King of the ancient seas.

Paleontologists have unearthed the nearly complete remains of an immense ichthyosaur with serrated teeth, an evolutionary innovation that would have rendered the behemoth the top predator in its ecosystem.

The marine creature, whose remains were discovered in central Nevada, lived about 240 million years ago, at a time early in ichthyosaur evolution, Nadia Fr6bisch of the University of Chicago reported September 23. Most of the ichthyosaurs known from this era have one of two tooth types: sharp, conical teeth that grabbed slippery fish or broad blunt teeth that crushed shell-bearing creatures. A few ichthyosaurs, presumably those with a more varied diet, had both tooth types. But the new creature's teeth are unlike any seen in an ichthyosaur of that era, Fr6bisch said.

Rather than having a round cross section, the teeth were roughly diamond-shaped with serrations along the front and rear edges--a dentition particularly well-suited to shearing flesh.

And the ancient creature was huge: Even though erosion had removed much of the snout, the fossil was more than 10 meters long. An adult of the species probably measured between 11 and 15 meters long, she noted.

"This ichthyosaur could have been the T. rex of the seas," Frobisch said. Although some ichthyosaurs that evolved millions of years later also had serrated teeth, those predators weren't nearly as large.