A simplified evolutionary tree of predatory dinosaurs (theropods) showing the time span in which Saltriovenator existed is pictured in this handout illustration Thomson Reuters By Will Dunham

WASHINGTON (Reuters) - Scientists have unearthed fossils of a large meat-eating dinosaur that stalked northern Italy 198 million years ago that was remarkable both in life and in death.

The researchers said on Wednesday Saltriovenator zanellai was about 25 feet long (7.5 meters) and weighed at least a ton, meaning that when it lived early in the Jurassic Period it was the largest-known carnivorous dinosaur that had ever existed.

Its demise also was noteworthy.

After dying, the Saltriovenator's carcass somehow floated into the sea and sank to the bottom, where it was scavenged over a period of months or years by numerous marine creatures before fossilizing, the researchers said. The bones bear marks likely left by the gnawing of sharks and fish as well as signs of feeding by invertebrates such as sea urchins and tiny holes penetrating the bone apparently left by marine worms.

"This is absolutely unique," said Milan Natural History Museum paleontologist Cristiano Dal Sasso, who led the research published in the scientific journal PeerJ. "In the scientific literature, there is mention of some dinosaur bones scavenged only by terrestrial animals, such as other dinosaurs, and, more rarely, insects. At least three kinds of marine animals left those traces on the bones of Saltriovenator."

Saltriovenator, which combined traits of primitive meat-eating dinosaurs with those of more advanced ones, foreshadowed a succession of even bigger predatory dinosaurs that lived later in the Jurassic and in the Cretaceous Period. It is the second dinosaur ever unearthed in Italy.

Saltriovenator, meaning "hunter from Saltrio," walked on two legs, had a skull 2-1/2-feet long (80 cm) studded with sharp serrated teeth and had hands with four fingers, three of which possessed claws. It was about 24 years old, still not quite fully grown. It lived in a coastal, Caribbean-like environment and likely hunted plant-eating dinosaurs and maybe smaller carnivorous dinosaurs, the researchers said.

Dinosaurs first appeared about 230 million years ago during the Triassic Period. The earliest meat-eating dinosaurs were overshadowed by larger non-dinosaur predators that died off by the end of the Triassic. With the competition gone, there was a great leap in size for carnivorous dinosaurs during the Jurassic.

The fossils were discovered in 1996 in a quarry near the village of Saltrio, roughly 50 miles (80 km) north of Milan in Italy's Lombardy region. This led to an arduous process of extracting the bones from the hard surrounding rock.

(Reporting by Will Dunham; Editing by James Dalgleish)