Researchers said on Thursday they discovered near the city of Zhaotong in northern Yunnan Province fossils about 6 million years old of an extinct panda called Ailurarctos that bore the oldest-known evidence of this improvised extra digit - actually a greatly enlarged wrist bone called the radial sesamoid.
"It uses the false thumb as a very crude opposable thumb to grasp bamboos, sort of like our own thumbs except it is located at the wrist and is much shorter than human thumbs," said Natural History Museum of Los Angeles County paleontologist Xiaoming Wang, lead author of the research published in the journalAilurarctos was an evolutionary forerunner of the modern panda, smaller but with anatomical traits signaling a similar lifestyle including a bamboo diet.
The panda's tight grip on bamboo acts against the jerking action of the mouth in order to quickly break food into bite-size chunks, Wang added. Pandas, one of the world's eight bear species, once inhabited large swathes of Asia. They now live primarily in temperate forests in the mountains of southwestern China, with a wild population estimated under 2,000.