A freshman geology student on a field trip stumbled across the fossil of an oversized, salamander-like creature with vicious crocodile-like teeth that lived about 300 million years ago, paleontologists said.

Scientists say the find is both a new species and a new genus, a broader category in the classification of plants and animals. Talks are under way about what to call the new species, starting with "Striegeli" — after the University of Pittsburgh (search) student who discovered it.

Initially, Adam Striegel picked up the softball-sized rock along a fresh road cut near Pittsburgh International Airport (search), and thinking it was of little interest, threw it aside. Walking back through the same area, he retrieved the stone and showed it to class lecturer Charles Jones.

Jones spotted the teeth first, then the outline of a skull.

"It was immediately clear that this was rare," Jones said Monday.

Paleontologists with the Carnegie Museum of Natural History (search) also were stunned when the impeccably preserved fossil from a trematopid amphibian was unearthed this past spring in their own back yard. The discovery has set off a hunt for bigger finds that could help define a gray area in the Earth's history in what is now the northeastern United States.

The creature, believed to have been 3 to 4 feet long, is "new to science but we know it belongs to fairly terrestrial-adapted amphibians living in the Pennsylvanian Period (search), about 300 million years ago," said Christopher Beard, curator of vertebrate paleontology at the museum.

Carnegie paleontologist Dave Berman knew exactly what the stone-encased skull fossil was because only two others of the same family are known to exist. He found one of them more than a decade ago in New Mexico.

The species has some characteristics of a crocodile, but is closer to a massive salamander — one that could tear its prey to shreds.

"This is much more advanced, meaning that they first appeared even further back then we had thought, perhaps another five or 10 million years, but that's still a guess right now," Berman said.

The rock encasing the fossil has been carefully chipped away by Berman and his team, revealing a boxy skull slightly larger than that of a large cat. The cheeks are roughly at right angles to the top of the skull. Long rows of spiky teeth along with three sets of "tusks" line the roof of the mouth.

In the coming months, Scientists will fan out across the area where the fossil was found as vegetation dies off, looking for the rest of the body, and possibly more.

"It was a lucky shot that kid found the fossil for sure, but at the same time the road construction in that area has revealed ancient layers of rock," Beard said. "It is now an optimal time to go back out. Ideally we may be able to reconstruct the entire ecosystem, plant and animal life of 300 million years ago," he said.

Striegel did not return phone calls Monday from The Associated Press.