Dinosaur with Super Strong Hands Found in Arizona

A dinosaur recently unearthed in Arizona possessed incredibly strong hands, according to a study published today in the journal Proceedings of the Royal Society B.

The new dinosaur, named Sarahsaurus aurifontanalis (after the philanthropist Sarah Butler), was a sauropodomorph, a small but closely related ancestor to sauropods, the largest land animals in history. Its hands were probably more powerful and dexterous than those for any other known sauropodorph, paleontologists believe.

(Illustration: John Maisano)

(Skeletal reconstruction; Credit: Nicola Wong Ken)

(CT scan of the left hand of Sarahsaurus; Credit: Matt Colbert and Tim Rowe)

It remains a mystery as to why the hands of Sarahsaurus were relatively tiny and yet so strong.

"We've never found anything like this in western North America," said Tim Rowe, who led the project and is a professor of paleontology at The University of Texas at Austin's Jackson School of Geosciences. "Its hand is smaller than my hand, but if you line the base of the thumbs up, this small hand is much more powerfully built than my hand and it has these big claws. It's a very strange animal. It's doing something with its hands that involved great strength and power, but we don't know what."

What is known is that Sarahsaurus lived about 190 million years ago during the Early Jurassic Period. The dino was 14 feet long and weighed about 250 pounds. It possessed physical traits usually associated with gigantic animals. For example, its thigh bones were long and straight like pillars, yet were not much larger than a human's thigh bones. Sarahsaurus shows that sauropodmorphs started out small and later evolved to a very large size.

(Cladogram indicating how Sarahsaurus is related to other dinosaurs; Credit: Tim Rowe)

The new species also suggests dinosaurs did not spread throughout the world by overpowering other dinos, but by taking advantage of a natural catastrophe that wiped out their competitors, according to Rowe and his colleagues Hans-Dieter Sues and Robert R. Reisz.

One of the five great mass extinction events in Earth's history happened at the end of the Triassic Period 200 million years ago, wiping out many of the potential competitors to dinosaurs. Evidence from Sarahsaurus and two other early sauropodomorphs suggests that each migrated into North America in separate waves long after the extinction and that no such dinosaurs migrated there before the extinction.

(Students carrying jacketed Sarahsaurus specimen in Arizona; Credit: Tim Rowe)

"We used to think of dinosaurs as fierce creatures that outcompeted everyone else," said Rowe. "Now we're starting to see that's not really the case. They were humbler, more opportunistic creatures. They didn't invade the neighborhood. They waited for the residents to leave and when no one was watching, they moved in."

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