Fossils help scientists put their finger on secret of panda thumb

Ancient fossils discovered in China have helped researchers get a grip on the enduring mystery of the panda's false thumb.

- Ian Sample

Modern giant pandas have a thumb-like sixth digit on their wrist, which scientists believe was pivotal in their transition from omnivores to bamboo-munching vegetarians.

While the stubby extra digit, known as a radial sesamoid, is not as versatile as the human thumb it does enable pandas to hold and crush bamboo stems into bite-size pieces and fuel their formidable appetite.

The panda's false thumb has been known about for more than 100 years, but a near-total lack of fossil evidence has left researchers puzzled as to when the digit evolved.