The discovery fills a void in the panda fossil record, confirming what palaeontologists have long suspected: that the modern panda traces its origins back millions of years.

Credit: Russell Ciochon

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CHICAGO: Palaeontologists have discovered the skull of the giant panda's earliest known ancestor, a "pygmy-sized" bear that lived in south China about two million years ago.

The well-preserved fossil has all the hallmarks of a panda skull, but measures about half the size of a modern panda bear (Ailuropoda melanoleuca) skull, suggesting the ancient ancestor (Ailuropoda microta) was probably a miniaturized version of its modern counterpart.

Mini-me

The ancient panda was over half a metre shorter in length than a modern panda and would have been more akin in size to a medium-sized dog, said researchers who publish the find in U.S. journal, the Proceedings of the National Academy of Sciences this week.

The discovery fills a void in the panda fossil record, confirming what palaeontologists have long suspected – namely that the modern panda traces its origins back millions of years, and through at least two different distinct sets of ancestors.

"This shows that the panda lineage has evolved over many millions of years separate from all the other species in the family of bears," said co-author Russell Ciochon, a palaeoanthropologist at the University of Iowa in Iowa City, USA.

Researchers have known for some time that the cuddly Chinese bear that is now largely confined to the mountainous upland bamboo forests of southwestern China, was descended from a larger bear (Ailuropoda baconi) that lived about half a million years ago.

There were some clues that another ancient forbearer of the giant panda was roaming the forests of eastern and southern China as long as three million years ago, but the fossil evidence was not conclusive – just a collection of isolated teeth found between 1985 and 2002.

Vegetarian heritage

The discovery of this skull, which Chinese researchers found in a limestone cave in Guangxi province in south China several years ago, seals the deal, according to Ciochon.

"This skull is well-preserved, and has all its teeth intact, and on the basis of this fossil we can say that this bear was a miniaturized version of the modern panda," said Ciochon.

Comparison of the skull and upper teeth of the fossil and living pandas. Ailuropoda microta is to the left, a living panda is to the right and the even chunkier extinct A. baconi is in the middle.

The fact that the fossil skull had the same anatomically unique features as modern pandas – heavy enamel on its teeth and a heavy-duty skull – shows the panda was adapted to eating bamboo from very early in its development, he said.

"Pandas are very unique bears: the only bear species that is known to exist on a wholly vegetarian diet," said Ciochon. "The evolution of this unique dietary specialization probably took millions of years to refine. Our new discovery shows the great time depth of this unique bamboo-eating specialization in pandas."

The study was co-written by Changzhu Jin and Jinyi Liu of the Chinese Academy of Sciences. Palaeontologist Robert Hunt of the University of Nebraska in Lincoln also worked on the project.