Biologists say dinosaur swam
An enigmatic predatory dinosaur that lived in northern Africa about 95 million years ago possessed a long, powerful tail that may have propelled it through water, new fossils suggest.
If true, this beast, close to 12 metres long and not yet fully grown when it died, was a rarity: a dinosaur that swam.
“What we have here is a dinosaur that was not just a wader but an animal that was actively pursuing prey in the water column,” said Nizar Ibrahim, a professor of biology at the University of Detroit Mercy in Michigan.
In a paper published in the journal Nature, Ibrahim and his colleagues described the skeleton of Spinosaurus aegyptiacus — its name means “Egyptian spine lizard.” Long spines rose vertically from the bones in the 4.5-metre-long tail, forming a finlike structure that, the scientists theorize, could undulate back and forth.
Think of it as a cross between a lizard and an eel — at the scale of a Tyrannosaurus rex.
“It’s an animal that really has no modern-day equivalent,” Ibrahim said. “You’re working on an extraterrestrial from outer space in many ways.”
In a water tank, the scientists showed that a plastic cutout in the shape of the tail was better at generating propulsion than the tails of other dinosaurs. The thrust and efficiency was comparable to contemporary aquatic creatures like crocodiles, the scientists said.
“In addition to the tail being weird-looking, it also made perfect sense,” said Matthew C. Lamanna, a paleontologist at the Carnegie Museum of Natural History in Pittsburgh, who was one of the reviewers of the Nature paper.
David Hone, a paleontologist at Queen Mary University of London in England, who was not involved with the research, lauded the fossil specimen.
“We don’t have too many good dinosaur tails, generally,” he said. “It’s really quite weird in lots of ways, which is really interesting and really neat.”
But, he added, “I’m extremely unconvinced by some of the ecological interpretations that they placed on it.
Hone said the small-scale experiments were intriguing, but that it was too much of a stretch to claim that Spinosaurus was a fast enough swimmer to chase down prey in the water.
“It’s not that they’re wrong,” he said. “It’s just I don’t think you can support that argument with the available data.”
In 2014, Ibrahim described a well-preserved fossil unearthed in Morocco, arguing that it possessed features — crocodile-like jaws, dense bones that might have served as ballast, flat feet that resembled paddles — that seemed suited for life in water.
Today, this region is the Sahara, the largest desert in the world. But in the days of the Cretaceous period, when Spinosaurus roamed, it was a vast system of rivers and lakes.