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Diggin' For Dinosaurs - Red Gulch Trackway

Updated on March 30, 2010

In the dusty badlands in northern Wyoming is a formation known as the Sundance Formation: marine sediments deposited by the Sundance Sea, which submerged much of the Interior West during the period known as the middle Jurassic. It's not real easy to find the Sundance Formation as it's not exactly on many maps, but then again not a lot of places in Wyoming are easy to find. Instructions usually start out with "drive to the end of the paved road then…" When you finally do manage to get there, the sandstone flooring beneath your feet is speckled with dinosaur tracks so well preserved it looked as if the creatures had passed through only a few hours earlier.

They had actually passed through about 165 million years ago, a time when geologists had thought Wyoming was underwater, although the tracks of the landlubbing dinosaurs now prove that at least some of it wasn't. Researchers examining the tracks believe that the dinosaurs left them in the well-sorted sand of a tropical beach, perhaps an island or peninsula in the Sundance Sea. Then the sea level rose, submerging and later burying the tracks beneath layers of sand and mud. Shrimp burrowed down through the mud and into the sand holding the tracks. You can still see their finger-sized burrows around the footprints. Millions of years after the sand and mud had hardened into stone, present-day Wyoming rose in elevation and then erosion went to work, peeling away rocks and sediment until the beachfront of the middle Jurassic came into view once again. A culvert installed by the U.S. Bureau of Land Management, which oversees the site and the surrounding land, washed soil off the dinosaur tracks.

The Red Gulch Dinosaur Tracksite, as the BLM has named it, opened a window on what had been a blank chapter in the history of dinosaurs in North America. Few known fossils of any kind date to that period, when evolution was turning carnivorous dinosaurs from lightweights into the heavyweight champions that would come to rule the world. The Wyoming beachgoers were probably descendants of the first group of meat-eating dinosaurs, called the ceratosaurs, and ancestors of the heavyweight Allosaurus of the late Jurassic and - much later - the blood-chilling Tyrannosaurus rex. Of the thousands of footprints, some run in parallel tracks, while others crisscross. Judging from the size range of the prints, some scientists surmise that a family of dinosaurs passed by, perhaps to scavenge shellfish or carcasses along the shoreline.

They left their tracks when Wyoming was a decidedly different place. North America hung at about the same latitude as the Bahamas do today; gentle waves washed the beach. Inland, a scattered subtropical forest of ginkgoes, conifers, and palm-like evergreens called cycads probably lined the horizon.

You can check for the latest developments at the small, friendly museum in nearby Greybull. Scientists may yet give us a closer look at the dinosaurs that left only their tracks behind. Until then, you can follow in their very formidable footsteps.

Continued in: Diggin' For Dinosaurs - Egg Mountain

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