Pandas evolved their most mysterious feature at least 6 million years ago.

But their ancestors, like most bears, ate a much broader diet that included meat, and the exclusive diet of modern pandas was thought to be relatively recent. However, a new study found that pandas’ particular passion for bamboo may have been at least 6 million years old – perhaps due to the plant’s wide availability year-round.

To survive solely on nutrient-poor bamboo, modern pandas (Ailuropoda melanoleuca) have evolved a peculiar sixth finger, a kind of thumb that allows them to easily grasp bamboo stems and strip off leaves.

“Holding bamboo stems tightly to crush them into pieces is perhaps the most important adaptation to consuming massive amounts of bamboo,” said study author Xiaoming Wang, curator of vertebrate paleontology at the Los Angeles County Museum of Natural History. statement.

Wang and his team found much earlier evidence that pandas had an extra toe and therefore an all-bamboo diet, in the form of a fossilized toe dating back 6-7 million years. The fossil, discovered in southwest China’s Yunnan province, belonged to a panda ancestor known as Ailurarctos.

The picture shows an artist reconstructing the giant panda's ancestor Ailurarctos from the Shuitangba fossil site in Yunnan, China.

The new study was published Thursday in the journal Scientific Reports.

While the giant panda’s sixth toe is not as elegant or dexterous as the human thumb, the persistence of this “distinctive morphology” over millions of years suggests it plays an important role in survival, the study notes.

Evolutionary compromise

But what particularly puzzled the scientists involved in the study was that this fossilized structure was longer than modern giant pandas, which have a shorter, hooked sixth toe.

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Wang and his colleagues believe that modern pandas have a shorter sixth digit. represents an evolutionary compromise between the need to manipulate bamboo and the need to walk and carry one’s hefty bodies.

“Five to six million years should be long enough for a panda to develop longer false thumbs, but it seems that the evolutionary pressure of having to travel and carry your weight has made the “thumb” short—strong enough to be useful but not be big enough. to get in the way,” study co-author Denise Su, an assistant professor in the School of Human Evolution and Social Change and a research fellow at the Human Origins Institute at Arizona State University, said in a statement.