Allosaurus jimmadseni, a new species of allosaurus, attacks a juvenile sauropod/Todd Marshall
Despite the imagery of dental picks, small handheld whisk brooms or paint brushes, and chisels, sometimes paleontologists need something bigger to get a fossil out of the rock. Like explosives and helicopters.
“One of the things that we do when we have a skeleton that’s all articulated, or all the bones are all fitting togerher, we like to keep those bones togerher in that way so we can preserve the context and how they fit together," explained Dr. Mark Loewen, a University of Utah paleontologist. "This was a very, very large block. In fact, it was the largest dinosaur block of bones that had ever been taken out in the state of Utah up to that point."
The "block," wrapped in plaster and burlap, weighed about two tons and was more than 30 feet long.
"The end result was a block of dinosaur that was so heavy that it had to be lifted by a giant helicopter,” added Loewen, who along with Dr. Dan Chure, long the National Park Service paleontologist at Dinosaur National Monument in Utah, came away not only with a monstrous, nearly fully complete fossilized skeleton, but it was of a new species of allosaurus from the Late Jurassic Period.
According to the palentologists, the animal "had relatively long legs and tail, and long arms with three sharp claws."
But the realization that they had a new species in front of them didn't come overnight, or even over a number of weeks or months. The skeleton had been found in July 1990 by George Engelmann of the University of Nebraska. But there was a problem. Its skull was missing.
"We had everything from the very end of the neck that connects to the skull, to the very tip of the tail, missing just a few tail bones in the middle of the tail, and the skull," said Loewen last week. “So they dug back into the hill, still no skull. But one of the things about a lot of the bones in the Morrison Formation in Utah and other places throughout the West is that the bones have collected radioactive uranium over time. That is, as the fossilization process progresses, some of these radioactive elements that are just in the system are washing in and collecting in the bones.
"You can actually run a radiation (scan) across the bones and often you’ll get a peak. So a radiology technician at the University of Utah got the bright idea that he would make a portable radiation detector on wheels, and they would use it to search the surrounding areas to look for a hot zone that might be radioactive," the paleontologist continued. "Sure enough, it shows up as being radioactive in this one certain place, and about four or five feet away from the skeleton they actually found most of the skull, missing just the right side of the face."
Utah Is A Hotbed (no pun intended) For Fossilized Dinosaur Remains.
Straddling the Utah-Colorado border, the landscape holding Dinosaur National Monument came to the world’s attention in 1909 when Earl Douglass, a paleontologist at the Carnegie Museum in Pittsburgh, found eight dinosaur tailbones protruding from a sandstone hill. That was the first modern paleontological discovery at the site, which was designated as a national monument in 1915.
Today people come to Dinosaur to marvel at the Quarry Exhibit Hall, where you can gaze at a rock wall of approximately 1,500 fossilized dinosaur bones. Or you can take a world-class rafting trip down the Yampa or Green rivers that course through the monument.
What many visitors might not know, is that all the while paleontologists are continuing to search the monument's landscape for new specimens. It's a search, actually, that goes on throughout the state.
“We are very lucky in Utah. We have dinosaurs from the dawn of the dinosaurs all the way to the bitter end," said Loewen, a research associate at the Natural History Museum of Utah and associate professor in the Department of Geology and Geophysics at the University of Utah who along with Chure led the studies into this new allosaurus species. "One of the best records of the time of the dinosaurs in the United States, if not the world. Just from Grand Staircase-Escalante National Monument, myself and my colleagues, we’re hoping to name four new dinosaurs within this calendar year from those rocks. The hits just keep coming.”
A cast of the skeleton and skull of Allosaurus jimmadseni as it was discovered and now on exhibit at Dinosaur National Monument in Utah. The original skeleton was molded and cast before it was taken apart and prepared for study and research/NPS
It took more than a little work for Loewen and Chure to conclude that the bones they had studied belonged to a new species, which they named Allosaurus jimmadseni in honor of the late Utah State Paleontologist James H. Madsen Jr. It began to roam the Earth millions of years before its more famous successor, Allosaurus fragilis, the Utah state fossil.
“This animal lived in the Morrison Formation, in the central part of North America. And it’s an area that we associate with flood plains. Forests, of conifer and araucaria-type trees. There are ginkos, there are cycads, ferns, things like that," said Loewen. "Not a flowering plant, not a single blade of grass. But along the rivers you would have had this lush vegetation setting up a place for lots of different animals to live.
“At the same time, where this particular specimen is found, it seems to be an area in which it’s semi-arid, we have seasonal droughts. In fact, the famous quarry wall at Dinosaur National Monument represents a flash flood after a time of drought," he added. “This dinosaur was found in rocks that are a little bit older and represent an even more arid time in which braided streams would have been flowing through the landscape, maybe the uplands were a little drier than the wetter sides of the river. Sometimes the rivers were ephemeral, meaning they didn’t flow all year long."
Discovery
- Allosaurus jimmadseni can be found in a geologic unit known as the Salt Wash Member of the Morrison Formation and its equivalents exposed in Colorado, Wyoming, and Utah.
- The first specimen of Allosaurus jimmadseni was discovered in Dinosaur National Monument in Uintah County, near Vernal, Utah.
- Allosaurus jimmadseni was first discovered by George Engelmann of the University of Nebraska, Omaha on July 15, 1990 during a contracted paleontological inventory of the Morrison Formation of Dinosaur National Monument.
- Another specimen of Allosaurus jimmadseni known as “Big Al,” was found on land administered by the U.S. Department of the Interior’s Bureau of Land Management in Wyoming.
- Further specimens of Allosaurus jimmadseni have been subsequently recognized in the collections of various museums.
- Allosaurus jimmadseni specimens are permanently housed in the collections of Dinosaur National Monument, Utah; the Museum of the Rockies, Bozeman, Montana; the Saurier Museum of Aathal, Switzerland; the South Dakota School of Mines, Rapid City, South Dakota; Brigham Young University’s Museum of Paleontology, Provo, Utah; and the United States National Museum (Smithsonian) Washington D.C.
- These discoveries are the result of a continuing collaboration between the Natural History Museum of Utah, the National Park Service, and the Bureau of Land Management.
The late paleontologist James Madsen Jr assembles a composite skeleton of Allosaurus from the Clevland Lloyd Dinosaur Quarry/University of Utah.
Since the early 2000s, Loewen and Chure have worked to decipher just what animal they had before them.
"Through all of our research, we’ve looked at dinosaur bones all over the world belonging to allosaurus. Virtually every specimen that’s known to exist has been looked at by Dan or myself," said Loewen. "And we can confirm that there were only two species living in North America. The first one, Allosaurus jimadseni was later replaced by the second one, Allosaurus fragilis.”
Helping them in their search was the fact that Utah is home to the Cleveland Lloyd Dinosaur Quarry, now known as Jurassic National Monument, which is overseen by the U.S. Bureau of Land Management. That quarry contains thousands of fossilized dinosaur bones, and by far the greatest number -- 70 percent, according to Loewen -- are from Allosaurus fragilis.
“Fortunately, the Natural History Museum of Utah at the University of Utah has the world’s largest collection of allosaurus bones. Most of them coming from that Cleveland Llyod Dinosaur Quarry," Loewen said. "And so by comparing those specimens, which we all know are Allosaurus fragilis, to these new skeletons and to some other specimens that have come from other quarries around the Intermountain West, we were able to determine what is the variation within each of the two species, what differences really matter."
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The major difference, he explained, is that the earlier allosaurus species had a lighter skull, one not as powerful as that of its successor.
"If ever you’re going to go attack something, bite it with your head and shake it to death, Allosaurus fragilis has a better capability of doing that than Allosaurus jimmadseni," explained Loewen.
While many who watch movies about dinosaurs might think Tyrannosaurus rex was the king of meat eaters, the paleontologist noted that "within its ecosystem, both Allosaurus jimmadseni and Allosaurus fragilis are the dominant predator. They represent the lineage of theropod dinosaurs that’s going to continue on into the Cretaceous (when the T-Rex arrived), and until it goes extinct, allosaurs and its descendants are the dominant predators in every ecosystem in which they existed."
Loewen pointed out that without cooperative agreements between the university and the land managers, the National Park Service and Bureau of Land Management, these discoveries would be hard to achieve.
“Recognizing a new species of dinosaur in rocks that have been intensely investigated for over 150 years is an outstanding experience of discovery. Allosaurus jimmadseni is a great example of just how much more we have to learn about the world of dinosaurs. Many more exciting fossils await discovery in the Jurassic rocks of the American West,” said Chure in a statement.
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