Palaeontologists have discovered that Spinosaurus, possibly the largest carnivorous dinosaur ever, was adept at moving and hunting in aquatic environments as well as on land.

Researchers have long known that dinosaurs often spent time near rivers and lakes, and from footprints on the riverbed concluded that some could likely swim or at least paddle in the water. However the discovery of a giant fossil in the Sahara desert of a Spinosaurus shows conclusive evidence of a dinosaur that was semi-aquatic, and as comfortable on land as it was in water, similar to crocodiles today.

Scientists from Morocco, Italy, and the US analysed recently uncovered fossils of Spinosaurus aegyptiacus from the Kem Kem Beds in the Sahara, and used them combined with previous finds of the species from around the world to digitally reconstruct a 3D replica of the skeleton.

Their model shows a dinosaur that was 15m long, 3m longer than the largest Tyranosaurus rex ever discovered, but with very unusual proportions, as Prof Paul Sereno from the University of Chicago said:

“What surprised us even more than the dinosaur’s size were its unusual proportions. We see limb proportions like this in early whales, not predatory dinosaurs.”

The Spinosaurus had a number of anatomical adaptations that suited its aquatic lifestyle including nostril higher up the skull to enable breathing while its head was partially submerged and neurovascular openings at the end of its snout, which likely contained pressure sensors to detect movement in the water much as crocodiles do today. It also had a small pelvis and short hind legs with muscular thighs which suited paddling in water and dense bones which aid buoyancy control.

Cristiano Dal Sasso of the Natural History Museum in Milan, Italy, said:

“In the last two decades, several finds demonstrated that certain dinosaurs gave origins to birds. Spinosaurus represents an equally bizarre evolutionary process, revealing that predatory dinosaurs adapted to a semiaquatic life and invaded river systems in Cretaceous North Africa.”

Lead author Nizar Ibrahim of the University of Chicago commented:

“Working on this animal was like studying an alien from outer space; it’s unlike any other dinosaur I have ever seen.”

The researchers’ findings were published in the journal Science in a study titled “Giant dinosaur was a terror of Cretaceous waterways“.