Helicoprion had a buzzsaw-shaped tooth whorl on its lower jaw, which is what it's famous for. The most up-to-date reconstruction suggests it being a shark-like fish with a long upper jaw and a long lower jaw. At the end of the lower jaw was where the tooth whorl was.
|© Life Before the Dinosaurs 2012|
Although it is sometimes reconstructed eating ammonites, the absence of broken teeth on most specimens of its tooth whorl suggests that instead of eating ammonites, it fed on animals such as squid, fish, and other animals without shells.
Although most specimens of Helicoprion's tooth whorl are about 10 inches in diameter, one specimen has a diameter of about 2 feet, suggesting that this odd shark-like cartilaginous fish might have grown more than 32 feet long, which makes Helicoprion one of the largest cartilaginous fish of all time. Only Megaladon, which didn't appear until the Tertiary period, was larger.
|© Shark Trust|
Helicoprion lived from the Carboniferous to the Triassic, which is quite a long time for a single genus to be around.
© Oleg Lebedev 2009
http://www.paleospot.com/galerie_rubrique.php?rub=2 (lots of amazing illustrations of prehistoric sharks)