ONE of the oldest mistakes in the prehistoric book has turned out not to be a mistake after all. Artists鈥� impressions of dinosaurs grazing on grassy plains were considered as bad as depictions of them cavorting with cavemen, but an examination of fossilised dung has shown that the prehistoric beasts did indeed eat grass.
Palaeobotanists had thought that grasses were not common until long after the dinosaurs died out at the end of the Cretaceous period 65 million years ago. But it now seems that the last massive plant-eating dinosaurs munched on at least five different types of grass.
The key evidence comes from silica crystals called phytoliths, which grow inside plant cells and can survive digestion and fossilisation. These appeared in fossil dung collected in Pisdura, near Nagpur in central India. Recognising that some of the phytoliths had the distinctive shapes found only in grasses 鈥渨as a complete shock鈥�, says team member Caroline Str枚mberg of the Swedish Museum of Natural History in Stockholm.
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At 65 to 70 million years old, the crystals are about as old as fossilised pollen samples found in India, South America and north Africa, which are the only other evidence of grass from that far back. As all grass pollen looks the same, researchers had thought these fossils came from a very primitive grass or an early relative.
The Indian phytoliths are more distinctive, however, and have been linked to five less primitive species of grass, indicating that grasses diversified before the dinosaurs鈥� demise (Science, vol 310, p 1177). The researchers now think the first grasses may have evolved more than 100 million years ago.
The dating seems to be confirmed by the fossil鈥檚 location below well-known deposits from the end of the Cretaceous. Although the claims are surprising, grass-evolution researcher Elizabeth Kellogg of the University of Missouri in St Louis says she agrees with the team鈥檚 identifications.
The only dinosaur bones found nearby are those of massive long-necked plant-eaters called titanosaurs, so Str枚mberg鈥檚 group thinks the droppings are theirs. If that is true, they were not fussy eaters. The grass was only a small part of their diet, which included other flowering plants, cycads and conifers.
