The fossils, found in Yunnan Province in southwest China, belong to a now extinct relative of the giant panda – Ailurarctos – that lived several million years ago.
The fossil shows the trace of the panda’s “sixth toe” which is used as a thumb and which the panda uses to grab bamboo and break bamboo. Researchers have known about the panda dates for around 100 years, but lack of fossil evidence has left unanswered questions about how and when the extra finger – which is not found among other bears – developed.
The discovery has been published in the latest issue of Scientific Reports.
The giant panda is a rare case of a large carnivore that has become a vegetarian, says Wang Xiaoming, curator of the Department of Vertebrate Paleontology at the Natural History Museum in Los Angeles.
– The false thumb in Ailurarctos shows, for the first time, the probable timing and steps in the development of pandas and bamboo as food.
The fossil, which is around six million years old, shows that the panda already then had a greatly enlarged wrist bone and a developed “extra finger”, but that it was then longer and not bent as on today’s giant pandas. The bend and the fleshy pad around the thumb were later developed to carry the burden of the panda’s significant body weight, writes Scientific Reports.
The pandas exchanged their versatile protein-rich diet for nutrient-poor bamboo billions of years ago. Pandas eat up to 15 hours a day and can ingest 45 kilos of bamboo daily. Their diet is largely vegetarian but it happens that wild pandas hunt small animals.