Spinosaurus is the biggest carnivorous dinosaur ever discovered—even bigger than T. rex—but the way it hunted has been a subject of debate for decades. It's hard to guess the behavior of an animal that we only know from fossils; based on its skeleton, some scientists have proposed that Spinosaurus could swim, but others believe that it just waded in the water like a heron. Since looking at the anatomy of spinosaurid dinosaurs wasn't enough to solve the mystery, a group of paleontologists are publishing a new study in Nature that takes a different approach: examining the density of their bones. By analyzing the density of spinosaurid bones and comparing them to other animals like penguins, hippos, and alligators, the team found that Spinosaurus and its close relative Baryonyx had dense bones that likely would have allowed them to submerge themselves underwater to hunt. Meanwhile, another related dinosaur called Suchomimus had lighter bones that would have made swimming more difficult, so it likely waded instead or spent more time on land like other dinosaurs.