Few scientists had ever thought that dinosaurs grazed, because there was no evidence that grasses existed that long ago.
They believed that the grinding teeth found in some dinosaur fossils were used for munching other plant matter, perhaps trees, like modern beavers chew on today.
So when Caroline Stromberg of the Swedish Museum of Natural History received photographs of fossilised dinosaur droppings from Vandana Prasad of the Birbal Sahni Institute of Palaeobotany in Lucknow, India, she hardly expected to see
pieces of grass in them.
"I was very surprised to see them and even more surprised to see that there was quite a diversity," Stromberg said in a telephone interview. "It was shocking but very exciting."
Fossils of rodents who may have
grazed have been found
Prasad's team had been analysing 65-million-year-old coprolites - fossilised droppings - that they believe were left by giant plant-eating sauropod dinosaurs.
They found the expected plant matter - cycads and conifers and other plants known to have grown during the Cretaceous
Prasad's team sent some photographs and then samples to Stromberg, who spotted tiny silica structures called phytoliths.
"It's indisputable that these are from grasses. The shape of these phytoliths indicate that they are from grasses," said Dolores Piperno, a paleobotanist at Washington's Smithsonian Institution who reviewed the study, published in the journal Science.
"It was shocking but very exciting"
Swedish Museum of Natural
Not only that, but they clearly came from very different species of grass.
"It's certainly the first unambiguous evidence that grasses had originated by the late Cretaceous period and also that they had considerably diversified," Piperno said in a telephone interview.
That suggests that grasses had been around for a long time even back then.
Stromberg said some of the grass phytoliths look like those found in modern day rice.
"One could imagine that at least some of them lived in rather humid areas perhaps, probably forest-living grasses," she said in a telephone interview.
"Those tend to have broader leaves than the grasses in your lawn, for example. They are not grasses that you normally associate with open habitat like the prairie. A guess would be that they looked more like herbaceous bamboos, but it's very much a guess."
The only other hints of such old grasses had come from pollen fossils, which are much more difficult to identify.
The findings also suggest that early mammals may have grazed. The few fossils that have been found from the rodent-like mammals that lived alongside dinosaurs have mystified scientists - especially the teeth.
"They look very much like teeth of animals that grazed today like horses, but much smaller of course," Stromberg said.
"This may explain it."