Miocene Epoch

23-5 million years ago


The common ancestors of higher apes--orangutans, gorillas, chimps, and humans--evolved a number of new features.

Higher apes increased the volume of limbic nuclei, which were subsequently increased again in humans. Cerebral asymetries are known in fossil hominids and apes including a longer left sylvian fissure. The cerebral asymmetries of higher apes and fossil hominids are similar to those found in modern humans. Higher apes developed a sulcus frontalis inferior and the gyrus postcentralis was separated from the parietal lobe. The ACC of non-apes lack clusters of spindle cell pyramidal neurons. Orangutans possess some clusters.

The ancestor of higher apes underwent a number of muscular changes. The extensor indicis usually didn't insert on digit IV and the rectus femoris developed 2 heads (variable in all but humans). Higher apes developed an articularis genus and an extensor pollicis brevis. The latissimus dorsi developed an additional origin on the iliac crest.

In the great apes, the sphenosquamosal suture may divide the foramen ovale. In robust australopithecines the smooth floor of nasal cavity resembled that of modern humans. This condition is also known in orangutans and about a third of chimps.
Higher apes share changes in eta globin: 3 deletions (positions 164, 966-70, 1,610-1,637), an insertion (245-82), and at least 24 substitutions (positions 5, 66, 383, 405, 495, 573, 780, 853, 926, 1268, 1278, 1334, 1422, 1667, 1859, 1949, 2002, 2093, 2137, 2138, 2161, 2188, 2193, and 2213). Higher apes also share 7 amino acid residues in red opsin and 9 in green opsin which are unique to higher apes compared to Old World monkeys (Deeb, 1994; gibbons not in analysis). Proteins of the electron transport chain have experienced positive selection in the lineage leading to higher apes (such as COX4-1, COX7AH, COX8L, and ISP). Zinc Finger Proteins 75A, 75B (a pseudogene), and 75C are highly conserved in humans, chimps, gorillas, and orangutans.