Dinosaurs' slow rise to dominance

 The dinosaurs might have gone out with a sudden bang, but their rise to dominance was a gradual ascent, not a sudden takeover, a study suggests. It shows that dinosaurs co-existed with a more primitive group of reptiles for millions of years before becoming the most common land animals on Earth. Experts had thought that once dinosaurs emerged, they swiftly replaced their relatives the dinosauromorphs. But the latest study in Science journal questions this idea. Dinosaurs first appeared around 230-220 million years ago, towards the end of the Triassic Period. By the beginning of the Jurassic Period, about 200 million years ago, they had become the dominant creatures on land - and would remain so for another 135 million years. But the reasons for their success - and why the dinosauromorphs faded away - are poorly understood. This is because the fossil record leading up to the Jurassic is relatively sparse.

Some researchers had assumed that dinosaurs were quick to supplant their more primitive relatives, the dinosauromorphs. In other words, they got a "lucky break". Dinosaurs may have either outcompeted their reptilian relatives for resources, or taken advantage of some catastrophe that devastated the Dinosauromorpha. But fossils described in the latest issue of Science suggest that if competition occurred, it was over a prolonged period, according to the team that unearthed them in the south-western US. The Late Triassic cache from Hayden Quarry, New Mexico, contains primitive dinosaurs and several species of dinosauromorph - including the newly identified species Dromomeron romeri.