Palaeontologists Sanghamitra Ray and Debarati Mukherjee at the IIT, Kharagpur, have found a rich storehouse of hundreds of fossilised bones from about 220 million years ago. They call it an upper triassic bonebed.
The bonebed, located near Tiki village about 250km southeast of Jabalpur, has yielded 617 fragments of a group of plant-eating reptiles called rhynchosaurs that reigned before the rise of the dinosaurs. The remains include fragments of skulls, pelvic bones, ribs, upper and lower jaw bones, limb and tail bones, from what the scientists estimate would have been 13 to 20 individual rhynchosaurs.
Rhynchosaur fossils have been reported in the past from Canada, Madagascar, South Africa, the US, and southern India, but Tiki has thrown up the first evidence that rhynchosaurs moved in herds, much like modern-day zebras.
“This is the largest collection of rhynchosaurs from a single locality in India,” said Ray, assistant professor at the IIT Kharagpur’s geology and geophysics department. “There are skeletal remains of juveniles, young, adults, and very old adults.”
“This gathering of the young and old suggests for the first time that rhynchosaurs lived in herds,” Ray told The Telegraph. “There has been no evidence so far to support herding in rhynchosaurs from elsewhere in the world.”
Ray and Mukherjee, a senior research fellow, have used calcium and iron coatings on the fossilised bones and the geological layers where they were found to piece together the likely scenario under which the reptiles died and their bodies fossilised.
“We’ve tried to understand the sequence of events from the deaths to the process of fossilisation,” said Mukherjee. Their findings appear this week in the international journal Paleogeography, Paleoclimatology, Paleoecology.
India at the time was in the southern hemisphere, a part of the supercontinent called Gondwanaland. Independent paleoclimate studies suggest that Tiki region at the time was extremely hot and arid, but had high seasonal rainfall.
The IIT researchers believe the rhynchosaurs had gathered near a river bank in search of water when mud and river water from a flash flood drowned them. When the water receded, their bodies were exposed.
“The calcium and the iron coatings on the bones show prolonged exposure to air,” said Mukherjee. During this exposure, the soft tissues decomposed and some of the bones separated or broke apart. Subsequent exposure to low-velocity water currents from the nearby river would have led to segregation of the skeletal remains until they were again buried under mud from a fresh flood, leading to eventual fossilisation.
Their study also reconstructs the ancient ecosystem, showing that the food pyramid in the Tiki region during the upper trassic era was similar to the present-day food pyramid with plants at the bottom, herbivores above plants, and carnivores at the top.
“The relative abundance of the Tiki fossils shows similar patterns,” said Ray.
The most abundant fossils in the bonebed are plants, including tree-trunks, followed in decreasing order of their abundance, the fossils of the plant-eating rhynchosaurs, and carnivorous reptiles called phytosaurs and archosaurs.
Author: G.S. Mudur | Source: The Telegraph/India [March 20, 2012]