The Spinosaurus Chronicles Part 5: The Tale of the Bones…

The field of paleontology experienced a massive boom right in the middle of my exam season.

Lucky me!

Spring is typically a busy time for paleontologists. After long summer digs and months of preparation in the winter, spring finally yields the fruits of their labour. Spring 2022 was no exception, with numerous papers and documentaries being released within this time frame. A dinosaur was also compared to the joker, but it’s probably best that we just ignore that…

Amidst this chaos came quite a few interesting studies. The most relevant to this blog was the latest update to my Spinosaurus saga, which now has more installments (on this website) than the Toy Story franchise. My reaction to seeing the news trending on Twitter looked something like this:

The last time I wrote about Spinosaurus was in response to a study proposing semi-aquatic shoreline behaviour akin to that of a modern stork. The study – published in January 2021 and written by paleontologists David Hone and Thomas Holtz – proposed a more mundane version of paleontology’s greatest enigma. Five months before that, paleontologists led by Nizar Ibrahim had declared it to be an aquatic hunter based on teeth distribution and anatomy. Talk about flip-flopping around!

To summarize, the last time I wrote about Spinosaurus I suggested it was not an aquatic hunter. Today, I will contradict myself and talk about how it was aquatic.

On March 23^rd, a massive team of paleontologists lead by Matteo Fabbri with collaborators including Ibrahim published a study measuring the bone density of Spinosaurus and two relatives – the European Baryonyx, and the African Suchomimus. By comparing the spinosaurids with living and extinct animals, the researchers discovered that Spinosaurus had increased bone density that correlates to an aquatic lifestyle. Increased bone density is an evolutionary trait designed to help organisms stay submerged underwater, giving credence to the theory that Spinosaurus hunted underwater as opposed to on the shorelines.

Animals with similar bone configurations include penguins and crocodiles, animals that hunt underwater. Additionally, Spinosaurus had denser bones than similarly sized predatory dinosaurs with known terrestrial behaviours like Tyrannosaurus, indicating that dense bones were not a common fixture of large theropods. Rather, it appears that Spinosaurus evolved aquatic behaviours to best exploit its ecosystems in Northern Africa during the early Cretaceous period. 

The more surprising result of the study was the bone density of Suchomimus and Baryonyx. For years, it was thought that the two exhibited similar behaviours based on anatomy. Some paleontologists have gone so far as to classify them as the same species. Yet their bone densities tell a different story; while Baryonyx had dense bones like Spinosaurus, Suchomimus had hollow bones in line with terrestrial dinosaurs.

Though this evidence points to Baryonyx being an aquatic hunter, it doesn’t necessarily exclude terrestrial behaviours. Fossils of Baryonyx have been discovered with the bones of a juvenile Iguanodon, a genus of herbivorous dinosaur, within the gut cavity. While the bone density demonstrates that Baryonyx was more aquatic than previously imagined, it still travelled on land to either hunt – or scavenge – every now and then.

The different bone densities of the spinosaurids signifies adaptive behaviours in response to different environmental conditions. Suchomimus lived alongside Sarcosuchus, a 12+ meter long crocodile, meaning that fully aquatic behaviours would have been a dangerous proposition. Baryonyx had no such mega-croc competition but did compete with a multitude of large theropod dinosaurs on land, thus making aquatic behaviours more advantageous.

For Spinosaurus, competition with the gigantic theropod Carcharodontosaurus may have factored into its aquatic behaviours. However, a much simpler answer presents itself in Northern African ecology 99 million years ago. At this time, much of Northern Africa – from Egypt to Morocco – comprised a vast system of river deltas that opened into the ancient Tethys Sea. River deltas are among the most fertile ecosystems in nature, and the sheer magnitude of the system in the Cretaceous is demonstrated in the fish.

Fish measuring over a meter long are exceedingly common in the area. Some fish, such as the sawfish Onchopristis and the coelacanth Mawsonia, reached over three meters in length. With such an abundance of giant fish, and no giant pescatarian to occupy the role of top predator, Spinosaurus took the plunge and developed subaquatic behaviours to best adapt with the environmental conditions.

Given the number of times I have flip-flopped in response to research, I want to give my general opinion. I now believe that the plethora of research in favour of aquatic behaviours outweighs the counterarguments. The chemical evidence (bone density), physical evidence (fluke-like tail and (possibly) webbed feet), and the circumstantial evidence (Spinosaurus teeth in ancient riverbeds) all point towards an animal with significant aquatic behaviours.

The extent of this behaviour can be debated. To some, forays into water to snack on giant fish may be all they envision. Others see an animal that rarely came onto land, possibly only to lay eggs. I think that Spinosaurus likely lived like a crocodile, with most time spent in water with frequent trips on land to rest, mate, and on some occasions hunt. Reducing Spinosaurus’ behaviours to that of a crocodile feels wrong, however; this was a complex organism with no living comparison, making any estimation imprecise and nigh impossible to confirm.

And that’s the fun of Spinosaurus. This is an organism that is unlike any other dinosaur, unlike any organism, to have ever existed. Speculating on its appearance, whether it hunted underwater, what the sail was for — it all adds layers of intrigue and excitement. So, when controversial studies are published, they add pieces to the picture of prehistory’s greatest enigma.

When the next Spinosaurus study comes out, I promise I’ll be there. Whether it’s in 15 months or 15 days, I will always love writing about Spinosaurus and use every opportunity I can to do so.

May Professor Ibrahim keep it up with his continued dedication, only rivaled by my borderline obsession.

Works Cited:

I do not take credit for any images found in this article.

Header image courtesy of FredtheDinosaurman, found at his page here

Underwater Spinosaurus courtesy of MALvit on deviantart, found here

Baryonyx courtesy of Lindsey Wakefield, found at her website here

Kem Kem fauna courtesy of Joschua Knüppe, found here

Sunset Spinosaurus courtesy of TALUNS on tumblr, found here

Fabbri, Matteo, et al. “Subaqueous Foraging among Carnivorous Dinosaurs.” Nature, vol. 603, no. 7903, 2022, pp. 852–857., https://doi.org/10.1038/s41586-022-04528-0.

Ibrahim, Nizar, et al. “Geology and Paleontology of the Upper Cretaceous Kem Kem Group of Eastern Morocco.” ZooKeys, vol. 928, 2020, pp. 1–216., https://doi.org/10.3897/zookeys.928.47517. 

Varricchio, David J. “Gut Contents from a Cretaceous Tyrannosaurid: Implications for Theropod Dinosaur Digestive Tracts.” Journal of Paleontology, vol. 75, no. 2, Mar. 2001, pp. 401–406., https://doi.org/10.1017/s0022336000018199.  

---