Stephen Jay Gould famously made the false thumb of the giant panda one of his hallmark examples of the structural vagaries of adaptation. His original essay, "The Panda's Peculiar Thumb" is available online, courtesy of the Unofficial SJG Archive.
Now, a PNAS paper by Manuel Salesa and colleagues reports evidence of a false thumb in a Miocene relative of the red panda:
The "false thumb" of pandas is a carpal bone, the radial sesamoid, which has been enlarged and functions as an opposable thumb. If the giant panda (Ailuropoda melanoleuca) and the red panda (Ailurus fulgens) are not closely related, their sharing of this adaptation implies a remarkable convergence. The discovery of previously unknown postcranial remains of a Miocene red panda relative, Simocyon batalleri, from the Spanish site of Batallones-1 (Madrid), now shows that this animal had a false thumb. The radial sesamoid of S. batalleri shows similarities with that of the red panda, which supports a sister-group relationship and indicates independent evolution in both pandas. The fossils from Batallones-1 reveal S. batalleri as a puma-sized, semiarboreal carnivore with a moderately hypercarnivore diet. These data suggest that the false thumbs of S. batalleri and Ailurus fulgens were probably inherited from a primitive member of the red panda family (Ailuridae), which lacked the red panda's specializations for herbivory but shared its arboreal adaptations. Thus, it seems that, whereas the false thumb of the giant panda probably evolved for manipulating bamboo, the false thumbs of the red panda and of S. batalleri more likely evolved as an aid for arboreal locomotion, with the red panda secondarily developing its ability for item manipulation and thus producing one of the most dramatic cases of convergence among vertebrates.
So not only is there the bamboo grasping story, there is also the climbing carnivore story. Incidentally, red pandas are much cuter than giant pandas, and they hardly get any attention at all.
UPDATE (1/6/06): I just saw that Carl Zimmer blogged this story long before I did. It's a good story.
Salesa MJ, Anton M, Peigne S, Morales J. 2006. Evidence of a false thumb in a fossil carnivore clarifies the evolution of pandas. Proc Nat Acad Sci USA Online early access. Abstract