New fossil suggests dinosaurs not so fierce after all

(Illustration: John Maisano)

by bjs on 05. Oct, 2010 in Blog Entry

A new species of dinosaur discovered in Arizona suggests dinosaurs did not spread throughout the world by overpowering other species, but by taking advantage of a natural catastrophe that wiped out their competitors.

The new dinosaur, named Sarahsaurus, was studied by an international team of scientists, including Robert R. Reisz, professor and chair of biology at the University of Toronto Mississauga, Tim Rowe, professor of paleontology at the University of Texas at Austin's Jackson School of Geosciences and Hans-Dieter Sues, curator of vertebrate paleontology at the National Museum of Natural History in Washington, D.C. The results of this research appear in the online edition of the journal Proceedings of the Royal Society B on Oct. 6.

"Until recently, we've viewed dinosaurs as very successful animals that outcompeted other species wherever they went," says Reisz. "But this study puts dinosaurs in a very different light — that they were more opportunistic creatures that moved into North America only when a mass extinction event made eco-space available to them."

Conventional wisdom says that soon after dinosaurs originated in what is now South America, they rapidly spread out to every corner of the world, overwhelming all the animals in their path. Sarahsaurus challenges that view.

One of the five great mass extinction events in Earth's history happened at the end of the Triassic Period — about 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.

Sarahsaurus lived in what is now the state of Arizona about 190 million years ago, during the Early Jurassic Period. The remains show that it was a 4.3-metre-long bipedal plant-eating animal with a long neck and small head, and weighed about 113 kilograms. Sarahsaurus is a sauropodomorph dinosaur, a relatively small predecessor to the giant sauropods, the largest land animals in history.

A team of researchers and students led by Rowe discovered an articulated skeleton of this creature during a field trip in Arizona in 1997. The team excavated the site over three years, exposed the skeleton in the Austin lab, but was stymied in the research because little of the skull was preserved.

Reisz and Sues had been working on a sauropodomorph skull from the same area in Arizona, and were ready to submit a paper describing and naming this new dinosaur, when they realized that the skull they were examining and the skeleton discovered by Rowe were the remains of the same species. Working together, the three scientists were able to put together their findings from different parts of the skeleton, and discover its evolutionary significance.

Sarahsaurus is named in honor of Sarah Butler, an Austin philanthropist and long-time supporter of the arts and sciences, who raised funds for an interactive dinosaur exhibit at the Austin Nature and Science Center. Funding for the research was provided by the Jackson School of Geosciences and the National Science Foundation.

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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.

(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."