…Science News reveals, they switched to their singular diet within human history – the blink of an eye in evolutionary terms:
Although modern giant pandas (Ailuropoda melanoleuca) chow almost exclusively on bamboo in the mountain forests of central China, these bears’ diet was much broader not so long ago, researchers report online January 31 in Current Biology. Analyses using chemical signatures from bones and teeth of both ancient and modern pandas indicate the bears’ hyperdependence on bamboo could have developed as recently as about 5,000 years ago. That’s roughly 2 million years later than previously assumed from molecular and paleontological data.
“It has been widely accepted that giant pandas have exclusively fed on bamboo for a long time, but our results show the opposite,” says Fuwen Wei, a wildlife ecologist at the Chinese Academy of Sciences’ Institute of Zoology in Beijing. “That made us excited.”
Wei and his colleagues compared the relative abundance of isotopes — atoms of the same element but with a different number of neutrons in the nucleus — in modern and fossil animals, including pandas. Animal diets contain different amounts of naturally occurring “heavy” and “light” isotopes of carbon, oxygen and nitrogen that are then incorporated into bones, hair, nails and teeth. The ratio in which the isotopes occur in the body depends on the animal’s position in the food chain and the climate in which the animal lives. Carnivores, for example, have a higher abundance of the heavy nitrogen-15 isotope because they almost exclusively consume meat, which is made of nitrogen-rich amino acids. And animals living in cold, dry places tend to consume a higher abundance of the heavy oxygen-18 isotope in what they eat and drink because the heavy isotope doesn’t evaporate from that environment as easily as it does in warm, wet conditions.
Because of their bamboo diet, modern pandas had much lower ratio of heavy-to-light nitrogen isotopes than other herbivores or carnivores living among the bears, Wei’s team found. But when isotopes in panda bone collagen from the mid-Holocene Epoch some 5,000 years ago were compared with those in other animal bones from the same time, pandas were indistinguishable from other herbivores, indicating the bears’ diet wasn’t as specialized as it is today.