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New Dinosaur Species Uncovered in Montana

Hillary Mayell
for National Geographic News
May 13, 2004
 
Scientists have uncovered a new species of dinosaur that roamed the long-gone Montana coastline around 150 million years ago.

Named Suuwassea emilieae, the 50-foot-long (15-meter-long) animal is a sauropod. Sauropods were plant-eating dinosaurs with long necks, whiplike tails, small heads, stubby legs, and huge bellies.


Montana has yielded many dinosaur fossils from the Cretaceous period (about 76 to 65 million years ago)—most famously the fierce meat-eater Tyrannosaurus rex and the rhinoceros look-alike Triceratops.

But Suuwassea was found in a geological formation that formed during the Jurassic period (about 150 million years ago). The landform, known as the Morrison formation, extends from New Mexico to Montana.

"No new sauropod has ever been described from Montana," said Peter Dodson, professor of anatomy at the University of Pennsylvania's School of Veterinary Medicine and the Department of Earth and Environmental Sciences. "We thought that all Morrison dinosaurs were known, that the book was closed. And here we find a new dinosaur and perhaps fauna just crying out to be studied," he said.

The new dinosaur is unusual in several ways. Sauropods found in the Morrison formation farther south, such as Diplodocus and Apatosaurus, are typically 70 to 90 feet (21 to 27 meters) long. At roughly 50 feet (15 meters), Suuwassea is small for a sauropod. In addition, it has two unexplained holes in its skull.

"For the past hundred years people thought all the animals in the Morrison formation were the same," said Jerry Harris, a doctoral candidate in the University of Pennsylvania's Department of Earth and Environmental Science. "Preliminary indications suggest something weird, something ecologically different, is going on up there. Whether it was climate or humidity or something else are questions that need to be looked at."

Dodson and Harris suggest that environmental conditions led to a very different kind of evolutionary pattern for dinosaurs in the southern and northern regions of the western United States.

Discovery

Dodson first learned of the Suuwassea fossil in September 1998. William Donawick, an emeritus professor of surgery at the University of Pennsylvania's School of Veterinary Medicine, had brought a bone back from a summer trip out West.

The bone preservation was quite good, so Dodson and his team of students and volunteers headed out to the site the following summer, expecting to find a fossil from the Cretaceous period.

When the fossil turned out to be in the Morrison formation, Dodson was initially disappointed.

"I thought, Well, look, people have been studying dinosaurs from the Morrison formation for well over a century. Nothing new is going to come out of the Morrison formation. This is probably just a garden variety Diplodocus."

Once Dodson returned to the laboratory, his outlook changed.

"When we started studying it, it quickly became apparent it was not the same-old, same-old. After 120 years the Morrison formation produced a new sauropod," he said.

Suuwassea, (pronounced SOO-ooh-AH-see-uh) means "the first thunder heard in spring" in the Native American Crow language. Emilieae is a reference to the late Emilie de Hellebranth, whose financial support funded the dinosaur's excavation. The team's findings appear in the current issue of the journal Acta Paleontologica Polonica.

Morrison Formation Revisited

The Morrison formation formed over a period of 6 to 8 million years beginning around 153 million years ago, as water flowing from mountains toward the sea deposited sediments. Prior to that time, the Sundance Sea, a saltwater extension of what is now the Arctic Ocean, extended down to southern Colorado.

The geological formation is particularly rich, containing numerous fossils of fish, frogs, salamanders, lizards, crocodiles, pterosaurs, small mammals, dinosaur eggs, and many dinosaurs, particularly sauropods. However, far fewer dinosaur fossils have been found in Montana than in southern sites in Colorado, New Mexico, Oklahoma, Utah, and Wyoming.

Morrison-formation dinosaurs were first described in 1877, in the southern part of the formation. Conditions in the formation's southern part are much different from those at the northern end.

It's very clear that, [just] as environmental conditions vary today as you sweep from Arizona to Montana, conditions certainly differed in the past, he said. "The southern part of the Morrison formation was much closer to the Equator and much drier than Montana, which was situated in the mid-latitudes in demonstrably wetter conditions during the Jurassic. There are coal swamps in the Morrison formation in Montana, which is a considerable contrast to sand dunes in the south."

In the past five years other scientists have reported similar findings of smaller sauropod fossils. However, none have been formally described, so it is unclear whether the fossils are of juveniles that would have attained a larger size upon reaching maturity, or, as in the case of Suuwassea, an "advanced teenager" of a species that is smaller than other sauropods of the Jurassic era.

"It's all still very preliminary, but beginning at the Big Horn Basin in northern Wyoming, things start to look a little bit different in terms of fauna," Harris said. "One of the extra holes in the skull is a mystery; it has only been seen before in two dinosaurs from Tanzania and one from South America. The two African dinosaurs are the same age as Suuwassea, and all three are related to the much larger Diplodocus and Apatosaurus."

Although evidence is mounting, it's too early to say whether the Morrison formation in Montana will turn out to have a highly distinctive dinosaur fauna, both researchers say.

But it's an exciting place and time to be a dinosaur paleontologist.

"The field of dinosaur paleontology is wide open, and people should expect the unexpected," said Dodson. "New discoveries are taking place all the time all over the world. The study of the Morrison formation in Montana is in its infancy."
 

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