Very few fossil remains of chimps and gorilla ancestors have been found anywhere in Africa but here are a few:
Nakalipithecus nakayamai was found in 2005 by a team of Japanese and Kenyan researchers in mud flow deposits in the Nakali region of northern Kenya’s Rift Valley Province. For short it is simply known as the “Nakali Ape.” The fossil remains consisted of a jawbone and 11 teeth that were dated at 10 mya. The enamel on the teeth was thick suggesting its diet consisted of hard nuts and seeds. It is believed that this species is close to the common ancestor shared between humans, chimps, and apes (gorillas). It resembles Ouranopithecus fossils found in Greece.
Ouranopithecus includes two species. One being O. macedoniensis (found in Macedonia and dated at between 9.6 mya- 8.7 mya) and the other being O. turkae (found in Turkey and dated at 8.7-7.4 mya). Fossil remains of Ouranopithecus were found in Greece and Bulgaria and it is believed to have been a Eurasian ape which is now extinct. Based on dental and facial anatomy this species may belong to the dryopithecines which were a tribe of Eurasian apes believed to be close early ancestors to gorillas, chimps, and humans (the Great Apes). However, opposing theories have this species more closely related to the Ponginae (orangutans). Some researchers consider this species to be the last common ancestor of humans and apes and the early ancestors of Australopithecines and Humans although this theory is highly controversial and not widely accepted.
Sahelanthropus tchadensis is dated at about 7 mya which puts it in the Miocene Epoch. It may have been close to when humans and chimps diverged from our last common ancestor. We actually have few specimens of this specimen other than a partial skull known as the Toumai Skull, meaning “hope of life.” Other fossil remains from this species include 5 pieces of a jaw and some teeth. The braincase volume is between 320-380 cm which is in the chimp range as opposed to the modern human range of 1350 cm. This species had a very distinct and thick browridge. It’s believed that this skull suffered a large degree of distortion during fossilization AND also during the time of its discovery! This is because the cranium is “dorsoventrally” flattened with the right side depressed.
This species, Sahelanthropus. MAY have walked on two legs at times but we don’t have any pieces of skeleton to say for certain and this, then, is simply conjecture. However, some researchers point to the position of the foramen magnum (the hole in the bottom of the skull where the spinal cord connects to the brain) as evidence for bipedal walking. Recently a femur was said to have been discovered near where the skull was found in Chad but its whereabouts are presently unknown nor has anything been published about the alleged find. Fossils from this species were found in the Djurab Desert in Chad between July 2001 and March 2002. Some researchers claim this species is the oldest known human ancestor after the split of humans from chimps.
Interestingly, when it comes to Sahelanthropus the fossils were found in an area where previously fossils of other hominins were also found. For example, it was in about the same location where a mandible was found belonging to Australopithecus bahreighazali in 1995. These two species closely resembled each other and, in fact, Sahelanthropus may NOT be a separate species at all but may be an Australopithecine.
It is believed by some researchers that Sahelanthropus is a common ancestor of humans and chimps. Other researchers such as Brigette Senut and Martin Pickford believe that this species has features consistent with a female proto-gorilla.
None of these species were very tall as they averaged around 3 feet tall and at most 4 feet tall, it is speculated. Looking at the reconstruction of Sahelanthropus it looks pretty much like a chimp of today. Further, I can’t help but notice the prominence of the heavy browridge in this species and in other pongids and wonder about the H. erectus “phenomena.” That is, later H. erectus had a much larger browridge than earlier H. erectus! One would expect this to be the other way around! BUT looking at the skull of Sahelanthropus I wonder, are the fossils from later H. erectus really from the ancestors of gorillas or chimps and not ancient human ancestors at all? If not then the striking differences between early and late H. erectus in terms of browridges is clear evidence of devolution likely due to retrobreeding (back-breeding)!! I think we might have a few skulls mixed up and misidentified!!