The discovery of fossils of an ancestor of pandas in China has allowed researchers to solve the mystery of the mammal’s “sixth finger”, which allows it to grasp the bamboo stalks that make up most of its diet.
The fossils, which are about six million years old, were discovered in the Yunnan province of southwest China. Between them is an especially large wrist bone called the radial sesamoid.
This is the oldest evidence of the existence of a “sixth finger”, which would act as an additional thumb, on the giant panda, which allows it to grasp and break thick bamboo stalks, the researchers point out in the latest issue of the journal Scientific Reports.
These fossils belong to a now extinct ancestor of the panda called Ailurctos that lived in China between six and eight million years ago.
“The giant panda is … a rare case of a large carnivore … turned herbivore,” said Wang Xiaoming, curator of vertebrate paleontology at the Los Angeles County Museum of Natural History.
“The ‘false thumb’ of Ailurctos shows (…) for the first time the chronology and probable stages of the evolution of bamboo feeding among pandas”, he added.
While the existence of the “false thumb” has been known to researchers for about a century, fossil evidence of this bone sheds light on several long-unanswered questions, including how and when this extra finger, which is not found in other bears, evolved.
Millions of years ago, pandas swapped the protein-rich, omnivorous diet of their ancestors for the nutrient-poor but year-round bamboo in southern China.
Pandas eat up to 15 hours a day and an adult can consume 45 kilograms of bamboo daily. Although their diet is primarily herbivorous, giant pandas are also known to occasionally hunt small animals.