By Helen Sewell
BBC News Online science staff
Fossil experts have discovered the teeth of the oldest known relative of the orang-utan.
3D JAW RECONSTRUCTION
Possible arrangement of male teeth
Grey denotes teeth actually recovered; Pink shows symmetric fossils
Blue are resized female teeth; Green are inferred from other fossils
Image courtesy of ESRF/ISE-M/Nature
They say the canines and incisors could help solve the long-standing mystery of how great apes evolved.
The teeth were embedded in coal in an area of northern Thailand, where the animal lived between 10 and 13.5 million years ago.
When the researchers compared them with dental records from other ancient apes, they worked out that the new species, Lufengpithecus chiangmuanensis, is more closely related to the orang-utan than any fossil ever found.
"We can never be sure if it's a direct ancestor, but it's something very close," said Jean-Jacques Jaeger, Professor of Palaeontology at the University of Montpelier in France, and one of the team who made the find.
In a letter to the journal Nature, the researchers explain how they also found fossilised pollen with the teeth, showing that L. chiangmuanensis once lived in a tropical forest.
They say families of apes probably came to gather ripe champoo, a fruit still commonly eaten in Thailand, before drinking from a nearby lake.
There, some of them were caught and killed by crocodiles, tigers or panthers.
The teeth of several individuals including young apes with milk teeth sank into the lake and became buried in the detritus which eventually turned into coal.
Professor Jaeger said the fossilised teeth answered some fundamental questions about the evolution of orang-utans.
On four feet
All great apes probably evolved from a common ancestor many millions of years ago. But the evolutionary family tree branched off into Pongo (orang-utans) in Asia, and into the ancestors of gorillas and chimpanzees in Africa.
Modern great apes get about by swinging from branch to branch in the trees, but fossil records show that early Pongos walked on four feet.
Professor Jaeger argues this means that the swinging locomotion must have evolved independently in Asia and Africa.
"This is a very big debate," he says. "We guess that our new taxa have the teeth of an orang-utan and a type of suspensory adaptation in a more primitive state. So the suspensory adaptation has evolved in parallel with the African apes."