By William A. Hoesch and Steven A. Austin*
More than one thousand large fossil bones stand out in bold relief upon the rock wall at the Quarry Visitor Center in Utah’s Dinosaur National Monument. The first-time visitor is stunned by the magnitude of the exhibit. The quarry face (known best as “The Wall”) is surely the finest on-location dinosaur display in the world. This tangled knot of dinosaur bones represents a classic “mass burial” deposit, a trademark of what geologists call the Morrison Formation. Extending from New Mexico to Canada, the Morrison Formation covers about 700 thousand square miles and has been assigned to the Jurassic System. How did such a burial take place? We seek to find the real significance of the deposit at Dinosaur National Monument (DNM) and to dispel myths that our culture has delivered to us.
History of “The Wall”
On the heels of the American “dinosaur rush,” Earl Douglass in 1909 discovered eight articulated brontosaur tail vertebrae, standing out in relief from a sandstone ridge in eastern Utah. As digging began, he was shocked at how the skeletons turned up, literally one on top of another, and how the smaller stegosaurs “got in the way” of the prized sauropods.1 The sedimentary rock package containing the bones can be called the “Quarry sandstone,” a lens-shaped pebbly sandstone up to 50 feet in thickness that is exposed for 3,000 feet along the ridge outcrop. The Quarry sandstone is composed chiefly of chert and tuff grains.2 Volcanoes certainly supplied the tuff grains, and perhaps the chert pebbles as well. It is part of the overall 470-foot-thick Brushy Basin Member of the Morrison Formation that is dominantly mudstone. No less than a dozen well-articulated sauropods were excavated over a 15-year period ending in 1924. Probably none was more famous than the original “Brontosaurus” excavated by Douglass, that remains the most complete ever found, and that has stood in Pittsburgh’s Carnegie Museum since 1915. The Quarry Visitor Center was opened officially to the public in 1958. Popular caricatures about dinosaurs can now be compared with the stark reality of the deposit itself, in an exhibit that is without parallel in the world.
We had the chance to participate in a hands-on experience with the stuff of the Museum to excavate a recently discovered skeleton of a dinosaur who gut burrien 360 Million years ago.
Our specimen was too large to be taken out in one piece. It has to be divided into sections which are numbered serially as they are taken out. Each section is bandaged in strips of burlap dipped in plaster of Paris. After the plaster has set, the section is turned over and the bottom is sealed with burlap and plaster. The section is labeled with the appropriate number and the section and number are shown on the diagram.
When all of the sections have been bandaged and numbered they are packed in strong wooden boxes and shipped to the laboratory.
The work in the laboratory is more involved than that in the field, and extreme care must be exercised to be sure that the bones will be undamaged. In most cases the bones have been broken by natural causes as they lay in the rock before discovery. All the pieces of each bone must be thoroughly cleaned and securely cemented together. 8 This is a very time-consuming task and for a large dinosaur like Apatosaurus it requires 3 men 4 or 5 years to complete the task.