LONDON Researchers working in Ethiopia have unearthed the fossils of a 10-million-year-old ape, a discovery they say suggests that humans and African great apes may have split much earlier than thought.
The Ethiopian and Japanese team named the species Chororapithecus abyssinicus and said it represents the earliest recognized primate directly related to modern-day gorillas, chimpanzees and bonobos.
"The human fossil record goes back six to seven million years, but we know nothing about how the human line actually emerged from apes," the researchers said in a statement on Wednesday that accompanied publication of their study in Nature magazine.
"Chororapithecus gives us the first glimpse of the ape side background to the human origins story."
The researchers found the fossils in steep, rough terrain about 170 km (105 miles) east of Addis Ababa.
The team, which dug up one canine tooth and eight molars, determined the molars were from a great ape because they shared special characteristics with modern gorillas for eating fibrous food such as stems and leaves.
They concluded Chororapithecus was either a primitive form of gorilla or an independent branch showing a similar adaptation at about the time when the gorilla line was emerging elsewhere.
"If it's not a gorilla relative, then it's something very similar to what an early gorilla must have looked like", Gen Suwa of the University of Tokyo, one of the researchers, said.
Peter Andrews, a paleontologist at the British Natural History Museum and expert on human origins, called the discovery exciting because the fossil evidence from great apes, the closest living relatives to humans, is almost non-existent.
But he said he was not certain enough about some of the characteristics of the new fossil ape's teeth to name a new species ancestral to gorillas-- as the researchers have done -- that pushes back the timeline of the ape-human split.
"It is stretching the evidence to base a timescale for the evolution of the great apes on this new fossil," Andrews said in a telephone interview.
Some scientists have also speculated that the direct line of ancestral ape that spawned gorillas, chimpanzees and humans came to Africa from Eurasia.
But the researchers said their findings added to evidence that Africa was the place of origin of both humans and modern African apes and indicated that gorillas split off from a common ancestor with humans and chimpanzees long before the generally accepted time of 7 to 8 million years ago.
"Chororapithecus indicates that a reconsideration of this assumption is needed," the researchers said. "In fact, if the orang line was present in Africa prior (to the) first migration of Miocene (some 23-25 million years ago) apes from Africa to Eurasia, then the human-orang split could have easily have been as old as 20 million years ago."