Until now, every known marine crocodilian had a head of one basic type, with a long snout and many sharp, identical teeth. But "Godzilla" had a short, high snout and teeth that were large and serrated, like a terrestrial reptile's.
"It is more like a carnivorous dinosaur than like a marine crocodilian," said James Clark, a dinosaur expert at George Washington University in Washington, D.C.
- "SuperCroc" Fossil Found in Sahara
- "Biggest Fish Ever Found" Unearthed in U.K.
- Holy Squid! Photos Offer First Glimpse of Live Deep-Sea Giant
- New "Hobbit" Human Bones Add to Evidence, Oddity
- Photo Gallery: "Godzilla" Fossils Unearthed in South America
- Photo in the News: Dino Species Flew Like a Biplane
Pol says Dakosaurus's anatomical changes over the generations represent "the most drastic evolutionary change in the history of marine crocodiles."
The animal's unusual features suggest that it had completely different feeding habits from its relatives. While other marine crocs fed on small fish, Dakosaurus hunted for marine reptiles and other large sea creatures, using its jagged teeth to bite and cut its prey.
"The most perplexing thing about the animal is that its head shape does not appear to be well suited to a fast swimming crocodilian, because rather than being streamlined, it is somewhat high and flattened from side to side," said Clark, who was not involved with the research.
"Presumably it moved its head mainly up and down rather than sweeping it from side to side, like fish-eating crocodilians."
Other paleontologists expressed admiration over the find.
"This new species is another expression of the incredible diversity of crocodile life during the dinosaur era," said Paul Sereno, a University of Chicago paleontologist and National Geographic Society Explorer-in-Residence.
"If you went to a crocodile worker and said, Let's say you had a chance to evolve something new out of this group, what would you do? And you gave them a pad and a pencil, the last thing they would draw would be a skull that looks like Dakosaurus.
"It's a beautiful example of the unpredictable nature of evolution, and the variety of things that dinosaur-age crocodiles did."
"The cranial anatomy of this species expands the known range of anatomical diversity to a realm no one thought could exist," said Hans Larsson, a paleontologist at McGill University in Montreal, Canada. "It's hard to imagine now a skull shape and ecological role that crocodyliforms did not achieve."
Sereno and Larsson were among a group of paleontologists working in Niger from 1997 to 2000 that found remnants of a 40-foot-long (12-meter-long) crocodilian they dubbed Supercroc.
Surprisingly, the nostrils, eye sockets, and other areas of Dakosaurus's skull suggest the animal was more closely related to the smallest of its crocodile relatives than to any of the larger species.
The researchers don't yet know what events triggered the relatively sudden emergence of Dakosaurus, nor do they know what caused it to go extinct.
But scientists do know that it was just one of the "sea monsters" that inhabited the world's oceans 250 million to 65 million years ago.
Others included a Loch Ness monster-like plesiosaur, with a 20-foot-long (6-meter-long) neck, and ichthyosaurs that may have grown to be 75 feet (23 meters) long.
"These groups all went extinct about the same time as the dinosaurs and the whales appeared shortly afterward and seemed to have replaced them ecologically," Clark said.
Free E-Mail News Updates
Sign up for our Inside National Geographic newsletter. Every two weeks we'll send you our top stories and pictures (see sample).
SOURCES AND RELATED WEB SITES