For a bear with a carnivorous shard, modern pandas carved a bizarre place in a plant eating the world.
Today's giant pandas (Ailuropoda melanoleuca) live in the chilly mountains of southwest China where they spend their days almost exclusively eating bamboo.
But their ancient ancestors living at least 5000 years ago had a much more varied diet of bamboo and other plants, according to a new study published today in Current Biology.
"We do not know exactly what plants are, but their eating was similar to herbivores such as deer during this time," said lead author Fuwen Wei of the Chinese Academy of Sciences.
Modern pandas have distinct teeth, skulls and muscles, and a specialized thumb that crushes each day and crushes between 12 and 38 kilograms of bamboo.
But they have a small intestine and microbiology that is not suitable for digestion of plant material, suggesting that they originally developed from an extinct carnivorous ancestor.
Previous fossil evidence suggests that the family of pandas began to breed plants about 2 million years ago.
At that time, the ancestors of today's pandas lived in a far wider area of China and Southeast Asia; from Beijing to the north to Myanmar, northern Vietnam, Laos and Thailand in the south.
In order to understand the diet of extinct species, Dr. Wei and his colleagues analyzed the chemical signatures in the bones of 12 ancient pandas that lived until about 5000 years ago.
They compared this with the carbon and nitrogen ratios of collagen and teeth from modern pandas and other mammals in the same area gathered between 1970 and 2000.
The analysis showed that all types of panda lived on pure plant diet C3 – the most common group of plants typical of forests – for the last 2 million years.
But nitrogen isotopes in the bones and teeth of modern and ancient groups were distinctly different.
"Modern panda, which feeds only bamboo, had very low nitrogen isotopes, but ancient pandas had very high levels as herbivores," said Dr. Wei.
This suggested that ancient pandas had a much more complex diet than today.
It also indicated that they could live in more diverse locations, such as subtropical zones and forest springs, and backed archaeological records from southern and northern China where fossils were found.
Move to 99 percent bamboo
It is unclear when or why huge pandas have become almost exclusively bamboo firs – even with strange lawns or meat offered in the wild.
The first description of their bamboo diet is only a few hundred years, but scientists assume that the shift occurred 5000 years ago.
To find out, they hope they will study other pandas fossils.
"We need to get more samples from different years 5,000 years ago, but it's hard to do it," said Dr. Wei.
Dr. Wei said that it is possible that the switch was created as an adaptation to a shrinking range, "but we do not know the exact reasons".
"Maybe it's complicated [mix of] climate change, human intervention, and generational competition for resources, "said Dr. Wei.
Bamboo provides pandas with a lasting source of food that can be used by very few other animals, said David Raubenheimer of the University of Sydney, who did not participate in the study, but had previously studied the animal's eating habits.
Not all bamboos are the same.
"It's not a question of just eating them," said Professor Raubenheimer.
"We have received evidence that they carefully choose between the different options available from the sea [of bamboo] in which they live. "
This evidence suggests that pandas must migrate to choose a bamboo that meets their seasonal nutritional needs.
"They migrate in the summer to get a high protein intake, then migrate down in the winter to sites that provide low protein levels but a high calcium content needed for reproduction," said Professor Raubenheimer.
"Probably the precursor was not necessary because they had a wider diet in any environment because they had proteins and calcium in some foods."
Today's huge pandas, which are listed as vulnerable, live on different species of bamboo scattered over 20 isolated patches in six mountain ranges in the provinces of Sichuan, Shaanxi and Gansu.
In a world of shrinking natural habitats, a blessing eater is both a blessing and a curse.