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The only surviving evidence of the prehistoric shark Helicoprion is a tight, curled-up coil of triangular teeth, a bit like a fruit roll-up, but considerably deadlier. As far as paleontologists can tell, this bizarre structure was attached to the bottom part of Helicoprion's jaw, but exactly how it was used, and on what prey, remains a mystery. Some experts think the coil was used to grind away the shells of swallowed mollusks, while others (perhaps influenced by the movie Alien) think Helicoprion unfurled the coil explosively like a whip, spearing any unfortunate creatures in its path. Whatever the case, the existence of this coil is proof that the natural world can be stranger than (or at least as strange as) fiction!
A recent fossil analysis, conducted with the aid of a high-resolution CT scanner, appears to have solved the Helicoprion enigma. Apparently, this creature's whirled teeth were actually housed inside the bone of its lower jaw; the new teeth gradually "unfurled" into Helicoprion's mouth and pushed the older ones further away (indicating either that Helicoprion replaced its teeth unusually rapidly, or that it subsisted on soft-bodied prey like squids). In addition, when Helicoprion closed its mouth, its distinctive tooth whorl pushed food further into the back of its throat. In this same article, the authors argue that Helicoprion was not in fact a shark, but a prehistoric relative of the cartilaginous fish known as "ratfish."