High frequencies of theropod dinosaur bite marks provide evidence for feeding, scavenging, and possible cannibalism in a stressed Late Jurassic ecosystem
Stephanie K. Drumheller, Julia B. McHugh, Miriam Kane, Anja Riedel, Domenic C. D’Amore
Summarized by Reynolds Hansen. Reynolds Hansen is an undergraduate geography major / geology minor at the University of South Florida. With a lifelong passion for paleontology instilled from an early age, Reynolds always knew the academic path ahead had a singular destination. Along the way, he picked up equal affinities for history and geography, and by the time he was in college, he worried he might have to choose one over the others. With the help of the university’s esteemed academic professionals and resources, he shifted focus with the goal of becoming a science communicator, telling the story of our world from the formation of the earth to the modern day as an interconnected narrative. Reynolds is set to graduate in the spring of 2021, after which he wishes to seek a post-graduate degree in paleontology, and a career as an educator. His academic focus is utilizing GIS to research paleoecological phenomena.
Methods: The study collected fossil data from the Upper Jurassic Mygatt-Moore Quarry in Utah, USA (MMQ). Out of 2,368 found specimens, 684 specimens positively displayed some damage resulting from contact with theropod dinosaur teeth. These damages were categorized into broad categories- pits, punctures, scores, and furrows (Fig 1.) The dimensions of these features, along with spacing between them, measured from raking light (light shone upon an object at a low angle in order to more easily observe details on its surface) and low magnification, helped the team to determine the species responsible for the damages. The marks here were also compared to identical features left by large, modern mammalian predators to determine intent- where on the body the animal was removing material, and whether this was done during predation of scavenging. These marks are considered in relation to ‘low’ and ‘high’ economy regions- meaning, the parts of prey animals that provide low or high nutritional benefit respectively. The goal of these methods was to determine the extent of scavenging behaviors among theropods- a group of mostly carnivorous, bipedal dinosaurs with hollow bones and three-toed limbs. The theropods in question in this region were primarily Allosaurus and Ceratosaurus.
Results: As in many cases, predation behavior is often dictated by environmental conditions. In the MMQ, sediment suggests an environment with low deposition rates, allowing for animal remains to be exposed for longer periods of time, which consequently allows for remains to be scavenged repeatedly. Tooth striations on the formation’s fossils suggests typical theropod behavior was targeting soft tissues near high-economy regions (regions that provide the most nutritional benefit). However, just less than half of all marks on herbivores are also located in low-economy regions, indicating that remains were stripped of any possible material by large theropods. These statistics flip when tooth marks are found on theropod remains, where more than half of the tooth marks are found in low-economy regions. Together, these findings may suggest that aside from remains being present for longer periods of time, the region may have also been prone to periods of nutritional hardship, leading to cannibalism among theropods when scavenging, and possibly even predation. For any of the theropods present in this ecosystem (Allosaurus, Ceratosaurus, and possibly Saurophaganax or Torvosaurus), these occurrences would mark the first recorded cases of cannibalism for these species, implying a need that is situational in times of hardship, rather than a trait reserved to specific species.
Why is this study important? The importance of this work is twofold. In the first manner, it provides insight into an area that is integral to understanding an extinct carnivorous animal: how it eats. The paper mentions on a couple of occasions that, to date, the conventional understanding of how theropods acquire nutrition was by focusing primarily, maybe even exclusively, on soft-body materials- the aforementioned ‘high economy’ zones. There had been little evidence up to this point for scavenging behavior among theropods, aside from some works regarding this behavior in tyrannosaurs, although even this was at least partially inferred to the development of osteophagy (the ability to eat and derive nutrients from bones) in these animals. So too with cannibalism, where Majungasaurus represented the only known case, again, for tyrannosaurs. With this study, theropods appear to resemble something more within the norm of how we understand most carnivores to behave: opportunistic consumers who take advantage of ‘free’ scavenge-able meals where they could get them, and who are none too picky in troublesome times. The second point of importance, and perhaps light criticism, from this piece is the allusion to the practice of fossil collection by institutions. The question is raised by the paper: if this behavior were to be commonplace, why is there so little evidence of it? The MMQ had recently undergone a transition of collection practices, from selective collecting to a more total method, taking in as many specimens as possible without too much scrupulousness for overall quality. The team cites this change as a likely reason for the abundance of tooth-marked fossils in the study, since they were not tossed aside preemptively for not being ‘aesthetically pleasing’, ‘good quality’ fossils.
The Big Picture: This paper does as much to reflect on paleontological research practices as it reveals about theropod behavior. On one hand, its revelations of how theropods survive difficult times by extensively scavenging every possible resource- and apparently from any source- is certainly a tremendous leap in this field for dinosaur behavior. The other side of the coin is that this study may not have had such diverse results if it were not for size and breath of the MMQ’s sampling. The commentary from the paper is subtle but cautionary: that we should aim to eliminate bias at every opportunity in research, but also in our very initial collection efforts.
Citations:
Drumheller SK, McHugh JB, Kane M, Riedel A, D’Amore D. 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
Rogers, Raymond R.; Krause, David W.; Curry Rogers, Kristina (2007). “Cannibalism in the Madagascan dinosaur Majungatholus atopus”. Nature. 422 (6931): 515–518