The discovery of a new species of great ape that roamed Africa 10m years ago has forced scientists to rethink the earliest steps of human evolution.
Fossil hunters working along the Afar rift in central Ethiopia unearthed remnants of teeth they claim belonged to the primitive ape, a previously unknown species of gorilla they named Chororapithecus abyssinicus.
The finding, if confirmed, will redraw the evolutionary tree of primates, suggesting that humans and chimpanzees must have split from their gorilla-like ancestors 3m years earlier than thought.
Geneticists have previously put the date at which the human and chimpanzee lineage split from gorillas at around 7m years ago, with humans and chimps diverging more recently, at 5m years ago.
In the teeth of it...
A team led by Gen Suwa at Tokyo University Museum recovered one canine and eight partial molars from rocky sediments in part of the rift called the Chorora Formation that has been dated to 10m to 10.5m years old.
The teeth are believed to come from as many as six apes of the same species, that lived in what would have been a forested valley following a river that drained into a lake.
The teeth were found to be close in shape and size to those of modern gorillas, with smaller versions of crests that are characteristic of gorilla teeth but are not seen in other apes, the researchers report in the journal Nature.
The crests help with chewing tough, fibrous material such as leaves and plant stems.
“The newly discovered teeth are starting to show this crestiness so we think this is an incipient form of a gorilla,” said Dr Suwa. “We were actually thrilled just to see little bits of unidentifiable fossil fragments.”
Peter Andrews, former head of human origins at the Natural History Museum in London, said the researchers needed more fossil evidence to be sure they had identified a new great ape species.
“They’re saying an awful lot from an awful little,” he said.
In particular, Prof Andrews added, it was impossible to identify the species as a primitive gorilla based on the crests of the teeth.
“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.
It is stretching the evidence to base a time scale for the evolution of the great apes on this new fossil,” he said.
The Guardian