Role of the giant panda's ‘pseudo-thumb’

Abstract

The way in which the giant panda, Ailuropoda melanoleuca, uses the radial sesamoid bone — its ‘pseudo-thumb’ — for grasping makes it one of the most extraordinary manipulation systems in mammalian evolution^1,2,3,4,5. The bone has been reported to function as an active manipulator, enabling the panda to grasp bamboo stems between the bone and the opposing palm²,^6,7,8. We have used computed tomography, magnetic resonance imaging (MRI) and related techniques to analyse a panda hand. The three-dimensional images we obtained indicate that the radial sesamoid bone cannot move independently of its articulated bones, as has been suggested^1,2,3, but rather acts as part of a functional unit of manipulation. The radial sesamoid bone and the accessory carpal bone form a double pincer-like apparatus in the medial and lateral sides of the hand, respectively, enabling the panda to manipulate objects with great dexterity.