Scientists Excavate Ancient Pit Filled with Dinosaur Bones

The Question Remains: What Killed these Ancient Predators?

Utah is known for its preservation of dinosaur fossils. A particular site that stands out is Cleveland-Lloyd dinosaur quarry, a national landmark that is 148 million years old. For decades, scientists have studied this region to understand the Jurassic dinosaur fossils that have been left behind. In particular, they want to understand why the quarry is so packed with carnivorous bones.

The very first excavation at Cleveland-Lloyd occurred in 1928 and was led by scientists from the University of Utah. Ten years later, William Lee Stokes, who studied at Princeton University, led an excavation at the site. Eventually he came to be a chief authority at the bone bed. Many years later, paleontologists continued to excavate the quarry and discovered that more than 75% of the bones found there came from a dinosaur called Allosaurus fragilis . This species was able to grow up to 30 feet long, had three large curved claws on each hand, and had sharp teeth. Along with Allosaurus, bones from other dinosaurs like Marshosarus and Stokesaurus also appeared at the quarry, but in significantly fewer amounts.

Initial hypotheses for the dense concentration of dinosaur fossils in the area involved the idea of a predator trap. Scientists hypothesized that dinosaurs in search of water accidentally stumbled into a drying lake bed. Slowly the dinosaurs sank into the mud and could not escape. Scientists believe this cycle of dinosaurs sinking and dying happened repeatedly over many years. The Allosaurus would come and most likely feast on the trapped dinosaurs, and get stuck themselves, therefore making Allosaurus a large part of the quarry.

Although this is a plausible hypothesis, new evidence has uncovered more information and helped develop alternative hypotheses that make more sense. Specifically, the use of photogrammetry has allowed researchers to map the quarry area in 3-D. This research method permits scientists to study whether the bones appeared in the area over time or during a single event. The evidence points that there were no signs of sticky substance that would’ve trapped the dinosaurs.

New data support the hypothesis that toxic water in the quarry was a potential factor which killed the dinosaurs and caused the accumulation of their bones. Despite these new insights, details about this hypothesis are still being studied and waiting to be published. They have recently uncovered a new section of the quarry which they are going to start excavating soon.

The history of the Cleveland-Lloyd quarry still remains a mystery. Many of the bones are waiting to be excavated. By studying this region, scientists continue to deepen their understanding of the Jurassic period and reconstruct what happened there during that mysterious time. Possibly, in the future we could have the true explanation of what happened in the quarry.

[Sources: Smithsonian ; Bureau of Land Management ]

Awesome article! keep it up. – Brandon , madison (2021-07-20 13:07)
Really good writing, Ellie. Fascinating topic and you did a very nice job summarizing the facts. – Shoko Miyagi , UW-Madison (2021-07-20 13:34)