A fossil of a giant dinosaur from 95 million years ago has been confirmed as that of the first-known swimming dino, researchers say.
Also considered the largest-known carnivorous dinosaur, Spinosaurus possessed flat feet that would have served as paddles and nostrils at the very top of its crocodile-like head that would have let it submerge itself in the ancient rivers of North Africa, they say.
A giant sail on the creature's back would have cut through the surface like a shark's fin as the 50-foot-long predator cruised in search of prey such as fish and crocodiles, researchers report in a paper in the journal Science.
Until Spinosaurus, dinosaurs had been confined to the land for 150 millions years, then "suddenly we see these adaptations in Spinosaurus where it is able to swim," says study co-author Paul Sereno, a paleontologist at the University of Chicago.
Bones of Spinosaurus aegyptiacus, including the skull, its claws, and the bones forming its sail, were unearthed in sandstone layers in the Moroccan Sahara.
While other creatures like the plesiosaur and mosasaur lived full-time in water, they were marine reptiles, not dinosaurs, the researchers note.
Spinosaurus represents only semi-aquatic dinosaur ever discovered, they say.
"It is a really bizarre dinosaur-- there's no real blueprint for it," says study lead author Nazar Ibrahim, also of the University of Chicago.
The body shape of Spinosaurus suggests it would not have been as agile while on land as other dinosaurs were, more evidence it passed a substantial portion of its life in water, he says.
Spinosaurus lived in an ancient waterway dubbed "the river of giants," a huge system of rivers and swamps that once stretched from Morocco to Egypt, the researchers say.
"The animal we are resurrecting is so bizarre that it is going to force dinosaur experts to rethink many things they thought they knew about dinosaurs," Ibrahim says.
The new findings are the culmination of almost 100 years of research.
A German paleontologist, Ernst Stromer, first described Spinosaurus from a partial skeleton he found in Egypt in 1915 and brought back to Germany.
Unfortunately, the fossil bones were destroyed during Allied bombing raids on Munich during World War II, and no further fossils -- except for some very small fragments -- were ever found until the discovery of the Moroccan example in 2008 that came to the attention of Ibrahim and his colleagues.
Subsequent finds have helped yield a picture of a unique creature, researchers say.
"It's a chimera. It's half-duck, half-crocodile," Sereno says. "We don't have anything alive that looks like this animal."
