Scientists solve mystery of pandas’ false thumb

Fossils found in China are helping scientists get a better grasp on one of the marvels of evolution: the giant panda’s false thumb, which helps this veggie-loving bear munch the bamboo that forms most of its diet.

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Researchers on Thursday said they discovered near the city of Zhaotong in northern Yunnan province fossils about six 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 closely resembles the false thumb of modern pandas, but is a bit longer and lacks the inward hook on the end in the extant species that provides greater ability to manipulate bamboo stalks, shoots and roots while eating.

The false thumb is an evolutionary adaptation to augment the existing five actual digits of the panda’s hand. A bear’s hand lacks the opposable thumb possessed by humans and various primates that enables the handling of objects using the fingers. The false thumb serves a similar function.