updated 11/17/2005 2:04:26 PM ET 2005-11-17T19:04:26

Dinosaurs grazed on grass?

Scientists have discovered the first evidence that when some dipped their long necks, they pulled up grass along with ferns and other greenery — a big surprise, since grasses were thought to have evolved after dinosaurs died off.

Fossilized dung tells the story: The most prominent plant-eating dinosaurs were digesting different varieties of grass at least 65 million years ago, researchers report in Friday’s edition of the journal Science. That’s roughly 10 million years earlier than the date of the earliest grass fossils.

A team of paleobotanists from India and Sweden analyzed the dung — the scientific term is coprolites — found in central India. It was from sauropods, those behemoths with long necks and tails and small heads.

The coprolites contained microscopic particles of silica called phytoliths, which form inside plant cells in distinctive patterns that essentially act as a signature.

Amid the palms and conifers that sauropods already were known to munch were numerous phytoliths certain to have come from the grass family. They included relatives of rice and bamboo and forage-type grasses, report lead researchers Vandana Prasad of India’s Birbal Sahni Institute of Palaeobotany and Caroline Stromberg of the Swedish Museum of Natural History.

Grasses must have originated considerably earlier, well over 80 million years ago, for such a wide variety to have evolved and spread to the Indian subcontinent by the waning of the dinosaur age, Prasad and Stromberg concluded.

“These remarkable results will force reconsideration of many long-standing assumptions” about dinosaur ecology, wrote Dolores Piperno and Hans-Dieter Sues of the Smithsonian Institution’s National Museum of Natural History in an accompanying review.

But beyond the great curiosity about dinosaur life, the discovery has implications about the coevolution of this huge plant family — there are about 10,000 separate grass species — with other plant-eaters, Piperno explained.

Grass wasn’t a big part of the dino diet, the new study found. After all, they didn’t have the grinding-style teeth good for grazing.

But a mysterious early mammal that roamed among the dinosaurs had more suitable teeth, raising the possibility of an early adaptation to abrasive grasses, the researchers note.

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