9 Extinct Exotic Sea Creatures

The Helicoprion, with its signature circular saw, was reconstructed for a traveling exhibition in 2006. Scott Heath/Flckr

This prehistoric shark (270 million years old) is best-known for its circular, toothy saw, a natural defense tool that was probably pretty effective in warding off underwater enemies. What paleontologists haven't been able to agree about is just where the whorl of teeth was located on the Helicoprion's body. Many assumed that it protruded from the animal's upper or lower jaw, while others surmised that it was connected to the creature's tail [source: Crew].

In 1950, a specimen of the saw was located in a bay in Idaho. The 117-tooth whorl included some cranial cartridge, according to researchers, indicating that it probably sat inside the Helicoprion's mouth. Still, there's little agreement about just where the saw would have been located. Some say it served as a tongue, and others maintain that it probably extended from the animal's lower lip and curled under the chin. Most recently, Idaho paleontologists have used new technology to create a 3-D animated model of what they believe was the shark's skull. It shows the saw connected to the Helicoprion's lower jaw [source: Crew].