The giant panda's paws grasp bamboo shoots and stems with a freedom and agility resembling human hands. This remarkable dexterity is attributed to the presence of a "sixth finger," enabling them to firmly grip bamboo. How did this skill of proficiently grasping bamboo originate and evolve in these carnivorous mammals? Furthermore, at what point in their evolutionary history did they transition to consuming bamboo? Despite belonging to the order Carnivora, these pandas have acquired a unique ability to manipulate bamboo, showcasing an intriguing aspect of their evolutionary journey.
Is the giant panda's "sixth finger" a true finger?
The answer is No.
The giant panda is famously known as the "hexadactyl bamboo wizard," with its well-known secret—the "sixth finger." However, it cannot be classified as a finger since it lacks a nail; it is merely a mobile projection.Therefore, pandas only have 20 toes.
Scientists have long sought to unravel the mystery of how and when this unique appendage evolved from the wrist bone.
Guest researcher at the Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences (IVPP-CAS), and researcher at the Natural History Museum of Los Angeles County, Dr. Wang Xiaoming, collaborated with Dr. Deng Tao, a researcher at IVPP-CAS, and Dr. Ji Xueping, a researcher at the Kunming Institute of Zoology, Chinese Academy of Sciences, along with their research peers. They have recently completed a study on crucial fossils of the earliest pandas from the Shuitangba Late Miocene site in Zhaotong, Yunnan (approximately 6 to 7 million years ago). The fossils include the "pseudo thumb" (also known as the "sixth finger") and molar fossils.
The research findings reveal that the earliest pandas, known as Ailuropoda microta, possessed the earliest enlarged radial sesamoid bone, which had already developed the function of a grasping "thumb." This significant achievement in paleontological research was recently published in the international scientific journal "Scientific Reports." It provides key evidence for answering questions regarding when the early pandas began consuming bamboo and whether the pseudo thumb aided pandas in gripping bamboo.
In contrast to the radial sesamoid bone in extant giant pandas, which features a sharply inward-bending hook near the end, the pseudo thumb of the early pandas initially underwent simple elongation and developed a more refined terminal hook. Simultaneously, there was a slight reduction in length at the end.
The elongation of fingers would undoubtedly enhance the ability to grip bamboo sticks. However, why did the pseudo thumb not become longer and more functionally complex?
The research team suggests that giant pandas made a trade-off between grasping ability and walking capability. The elongated radial sesamoid bone in extant pandas, favorable for gripping bamboo, inevitably interferes with walking by requiring a strongly extended contact with the ground by the front and hind paws during locomotion. This adaptation can be likened to a shoe sole catching a pebble, causing discomfort. Therefore, modern giant pandas balance these conflicting functions by having the pseudo thumb's end sharply bend inward into a hook and flatten outward, resolving the trade-off between grasping and walking capabilities.
Therefore, to be precise, pandas only have 20 toes.