A fossilised skeleton of a tiny creature with a long tail, sharp teeth and monkey-like feet has turned out to be the oldest-known primate – the group that includes gorillas, chimps and humans.
Scientists discovered the fossil in the solidified sediment of an ancient lake bed in China and have dated it to about 55 million years ago, about 10 million years after the demise of the dinosaurs and seven million years before the date of the previous oldest-known primate.
The researchers said it is one of the most exciting fossil discoveries in recent years because the animal – called Archicebus achilles – is the closest-known relative of the common ancestor to the entire “anthropoid” lineage encompassing monkeys, apes and man.
Archicebus grew no bigger than a modern-day pygmy shrew and from its relatively small eye sockets scientists believe it was active during the day rather than at night, feeding off insects and small invertebrates.
“Archicebus differs radically from any other primate, living or fossil, known to science,” said Christopher Beard of the Carnegie Museum of Natural History in Pittsburgh, co-author of the fossil’s scientific description, published in the journal Nature. “It looks like a hybrid with the feet of a small monkey, the arms, legs and teeth of a very primitive primate and a primitive skull bearing surprisingly small eyes. It will force us to re-write how the anthropoid lineage evolved,” Dr Beard said.
Although Archicebus (which means “first, long-tailed monkey”) is close to the common ancestor of all anthropoids, scientists believe it was not a direct ancestor of humans but instead had begun to evolve along the alternative primate lineage that eventually gave rise to the tarsiers – a specialised group of small, nocturnal primates.
“This is not a direct ancestor of humans but for the first time it sheds light on this pivotal episode of primate evolution when two branches of primates – the anthropoids and the tarsiers – split apart,” Dr Beard said.
A farmer discovered the fossil in an ancient lakebed in China’s Hubei Province.