"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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