Dinosaurian Beginnings

Till recently, the events that led to dinosaurs’ dominance of the planet had remained unknown.

Before the dinosaurs ruled earth, there were the crurotarsans. What survives of the lineage today are crocodiles, alligators and gharials. The era of crurotarsans was an age when crocodilians dominated the earth and the waters. Most were over 10 feet long with an elongated snout, thick neck and a body protected by two or more rows of armoured plates. Some reached lengths of 40 feet.

For 50 million years after the Permian-Triassic extinction 251 million years ago (the greatest mass extinction in the history of the planet), crurotarsans were the dominant vertebrates. During this period, the dinosaurs were overshadowed by their fellow reptiles and rarely exceeded 10 feet in length. Then 200 million years ago, they got lucky. In a study published in the Proceedings of the National Academy of Sciences, Brown University paleobiologist Jessica Whiteside and her team have shown what led to the demise of crurotarsans. “The big thing is many people have heard why dinosaurs went extinct,” said Whiteside, “but the question why they came to be is much more exciting.” At the time, all the land on the planet was consolidated in one supercontinent Pangea. As the North American and the African plates started drifting apart, the giant continent split, creating the basin we now know as the Atlantic Ocean. For the next 600,000 years, outpourings of lava covered almost 9 million sq km of the basin, a feature scientists refer to as the Central Atlantic Magmatic Province (Camp).

The researchers studied areas of the Camp. The fossils they found in the Hartford and Newark areas of the northeast US reveal that almost half the plant species went extinct during this phase. They also found that after the lava flows, the ‘fossil record for crurotarsans is nearly completely gone.’ The disappearance of crurotarsans left the earth free for their main competitors, the early therapods—a category including all meat-eating dinosaurs from velociraptors to Tyrannosaurus rex.

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Hartosh Singh Bal