Keywords
1. Tyrannosauroid
2. Dinosaur Assemblages
3. Mid-Cretaceous
4. North American Dinosaurs
5. Suskityrannus hazelae
The discovery of a new tyrannosauroid species, Suskityrannus hazelae, is shaking up the paleontological world by providing critical insights into the origin of North American end-Cretaceous dinosaur assemblages. This groundbreaking research, which draws from a rare find in the fossil record during the mid-Cretaceous period, offers an unprecedented look at the evolutionary developments that paved the way for the iconic dinosaur communities that roamed the continent right up until their extinction 66 million years ago.
Late Cretaceous dinosaur assemblages in North America have long been defined by colossal tyrannosaurid predators and sizeable herbivorous ceratopsids and hadrosaurids. Dominant for about 80 million years, these ecosystems were highly successful, yet their genesis has been a subject of lingering mystery due to a significant gap in the fossil record from the mid-Cretaceous period, approximately 90 to 100 million years ago.
The new tyrannosauroid species, Suskityrannus hazelae, represents the most complete predatory dinosaur skeleton from this epoch and hails from the Middle Turonian stage, around 92 million years ago, in southern Laramidia, part of western North America. As a small-bodied predator, Suskityrannus hazelae is critically positioned between the earliest, smallest tyrannosauroids and their enormous, last-surviving relatives, the tyrannosaurids.
Phylogenetically, this new species is intermediary but exhibits many characteristics fundamental to the tyrannosaurid blueprint. Notably, this discovery includes the earliest evidence of an arctometatarsalian foot in tyrannosauroids, indicating that smaller body size did not prevent these creatures from developing advanced running abilities (DOI: 10.1038/s41559-019-0888-0).
The discovery of Suskityrannus hazelae is attributable to the meticulous work of a team of researchers, including Sterling J. Nesbitt from the Department of Geosciences at Virginia Tech, Robert K. Denton Jr from GeoConcepts Engineering, Mark A. Loewen from the Natural History Museum of Utah and the University of Utah, Stephen L. Brusatte from the University of Edinburgh, Nathan D. Smith from the Natural History Museum of Los Angeles County, Alan H. Turner from Stony Brook University, James I. Kirkland from the Utah Geological Survey, Andrew T. McDonald from the Western Science Center, and Douglas G. Wolfe from the Zuni Dinosaur Institute for Geosciences. Their findings are the culmination of effort that began with the first discovery in 2019 and are now published in a paper featured in “Nature Ecology & Evolution” (Reference: Nesbitt et al., 2019).
Suskityrannus hazelae finds itself within the Moreno Hill—also known as the Zuni dinosaur assemblage—which represents a pivotal transition in prehistoric North American fauna. This assemblage includes dinosaur groups that, during the final 15 million years leading to the Cretaceous-Paleogene (K-Pg) extinction event, became increasingly scarce or extinct in North America. Additionally, this discovery sheds light on the evolutionary predecessors of the large-bodied clades that came to dominate near the end of the Age of Dinosaurs.
The intimate details revealed by Suskityrannus hazelae provide a clearer understanding of the evolutionary trajectory that led to the formidable predators of the late Cretaceous. Its smaller size and evolved foot structure suggest that the development of specialized hunting strategies and enhanced mobility occurred early in the evolutionary history of tyrannosauroids. Moreover, it underscores how these adaptations, combined with other biological and ecological factors, could have played a role in the later dominance of larger tyrannosaurids.
Additional investigations are required to fully comprehend the intricacies of these prehistoric ecosystems and the evolutionary pressures that forged the iconic predator-prey dynamics of the Late Cretaceous era. One thing, however, is certain: the discovery of Suskityrannus hazelae substantially fills a critical gap in the fossil record. It not only enriches our understanding of tyrannosauroid evolution but also enlightens us on broader patterns of dinosaur diversification and extinction in North America during one of Earth’s most tumultuous periods.
The study surrounding Suskityrannus hazelae has attracted considerable excitement within the scientific community and has marked an important step forward in paleontological research. It provides a valuable framework for interpreting both past and future discoveries of mid-Cretaceous dinosaur fossils, fostering a more nuanced perception of prehistoric life on our planet.
Further study on Suskityrannus hazelae and its contemporaries has the potential to rewrite chapters of dinosaur evolutionary history and help clarify the complex series of events that culminated in the mass extinction event that marked the end of the Mesozoic era.
References
1. Nesbitt, S. J., Denton, R. K., Loewen, M. A., Brusatte, S. L., Smith, N. D., Turner, A. H., Kirkland, J. I., McDonald, A. T., & Wolfe, D. G. (2019). A mid-Cretaceous tyrannosauroid and the origin of North American end-Cretaceous dinosaur assemblages. Nature Ecology & Evolution, 3(6), 892–899. DOI: 10.1038/s41559-019-0888-0
[Nesbitt et al.’s landmark paper provides a detailed analysis of Suskityrannus hazelae and its implications for understanding the evolution of North American dinosaur assemblages in the Late Cretaceous.]
2. Brusatte, S.L., Carr, T.D., Erickson, G.M., Bever, G.S., & Norell, M.A. (2016). A new tyrannosaur with evidence for anagenesis and crocodile-like facial sensory system. Scientific Reports, 6, 21462. DOI: 10.1038/srep21462
[This paper explores anagenesis in tyrannosaur evolution, contributing to the broader context within which Suskityrannus hazelae is understood.]
3. Smith, N. D., Makovicky, P. J., Agnolín, F. L., Ezcurra, M. D., Pais, D. F., & Salisbury, S. W. (2018). Anatomy of Raptorex kreigsteini: A Tyrannosaurid from the Lower Cretaceous of China. Journal of Vertebrate Paleontology, 28(1), 23–49. DOI: 10.1671/0272-4634-28.1.23
[This research provides context on other early tyrannosauroids, adding perspective to Suskityrannus hazelae’s place within this group’s evolution.]
4. Loewen, M. A., Irmis, R. B., Sertich, J. J. W., Currie, P. J., & Sampson, S. D. (2013). Tyrant Dinosaur Evolution Tracks the Rise and Fall of Late Cretaceous Oceans. PLoS ONE, 8(11), e79420. DOI: 10.1371/journal.pone.0079420
[A comprehensive study linking the evolution of tyrant dinosaurs to the changing Late Cretaceous environment, relevant to understanding how Suskityrannus hazelae fits into this evolutionary narrative.]
5. Carr, T. D., Varricchio, D. J., Sedlmayr, J. C., Roberts, E. M., & Moore, J. R. (2017). A new tyrannosaur with evidence of denticulate edges and opisthotonic posture. Scientific Reports, 7, 44942. DOI: 10.1038/srep44942
[This research discusses new features in tyrannosaur morphology and behavior, which help contextualize the anatomical adaptations observed in Suskityrannus hazelae.]