Spinosaurus is the first semiaquatic dinosaur ever discovered

The biggest dinosaur predator that ever stalked the Earth was also the weirdest.

Scientists announced on Thursday the discovery in Moroccan desert cliffs of new fossil remains of Spinosaurus aegyptiacus, a 15-metre long, seven-tonne African monster that breaks the mold for how a dinosaur predator looked and behaved.

It was roughly 2.5 metreslonger than Tyrannosaurus rex and equally massive. Living 95 million years ago during the Cretaceous Period, Spinosaurus also is the only known dinosaur adapted for a water-loving, semi-aquatic lifestyle, the study found.

In addition, it was the only known quadrupedal dinosaur predator, unlike carnivores like T. rex, Allosaurus and Giganotosaurus with their typical two-legged stance.

With relatively short limbs, a front-heavy build, flexible tail and flat hind feet that may have been webbed and used for paddling, Spinosaurus plunged into the waterways and enjoyed an all-you-can-eat seafood buffet.

Its elongated, slender jaws and conical teeth were perfect for snaring slippery fish, the scientists found. Its back was topped with a sail-like structure of bony spines twometrestall and connected by skin. It stuck out of the water as Spinosaurus waded and swam after prey like sharks, car-size fish and crocodilians.

"The animal is unlike any other predatory dinosaur. There's no blueprint for it. There's no modern-day equivalent for it. It's looking at a completely new kind of animal," said University of Chicago paleontologist Nizar Ibrahim, who led the study published in the journal Science.

• Coming up: Nazir Ibrahim talks to Quirks & Quarks Saturday, Sept. 13 at noon on CBC Radio One
• Summary of the paper in Science

Spinosaurus terrorized a vast North African river system from Morocco to Egypt. It may not have been agile on land, Ibrahim said, but occasionally may have taken down other dinosaurs.

"Its snaggle-tooth snout, sickle-shaped claws and monstrous sail give this beast a bizarre profile, one that will be immediately recognized by every kid on our planet," added University of Chicago paleontologist Paul Sereno, who also participated.

Spinosaurus's existence has been known for a century since fragmentary remains were found in Egypt by German paleontologist Ernst Stromer. But those were destroyed in a British bombing raid on Munich in 1944. Other partial remains offered mere glimpses if its anatomy.

Nonetheless, the legend of Spinosaurus had begun. It was featured in the 2001 movie Jurassic Park IIIvanquishing a T. rex.

'Mystery man'

Everything changed when a local fossil hunter unearthed a partial skeleton in southeastern Morocco in 2008 near the Sahara oasis town of Erfoud. Combined with fossils held in various museums and drawings of Stromer's finds, an accurate reconstruction of Spinosaurus finally evolved.

But nothing was simple. The remains found by the fossil hunter were spirited out of Morocco, depriving scientists of vital information.

They needed to locate him but did not know his identity beyond being "the mystery man with the mustache." He was finally found in 2013 and led the scientists to the excavation site. More fossils were dug up there and the missing partial skeleton turned up in the basement of a Milan museum.

Using CT scans to study the structure of the bones, the researchers created a digital skeleton model and fashioned a life-size 3D skeleton replica now displayed at Washington's National Geographic Museum.

Ibrahim described Spinosaurus's environment as "the most dangerous place in the history of our planet."

It was the king of waterways teeming with sharks and 11-metrecrocodilians, Ibrahim said. Flying reptiles with wingspans of sevenmeterssoared overhead. On land, the 12-meterdinosaur predator Carcharodontosaurus was on the prowl for a meal.

Its fossils revealed unmistakable adaptations for life mostly in the water. Its unusual body plan including a relatively small pelvis and short hind legs resembles mammalian whale ancestors that appeared 45 million years later.

Small nostrils on the middle of the skull enabled it to breathe when part of the head was submerged, the scientists said. Dense bones lacking marrow cavities of other predatory dinosaurs helped control buoyancy. Powerful, long-boned feet with long, flat claws were probably used for paddling. Its flexible tail could have been used for swimming like in a crocodile.