Enormous Spinosaurus was likely the first dinosaur to swim — 97 million years ago

Researchers now believe the 50-foot-long Spinosaurus may have been the first dinosaur to take the plunge, swimming in the rivers of North Africa 97 million years ago.

The dinosaur had a giant sail on its back, much like a shark's fin, and likely ate ancient crocodiles, fish, and other floating objects. "It was the biggest carnivorous dinosaur, but Spinosaurus wasn't a land animal," University of Chicago paleontologist Nizar Ibrahim told National Geographic. "This was a creature adapted to life in the water."

Before Spinosaurus, researchers say, dinosaurs were only on land, and after 150 million years of evolution "suddenly we see these adaptations in Spinosaurus where it is able to swim," University of Chicago paleontologist Paul Sereno said.

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The paleontologists studied Spinosaurus fossils — including a skull, claws, and the back sail — found in the Moroccan Sahara, and found that the predator had a snout similar to a crocodile's, paddle-like feet, and dense bones that helped with buoyancy. "Spinosaurus has almost no 'junk in the trunk,'" dinosaur expert Thomas Holtz told National Geographic. "This doesn't make much sense for a land animal that makes a living chasing other land animals. But if it is an animal that doesn’t spend most of its time on land, but instead in the water, it doesn't need strong leg muscles."

Spinosaurus was discovered in Egypt in 1912 by the German paleontologist Ernst Freiherr Stromer von Reichenbach. His findings were destroyed during a World War II bombing in Munich, which brought research to a standstill. Read more about the Spinosaurus and how the paleontologists found these new fossils at National Geographic.