We constructed a modular, biomimetic red panda paw with which to experimentally investigate the evolutionary reason for the existence of the false thumbs of red pandas. These thumbs were once believed to have shared a common origin with the similar false thumbs of giant pandas; however, the discovery of a carnivorous fossil ancestor of the red panda that had false thumbs implies that the red panda did not evolve its thumbs to assist in eating bamboo, as the giant panda did, but rather evolved its thumbs for some other purpose. The leading proposal for this purpose is that the thumbs developed to aid arboreal locomotion. To test this hypothesis, we conducted grasp tests on rods 5-15 mm in diameter using a biomimetic paw with 0-16 mm interchangeable thumb lengths. The results of these tests demonstrated an optimal thumb length of 7 mm, which is just above that of the red panda's true thumb length of 5.5 mm. Given trends in the data that suggest that smaller thumbs are better suited to grasping larger diameter rods, we conclude that the red panda's thumb being sized below the optimum length suggests an adaptation toward grasping branches as opposed to relatively thinner food items, supporting the new proposal that the red panda's thumbs are an adaptation primary to climbing rather than food manipulation.

翻译：我们构建了一个模块化的仿生小熊猫爪，用于实验研究小熊猫假拇指存在的进化原因。这些假拇指曾被认为与大熊猫的类似假拇指有共同起源；然而，由于发现了一具具有假拇指的小熊猫食肉化石祖先，表明小熊猫并非像大熊猫那样为了协助食用竹子而进化出拇指，而是为了其他目的进化出拇指。这一目的的主要假说认为，拇指是为了帮助树栖运动而发育的。为验证该假说，我们使用具有0-16毫米可更换拇指长度的仿生爪，对直径5-15毫米的杆进行了抓握测试。测试结果显示，最佳拇指长度为7毫米，略高于小熊猫真实拇指长度5.5毫米。根据数据趋势（表明较小的拇指更适合抓握较粗的杆），我们得出结论：小熊猫的拇指尺寸低于最佳长度，表明其适应于抓握树枝而非相对较细的食物物品，从而支持了新假说——小熊猫的拇指主要适应于攀爬而非食物操控。