Ancient fossils discovered in China have helped researchers understand the enduring mystery of the panda’s fake thumb.
Modern giant pandas carry a thumb-like sixth digit on their wrists, which scientists believe was instrumental in their transition from omnivores to bamboo-eating vegetarians.
The bones of the hand of the modern giant panda. Illustration: LA / Reuters County Museum of Natural History
Although the extra digit, known as the radial sesamoid, is not as versatile as the human thumb, it allows pandas to hold and crush bamboo stalks into bite-sized pieces and feed their formidable appetite.
The panda’s fake thumb has been known for more than 100 years, but the almost total lack of fossil evidence has left researchers baffled as to how the digit evolved.
Writing in Scientific Reports, Xiaoming Wang, curator of vertebrate paleontology at the Los Angeles County Museum of Natural History, sheds light on the mystery. New fossils of an ancient panda discovered near the city of Zhaotong in Yunnan Province in northern China not only fight the fake thumb, but suggest that it was previously larger than those seen in pandas. current.
The fossils, which are between 6 and 7 million years old, belong to an extinct relative of the panda called Ailurarctos and are believed to be the oldest known evidence of the unusual digit.
Denise Su, an associate professor at Arizona State University and co-leader of the project that recovered the panda specimens, said modern pandas have had enough time to develop longer false thumbs, but the evolutionary pressure of need of walking on their hands, as well as The bamboo with handle seems to have kept them short and strong.
In evolving from a carnivorous ancestor to a bamboo feeder, the panda had to overcome many obstacles, Wang added. “An opposable‘ thumb ’of a wrist bone may be the most striking development against these obstacles,” he said.
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Researchers found a bone in Ailurarctos’ arm in 2010 and discovered the false teeth and thumb in 2015. To date, the earliest known evidence of the thumb-like structure came from fossils of modern panda species. dated about 100,000 years ago. In addition to being shorter than his ancestor, the modern panda’s fake thumb has a hook at the end, which the authors believe could help him grab the bamboo.
Although the panda’s diet is 99% vegetarian, they occasionally eat small animals. To meet their nutritional needs, pandas eat up to 14 hours a day, consuming almost 40 kg of bamboo a day when they are adults.