King of the ancient seas

Bus-sized marine reptile had teeth with serrated edges

BRISTOL, England — 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 newly described marine creature, whose remains were discovered at a remote site in central Nevada, lived about 240 million years ago, at a time early in ichthyosaur evolution, Nadia Fröbisch reported September 23 at the Society of Vertebrate Paleontology annual meeting. Most of the ichthyosaurs known from this era have one of two types of teeth: sharp, conical teeth that grabbed slippery prey such as fish or broad blunt teeth that crushed shell-bearing creatures like today’s nautilus. A few ichthyosaurs, presumably those with a more varied diet, had both types of teeth. But the new creature’s teeth are unlike any seen in an ichthyosaur of that era, said Fröbisch, a vertebrate paleontologist at the University of Chicago.

Rather than having a round cross-section, the teeth were roughly diamond-shaped with serrations along their front and rear edges — a type of dentition particularly well-suited to shearing flesh, Fröbisch said. This might have allowed the ichthyosaur to bite chunks out of large prey.

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,” Fröbisch said. Although some ichthyosaurs that evolved millions of years later also had serrated teeth, those predators weren’t nearly as large.

Knife-toothed ichthyosaurs may have been relatively widespread, says Donald Henderson, a paleontologist at the Royal Tyrrell Museum in Drumheller, Canada. Just two weeks ago, he excavated isolated specimens of similar but larger teeth from rocks of nearly the same age during a field trip in British Columbia. “I was mystified when I first saw them,” he says. “I thought they had possibly belonged to a dinosaur.”

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