The discovery of panda fossils in China has helped researchers solve the mystery of how this giant species developed “false thumbs” and became the only dedicated vegetarian in the bear family.
Fossils dating back about six million years old found in Yunnan province in southwestern China include a massively enlarged wrist bone known as a radial sesamoid.
The scientists who wrote in a research paper published in the latest edition of Scientific Reports say this is the oldest known evidence of a modern giant panda’s prosthetic thumb for allowing it to grip and break the heavy bamboo stalks.
The fossils belong to a now-extinct ancient relative of the panda named Ailurarcto that 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 … which has become a specialized herbivore,” said Wang Xiaoming, curator of the neck. vertebrates at the Natural History Museum of Los Angeles County.
“The Ailurarctos prosthetic thumb shows for the first time … the timeline and steps in the development of bamboo eating in pandas.”
Researchers have known about pandas’ prosthetic thumbs, which function similarly to human thumbs, for about a century. But the lack of fossil evidence has left unanswered questions about how and when the extra digit – not seen in any other species of bear – evolved.
“Although the giant panda’s prosthetic thumb is not the most elegant or dexterous…even a small protruding lump on the wrist can be a modest aid in stopping bamboo,” wrote Wang. slip off the curved fingers,” wrote Wang.
Fossils found near the city of Zhaotong in northern Yunnan include a false thumb that is longer than the one found in modern pandas, but without an internal hook at the end.
The hook and a fleshy pad around the thumb have evolved over time as it has to “bear the brunt of considerable body weight”, the article said.
Pandas traded their ancestors’ high-protein, omnivorous diets for bamboo, a low-nutrient year-round plant in South China millions of years ago.
They eat up to 15 hours a day and an adult panda can consume 45kg of bamboo per day. While their diet is mostly vegetarian, wild pandas are known to occasionally hunt small animals.
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