The Spinosaurus Saga
The giant sail-backed predatory dinosaur Spinosaurus has always been a source of confusion and mystery to scientists, something that continues to this very day.
The dinosaur was first collected from Egypt and described by the great German paleontologist Ernst Stromer in 1915. This original specimen consisted of a handful of vertebrae, plus half of a lower jaw. Stromer knew these were the remains of a big theropod dinosaur, but it was pretty different from the species known from Europe and North America at the time. The jaw bones were long and narrow, the teeth were conical instead of flat and blade-like, and the vertebrae had those towering spines growing off the top, forming a giant sail. Having relatively little to go on, Stromer reconstructed Spinosaurus as basically a typical, tyrannosaur-like theropod dinosaur- just one with a sail on its back and crocodile-like teeth.
For almost 100 years, that’s just about all we knew about Spinosaurus. As the famous story goes, during WWII Stromer’s Spinosaurus fossils were destroyed by a British bombing raid that hit the museum. The paleontology collections manager was a Nazi party supporter, and Stromer was not. For his defiance, Stromer was forbidden from moving his fossils to safety- talk about being punished for doing the right thing. And so all we’re left with is Stromer’s published descriptions and illustrations, plus one photograph of the specimen on display before it was destroyed. Spinosaurus remained a sail-backed but otherwise completely typical meat-eating dinosaur in the minds of the public. At least it got to star as the antagonist in Jurassic Park 3.
All this was upended in 2014 by a study led by Dr. Nizar Ibrahim, whose team had been on the hunt for Spinosaurus remains all over northern Africa. By combining their newer specimens with what was known of Stromer’s material, they argued that Spinosaurus was an exceptionally weird dinosaur- with short stout legs and flat webbed feet, bulky arms, an extra-long torso, and a strange M-shaped sail, their Spinosaurus looked like no other dinosaur we’d ever found. Ibrahim and his colleagues believed these features proved that Spinosaurus was poorly adapted for life on land, and had a much more crocodile-like lifestyle, swimming around and preying on giant fish in the vast swamps of Cretaceous North Africa.
This view of Spinosaurus has been polarizing ever since, and recently Dr. Donald Henderson of the Royal Tyrrell Museum has weighed in. In a new article published in PeerJ, Dr. Henderson argues that Spinosaurus was not as well adapted to an aquatic lifestyle as others have thought. Using a digital model of Spinosaurus with the right kind of proportions and density, Dr. Henderson dropped the dinosaur into a virtual pool of water to see what would happen to a real Spinosaurus in real water, and compared the results to tested models of other predatory dinosaurs, alligators, and penguins.
The results showed that Spinosaurus actually floated pretty well, with its long pointed head easily sticking out of the water. This indicated that Spinosaurus was certainly capable of swimming to some degree. However, all the other theropod dinosaurs, which included the small and slim Coelophysis, the bulky Tyrannosaurus, and close spinosaur cousin Suchomimus, also floated with ease. Dr. Henderson found Spinosaurus’ center of gravity to be pretty close to the hips like in other bipedal dinosaurs, not near the middle of the body as in most aquatic animals. This contradicts Ibrahim and colleague’s ideas, and doesn’t set Spinosaurus apart as being much more adapted to an aquatic lifestyle than any other dinosaur it was compared to. Henderson also found that alligators, which are often compared to Spinosaurus in form and lifestyle, were able to sink fairly quickly when their lungs deflated, and easily turned right-way up if they were spun in the water. Similar results were found in penguins, our modern-day aquatic predatory dinosaurs, who are able to use their powerful flippers to dive to great depths and swim effectively. Spinosaurus did not fair nearly as well in these tests- Henderson observed that it would have bobbed on the surface and was easily flipped over in the water. Not exactly good traits to have if you’re an aquatic animal.
So is our image of Spinosaurus as a watery river-dweller as extinct as the creature itself, with it having been bound to only dry land? Not completely. While Henderson states that the animal was more competent on land than previously thought, he also doesn’t rule out the possibility of it having lived and hunted in shallow water or along shorelines. The teeth and jaws of Spinosaurus match that of an animal adapted to eating fish, and perhaps its broad, webbed feet allowed it to punt through shallow swamps or wade along muddy tidal flats. Whatever the whole truth is, Spinosaurus continues to be a dinosaur worthy of the mystery and grandeur of ancient Egypt.
Henderson (2018), A buoyancy, balance and stability challenge to the hypothesis of a semi-aquatic Spinosaurus Stromer, 1915 (Dinosauria: Theropoda). PeerJ 6:e5409; DOI 10.7717/peerj.5409
Ibrahim N, Sereno PC, Dal Sasso C, Maganuco S, Fabbri M, Martill DM, Zouhri S, Myhrvold N, Lurino DA. 2014. Semiaquatic adaptations in a giant predatory dinosaur. Science 345(6204):1613–1616
If you want to support paleontology in Alberta, consider coming out to our Night for the Museum fundraiser event on August 25th, 2018! There’s also still time to come on a tour of the Pipestone Creek bonebed while August lasts! And as a notice, the museum will be closed from September 11-12 for a changeover of gallery displays.