As September 29th, 2020, I have written more articles dedicated to the paleontological phenomena that is Spinosaurus than any other animal. Okay fine, I have written three articles about Tyrannosaurus as well; but two of them focus less on the species itself and more about the commercial side of paleontology. In contrast, my articles on Spinosaurus focus on its bizarre anatomy and behaviours, including how it may have been the first aquatic dinosaur known to science. Undoubtedly, the notion that the largest known carnivorous dinosaur lived far more like a crocodile than a Tyrannosaur is a subject of endless fascination to me. So, when new evidence emerges to help prove this theory, as it has recently, I will always feel compelled to write about the so-called “dino-croc”.
The last time I wrote about Spinosaurus was because of the discovery of a ground-breaking tail; this time it is the discovery of teeth that has fired up my Spinosaurus instinct. Under usual circumstances, the discovery of loose dinosaur teeth wouldn’t exactly be something of interest to me. Since dinosaurs routinely shed and replaced their teeth in a manner similar to modern crocodiles, teeth are far and away the most common feature of the skeleton known. Even for a rare dinosaur like Spinosaurus teeth are common; so common in fact that you can buy real ones on platforms such as eBay. This discovery isn’t special because Spinosaurus teeth were found; it is special because of where they were found.
Near the Moroccan village of Tarda lay two fossil sites of ancient riverbeds. These sites had experienced outside interference from townspeople taking fossils for income (those eBay teeth have to come from somewhere) but were nonetheless still teeming with fossils. In a surprise to the excavating paleontologists, the most common fossil present in both riverbed sediments were the teeth of Spinosaurus. At one location, Spinosaurus teeth accounted for a third of all vertebrate fossils and the majority of teeth present; at the other site, they accounted for half of all teeth present. The accumulation of Spinosaurus teeth is no accident either, as the teeth of land-based dinosaurs were rare at these sites while the “teeth” of the ancient sawfish Onchopristis (who is commonly depicted as Spinosaur lunch) were overwhelmingly common. The sheer volume of teeth present in aquatic deposits further validates the already strong aquatic Spinosaurus theory.
Including this new evidence, the amount of evidence to support the ‘dino-croc’ theory is overwhelming. Since its initial discovery, the skull of Spinosaurus has been compared to that of a crocodile, due to its long and thin proportions and conical teeth. Whereas other theropods have knife-shaped teeth with serrated edges meant for cutting flesh, the conical teeth of Spinosaurus are perfectly adapted for catching fish. Next came the 2010 analysis done by Amiot et al of Spinosaurus’ bone chemistry; here, oxygen isotopes consistent with aquatic animals like crocodiles and turtles were revealed. Even though these traits pointed towards aquatic behaviours, some scientists still doubted this theory as the anatomy of Spinosaurus was still relatively unknown. This finally changed in 2014 with the discovery of a new and incredible fossil specimen by the paleontologist Nizar Ibrahim and his team.
Dr. Ibrahim’s discovery in 2014 finally established a true identity for Spinosaurus. Instead of being a biped as what had been assumed previously, the new specimen revealed that Spinosaurus was actually a quadruped with reduced rear limb sizes. These proportions don’t make sense for a terrestrial predatory dinosaur, but they sure do for an aquatic genus. Any remaining doubt was put to rest in early 2020 when a near-complete tail was discovered. This tail undoubtedly belonged to a swimmer, as the vertical extensions of vertebrae transformed the tail into a flexible paddle capable of propelling a multi-tonne animal through currents. Given the magnitude of evidence, I think it is safe to say that Spinosaurus is the first aquatic dinosaur known to science.
As noted, our understanding of Spinosaurus is due to the contributions of Professor Ibrahim. He led the teams who discovered the 2014 specimen, the 2020 tail and the recent deposit of teeth. Without his persistence, it is likely that we would never be fully aware of the magnificent oddity that is Spinosaurus. Dr.Ibrahim truly is the Spinosaur connoisseur, through and through.
Last time I wrote about Spinosaurus, I said I’d be writing about it again in a year or two; it turned out to be a little over three months. Way to jinx myself, right? Well, I’ll do it again and say my next Spinosaur article will come out in six months. Having said this, I won’t be surprised if it ends up being three days.
Nizar Ibrahim, please: for my sanity, take a break so I can rest my Spinosaurus fatigue.
I do not take credit for any images found in this article.
Free-flowing Spinosaurus courtesy of Gustavo Monroy-Becerril, found here
Photo of the Kem Kem group found here
Spinosaurus vs Onchopristis courtesy of Davide Bonadonna, whose website can be reached here
Spinosaurus teeth courtesy of Radiance and Grit on Pinterest
Swimming Spinosaurus courtesy of Raynald Kudemus, whose work can be found here
Professor Nizar Ibrahim’s website – https://www.nizaribrahim.net/
Amiot, Romain, et al. “Oxygen Isotope Evidence for Semi-Aquatic Habits among Spinosaurid Theropods.” Geology, vol. 38, no. 2, 2010, pp. 139–142., doi:10.1130/g30402.1.
Beevor, Thomas, et al. “Taphonomic Evidence Supports an Aquatic Lifestyle for Spinosaurus.” Cretaceous Research, vol. 117, 2020, p. 104627., doi:10.1016/j.cretres.2020.104627.
Greshko, Michael. “Case for ‘River Monster’ Spinosaurus Strengthened by New Fossil Teeth.” National Geographic, 23 Sept. 2020, www.nationalgeographic.com/science/2020/09/case-for-river-monster-spinosaurus-strengthened-by-new-fossil-teeth/.
Ibrahim, N., Maganuco, S., Dal Sasso, C. et al. Tail-propelled aquatic locomotion in a theropod dinosaur. Nature 581, 67–70 (2020). https://doi.org/10.1038/s41586-020-2190-3
Ibrahim, N., et al. “Semiaquatic Adaptations in a Giant Predatory Dinosaur.” Science, vol. 345, no. 6204, 2014, pp. 1613–1616., doi:10.1126/science.1258750.
Treat, Jason, and Mesa Schumacher. “Reconstructing a Gigantic Aquatic Predator.” National Geographic, 1 May 2020, http://www.nationalgeographic.co.uk/science-and-technology/2020/04/reconstructing-gigantic-aquatic-predator.