Strong headed dinosaur may shatter assumptions

Brian HANDWERK- National Geographic News

Fossils of an intriguing new species with a powerful hand may reveal an edgier side of some supposedly peaceful, plant-munching dinosaurs, a new study says.

The discovery of Sarahsaurus aurifontanalis, which roamed North America about 190 million years ago, also boosts the idea that at least some dinosaurs became masters of their domain less by dominance than by opportunistic behaviour and a bit of good luck.

A remarkably complete Sarahsaurus skeleton, found in Arizona, shows that the early Jurassic herbivore was, at 14 feet (4.3 meters) long and 250 pounds (113 kilograms), smaller than its enormous sauropod cousins such as Apatosaurus, which arose later.

Like the sauropods - the largest animals to walk Earth - Sarahsaurus featured a long neck and small head. But the newly identified creature also boasted strong teeth and an unusual clawed hand, that, while only human size, was clearly built for enormous power and leverage, according to paleontologists.

“The dogma is that these animals were herbivores, but these hands and massive claws reopen the door to what they might have been doing with them,” study leader and a paleontologist at the University of Texas Tim Rowe said.

“Looking at the teeth, I think they could have eaten anything that they wanted, so they may have also been scavengers and not pure herbivores.”

Mass extinction prompted dinosaur migration

Beyond its bizarre appearance, the new species lends support to the relatively new view that dinosaurs came to dominate North America by being opportunistic, not necessarily by overpowering their competitors.

Dinosaurs, including Sarahsaurus, are generally believed to have originated in South America - then part of the ancient southern super continent Pangaea. But how and why they conquered the rest of the world is a matter of more debate.

By dating bones of Sarahsaurus and two other previously described species, scientists suggest that sauropod ancestors migrated to North America in several waves after the Triassic-Jurassic mass extinction killed off the dinosaurs’ North American competition 200 million years ago.

“It’s not as if they stormed the beaches,” Rowe noted.

“They had to wait for this natural catastrophe to empty the neighbourhood. So they were opportunists, not completely superior invaders.

The poignant story to me is that of recovery after a great extinction.”

The Sarahsaurus skeleton also spurred a reanalysis of existing fossil fragments in other species, Rowe said. For instance, the team now asserts that sauropods were completely absent in North America prior to the Triassic-Jurassic extinction that wiped out more than half of the planet’s species.