Spinosaurus: A Changing Aquatic Predator!

An old model Spinosaurus in a Cretaceous River Delta. Our new understanding of the creature has a much rounder body.

Our understanding of dinosaurs is always in flux. The discovery of a new fossil, or the reexamination of an old one, can upend everything we know about a given species. Consider the Spinosaurus, one of the largest carnivorous dinosaurs to ever walk the Earth. This massive theropod topped out at about 60 feet, and weighed 8.8 tons. Still, so much remains unknown about these giant hunters and what we do is subject to constant reexamination.

Nearly everything about Spinosaurus defies traditional thought about carnivorous dinosaurs. To begin with, Spinosaurids are the only known family of semi-aquatic dinosaurs, paddling around shallow water to snap up unsuspecting prey. They also had long, narrow skulls, almost crocodile-like in appearance, and their jaws were lined with conical teeth instead of the curved, blade-like ziphodont teeth of most theropods.

A group of fossil Spinosaurus teeth from Mini Museum

As its name suggests, Spinosaurus also had elongated neural spines forming a massive dorsal sail. In some species, the spines in the namesake sail measure more than 6ft (2m) in length, providing the framework for an impressive structure that would rise high above the water. The shape and function of this spine sail have been hotly debated topics, with no consensus formed on the spine’s exact evolutionary function.

Some theories suggest that the sail wasn't a sail at all but a "fatty-hump". However, a detailed reconstruction in 2014 concluded that the spines were too poorly vascularized to support such a structure and the spines were likely covered by skin and used for display. The same study also suggests that its limbs were somewhat shorter than previously thought, and appear to be specifically adapted to paddle-swimming like early whales

A Spinosaurus skeletal formation posed in a swimming motion to mimic its movement in life.

The species was first discovered by explorer and fossil collector Richard Markgraf in 1912 near the Bahariya Oasis in Western Egypt. At the time, Markgraf was working for German paleontologist Ernst Stromer. He sent the partial remains to Stromer in Munich who announced the discovery in 1915 and named the species Spinosaurus aegyptiacus. But in 1944, the allied bombing of Munich destroyed Erich Stromer's entire dinosaur collection including the holotype, or original, specimen of Spinosaurus aegyptiacus.

Recently, a brand new paper has turned the Spinosaurus' lifestyle on its head once more. A study of the animal's bone density shows Spinosaurus would have been quite heavy, which may have helped it submerge and hunt below the water as well. Without flippers, compacted bones may have been a solution for the species to move underwater. Not only would this be a new way of looking at Spinosaurus, but it would change our understanding of all dinosaurs, as previously underwater hunting was only within the realm of marine reptiles outside the dinosaur group, such as Mosasaurs and Plesiosaurs.

This is how the new Spinosaurus may have looking while hunting. (Illustration from Davide Bonadonna)

This new Spinosaurus would have been much rounder as well, helping it make swifter diving and swimming movements. A thick, paddle-like tail could give it powerful propulsion capabilities to catch up with prey. It's easy to see the connection between a creature like this and the hunting styles of modern water birds that dive after fish.

Perhaps soon another, more complete Spinosaurus fossil will be discovered that will again upend everything we know about this creature, or else further cement our current theories. 

The Spinosaurus is a reminder that the work of paleontology is never quite complete, that our understanding of any fossil must always be open to evolve as we discover more.

Read More!

Brusatte, Stephen L. “Spinosaurus.” Current Biology 31.20 (2021): R1369–R1371. Web.

Ibrahim, Nizar, et al. "Semiaquatic Adaptations in a Giant Predatory Dinosaur." Science 345.6204 (2014): 1613-1616.

Smith, Joshua B., et al. "New Information Regarding the Holotype of Spinosaurus Aegyptiacus Stromer, 1915." Journal of Paleontology 80.02 (2006): 400-406.

Stromer, Ernst. "Wirbeltier− Reste der Baharije− Stufe (unterstes Cenoman). 3. Das Original des Theropoden Spinosaurus Aegyptiacus nov. gen. nov. spec." Abhandlungen der Königlichen Bayerischen Akademie der Wissenschaften, Mathematisch− Physikalische Klasse 28 (1915): 1-32.

Fabbri, Matteo, Guillermo Navalón, Roger BJ Benson, Diego Pol, Jingmai O’Connor, Bhart-Anjan S. Bhullar, Gregory M. Erickson et al. "Subaqueous foraging among carnivorous dinosaurs." Nature (2022): 1-6.