Miocene: The Real Planet of Apes

The Miocene epoch is known as "the real planet of the apes", because over fifty hominoid genera roamed across various regions of the world.
This epoch, from 25 to 5.5 million years ago, marked the emergence of mammalian fauna resembling modern ones. It also witnessed the significant diversification of hominoid primates, leading to forms that share many characteristics with today's apes and humans. However, determining the specific relationships within this group remains contentious.

Besides the lack of a tail, anthropologists have identified key features in the evolution of apes. These are the evolution of ape-like dental features like the Y-five pattern in molar cusps, the evolution of shoulder anatomy meant for arm swinging or brachiating and the evolution of knuckle-walking.

The oldest known African apes lived about 23 million years ago. These early apes lived in forests and woodlands across Africa, thriving alongside many different types of monkeys and apes. They were smaller than modern apes and walked on the soles of their feet instead of on their knuckles. These apes are often called dental apes because they had Y-five type patterns in molar cusps similar to apes but with bodies more like monkeys.

Proconsul and Ekembo are the best-known of the many fossil apes from the early Miocene of East Africa. Ekembo and Proconsul were components of a diverse and successful group, which lasted roughly 12 million years, from about 22 to 10.5 Million years ago, though it is mostly known from the early Miocene, becoming rare after about 17.5 million years ago.

Another ape, Morotopithecus bishopi, lived around 20.6 million years ago in Uganda and had anatomy similar to modern apes, suggesting it could swing from branch to branch.

Around 17 million years ago, early apes from Africa expanded into Eurasia. These apes, called Griphopithecus, had teeth adapted for a diet with abrasive foods, indicating a change in diet and habitat from earlier apes.
Between 11 and 5 million years ago, there's a lack of fossils that show the transition from apes walking on all fours to humans walking upright. However, a lower jawbone and teeth found in Kenya suggest a new species, Nakalipithecus nakayamai, which could be related to the common ancestor of gorillas, chimpanzees, and humans.
Around 18 to 12 million years ago, the basic body plan of large hominoids, like gorillas and orangutans, emerged. Then, between 8 and 5 million years ago, there was another burst of evolutionary activity, producing four lineages, one of which led to hominins, including humans.
Molecular studies confirm that African apes and humans are similar, orangs roughly twice as distant, and gibbons a bit more dissimilar than orangs. Chimpanzees share more than 99 per cent of their genetic material with humans, even though it is packaged in their chromosomes in a different way. However, the precise relationships between any genetic differences and the geologic timescale are still uncertain and the subject of much discussion.
We are unlikely to achieve a greater understanding of very early human evolution unless we discover hominoid fossils dating to between 10 and 5 Ma. These 5 million years were yet another period of major environmental change.