It gives scientists a first look at the early use of this extra (sixth) digit–and the earliest evidence of a bamboo diet in ancestral pandas–helping us better understanding the evolution of this unique structure.Ĭhengdu panda eating bamboo. A fossil false thumb from an ancestral giant panda, Ailurarctos, dating back 6–7 million years ago was uncovered at the Shuitangba site in the City of Zhaotong, Yunnan Province in south China. While the celebrated false thumb in contemporary giant pandas ( Ailuropoda melanoleuca) has been known for more than 100 years, it was not understood how this wrist bone evolved due to a near-total absence of fossil records. The research was conducted by the Natural History Museum of Los Angeles County’s Curator of Vertebrate Paleontology Xiaoming Wang and colleagues. In a new paper published today (June 30, 2022), scientists report the discovery of the earliest bamboo-eating ancestral panda to have this “thumb.” Surprisingly, it’s longer than its modern descendants. This unique adaptation helps these bears subsist entirely on bamboo despite being bears (members of the order Carnivora, or meat-eaters). Instead, it evolved a thumb-like digit from a wrist bone, the radial sesamoid. Through its lengthy evolutionary history, the panda’s hand has never developed a truly opposable thumb. When is a thumb not really a thumb? When it’s an elongated wrist bone of the giant panda that is used to grasp bamboo.
Credit: Illustration by Mauricio Anton Eating bamboo? It’s all in the wrist. The grasping function of its false thumb (shown in the right individual) has reached to the level of modern pandas, whereas the radial sesamoid may have protruded slightly more than its modern counterpart during walking (seen in the left individual). An artist reconstruction of Ailurarctos from Shuitangba.
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