Pandas spend their days lazing around the mountains of China, giving conservationists sleepness nights, and munching down on a diet of essentially just bamboo shoots. However, these chilled-out bears were not always so fussy with their food.  

Up to 99 percent of the giant panda's diet is made up of bamboo, but this is a relatively recent development in their evolutionary history. According to a new study, pandas actually had a much more varied diet until just a few thousand years ago. 

Ancient ancestors of the panda were actually carnivorous, just as you’d expect from a bear. Even modern pandas still have the digestive system of a carnivore and can, occasionally, eat meat.

This new research shows that pandas did not have a straightforward switch from meat to bamboo millions of years ago. Instead, they kicked the meat and had a relatively varied diet of vegetation until at least 5,000 years ago. Then, for some obscure reason, they made another switch to a diet comprised almost exclusively of bamboo.

"It has been widely accepted that giant pandas have exclusively fed on bamboo for the last two million years," Fuwen Wei of the Chinese Academy of Sciences said in a statement. “Our results showed the opposite."

Reporting in the journal Currently Biology, scientists from the Academy dug into the diet of giant pandas through the ages by analyzing the composition of stable isotopes found in their teeth, hair, and bones. This nifty technique looks for different isotope ratios that can reveal insights into their habitat, environmental conditions, and diet.

After studying modern-day pandas, the team then turned to 12 ancient pandas collected from seven archaeological sites in southern China dating back to around 5,000 to 7,000 years ago. The results showed that modern and ancient pandas had a moderately different isotope balance from one another, suggesting differences in their diet.

Nevertheless, it still remains a mystery why pandas evolved their super-specialized limited diet of just bamboo. As you can imagine, bamboo is not the most nutritious of foodstuffs, so pandas have to eat between 12 to 38 kilograms (26 to 83 pounds) of the stuff each day.  As a result, they have a lower metabolic rate and a very lazy lifestyle.

To find out why pandas developed their taste for bamboo, the team are planning to look at even more panda fossils.

"We need to get more samples from different years after 5,000 years ago, but it is hard to do this," Dr Wei told ABC News. "Maybe it is a complicated [mix of] climate change, human encroachment and species competition for resources."