The terrifying spinosaurus wasn’t the scourge of the prehistoric seas after all

The terrifying spinosaurus wasn’t the scourge of the prehistoric seas after all

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The largest predatory dinosaur to ever walk the Earth had a huge sail that rose from its back, but it turns out this imposing creature would have been a very slow and clumsy swimmer, according to new research.

Spinosaurus was even bigger than Tyrannosaurus rex, measuring 13.7 meters in length. The behemoth had an unusual skull shape that made it look more like a crocodile with teeth than a bird of prey, says Paul Sereno, a professor of biology and anatomy of organisms at The University of Chicago.

Spinosaurus mainly hunted very large fish, such as sawfish, lungfish and coelacanths, and had long, scythe-shaped hand claws for catching and tearing them apart. However, the dinosaur was more adapted to living on land and hunting from shore rather than filling the niche of an underwater predator in the water, said Sereno, lead author of a new paper published Nov. 30 in the journal. eLife.

“Do I think this animal would have regularly bathed in the water? Absolutely, but I don’t think it was a good swimmer nor capable of full submersion behavior,” Sereno said.

“This is just not an animal that in your wildest dreams would be as dynamic as a swimmer above water, let alone underwater.”

Spinosaurus has long intrigued scientists.

German paleontologist Ernst Stromer called the prehistoric predator Spinosaurus aegyptiacus in 1915 after the first partial skeleton was discovered by his fossil hunter Richard Markgraf in Egypt.

Stromer, who suggested the dinosaur stood upright on its hind legs and ate fish, exhibited the find at the Munich Paleontological Museum. The fossils were destroyed during Allied bombing in World War II, and only Stromer’s notes and drawings survive.

Many decades later, more fossils were unearthed by miners in the sandstone rocks of southeastern Morocco. Sereno and his team studied the fossils, as well as museum specimens and Stromer’s original notes, and shared their findings in 2014.

A more complete depiction of the predatory dinosaur emerged as one with interlocking oblique teeth perfect for catching fish, a long neck and torso, short back legs, and a towering sail made up of dorsal spines covered in skin.

The dinosaur’s tiny nostrils were further into the skull, allowing it to breathe even when partially submerged in the water. This anatomical clue suggested that Spinosaurus was “semi-aquatic” and waded in the shallows along riverbanks for its prey.

In recent years, other teams have published research while studying new fossils that suggested that Spinosaurus was an entirely aquatic predator with a fleshy paddle-like tail that allowed it to move like an eel, and dense bones that acted as ballast, allowing it to dive deep into the water column.

Sereno and his team returned to their work with Spinosaurus in search of answers about what the terrifying dinosaur’s life had really been like.

Sereno started by facing a mistake in the 2014 paper. When he and his team calculated the dinosaur’s center of gravity, the software didn’t extract enough mass to explain its lungs. This made it look like Spinosaurs had to walk on all fours.

“I like to admit mistakes, especially when I can correct them myself,” said Sereno.

The team collected CT scans of the Spinosaurus skeleton and added layers of muscle and body mass, based on modern reptiles, to virtually construct a new model. This time, Spinosaurus had a center of gravity above its hips and stood erect, just like T. rex and other towering dinosaur predators.

“The stout limbs aren’t there for ballast while swimming, but rather to support the beast’s great weight,” Sereno said.

Spinosaurus was probably better adapted for hunting along coasts rather than diving underwater.

Next, the team turned to Spinosaurus’ tail. Dr. Frank Fish, an expert in tail mechanics and a professor of biology at West Chester University of Pennsylvania, led the way.

Fish compared Spinosaurus’ tails to those of alligators and other reptiles and found that the dinosaur would have been too rigid to function properly underwater. While alligators tuck their limbs in as they swim and have the flexibility to twist and roll underwater to chase prey, Spinosaurus’ massive body mass, high sail, and dangling hind legs would have been a hindrance.

“The back paddles are an order of magnitude too small to produce any resulting paddle motion or force,” Sereno said. “In contrast, no fully aquatic animals have forelimbs proportionally as large as Spinosaurus, since the forelimbs are very inefficient as paddles.”

Its bony, muscular tail wouldn’t have had the flexibility of a whale or fish, and its heavy sail would have been more of an obstacle than a useful aid.

If Spinosaurus had crashed into deep water, the results wouldn’t have been very pleasant.

“His chest would be crushed and he would die in a minute,” Sereno said, not to mention the resistance of his “super ungainly stiff sail and droopy limbs.” And it wouldn’t have been able to catch a fish by swimming after it.

So what was the purpose of the sail?

“Display, like a billboard,” Sereno said. Like some lizards today that have spine-supported sails, Spinosaurus probably used its sail during competition and courtship, he said.

The fossil record also suggests that Spinosaurus was more adapted to rivers and lakes than oceans. Spinosaurus fossils have largely been found in the riverbank deposits of Niger’s inland waterways, which are far removed from prehistoric marine coastlines.

Intriguingly, the dinosaur probably lived along marine and freshwater habitats like other semi-aquatic reptiles, but it’s not something that other extinct or extant large aquatic vertebrates like ichthyosaurs or sea turtles did. So Spinosaurus would have roamed coastal and inland waterways, ambushing prey while wading in shallow waters.

“Nonavian dinosaurs dominated the world for 150 million years, but they never got serious about water,” Sereno said. ‘Of course they can swim like us, but that doesn’t mean we live in the water. We’re talking about whether they were really adapted to aquatic life, and that’s the central question behind all this attention to Spinosaurus.”

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