As you approach Dinosaur National Monument—America’s most celebrated dinosaur graveyard—you can’t miss all the prehistoric beasts dotting the roadside. To the east, tail-dragging, misshapen dinosaur statues that would make a paleontologist cringe menace the small town of Dinosaur, Colorado. To the west, monsters stalk Highway 40 from downtown Vernal, Utah to the entrance of the park. A miniature “Brontosaurus” stands behind a chain link fence at a Sinclair gas station, and a lumpy Diplodocus with a goofy smile greets visitors turning off the highway.
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Actual dinosaurs were discovered here a century ago. Starting in 1909, fossil hound Earl Douglass found fantastic remains of gigantic dinosaurs, and his timing was perfect. The great natural history museums of the East—in New York, Pittsburgh, Chicago and Washington, D.C.—were competing to acquire the biggest and best dinosaur specimens in a great Jurassic dinosaur rush. Douglass uncovered fossils of Apatosaurus, Diplodocus, Barosaurus, Allosaurus, Ceratosaurus, Stegosaurus and more, and his finds helped fill collections.
Unlike many other bone hunters, though, Douglass did not excavate all the fossils he could. In a letter to Charles Doolittle Walcott, then the Secretary of the Smithsonian Institution, he wrote: “I hope that the Government, for the benefit of science and the people, will uncover a large area, leave the bones and skeletons in relief and house them. It would make one of the most astounding and instructive sights imaginable.”
He got his wish. In 1915, Douglass’ field area was turned into a national monument. Its highlight has been a particularly rich deposit of dinosaur bones, known simply as the quarry wall, that was protected by an intricate glass building since 1958. Millions of visitors watched paleontologists pick away at the 150-million-year-old rock face to expose the full extent of the mass grave. But in 2006, the structure was judged unstable and the area was closed. This past fall, a new observation center was opened to the public, and visitors can now once again see the nation’s most productive Jurassic park.
But the fossil riches of Dinosaur National Monument extend beyond the quarry wall, and paleontologists continue to make new discoveries that Douglass and his contemporaries could only have imagined. Last summer I hiked out to the field sites and visited some of the labs where the monument’s prehistory is being revealed.
Randall Irmis, the Natural History Museum of Utah’s paleontology curator, was leading a team studying a curved cross-section of rock striped with reds, browns and yellows called the Racetrack. I joined them for a week and a half to prospect for fossils, watching out for rattlesnakes and picking itchy cheatgrass out of my socks as I followed the fossil hunters along the steep exposures. The rock is about 200 million to 220 million years old, a period when the dinosaur dynasty was on the rise.
No one knew what might be in these rocks; this was the first systematic survey. The team found numerous burrows of small invertebrates that lived in sediments of ancient lakes, some vertebrate bones and, most intriguingly, some distinctive three-toed tracks that could only have been made by dinosaurs. The shapes and claw impressions were sure signs that small predatory dinosaurs once roamed the area.
Traces of prehistoric life also abound in a roughly 185-million-year-old layer of pockmarked sandstone, including footprints left by some of our own distant cousins. On one cloudy morning, park paleontologist Dan Chure, paleontologist George Engelmann of the University of Nebraska, Omaha and I hopped into an SUV and bounced up a pair of runnels towards a wide slab of tilted rock covered in nickel-size divots. At midday it would look like just another bit of stone on the wall of a small, shrub-filled gorge, but as the clouds burned off and the angled light of the rising sun shone on it, more than 300 small, rounded footprints stood out in relief against their sandstone bed. A few still have the scratches of tiny prehistoric claws. Chure’s discovery of the site in 2009 caused the paleontologist to rethink what might be found in the Early Jurassic rock of the monument and what the fossils might look like. After scrambling up the slab to point out the trackways, Chure stood on the footprints of his ancient kin and said: “When we saw this, we said ‘Yeah, we have to expand our search image a bit.’”
The tracks were most likely made by therapsids, archaic forerunners of mammals. The creatures were covered with fur and had teeth in a variety of different shapes, characteristics that set therapsids apart from reptiles. The creatures shuffled up and down massive sand dunes during a time when the area looked like the Gobi Desert. The fact that so many small creatures left tracks hints at the ancient ecology—they could not have survived in a totally dry desert. “There’s a good possibility there was some kind of water nearby” in the form of a lake or other oasis, Engelmann said. Since the slab is far too large to extract, Chure and Engelmann plan to pour latex over the rock and make a peel of all the tiny footprints to study how the hairy little critters moved around.
During the time that therapsids were skittering over ancient dunes, a group of more than 20 predatory theropod dinosaurs died during a drought. If they had held out a little longer they might have survived, for water soon covered their bodies, and their carcasses become preserved in a temporary pond. Three years ago, on the last day of the summer field season, Chure and Engelmann found the theropod bones just outside the park boundary and, with their Brigham Young University (BYU) colleague Brooks Britt, collected as many bits and pieces as possible.