrhines share.

In Aegyptopithecus (ancestor of Old World monkeys and Apes) and Proconsul (the first ape), the two frontal bones fused to form one frontal bone in adults. In catarrhine primates, the sphenoidal recess is absent. In the knee, most menisci of Old World monkeys are disk shaped, as are those of apes (with the exception of orangutans).
Parapithecus and Apidium were fruit eating primates with a 2-1-3-3 tooth pattern of prosimians and New World monkeys. They may be close to the ancestral stock of both groups of anthropoids. Unlike New World monkeys, however, they had 5 cusps on lower molars. After the loss of a premolar, the dental formula of catarrhines became 2123/2123.

In catarrhines, blood returns from the brain through the internal jugular as opposed to the external jugular and vertebral veins as is typical of other mammals.

Male catarrhines underwent a reduction of penile spines.

The majority of the genes in the MHC class II families are of recent origin, being shared by Old World monkeys and apes but not by New World monkeys. There may be ancient genes which predate the split of anthropoid primate lineages, such as DQB, but this gene seems to be nonfunctional. Although the DR region of the MHC complex was established before the split with NW monkeys, many of the DRB genes have arisen since then. The number of functional alleles of the MHC-G varies in different primate groups: there are the highest number of alleles in New World monkeys, less in Old World monkeys, and the greatest invariance in apes, especially humans. The selection for this invariance may be related to the increased length of pregnancy in apes and humans.
Many retroviral sequences of cattarhine primates share a common ancestry from an ancestral infection.

Catarrhines underwent a number of genetic changes. The 5HTT gene is regulated by an upstream polymorphic repetitive element.
The gene COX8H became an inactivated pseudogene in Old World monkeys, apes, and humans.
Apolipoprotein(a) is homologous to plasminogen and the gene possessed by humans is known only in Old World monkeys and apes.
In ancestral catarrhine primates, there were 17 separate insertions/deletions in intergenic DNA between and globin. The insertion of intergenic DNA which increased the distance between and genes; changnig distance from 5-7 kilobases to 13 kb. The globin gene was no longer used during fetal development.
Proteins of the electron transport chain have experienced positive selection in the lineage leading to catarrhine primates SUCH AS COX2, COX6B, COX6C, COX7C, CYCS, and ISP.