YUNNAN – The discovery of panda fossils in China has helped researchers solve the mystery of how the giant species developed a “false thumb” and became the bear family’s only devoted vegetarian.
Fossils around six million years old found in Yunnan province in southwest China included a greatly enlarged wrist bone called the radial sesamoid.
This is the earliest known evidence of the modern giant panda’s false thumb, which allows it to grasp and break heavy bamboo stalks, scientists wrote in a research paper published in the latest issue of Scientific Reports.
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The fossils belong to a now extinct ancient relative of the panda called Ailurarcto, who lived in China six to eight million years ago.
“The giant panda is…a rare case of a large carnivore with a short, carnivorous digestive tract…that became a dedicated herbivore,” said Wang Xiaoming, curator of vertebrate paleontology at the Los Angeles County Museum of Natural History, said.
“Ailurarctos false thumb shows…for the first time the likely timing and stages of bamboo-eating evolution in pandas.”
The panda’s false thumb, which functions similarly to the human thumb, has been known to researchers for about a century. But the lack of fossil evidence has left questions about how and when the extra toe – which is not seen in any other bear – evolved.
“Although the giant panda’s fake thumb isn’t the most elegant or dexterous…even a small protruding bump on the wrist can be a modest aid in preventing the bamboo from slipping off bent fingers,” Wang wrote.
Among the fossils found near the city of Zhaotong in northern Yunnan was a false thumb, longer than that found in modern pandas but lacking an inner hook at the end.
The hook and a fleshy padding around the base of the thumb evolved over time as they had to “carry the burden of considerable body weight”, according to the newspaper.
Millions of years ago, pandas swapped the protein-rich omnivorous diet of their ancestors for bamboo, which is still poor in southern China.
They eat for up to 15 hours a day, and an adult panda can consume 45 kg of bamboo per day. While their diet is primarily vegetarian, wild pandas occasionally hunt small animals.