An enigmatic theropod Cryolophosaurus: Reviews and comments on its paleobiology
By: Changyu Yun
Summarized by Ohav Harris, a geology major at the University of South Florida and is currently a junior. He plans to pursue a doctorate degree in paleontology and become a paleo-educator in some capacity, either working in a museum or a university. In his free time, Ohav enjoys collecting Pokémon cards, reading manga, and fishing.
What data were used? The author, Yun, used many previously published peer reviewed papers to review and evaluate the ideas that exist regarding Cryolophosaurus’s evolutionary relationships, or phylogenetics. The only known fossil data for this dinosaur are hip fragments, various vertebrae, rib fragments, femurs, part of its foot, and the holotype (the fossil that the description of the genus/species is based on), which include the skull and neck vertebrae – all of which were found in Antarctica. The sparse remains of Cryolophosaurus make it difficult to make definitive statements of its relationship to other theropods (bipedal dinosaurs that are primarily carnivorous), though researchers are confident that it is a theropod. Yun includes an array of possibilities from various sources that attempt to answer the question of this dinosaur’s phylogeny and examines what fossil data of Cryolophosaurus there are to make comments on its ecology and biology.
Methods: Yun analyzes Cryolophosaurus’ anatomy and geographical placement, makes comparisons to better known dinosaurs, and references scientific papers that discuss this Cryolophosaurus to draw conclusions regarding its possible phylogeny, ecology, and biology. Certain features of this animal, like the shape of its skull, the structure of its feet, and the purpose of its skull crest, are discussed and used to support Yun’s claims of the nature of Cryolophosaurus.
Results: While the exact phylogeny of Cryolophosaurus is tricky, and not yet fully understood, there are a few things that can be said about it. The skull of Cryolophosaurus has features of tetanurans, dinosaurs that are more closely related to modern birds, like Allosaurus, and earlier, more primitive therapods like Ceratosaurus. Tetanurans and Ceratosaurus are closely related, but took different evolutionary paths. The tetanurans are made up of two groups, carnosaurs and coelurosaurs, which contain a majority of the most famous therapods like Allosaurus and Tyrannosaurus respectively, and all modern birds (descending from the coelurosaurs). Because Cryolophosaurus’ skull has both features of tetanurans and earlier theropods, it can be inferred that it is a transitional fossil that links the first theropods in the Jurassic and all subsequent therapods and modern birds. It is also likely that, based on its shared features between both theropod groups, Cryolophosaurus is an early tetanuran. This possibility is briefly discussed in the paper. It was also determined that Cryolophosaurus was an apex predator in its Antarctic environment, able to make swift movements and out-speed its prey to capture them. This is based on the animal’s astragalus (the bone in the foot between the shin and tarsals) and calcaneum (the bone just under the astragalus that forms the heel) being fused through ossification, or the growth of new bone material. Because dinosaurs walked on their tiptoes, this would not affect their stability as it would for humans. Additionally, those two bones are located right next to each other in dinosaur feet, which means that Cryolophosaurus only had one “ankle” bone where it would usually have had two. Taphonomic evidence (relating to the processes a body undergoes after death, including fossilization), supports the idea of Cryolophosaurus being an apex predator, as herbivore teeth have been found in its stomach. Sauropods, the long-necked dinosaurs, have also been found in the same formation as Cryolophosaurus, which could suggest they were also potential prey. Interestingly, the Cryolophosaurus holotype was found disarticulated with shed teeth nearby. These teeth are believed to have belonged to another Cryolophosaurus, suggesting that this dinosaur may have had cannibalistic tendencies. The characteristic crest of the dinosaur (Fig. 1) is believed to have been used as a display for attracting mates, with differences in bodily characteristics between males and females.
Why is this study important? Cryolophosaurus is an important dinosaur for theropod evolution because it is likely a transitional fossil connecting the earliest therapods to the tetanurans that came after. Understanding this dinosaur’s place in the phylogeny of theropods is important because it can elucidate various unknowns about their evolution. Cyrolophosaurus’ environment was also unique, being the only therapod yet discovered in Antarctica, which was a colder climate than what other dinosaurs in the Jurassic were living in. This provides a new perspective into dinosaur ecology, particularly through the lens of dinosaurs adapted for colder climates.
The big picture: Dinosaur paleontology is generally regarded by the public as being centered around the most popular Late-Cretaceous genera like Tyrannosaurus, Triceratops, and Velociraptor without much consideration for their ecology or even other dinosaurs from different periods. This study sheds light on one such lesser-known dinosaur, Cryolophosaurus, and states its importance to the phylogeny of theropod dinosaurs as well as its ecological role. Understanding the “niche” and lesser known dinosaurs is extremely important to the understanding of dinosaur paleontology, as those dinosaurs often provide much insight, not only into their evolution and development, but also to the unique nature and attributes of dinosaurs as a whole.
Citation: Yun, Changyu, 2020. An enigmatic theropod Cryolophosaurus: Reviews and comments on its paleobiology. VOLUMINA JURASSICA, 2019, XVII: 103–110