Picture a shark-like animal, not with rows of razor-sharp teeth like modern sharks, but with a jaw that unfurls into a perfect spiral—like a buzzsaw made of teeth. Meet Helicoprion, the ...

The Jurassic shark, Hybodus, had a pair of small horns on its head while another species, Stethacanthus, had a dorsal fin shaped a lot like an iron. Weirdest of all was probably Helicoprion ...