In fact, the giant panda is a striking example of a highly specialized member of the bear family (Ursidae) that has become a dedicated herbivore, a rare case of a large carnivore with a short, carnivorous digestive tract 10 that became a low-level consumer with a greatly altered gut microbiota 11.ĭespite its celebrated status, the panda’s false thumb is a small, flat structure that barely protrudes out of the palmar surface, and this relatively obscure anatomy understandably baffled early anatomists (e.g., Wood-Jones 3). Gould’s essay also highlights an exclusive association of this unique anatomic structure with an equally unique diet of bamboo herbivory, although a false thumb has been shown also to have evolved independently in the red panda and its distant relatives 6, 7, in tremarctine bears (either convergently or as a shared plesiomorphic trait) 8, as well as in a distant relative of the giant panda clade 9. In recent decades, as popularized by Gould 4, 5, it has become a celebrated case of evolutionary adaptation to independently acquire an opposable thumb-like structure when the need arose. The false thumb of the giant panda (“panda” throughout text below unless otherwise specified) fascinated early naturalists 1, 2, 3. This crude “thumb” suggests that the origin of the panda’s dedicated bamboo diet goes back to as early as 6–7 Ma. The latter constraint could be the main reason why the panda’s false thumb never evolved into a full digit. This morphological adaptation in panda evolution thus reflects a dual function of the radial sesamoid for both bamboo manipulation and weight distribution. However, since the late Miocene, the “thumb” has not enlarged further because it must be balanced with the constraints of weight bearing while walking in a plantigrade posture. We report the earliest enlarged radial sesamoid, already a functional opposable “thumb,” in the ancestral panda Ailurarctos from the late Miocene site of Shuitangba in Yunnan Province, China. In addition to the normal five digits in the hands of most mammals, the giant panda has a greatly enlarged wrist bone, the radial sesamoid, that acts as a sixth digit, an opposable “thumb” for manipulating bamboo. ![]() ![]() Of the many peculiarities that enable the giant panda ( Ailuropoda melanoleuca), a member of the order Carnivora, to adapt to life as a dedicated bamboo feeder, its extra “thumb” is arguably the most celebrated yet enigmatic.
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