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Mid-Jurassic Wyoming Trackways Found North American geography different than previously thought May 1, 1998

It has long been thought that most of North America was under a shallow sea during the mid-Jurassic period (also called the Dogger epoch). Recently, however, thousands of fossilized dinosaur tracks were found in 165 million year old mid-Jurassic sandstone sediment in Wyoming, USA.

The Sundance Sea was a shallow sea that covered most what is now Montana, Wyoming, Colorado, North and South Dakota, Utah and Nebraska during the mid-Jurassic period. The mid-Jurassic period was a time when the climate was mild and warm and there was no polar ice, making sea levels relatively high.

The supercontinent Pangaea about 190 million years ago

Beth Southwell, a research associate at the University of Wyoming Geological Museum in Laramie, said, "Middle Jurassic dinosaurs are known from England, Argentina, China, but we just haven't found dinosaurs in that age sediment in the United States. So that's why it's an important piece of information. This brings us an entirely new interpretation of this little piece of the world during that time, and it rewrites geology, too.''

These tracks were found in September, 1998 by Erik Kvale, who is from the area and is a geologist with the Indiana Geological Survey. They are located on 40 acres of public land south of Shell in the Big Horn Basin. Kvale said that some of the tracks were probably made by a 6-foot-tall theropod (a meat-eater) that walked on its rear legs. Many other species are represented in the trackways. Other scientists, including James Farlow, a trackways expert, will study the site soon.

RELATED LINKS
Information about the Jurassic period, including which dinosaurs have been found on which continents.

More information on trackways and other trace fossils.

What is a theropod dinosaur?

Other fossils found in North America.

Chart of geological time.

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