The giant wrong thumb of a panda

The only animals that possess an opposite thumb, and therefore are able to grasp objects with their claws, are some species of primates, including humans. It’s information also taught in school that, however, can be confusing when faced with an image of a panda eating: If a panda doesn’t have opposite thumbs, how do they pick up, tear, and grab bamboo canes and vegetables? that make up 99 percent of their diet?

The answer is that they have false thumbs: protrusions on the wrists of the front legs perform the function of the opposite thumb, while the true thumb aligns with all the other fingers.

How Pandas Catch Bamboo: Photo by Sharon Fisher, shows a panda from the Panda Research Center in Chengdu, China; In the photo below, a sesamoid bone is superimposed on the photo in alignment with the pseudo-thumb (Scientific Reports)

The bones under the false thumb are sesame bone Radial: Also found in human hands, the thumbs more or less stick to their hands, and they owe their name to the fact that they resemble sesame seeds for their shape. However, in pandas, they are not as small as human hands, but greatly enlarged, which is why they can perform the function of a thumb.

Compared to the thumbs of opposing primates, it is shorter, but still allows the panda to grip a bamboo cane tightly while chopping with its teeth to eat it. In fact, they have a vaguely hook-like shape, which allows you to lock the bars well.

The panda’s false thumb is an example of evolutionary adaptations that may arise from what may appear to be defects, in this case from overgrown sesamoids. The famous biologist and scientist Stephen Jay Gould generalized them as such in many of his articles, beginning with the book called panda thumb (1980). in Good Brontosaurus (1991) explains:

The complex and exotic methods of history ensure that most organisms and ecosystems cannot be the result of optimal design. Indeed, to make a stronger claim, imperfections are the primary evidence of sophistication, as optimal designs obliterate all the contours of history.
This principle of imperfection has been a major topic of my articles for several years. I call it the Panda Principle to honor my favorite ideal, the Panda’s False Thumb. Pandas are descendants of carnivorous bears. Their true anatomical thumb has been irrevocably committed, for a long time, to carrying out the limited movements appropriate to this way of life and universally developed by carnivorous mammals. When adapting to a bamboo diet required greater flexibility in manipulation, the panda could not redesign its thumb, but had to adapt to a well-manipulated alternative: the enlarged radial sesamoid bone of the carpal (carpal), the panda’s “false thumb”. Sesame thumb is rough, far from optimal in structure, but it works. The methods of history (the engagement of the true impulse in other roles during the irrevocable past) impose temporary solutions similar to those on all living things. History shows its existence in the defects of living things: in this way we know that modern creatures have a different past, which evolution has transformed into their present state.

How are the front leg bones made of a panda, in this left case, compared to the sesamoid of Ailurarctos, denoted by the letters B and D (Scientific Reports)

For years, naturalists have wondered why pandas didn’t develop longer rays through evolution that allowed them to better grab and squeeze bamboo canes. study Posted on June 30 on Scientific Reports Let’s now make a hypothesis: the tallest sesame will be uncomfortable for walking.

The study relates to some fossils of an extinct genus of pandas, which is the ancestor of the current panda and is called Ilorarctus, found between 2010 and 2015 in the Yunnan region of China and about 6 or 7 million years old. The Ilorarctus They were smaller than pandas, but as far as we know they shared a bamboo diet with them.

Fossils – anterior tibia bone, teeth, and overgrown sesamoid – are the oldest evidence of a pseudofollicular thumb ever discovered; Previously, the oldest pseudo-thumbs were found tens of thousands of years ago and belonged to pandas of the same species as the contemporary species. Compared to today’s pandas, pandasIlorarctus It’s a bit longer and less arched in the last part.

Illustration of how Ailurarctos are made, by artist Mauricio Antón (Scientific Reports)

“False hook thumb allows for a firm grip of bamboo and at the same time, since it has a less prominent tip, because it is arched, it is less of a hindrance to movement”, He explained Los Angeles Museum of Natural History Paleontology Xiaoming Wang, first author of the study published in Scientific Reports: “Imagine a panda stumbling on its pseudo-thumb every time it moves…which is why we think the pseudo-thumbs in modern pandas are getting shorter, not longer.”

– Read also: The evolutionary dilemma of the panda

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Harold Manning

"Infuriatingly humble social media ninja. Devoted travel junkie. Student. Avid internet lover."

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