Dinosaurs Scavenged and Cannibalized at a Jurassic Site in Colorado
The Mygatt-Moore Quarry in the McInnis Canyons National Conservation Area of Western Colorado is barren and rocky, but turn the clocks back 150 million years to the Upper Jurassic and you would find a lush riparian paradise exploding with plant and animal life. Those animals? Dinosaurs. But this wet and rich environment could occasionally turn bone dry. When that happened, rich topsoils cracked like dry skin, plants shriveled, grazers move on or died off, and predators turned to scavenging or even cannibalism. In short, it was chaos.
Researchers led by Stephanie K. Drumheller, an adjunct assistant professor in paleontology at the University of Tennessee, painted this vivid picture in a report published to the journal PLoS ONE after examining thousands of fossils collected from the Mygatt-Moore Quarry. They found something on the bones that surprised them: tooth marks, lots of tooth marks, particularly from a class of dinosaurs called theropods, which included carnivores like Dilophosaurus, Megalosaurus, and the infamous Tyrannosaurus.
"Theropod bite marks are particularly rare, suggesting that members of this clade might not often focus on bone as a resource, instead preferentially targeting softer tissues," the researchers wrote.
By far the most predominant theropod at Mygatt-Moore was Allosaurus, which was essentially a slightly smaller Tyrannosaurus rex. Their bones litter the site, and their bite marks are prevalent on a significant number of bones.
Curiously, Allosaurus bites disfigured a surprising number of less nutritious body parts like skulls, limbs, and feet. This suggests that there was significant scavenging at the site, where the dinosaurs would pick through the remnants of decaying carcasses after the bulk of the muscle and fat had been stripped away.
Even more curious, there were Allosaurus bite parks present on many Allosaurus skeletons, suggesting intense, violent competition followed by cannibalism. This would be the first known example of Allosaurus cannibalism in the fossil record, the researchers say.
The immense abundance of carbonized plant matter and dinosaur bones at Mygatt-Moore suggests it was once a verdant environment that supported lots of herbivores and carnivores, but the significant evidence of scavenging presented in the current study hints that this booming ecosystem could, at times, go bust, perhaps due to sustained drought, transforming a prehistoric haven into a desperate hell.
Source: Drumheller SK, McHugh JB, Kane M, Riedel A, D’Amore DC (2020) High frequencies of theropod bite marks provide evidence for feeding, scavenging, and possible cannibalism in a stressed Late Jurassic ecosystem. PLoS ONE 15(5): e0233115. https://doi.org/10.1371/journal.pone.0233115