The fearsome, toothy star of Jurassic Park III, Spinosaurus came roaring on to the scene just over a century ago and has been confusing paleontologists ever since. Living 95 million years ago, Spinosaurus is the largest meat-eating dinosaur ever discovered and also the first known aquatic predatory dinosaur – possibly.
Last year, a study seemingly confirmed that Spinosaurus aegyptiacus is the world’s only known swimming dinosaur (no, mosasaurs are not dinosaurs) due to its paddle-like tail that could move laterally, allowing it to hunt by thrusting its way through water like a crocodile. Now, a new study in Palaeontologia Electronica has challenged that theory, instead suggesting that while it may well have swum, it wasn’t actually adapted to chasing down prey in water. It was more like an ancient giant heron or stork, a wader snatching prey from both the water and shoreline.
First discovered in 1915 in the Egyptian Sahara, scientists have been painstakingly trying to piece together this curious dinosaur’s behavior and ecology based on its strange physical attributes ever since.
"Spinosaurus was a bizarre animal even by dinosaur standards, and unlike anything alive today, so trying to understand its ecology will always be difficult,” co-author Dr Tom Holtz from the University of Maryland said. “We sought to use what evidence we have to best approximate its way of life. And what we found did not match the attributes one would expect in an aquatic pursuit predator in the manner of an otter, sea lion, or short-necked plesiosaur."
Around 15 meters (49 feet) long, Spinosaurus had a whole suite of strange adaptations that indicate it may have been equipped for water. Alongside its powerful tail, it had huge, slanted, conical teeth that locked together, excellent for catching hold of slippery prey. An abundance of teeth found in ancient river beds in Morocco last year supports the idea it feasted in rivers.
Its sail, however, has never been suggested to have been used for aquatic purposes, though what it may have been for is a hotly disputed topic. Some suggest it was related to socio-sexual signaling, while others have put forward that it was a fat-storing hump similar to bison.
For the new study, researchers compared the features of Spinosaurus with the skeletons of other dinosaurs and living and extinct reptiles that lived on land, in water, or both. When comparing it to a crocodile, they found that Spinosaurus had fewer muscles in its tail than a croc, and due to its size, it would have had a lot more drag in the water. Crocodiles may be effective hunters in water, but they don't actively chase after fish. Lead author Dr David Hone, from Queen Mary University of London, argues if Spinosaurus had fewer muscles in its tail, more drag, and was generally less efficient in the water, then "it's hard to see how these dinosaurs could be chasing fish in a way that crocodiles cannot."
They suggest that though there is plenty of evidence Spinosaurus could swim, it wasn't fast or efficient enough for this to be an effective hunting method, and so it probably wasn't a highly specialized aquatic predator. It's more likely that it hunted similar to wading birds, fishing from the shoreline or in shallow water.
"We certainly add that the evidence points to Spinosaurus feeding partly, even mostly, in the water, probably more so than any other large dinosaur. But that is a different claim than it being a rapid swimmer chasing after aquatic prey," Dr Holtz said.
“Our findings suggest that the wading idea is much better supported, even if it is slightly less exciting," added Dr Hone.
While there's a lot we still don't know about this truly weird dinosaur, there is one thing we know for sure. Jurassic Park III would look very different if it was made today.