Taphonomic evidence supports an aquatic lifestyle for Spinosaurus
By: Thomas Beevora, Aaron Quigleya, Roy E. Smith, Robert S.H. Smyth, Nizar Ibrahim, Samir Zouhric, and David M. Martill
Summarized by Jerold Ramos
Jerold Ramos is a senior at The University of South Florida studying geology. Once he graduates, he hopes to develop experience working in a museum environment to one day become a museum educator. Captivated by the beauty and mystery of dinosaurs from a young age, he hopes that as a museum educator he can share the excitement and wonder that Earth’s history has to offer with people from around the world. In his free time, he enjoys hosting game nights with his friends and creating poorly photoshopped projects.
What data were used? Two collections of fossilized teeth found in separate riverbed deposits within South Eastern Morocco were used for this study. In total, 1,245 teeth were collected and sorted into appropriate groups based on their taxonomic order or genus.
Methods: Fossils were collected at two different sites in Morocco. Site One excavated fossils from an exposed bed, while the fossils from Site Two were bought from a mining group that had discovered them previously. Beevora and their team chose to focus on teeth, as they could assign these teeth to a taxonomic order (e.g., Carnivora [dogs and cats], Primates [including chimps and humans], and Saurischia [theropod and sauropod dinosaurs]) or even more specifically to a family or genus level. In this case, Beevora and their team were able to assign many of the teeth to the genus Spinosaurus.
Results: After analyzing the fossils collected from both sites, this study found that the amount of Spinosaurus teeth at each site was abnormally high when compared to the teeth of other creatures found in the area. At Site One, 921 fossils were uncovered and of these 921, a total of 317 of these were teeth. From these teeth, about 47.9% (152) of these teeth were Spinosaurus teeth. The only creature to have a similar count in teeth was Onchopristis, an ancient sawfish from the Cretaceous Period, with 50.2% (159) of the teeth belonging to this fish. At Site Two, 1261 fossils were purchased from a miner and of these 1261 fossils, a total of 928 of these fossils were teeth. At this location, a greater assemblage of Spinosaurus teeth were identified. Here Spinosaurus teeth made up about 43.9% (407) of the teeth found, making it the most abundant species represented at this site. Once again, the only other creature to have a similar representation at the site is Onchopristis, with 40.4% (375) of its teeth making up the collection found at Site Two. The rich supply of Spinosaurus teeth found at both sites suggest a more aquatic lifestyle for Spinosaurus. From the data collected in both sites, these sites likely represented aquatic environments due to the high presence of teeth from Onchopristis, an entirely aquatic animal, making up about half of the teeth found at each site. A creature that does not live an aquatic lifestyle, or spend a significant time in the water, would not leave as many remains in the environment. As an example, Site One discovered a single tooth from Carcharodontosaurus, another large therapod dinosaur that is thought to be strictly land-dwelling. This single tooth is more in line with what would be expected from a creature with a terrestrial lifestyle as it would only approach the water to drink or feed on a creature nearby. If Spinosaurus was terrestrial like Carcharodontosaurus, then it would not have such a prominent representation at these sites. Rather than wading by the water’s edge like a heron or flamingo, Spinosaurus may have spent much of its time in the water actively swimming to catch prey. This collection of teeth in aquatic deposits and Spinosaurus’ established morphology, including reduced hind legs, elongated skull, and paddle-like tail structure, further support the hypothesis that Spinosaurus lived an aquatic lifestyle.
Why is this study important? The findings from this study change what we know about both Spinosaurus and how we define dinosaurs today. Like other non-avian (i.e., non-bird) dinosaurs, Spinosaurus was often pictured to be a terrestrial creature, only visiting aquatic areas when it needed water. However, thanks to recent discoveries in the last five years, we now know that it likely lived a more aquatic lifestyle. This lifestyle is something that is not seen with any other known non-avian dinosaur so far. Dinosaurs are often defined as exclusively terrestrial creatures, a definition that no longer applies to the Spinosaurus. With the recent discoveries involving Spinosaurus, it may be worth reevaluating the lifestyles of other members of the family Spinosauridae, as it is possible that other Spinosauridae adopted an aquatic lifestyle long before Spinosaurus.
The big picture: Spinosaurus has been an enigmatic fossil ever since it was discovered in 1915. After its remains were destroyed during World War II, the image and lifestyle of Spinosaurus remained a mystery to paleontologists for several years. Now that more of its fossils are being unearthed, paleontologists can reconstruct this unique creature and illustrate the environment it inhabited. From these recent discoveries, we now know that Spinosaurus lived a life unlike any other dinosaur recorded in the fossil record. As there are numerous dinosaurs missing from the fossil record, whether it be through failed preservation or destruction by plate tectonics, it is possible that there are others that share this aquatic lifestyle.
Citation: Beevor, T., Quigley, A., Smith, R. E., Smyth, R. S. H., Ibrahim, N., Zouhri, S., & Martill, D. M. (2021). Taphonomic evidence supports an aquatic lifestyle for Spinosaurus. Cretaceous Research, 117. https://doi-org.ezproxy.lib.usf.edu/10.1016/j.cretres.2020.104627