Paleontologists Unearth Fossils Of Spinosaurus, The First-Known Aquatic Dinosaur

Paleontologists in the Moroccan Sahara unearthed one of the largest intact dinosaur fossils ever found in the region: a mostly-complete tail of the first-known aquatic dinosaur.

Scientists think 50-foot-long Spinosaurus aegyptiacus sported a large sail on its back and cruised ancient rivers about 100 million years ago. The findings were published in the journal Nature last month.

The massive fin-like Spinosaurus tail is “utterly bizarre” and unique, says Nizar Ibrahim, a National Geographic explorer and University of Detroit Mercy paleontologist whose work was funded by the National Geographic Society. The propulsive organ moved the animal through the water, he says.

Spinosaurus also had a long, narrow snout comparable to a crocodile with cone-shaped teeth to catch slippery prey like fish, he says. The dinosaur also had dense bones to control buoyancy and relatively small hind limbs.

“There are a number of clues in the skeleton that tell us that this was a water-loving dinosaur,” he says. “But the tail really is the most important part because it's absolutely huge and it really does look like a giant paddle.”

Before digging up the tail, Ibrahim’s team worked on the site for a number of years and most people thought everything was uncovered. But he thought the largest part of the skeleton was buried under 15 tons of rock.

After removing the rocks on a steep escarpment during 120-degree heat, the team “hit the jackpot,” he says. That’s when Ibrahim’ realized this discovery would change the way scientists look at dinosaurs.

“Everything that could possibly go wrong did go wrong. We had sandstorms and close encounters with snakes and flooding in the Sahara. You name it, we experienced it,” he says. “But it was worth it.”

While Spinosaurus’s tail, teeth and jaw are often compared to crocodiles, the two animals are only distantly related. These similarities are examples of convergent evolution, he says, which is the independent evolution of similar features in species from different periods.

Since there’s no modern-day equivalent to Spinosaurus, Ibrahim compares examining how the specimen feels to working on an extra-terrestrial. The giant predator looks like a river monster out of a story about dragons, he says.

Massive river systems existed in the area we now call the Sahara Desert. Enormous fish called these rivers home: coelacanth the size of cars, 25-foot long sawfish and giant lungfish, he says.

For a long time, scientists believed dinosaurs didn’t invade aquatic habitats, he says. Spinosaurus is the first example of a water-loving dinosaur, which he says “opens a whole new window of ecological opportunities for dinosaurs.”

Ibrahim thinks this study will inspire museums around the world to take another look at the fossils in their paleontological collections for similarities with Spinosaurus, like dense bones and long spines on the tail. His team presented evidence for this dinosaur’s aquatic habits, but it’s unclear if Spinosaurus was the only creature of its kind to explore the water.

“For now, Spinosaurus is the only dinosaur that shows unambiguous evidence for essentially a fully aquatic lifestyle,” he says.

For more on this discovery, visit natgeo.com

Chris Bentley produced and edited this interview for broadcast with Peter O'Dowd. Allison Hagan adapted it for the web.