(CBS) — It’s taken over a century to put together the skeleton of a dinosaur that nightmares are made of.

University of Chicago Paleontologist Paul Sereno says 50-foot long Spinosaurus Aegyptiacus was a cross between a duck and a crocodile with a pointy face filled with sharp teeth, paddling feet, and a huge sail on his back.

Professor Sereno says while it was the largest land predator ever discovered, it actually spent most of its time in the water paddling around and hunting for fish. Sereno says it’s significant because this is the first known instance of a land vertebrate moving its life into the sea as did whales.

Its bones were first discovered over a hundred years ago in Egypt but demolished in World War II. Others were found in an Italian museum and others by nomads in the Kem Kem cliffs of eastern Morocco.

Professor Sereno says he and colleague Nizar Ibrahim and a team from the U of C digitally combined drawings of the original Egyptian bones, isolated bones from the Kem Kem, and the partial skeleton found in Italy to create a skeletal model.

Sereno said the nostrils are moved back halfway up the long snout, suggesting an animal that spent time snatching fish out of the shallows. He says the flat, clawed, and webbed feet point to an animal that paddled around as well as walked on land.

Sereno says Spinosaurus had rather heavy, solid leg bones often associated with terrestrial vertebrates that are moving back into the water.

While Spinosaurus is the longest documented land predator and Sereno says it was hardly carefree – having to keep an eye out for other predators living 95 million years ago, including a 25-foot long sawfish shark sporting a head like a double edged saw with dagger-like teeth on each side of its snout.