More than 95 million years ago, a mighty river system flowed through what is now the Moroccan Sahara, providing a home to one of the most unusual dinosaurs known to science: Spinosaurus, a 49-foot-long, seven-ton beast with a crocodile-like snout that bristled with conical teeth. 

Paleontologists agree that Spinosaurus and its kin had strong ties to water, but for years, they have debated whether this bizarre, crested creature swam through the water as a fish-nabbing “river monster,” prowled the shores like a reptilian mega-heron, or something in between.

Now, using the biggest dataset of its kind, researchers have compared the density of the prehistoric carnivore’s bones to a wide array of living and extinct animals. The analysis found that Spinosaurus—and, surprisingly, its