(CN) — New evidence suggests a group of dinosaurs that inhabited what is now Colorado would turn to scavenging and possibly even cannibalism in response to environmental stresses that dried up food resources.
In a study published Wednesday in the journal PLOS ONE, lead author and professor of paleontology Stephanie Drumheller of the University of Tennessee, Knoxville, and her team reveal what they learned by studying tooth marks on dinosaur bones.
Archaeologists often examine tooth marks on the bones of excavated fossils to determine dinosaurs’ feeding habits, but such marks inflicted by carnivorous dinosaurs — theropods — are rarely found. In fact, Drumheller noted that in previous, large-scale surveys of museum collections, theropod bite marks were found on less than 5% of the bones, likely because they did not actively seek out the bone as a food resource.
One dig site, known as the Mygatt-Moore Quarry of Colorado, harbors a gold mine of fossils dating back to the late Jurassic Period around 150 million years ago and is an exception to this rule. Unlike other surrounding region, the quarry experienced wet and dry seasons which Drumheller suggests may have forced the theropods to eat all available food resources during environmental stress.
In their study, Drumheller and her team analyzed 2,368 bones from this Quarry, looking for any specific features related to tooth shapes or feeding behaviors to determine who made the bite. They discovered that about 29% of the bones bore the telltale bite marks of the theropod dinosaurs. After further examining the damage, the authors determined that the bites were most likely made by the serrated-edged teeth of the large predator Allosaurus, the most common theropod found in the quarry region roughly 150 million years ago.
“There are two possibilities to explain this. Either something was making these animals more completely break down remains than they would usually, such as a highly stressed environment that made them seek out any available resource, or this is actually normal for these animals, and the way we have been collecting fossils has skewed our dataset,” Drumheller said in an interview.
The direct translation of this creature’s name means “different lizard,” a reference to its uniquely shaped, curved vertebrate and a large skull equipped with dozens of sharp, serrated teeth. Similar to the velociraptor, this predator was bipedal with sharp talons and had a large, muscled tail used for balance. In short, it likely would have been the top of its food chain in its prime.
Drumheller notes her co-author Domenic D’Amore previously developed a method to measure the spacing between the striation marks of a theropod bite, the signature from their serrated teeth, and infer an estimate of minimum body size. With this strategy, they were able to narrow down which creature left the marks on the bones in Mygatt-Moore. Furthermore, co-author Julia McHugh was responsible for the fortuitous findings of these bones after setting up a bulk collection at this site, which allowed them to collect the damaged bones that normally would have been looked over in favor of pristine ones.
Most of the bite marks were found on the bones of herbivorous dinosaurs, which was the Allosaurus’ prey of choice, but the authors point out that about 17% of the theropod bites were inflicted on the bones of other theropods. Previous studies have shown that it’s not unlike predators to resort to cannibalism when pushed to their limits on resources, but this is the first evidence of the Allosaurus engaging in this behavior — especially odd because many paleontologists believe the species hunted in packs.
Furthermore, about half of the bites were focused around less nutritious parts of the body, leading the authors to believe that these bites were the actions of scavengers who arrived after the best parts had either decomposed or been eaten previously by other carnivores. Another theory about the Allosaurus’ feeding habits suggests that not only did they regularly scavenge, but they may have even rationed their kill to feed themselves for multiple days.
“The presence of bite marks on what we call low economy bones, anatomical regions that aren’t associated with lots of overlying soft tissue, suggest that these trace makers were probably eating after the better options were already gone, eaten by other predators or simply too decomposed to eat anymore,” said Drumheller.
The authors suggest the unusual state of these bones could be due to the circumstances of the ancient environment, where the carcasses were buried slowly, and scavengers were given more than enough time to find them. These increased findings of scavenging are likely the result of a stressed ecosystem where the large predator inhabitants suffered from a scarcity of food.
Also, since so many of the Allosaurus bite marks were found on the bones of other Allosaurus, it could signal the findings of a rare case of dinosaur cannibalism and the first conclusive evidence of its kind for this famous Jurassic predator. Cannibalism, although highly suspected in theropods, is difficult to detect from fossils, making this one of the rare species where this kind of feeding behavior is confirmed.
“Big theropods like Allosaurus probably weren’t particularly picky eaters, especially if their environments were already strapped for resources. Scavenging and even cannibalism were definitely on the table,” Drumheller said. “Some of these scavenging traces were found on the remains of Allosaurus, which given the overwhelming abundance of this theropod at the site, strongly suggests that cannibalism was involved.”