After all, the fearsome Spinosaurus was not the scourge of the prehistoric seas

Subscribe to CNN’s Wonder Theory Science Newsletter. Explore the universe with news about fascinating discoveries, scientific advances and more.

CNN
—

The largest predatory dinosaur to ever walk the Earth sported a massive sail rising from its back, but it turns out this imposing creature would have been a very slow and awkward swimmer, according to new research.

Spinosaurus was even larger than Tyrannosaurus rex, measuring 45 feet (13.7 meters) long. The colossus had an unusual skull shape that made it look more like a toothy crocodile than a raptor, said Paul Sereno, a professor of organismal biology and anatomy at The University of Chicago.

Spinosaurus mainly hunted very large fish, such as sawfish, lungfish and coelacanths, and had long scythe-like hand claws to grab and tear them apart. However, the dinosaur was better suited to living on land and hunting from shores rather than filling the niche of an underwater aquatic predator, said Sereno, lead author of a new paper published on 30 November in the magazine. eLife.

“Do I think this animal would have gone into the water regularly? Absolutely, but I don’t think it was a good swimmer or capable of full immersion behavior,” Sereno said.

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

Spinosaurus has long intrigued scientists.

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

Stromer, who suggested the dinosaur was standing on its hind legs and snacking on fish, displayed the find at the Paleontological Museum in Munich. The fossils were destroyed during Allied bombing in World War II, and only Stromer’s notes and drawings survived.

Many decades later, miners discovered more fossils 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 slanted, interlocking teeth perfect for catching fish, a long neck and trunk, short hind legs, and a towering sail made up of fur-covered spines.

The dinosaur’s small nostrils were further back on the skull, allowing it to breathe even when partially submerged in water. This anatomical clue suggested that Spinosaurus was “semi-aquatic” and entered the shallow waters along river banks to search for prey.

In recent years, other teams have published research while studying new fossils this suggested that Spinosaurus was a fully aquatic predator with a fleshy paddle-like tail that would have 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 life was really like for the fearsome dinosaur.

Sereno began by confronting a bug in the 2014 paper. When he and his team calculated the dinosaur’s center of gravity, the software didn’t deduce enough mass to account for its lungs. This made it look like Spinosaurs would have to walk on all fours.

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

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

“The solid limbs are not there for ballast while swimming, but to support the great weight of the beast,” Sereno said.

Next, the team headed to Spinosaurus’ tail. Dr. Frank Fish, an expert on tail mechanics and professor of biology at West Chester University in Pennsylvania, took the lead.

Fish compared the tail of Spinosaurus to that of alligators and other reptiles and found that the dinosaur would have been too stiff to function well underwater. While alligators stick out their limbs while swimming and have the flexibility to turn and roll underwater in search of prey, Spinosaurus’s huge body mass, tall sail and dangling hind legs would have been a hindrance .

“The back paddles are an order of magnitude too small to produce any consequential paddle motion or power,” Sereno said. “No fully aquatic animal, by contrast, has forelimbs as large as Spinosaurus, since the forelimbs are very inefficient as paddles.”

Its bony, muscular tail would not have had the same flexibility as a whale or fish, and the heavy sail might have been more of a hindrance than a useful tool.

If the Spinosaurus was sunk in deep water, the results would not have been very pleasant.

“His thorax would be crushed and he would die within a minute,” Sereno said, not to mention the drag of his “super stiff, frayed sail and dangling limbs.” And I wouldn’t have been able to catch fish swimming after them.

So what was the purpose of the candle?

“Display, like a billboard,” Sereno said. Similar to some modern lizards that have spine-supported sails, Spinosaurus likely used its sail during competition and courtship, he said.

The fossil record also suggests that Spinosaurus was more adapted to rivers and lakes than to oceans. Fossils of Spinosaurus have been found largely in riverbank deposits of the Niger interior basins, which are far from prehistoric marine shores.

Interestingly, the dinosaur probably lived throughout marine and freshwater habitats like other semi-aquatic reptiles, but not something other extinct or extant large aquatic vertebrates like ichthyosaurs or sea turtles did. So Spinosaurus would have prowled coastal and inland waterways, ambushing prey as they ventured into shallow water.

“Ancient dinosaurs ruled the world for 150 million years, but they never entered the water in a serious way,” Sereno said. “Sure, they could swim just like us, but that doesn’t mean we’re aquatic. We’re talking about whether they were really adapted to life in water, and that’s the central question behind all this attention on Spinosaurus.”