Solving a Dinosaur Quandary with Modern Methods

 

 

 

PRESS RELEASE

August 2, 2013

Christine K. Trease, 435-613-5757: christine.trease@usu.edu

Solving a Dinosaur Quandary with Modern Methods

Ever since the discovery in 1909 of what is now called Dinosaur National Monument in 1909, people have wondered how the thousands of fossilized dinosaur bones accumulated.  In the first of its kind in-depth study, Utah State University Eastern paleontologist Kenneth Carpenter thinks he may finally have the answer.

“I approached this study differently than has been done in the past,” Carpenter said, “by including old archival photographs, letters, maps, and notebooks of Carnegie Museum paleontologist Earl Douglass.” Douglass is credited with the discovery of the site, which President Woodrow Wilson made into a National Monument in 1915. Laboring for 13 years, Douglass and a small team of men removed hundreds of tons of fossilized bones from near Vernal, Utah and shipped them east to the Carnegie Museum in Pittsburgh, Pennsylvania.. Carpenter noted that the most complete skeletons on display at the Carnegie Museum come from the large portion of the rocky hillside stripped away by Douglass. “What remains today is only a small portion of what was originally there,” Carpenter added. As a result, Carpenter believes that any study of the current quarry at the Monument Visitor Center can only tell a small part of the story.

Studying the sandstone that still adheres to some of the dinosaur bones Douglass had collected, as well as conducting field work in and around the Quarry Visitor Center, Carpenter realized that the dinosaur bones did not accumulate in a lazy meandering river as some geologists thought, but in a braided river like the Platte River in southern Nebraska. By using freely available software by the Army Corps of Engineers, Carpenter modeled on a computer the ancient river that ran through the quarry (the Quarry River) after the Platte River. Seeding the bottom of the virtual river with dinosaur bones, Carpenter was amazed that hundreds of bones scattered across a section of river bottom had a greater influence on the river than a single large dinosaur carcass. Carpenter also used a strain gauge to measure the amount of force needed to move weighed casts of various dinosaur bones along the river bottom. These results gave an estimate of the amount of water flow and the speed of the ancient river that would have been needed to move the bones downstream from their carcasses. 

Carpenter also concluded that the alignment of bones indicated the ancient river flowed south-southeast. This interpretation is based on a new map of the bone deposits created using Douglass’ original quarry map, supplemented with archival photographs of the excavations by Douglass and some taken later in the 1950s and 1960s by the National Park Service.

Previous studies concluded that the Quarry River flowed to the east, “But that was because people were not looking at the whole picture,” Carpenter said. “This interpretation of the type of river and the direction of flow is also supported by the elongate shape of underwater sand dunes like those seen in the Platte River.” These dunes preserved in the sandstone can be seen in the archival photographs, as well as in and around the Visitor Center Quarry. To see them, however, “you have to tilt your head to see the sandstone beds as if they were horizontal, the way they were deposited,” Carpenter added. Today, the beds are tipped at an angle of 70 degrees, which is what makes viewing the dinosaur bone deposit possible today in the new Visitor Center. The new building was opened in October, 2011, after 18 months of construction to replace the condemned fifty year-old visitor center. 

The new map Carpenter produced also showed that many of the bones seen today at the Monument belong to some of the incomplete skeletons removed by Douglass. The individual bones remaining in the Quarry had been pushed downstream of the main skeletons by the ancient Quarry River.  Carpenter thinks he has solved a mystery of why so many individual dinosaurs were found there. He noted that the bones and skeletons showed a similar pattern of bone scattering as that of as cattle killed during a prolonged drought in Africa. Animals that died early in the drought had a longer time to decay, and their bones were more scattered than animals that died later. The most likely scenario for the fossils in the Quarry is that the dinosaurs died at various times in a shrinking river, where they had sought refuge. Lacking sweat glands, they probably could not venture far from water. By depleting the vegetation within walking distance, many of the dinosaurs eventually starved. Their rotting bodies polluted the water, making the situation worse by making the animals drinking the water sick.

Evidence that some of the dinosaurs were sick is seen in the posture of some of the skeletons. The neck is pulled back over the body, and the legs pulled up close. Carpenter documents the same posture in a modern ostrich an hour after its death. .

“The quarry at Dinosaur National Monument is a remarkable snapshot of the prehistoric past. At least three different layers of bones are preserved and these show repeated episodes of drought 150 million years ago,” Carpenter concluded.

The study, History, sedimentology, and taphonomy of the Carnegie Quarry, Dinosaur National Monument, Utah, appears in the Annals of the Carnegie Museum.

 

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Prehistoric Museum

Utah State University – Eastern

155 East Main, Price, Utah 84501 USA

usueastern.edu/museum