Ancestral giant pandas had one feature in common with present-day pandas. The finding of fossils with thumbs confirms this. Pandas ate bamboo millions of years ago.
Not only that. Modern giant pandas have a wrist bone with a particular structure. It is similar to the thumb they use to manipulate bamboo. This is thought to have existed some 100,000 to 150,000 years ago.

Ancient trait
Xiaoming Wang and his colleagues at the Natural History Museum in Los Angeles made a discovery. They were examining the wrist bone of an ancestral panda. It dated from the late Miocene (about six to seven million years ago).
As published in Scientific Reports, this revealed something. They compared it to the wrist bones of modern giant pandas. In addition, it was compared to Indarctos arctoides. This is an ancient bear that lived nine million years ago. It might share the same common ancestor as giant pandas.
This thumb shape of the modern giant panda has the same shape as the wrist bone of the modern panda. But it was not that of ‘I. arctoides’, which was larger, broader and hooked.
This indicates that this thumb was present in the panda lineage for at least six million years. So, pandas eat bamboo millions of years ago.

Changes in shape
It is true that this characteristic is shared among species. However, there are some differences in their size and shape. The digit of the modern giant panda is significantly shorter than that of Ailurarctos relative to its body size. It has a hook at its end and a flattened outer surface.
The authors propose that the hook may help modern pandas to better grasp bamboo. And the shorter length and flattened surface may help distribute weight when walking. These limitations are there to support the weight. It may be why the giant panda’s thumb never evolved into a full digit.