By Liz Seward
The teeth have gorilla-like characteristics, say researchers
The 10 million-year-old fossils belong to an animal that has been named Chororapithecus abyssinicus by an Ethiopian-Japanese team.
This new species could be a direct ancestor of living African great apes, say the researchers.
The finds from the Afar rift, in eastern Ethiopia, raise questions on current theories of human evolution.
The researchers say the fossils from Ethiopia probably belonged to an ape from the gorilla family.
Evolutionary divide
Based on genetic evidence, gorillas and humans were thought to have split away from a common ancestor about eight million years ago.
The 10-million-year age of the fossils led the research team to suggest that the split must have happened earlier than 10.5 million years ago.
If correct, molecular and DNA studies will need to be revisited.
The fossils were found at a site in eastern Ethiopia's Afar rift
They carried out cutting-edge 3D analysis of the molar tooth's structure and found that both gorillas and the new species had a unique specialisation for eating fibrous foodstuffs such as stems and leaves.
"It's a subtle distinction, but we've compared it with everything we could think of," said Dr Suwa from the University of Tokyo and a member of the research team.
"And it does show some telling signs of gorilla-like molar structure. If it's not a gorilla relative, then it's something very similar to what an early gorilla must have looked like."
Vegetarian tastes
Gorillas are unique among modern and fossil large-bodied apes in having molars that are specialised for shredding fibrous vegetation. The reason for this is that large-bodied gorillas depend on stems and leaves as an important part of their diet.
Not everyone agrees with the team's conclusions, however. Professor Peter Andrews, from London's Natural History Museum, commented: "It is stretching the evidence to base a time scale for the evolution of the great apes on this new fossil."
Professor Andrews believes the structures found on the teeth could be related to the diet of the animal.
He added: "These structures appear on at least three independent lineages of apes, including gorillas, and they could relate to a dietary shift rather than indicating a new genetic trait."
Fossil record
What is not in doubt is that the find itself is impressive.
"The ancestry of humans is increasingly well known, but the fossil evidence for the evolution of our closest living relatives, the great apes, is almost non-existent," Professor Andrews explained.
"It is really exciting therefore to find a fossil ape from this time period - about 10 million years ago - since there is only one other fossil ape known from this time, the more complete Samburupithecus."
The find also supports data that suggests Africa was the origin of both humans and modern African apes.
The teeth were discovered in a region that is about 170km (110 miles) east of Addis Ababa.
In an area of the Oromiya National Regional State, there are exposed patches of sediments that are 10 to 11 million years old, putting them in the Miocene Epoch. Hence, they are known as Miocene Chorora Formation.
The name of the ape is taken from the geological formation Chorora and the former name of Ethiopia, Abyssinia.
Researchers say that new, ten million-year-old fossils found in Ethiopia, prove that the theory that humans may have evolved from a species of great apes eight million years ago, may not be true, but that humans may have split from apes as long as 10.5 million years ago.

At least nine fossilized teeth, one canine tooth and eight molars, of a previously unknown species of apes found in Africa were discovered by a team of researchers from Ethiopia and Japan who then compared the 3-D make up of the teeth to other fossils that date back as far as 8 million years and found that the fossils are likely a "direct ancestor" of apes currently living in Africa and that the new ape fossils were that of a species of gorilla who ate mostly plants high in fiber.

Current fossils and research say that the evolutionary split from apes to humans occurred at least eight million years ago. The new fossils say that the split may have happened as long as 10.5 million years ago.

"Based on this fossil, that means the split is much earlier than has been anticipated by the molecular evidence. That means everything has to be put back," said researcher at the Rift Valley Research Service in Ethiopia and a co-author of the study, Berhane Asfaw. 

Despite the finds, other researchers are not convinced that the findings are correct.

"It is stretching the evidence to base a time scale for the evolution of the great apes on this new fossil. These structures appear on at least three independent lineages of apes, including gorillas, and they could relate to a dietary shift rather than indicating a new genetic trait," said a Professor at the London Natural History Museum in the United Kingdom, Peter Andrews who also added, "but the fossil evidence for the evolution of our closest living relatives, the great apes, is almost non-existent.

Researchers have named the newly discovered species ''Cororapithecus abyssinicus'' whose remains were found in the Afar Region of Ethiopia, the same place where the remains of Lucy were discovered in 1974.