Panda bears have been eating bamboo for much longer than we imagined. They get 50% of their energy from their protein, like wolves or wild cats. A new analysis of fossils has revealed the secrets of pandas ‘ enigmatic extra ‘thumb’ . In addition to the normal five toes on the paws of most mammals, giant pandas also have a greatly enlarged wrist bone, the radial sesamoid, which acts as a sixth toe, an opposable “thumb” for manipulating bamboo. This is a unique adaptation and is part of the reason pandas can eat bamboo, even though other bears can eat meat.
Now, the new paleontological study shows that the origin of the modern panda’s ( Ailuropoda melanoleuca) bamboo diet dates back to 6-7 million years ago during the late Miocene. (Previous research documented evidence of this thumb-like structure only 100,000 to 150,000 years ago, making it the earliest evidence of the appendage by more than 5.8 million years.)
differences in size and shape
“Deep in the bamboo forest, giant pandas traded an omnivorous diet of meat and berries for leisurely eating bamboos, a plant abundant in the subtropical forest but of low nutritional value,” explains Xiaoming Wang, lead of the study. published in the journal Scientific Reports . “Firmly holding bamboo stalks to grind them into bites is perhaps the most crucial adaptation for consuming a prodigious amount of bamboo.”
Paleontologists have discovered at the Shuitangba site in the city of Zhaotong, Yunnan province in southern China, the first ancestral panda that ate bamboo and had this “thumb”, although it was larger, wider and more hooked; longer than its modern descendants. Ailurarctos, the ancestor of pandas, gives scientists a first look at the early use of this extra digit, and the earliest evidence of a bamboo diet in ancestral pandas, helping us better understand the evolution of this species. unique structure.
Eating bamboo for 6 million years
The researchers said this indicates that the digit and a diet dedicated to bamboo have been present in the panda lineage for at least six million years. This discovery could also help solve an enduring panda mystery: why do their fake thumbs look so underdeveloped?
“The panda’s false thumb must walk and ‘chew ‘. Such a dual function serves as the limit on how big this ‘thumb’ can get,” Wang says. This means that pandas evolved shorter thumbs to be able to manipulate bamboo and then allow them to move forward to find the next meal. “Evolving from a carnivorous ancestor and becoming a pure bamboo feeder, pandas have to overcome many obstacles. An opposable ‘thumb’ from a wrist bone may be the most amazing development against these obstacles”, says the expert.
Thus, this evolutionary compromise between the need to walk and manipulate bamboo at the same time made the false thumbs of modern pandas shorter. After all, the “thumb” does double duty as a radial sesamoid: a bone in the animal’s wrist whose shorter length and flattened outer surface can help with weight distribution when walking.
“Five to six million years should be enough time for the panda to develop longer false thumbs, but it seems that the evolutionary pressure of having to travel and support its weight kept the ‘thumb’ short and strong enough to be useful.” without being big enough to get in the way,” said Denise Su, an associate professor in the School of Human Evolution and Social Change and a research scientist at the Arizona State University Institute of Human Origins, and co-director of the project that retrieved the panda specimens.
Referencia: Xiaoming Wang, Earliest giant panda false thumb suggests conflicting demands for locomotion and feeding, Scientific Reports (2022). DOI: 10.1038/s41598-022-13402-y. www.nature.com/articles/s41598-022-13402-y
