Do you eat bamboo? It’s all in the wrist.
When is the thumb not really a thumb? When it is an elongated fruit bone of the giant it is always used to catch bamboo. Through his long evolutionary history, his hand has never developed a truly opposite thumb. Instead, it evolved a digit that looks like a thumb from a wrist bone, the radial sesame. This unique adaptation helps these bears survive entirely on bamboo, even though they are bears (members of the Carnivora order or carnivores). In a new study published today (June 30, 2022), scientists report the discovery of the first ancestor to ever eat bamboo and have this “thumb”. Surprisingly, he is farther away from his modern descendants. The research was conducted by Vertebrate Paleontology Curator of the Los Angeles County Museum of Natural History Xiaoming Wang and colleagues. While the famous fake thumb in modern giants (Ailuropoda melanoleuca) has been known for more than 100 years, it has not been understood how this wrist bone evolved due to the almost complete absence of fossils. A fossil fake thumb from an ever-ancestral giant, the Ailurctos, dating to 6-7 million years ago, has been unearthed at the Shuitangba site in Zhaotong City, Yunnan Province in southern China. It gives scientists a first look at the early use of this extra (sixth) digit – and the earliest evidence of bamboo diet in ancestral backgrounds – helping us better understand the evolution of this unique structure. Always Chengdu eating bamboo. Credit: Photo reproduction by Sharon Fisher “Deep in the bamboo forest, the giants have always exchanged an omnivorous diet of meat and berries with bamboo that they ate quietly, a plant abundant in the subtropical forest but of low nutritional value,” says NHM Vertebrate Curator Dr. Xiaoming Wang. “Holding bamboo stems tight to crush them to bite sizes is perhaps the most critical adjustment to consuming a huge amount of bamboo.”
How to walk and chew bamboo at the same time
This discovery could also help solve a perpetual mystery of everything: why are their fake thumbs so seemingly underdeveloped? As the ancestor of the modern ever, Ailurctos could be expected to have even less developed fake “thumbs”, but the fossil discovered by Wang and his colleagues revealed a longer fake thumb with a straighter tip than the shortest, hooked digit of of his modern descendants. So why did their fake thumbs always stop growing to achieve a bigger digit? “Panda ‘s fake thumb has to walk and’ chew, ‘” Wang says. Such a dual function serves as the limit for how big this “thumb” can become. Always grip against walking (white bone is the fake thumb). Credit: Courtesy of Los Angeles County Museum of Natural History Wang and his colleagues believe that the shorter false thumbs of the modern panda are an evolutionary compromise between the need to handle bamboo and the need to walk. The hooked tip of the second thumb of a modern panda allows them to handle the bamboo while letting them carry their impressive weight at the next bamboo meal. After all, the “thumb” does a double job as the radial sesame – a bone in the animal’s wrist. “Five to six million years should be enough time for forever to develop longer fake thumbs up, but it seems that the evolutionary pressure of the need to travel and bear the weight has kept the ‘thumb’ short — strong enough to be useful. without being big enough. to prevent it, “said Denise Su, an associate professor at the School of Human Evolution and Social Change and a researcher at the Institute of Human Origins at Arizona State University, and co-leader of the project that discovered the panda specimens. “Evolving from a carnivorous ancestor to becoming pure bamboo feeders, everything has to overcome many obstacles,” says Wang. “An opposite ‘thumb’ from a wrist bone may be the most amazing development in the face of these obstacles.” Reference: “The giant’s first fake thumb always suggests conflicting demands for movement and feeding” by Xiaoming Wang, Denise F. Su, Nina G. Jablonski, Xueping Ji, Jay Kelley, Lawrence J. Flynn and Tao Deng, June 30, 2022 , Scientific Reports .DOI: 10.1038 / s41598-022-13402-y The authors of this article are affiliated with the Los Angeles County Museum of Natural History, Los Angeles, California, USA. Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing, China. Arizona State University, Tempe, Arizona, USA Pennsylvania State University, University Park, Pennsylvania, USA Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming, Yunnan, China. Yunnan Institute of Cultural Relive and Archeology, Kunming, Yunnan, China. Harvard University, Cambridge, Massachusetts, USA. Funding was provided by the US National Science Foundation, the Yunnan Institute of Natural Sciences, the National Science Foundation of China, the Zhaotong and Zhaoyang governments, the Institute of Paleontology and Vertebrate Anthropology.
