Until now "it has been assumed that dinosaurs lived in virtually grass-free ecosystems," said Caroline A.E. Strömberg.
Strömberg is a coauthor of the paper and a researcher at the Swedish Museum of Natural History in Stockholm.
Grasses exist today on every continent except Antarctica, and many animalsincluding humansdepend on them for food.
Scientists have long believed that the now ubiquitous plants first began to spread and diversify some 70 to 60 million years ago.
Fossil evidence had suggested that grasses evolved along with early plant-eating mammals. Hoofed animals with high-crowned teeth suitable for chewing grass first began to appear about 25 million years ago.
But the grass minerals in the Indian coprolites were much older than the hoofed mammals and were already diverse. Five different species were evident, which means that grasses likely diversified substantially before the end of the late Cretaceous.
The researchers believe that various species of grass had spread before India became geographically isolated from other continents about 125 million years ago.
Along with the grass minerals, the coprolites contained evidence of other plants, including broad-leaved flowering plants, palms, and conifers.
The grasses formed a relatively low proportion of the total plant material found in the coprolites, which indicates that they did not form the major part of the titanosaurs' diet.
Still, the inclusion of grass in the dinos' diets might mean that widespread occurance of grasses contributed to the titanosaurs' success, said Kenneth Carpenter, a curator at the Denver Museum of Nature and Science.
"Cropping low vegetation, such as grass, may explain why some of these titanosaurs have very wide mouths reminiscent of the wide mouth of the grass-feeding hippo and white rhino," he said.
Mammals called gondwanatherians also lived during the late Cretaceous and might have been more dependent on grasses for food.
The early mammals had high-crowned teeth, which puzzled paleontologists, because it was thought that grasses were quite rare at this time.
Some researchers felt the teeth must have evolved for digging or gnawing on wood.
"Our study shows that grasses existed in India simultaneously with the gondwanatherians," Strömberg said.
"These remarkable results will force reconsideration of many long-standing assumptions about grass evolution, dinosaurian ecology, and early plant-herbivore interactions," Piperno and Sues wrote in their review.
But, she added, "I think it is fair to say that the classic hypothesis is still that [hoofed mammals] evolved [high-crowned teeth] during the Tertiary, primarily in response to the spread of grasslands."
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