Fossils of the monster croc were uncovered in a desert in Niger last year by Sereno and his team. The species, called Sarcosuchus imperator, or "flesh crocodile emperor," was first discovered by French scientists in 1964, but the Sereno find is the most complete fossil skeleton known.

"This new material gives us a good look at hyper giant crocodiles," said Sereno in a statement. "No one had enough of the skull and skeleton to really nail any of the true croc giants until now."

A report on the discovery is to be published today by the journal Science on its Web site Science Express.

Built to Ambush Land Dinos

Sereno said that the elongated skull of the Sarcosuchus is about 6 feet (2 meters) in length and dominated by narrow jaws studded with more than 100 teeth. The upper jaw, tipped with large, sharp and powerful incisors, overlaps the lower jaw, an ideal design to lock and hold onto flesh.

"The teeth are incredibly stout," he said. "They are crushing, penetrating teeth," which means the animal probably fed on land animals more than on fish and turtles, the most common food of modern crocodiles and alligators.

Sereno said the animal's eye sockets are rotated upward, enabling it to remain submerged in water while watching the shoreline.

"This suggests it was an ambush predator, hiding under the water and then surging out to grab anything lounging on the shore," he said.

Snacking on Sauropods

Modern crocodiles living in African rivers often grab large animals, such as wildebeest and zebras, and drag them into the water where they are drowned and then torn apart.

Sarcosuchus probably did the same thing, said Sereno, but because the ancient animal was so large it could easily handle huge dinosaurs, including the massive long-necked, small-headed sauropods that were common in that African region.

"A small sauropod, 20 feet (6 meters) or 30 feet ( 9 meters) in length, would have been no problem," said Sereno. He said the giant croc probably remained still in the water until an animal came to drink and then it whipped its jaws out and sunk its teeth into its prey.

"And that would have been it," Sereno. "Once one of these clamped onto the leg or neck of an animal, there wasn't a lot it [the prey] could do."

Armor Suggests Long Life?

The head, body and part of the tail of the giant crocodile was covered with armor-like bony plates called scutes. Each of these scutes had 40 growth rings and Sereno estimated the animal was about 80 percent fully grown. Based on an analysis of these rings and other signs, Sereno said it probably took 50 to 60 years for the animal to reach full growth.

He said that unlike dinosaurs, which grew rapidly and lived a shorter time, the croc apparently achieved its giant size by living long with an extended growing time.

Michael Parrish, chairman of biology at Northern Illinois University and a noted dinosaur researcher, called the Sereno discovery "an important find."

Sarcosuchus was already known, said Parrish, "but this is a much more complete skeleton" and proves how big the animal was.

"A lot of people have not appreciated how big these crocodiles got," he said.

Parrish, however, noted that measuring age with growth rings in the these animals is an imperfect science and that Sereno's interpretation may not be universally accepted.