Evolution of Apes in Africa (22-16 million years ago)
So far, I have tracked the evolution of first primates at 55 million years ago upto the emergence of first apes, the Proconsuls, about 22 million years ago. I have also presented many of the key fossils that show the emergence of key biological characteristics that separate out apes from other living primates. Following Proconsul, apes continued to evolve and diversify in Africa. Africa in those times were filled almost entirely with tropical rainforests extending from coast to coast and north to south, right into Sahara and Arabia (which was part of Africa then). There was no ice sheets yet in the North Pole or Greenland and neither the Alps, nor the Himalayas have formed. Warm and moist climate prevailed over much of the world and in Africa, this resulted in an explosion of forest dwelling fruit eating apes of various sizes and shapes.
A very interesting species of ape that was found from this period is
Nacholapithecus which lived in Africa at 16 million years
While it is very similar to Proconsul in the shape of skeleton and the joints, one important difference is that, like modern apes, its forelimbs are much longer than its hindlimbs and its wrist and footbones have become bigger and stronger with more powerful grasping ability. It could probably climb up tree trunks like modern apes and use its long big upper limbs to reach for and jump towards far away branches in trees. Modern ape-like skeletal features are more visibly present in another fossil of this era called
Morotopithecus whose fragmentary skeleton and spinal column from 18 million years suggests that it moved through the trees by hanging from the the branches with its hands or feet like modern apes. Overall by about 16 million years quite a few species of distinct ape families with various features adapted to living in trees and different from monkeys have evolved in Africa.
Migration of Apes to Asia and Europe (17 million years ago)
At around 17 million years, the oceanic sea level dropped and a land bridge connected Eurasia and Africa for the first time. This led to a large exchange of animals and plants between the two continents. Many ape species began to migrate into Asia and evolve quickly into new species that took advantage of the new forests of Europe and Asia that were now available to them.
Griphopithecus was the earliest ape found in Asia (Turkey and Germany by 16 million years). But the most remarkable fossil ape from Eurasia is that of
Pierolapithecus from
12 million years, which is considered to be from the group that is the last common ancestor of all modern great apes (chimps, orangs, gorillas, humans). With Pierolapithecus , scientists see for the first time, most of the distinctive traits that are present in all great apes and not present in the lesser apes (gibbons). T
hus Pierolapithecus represents the group of ancient ape ancestors that is at the divergence point of great apes and lesser apes.
http://www.sci-news.com/paleontology/article01052.html
Between 12- 8 million years, the great apes in Eurasia radiate into many species. Some like Sivapithecus (India), Ankarapithecus (Turkey), Lufengpithecus (China) are seen to be related to the line that leads to modern Orangutans. Others like Dryopithecus (all of Europe), Ouranopithecus (Greece) and Oreopithecus (Italy) have traits that make them closer to the gorilla/chimp/human line. After about 9 million years, the cooling of Europe and the drying of Middle East causes the apes of the Orang-like group to retreat to East and South-East Asia while the apes of Europe or West-Asia disappear from Europe and retreat into North Africa where they eventually give rise to chimps, gorillas and humans.
DRYOPITHECUS
SIVAPITHECUS
Conclusion:- Rise and Fall of the Planet of the Apes (22-6 mya)
1) Between 22 million years and 6 million years, apes were the dominant primates of Eurasia. Known fossils span 24 groups and 100 species, and probably the actual number of species were 5 times that number. This was an era before the ice-age of the Northern Hemisphere. Tropical rainforests covered the entirety of Africa and moist and dense subtropical forests covered Europe and Asia as well. Thus many types of ape species, starting from Proconsul, evolve in Africa and flourish. When Asia and Africa connect, the apes migrate into the Asian and European forests and diversify there as well after 16 million years. The great apes diverge from gibbons at about 13 million years while orang ancestors of East Asia diverge from gorilla/chimp ancestors at about 10 million years. While early apes retain many of the monkey-like characters, by 16 million years, many of the newer species begin to look more like modern apes with bigger fore-limbs, stronger and broader chests, powerful grips, more flexible joints and bigger brains. They also sport big jaws and sharp canines that are excellent for eating big ripe fruits and crack nuts.
2) After 14 million years, the great Rift Valley, the volcanic mountains and Ethiopian plateau of East and South-East Africa begin to form. This creates large rain-shadow in Africa and the African rainforests begin to recede. This causes African apes to dwindle. Very few ape fossils are found in Africa after this perid.
3) Between 10-8 million years, African and South Asian plates collide with Eurasian plates causing the rapid rise of the Alps in Europe and the Himalayan mountain range along with the Tibetan and Iranian plateau in Asia. These events cause the entire Middle East to dry out from subtropical rainforests to open woodlands, while climate in East and South Asia becomes extremely seasonal dominated by the monsoon. Western and Central Europe, cut off from the smaller Mediterranean by the Alps, becomes cold, while Mediterranean and North Africa themselves become drier and become open wooded grasslands.
4) The collapse of the tropical forests are catastrophic for apes. All apes in Europe and West Asia die out, while a few migrate back into Northern Africa. Apes in Asia retreat into South-East Asia and China. The collapse of the apes continue to the present with today only 7 species (two gorilla, two chimps, two orangs, 1 human) remain of the many many species that existed in the past. The lesser apes (gibbons) have fared somewhat better with 17 gibbon species, though all located in the rainforests of South and South-East Asia.
5)
The early history of human evolution (from 8 million years onwards) is to be considered in the context of these evolutionary pressures that drove our lineage to evolve features that make our ancestors better able to handle open woodlands and grasslands that replace the forests of the world from 8 million years onwards.
