A fierce prehistoric seagoing creature--an animal so bizarre it was dubbed "Godzilla" by scientists who found it--has been unearthed in a fossil-rich Argentine desert at the foot of the Andes.

Between 12 and 15 feet long, with a bullet-shaped head like a meat-eating dinosaur, large, serrated teeth, flippers instead of legs and a fishlike tail, it is considered a "crocodyliform," the term for crocodiles and their extinct relatives.

But the features of this animal, described online Thursday by the journal Science, are drastically different from other crocodyliforms, which had long, slender snouts.

During the late Jurassic Period 135 million years ago, when this animal was alive, it may have been a top ocean predator capable of gobbling other marine reptiles and large prey, scientists said. The region where it was discovered used to be a deep, tropical ocean bay.

"The recent film monster Godzilla frightened the people of New York City, but our Godzilla terrorized creatures in the Pacific Ocean," said the leader of the discovery team, Argentine paleontologist Zulma Gasparini, of the National University of La Plata.

"We are calling him the chico malo--the `bad boy' of the ocean."

Gasparini has spent 30 years exploring the Nequen Basin, an area of northwestern Patagonia, with colleagues from Argentina and elsewhere. The paleontologist has accumulated the largest and most diverse collection of prehistoric marine reptiles ever found in the Southern Hemisphere.

"The new discovery is quite stunning. The skull shape is really bizarre and the long, curved teeth and short snout is an amazing combination," said University of Chicago paleontologist Paul Sereno, who in the Sahara discovered the 110 million-year-old "SuperCroc" (Sarcosuchus imperator), which was 40 feet long and weighed 17,500 pounds.

"We're finding other kinds of combinations in Africa that sort of break the mold for crocodiles," Sereno said. "But let's make room for this new kid on the block because it's really strange."

The Argentine scientists are credited with expanding knowledge of ichthyosaurs that may have reached 75 feet in length, Loch Ness monsterlike plesiosaurs with 20-foot necks, and crocodiles and turtles from fossils formerly found only in the Northern Hemisphere.

Such "sea monsters," as scientists whimsically call them, lived in the world's oceans 250 million to 65 million years ago. Marine crocs were abundant and found worldwide. Shallow seas and lack of marine predators created new niches for many reptiles that had developed on land.

The paper announcing the find was published on the ScienceExpress Web site and will be printed later in Science; the creature also appears on the December cover of National Geographic magazine. The research was partly funded by the National Geographic Society.

Scientists know that Godzilla is a crocodyliform because its skull, however unusual, shares key characteristics with other crocodiles. But the creature, whose scientific name is Dakosaurus andiniensis, "is certainly the most bizarre of all marine crocs," said a member of the research team, Diego Pol of Ohio State University.

"This animal forms a very distinct lineage that appears early in the evolution of crocodiles--invading the sea and showing outstanding adaptation to the marine environment," Pol said. "This was a top predator that probably was 12 feet long and swam around using its jagged teeth to bite and cut its prey, like dinosaurs and other predatory reptiles did. Nobody had expected to find these features in a marine croc."

Unlike most modern crocodiles and alligators, which are freshwater reptiles and divide their time between land and water, Godzilla would have lived in the sea, regularly swimming up for oxygen and returning to the depths for hunting. It probably ate large marine reptiles like ichthyosaurs and plesiosaurs, Pol said.

The creature was not a direct ancestor of crocodiles, and scientists don't know why it became extinct. Crocodiles are one of the most successful reptilian predators, outliving dinosaurs after evolving to become widespread during the Cretaceous Period more than 65 million years ago.

"This new creature was doing things that were different--for example, it wasn't able to move its head quickly from side to side, like other fish-eating crocodilians. Its teeth are more like you see in dinosaurs," said Greg Buckley, a fossil crocodile specialist at Roosevelt University in Chicago.

"This discovery was special. Nothing like it was ever found before. Today, we have a few croc species that can deal with a saltwater environment, but we're pretty limited with crocodile diversity.

"What strikes me is that this is another new thing, another new animal that was discovered that's completely unexpected. These finds seem to be happening all the time."

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pgorner@tribune.com