| The lump of dung
New Delhi, Nov. 17: Fist-sized lumps of fossilised dinosaur dung scattered on a hillside about 150 km south of Nagpur have provided scientists the first evidence to show that dinosaurs sometimes ate grass.
The discovery by scientists in Chandigarh and Lucknow with a collaborator in Sweden will change long-standing beliefs about both the evolution of grasses on earth and the feeding habits of the dinosaurs.
Until now, plant-eating dinosaurs had been portrayed as feeding exclusively on trees because there had been no fossil evidence to show that grasses had even existed during the era of the dinosaurs.
The earliest grass fossils detected so far are about 56 million years old, a period long after the extinction of the dinosaurs 65 million years ago. But in tomorrow’s issue of the US journal Science, the Indian and Swedish researchers will report their discovery of undigested remains of grass in fossilised dinosaur dung between 65 and 70 million years old.
Studies of dinosaur dung in the past have revealed residues of trees such as conifers and cycads, micro-organisms and algae. “These grass residues tell us that herbivorous dinosaurs were indiscriminate eaters. They’d eat whatever vegetation they’d get,” said Vandana Prasad, a scientist at the Birbal Sahni Institute of Paleobotany in Lucknow who detected the microscopic grass residues called phytoliths in the dung.
“But the small amounts of grass residues in the fossilised dung clearly shows that grass was not the primary food of these dinosaurs,” Prasad said.
“This finding pushes back the antiquity of grass on earth,” said paleontologist Ashok Sahni, a co-author at Punjab University in Chandigarh who had picked up the dung samples during field trips to Pisdura, a village south of Nagpur.
“We’re lucky Pisdura has the world’s highest abundance of fossilised dinosaur dung,” Sahni said. Dung exposed to air is rapidly degraded by micro-organisms and vanishes in days. “Something must have happened there ' perhaps a flood ' to quickly bury the dung and allow it to fossilise,” he said.
Studies of the dung samples suggest that they belonged to Titanosaurids, large herbivorous dinosaurs that roamed in India at the time, Sahni said.
The Titanosaurids belonged to a family of giant to medium-sized dinosaurs ' typically about 20 metres in length ' whose fossils have been detected in lake and river sediments across Madhya Pradesh and Gujarat in the past.
Scientists elsewhere have hailed the new find as the first “unambiguous evidence” that grasses had become widespread much before the demise of the dinosaurs.
“These remarkable results will force reconsideration of many long-standing assumptions about grass evolution, dinosaurian ecology, and early plant-herbivore interactions,” scientists Dolores Piperno and Hans-Dieter Sues at the National Museum of Natural History in Washington DC said in a commentary in the same issue of Science.
The grass residues in dinosaur dung also solve a puzzle about primitive mammals called Gondwanatheres that existed in India, Madagascar and Argentina during the dinosaur era.
In 1997, Indian and US fossil-hunters had detected high-crowned teeth ' associated with grass-grazing ' in Gondwanathere fossils.
“With no grass to graze, we had no idea why these primitive mammals had high crowned teeth,” Sahni said.
“Now it appears very likely that the high crowned teeth in these mammals was a response to the evolution of grasses at about the same time,” Sahni said.
Grasses today cover 25 per cent of the earth’s surface and make up an important source of food for humans and animals.
Sahni said the site near Pisdura has hundreds of fossilised remains of dinosaur dung and turtles and other ancient animals. “I’m uncomfortable with giving away details of the exact location,” he said.
A few years ago, Sahni had conducted an expedition in which he had marked several sites near Jabalpur that had fossilised dinosaur eggs. “Over time, people carried them away, perhaps as souvenirs.”