If you dug up a fossil that looked like a circular saw blade made of teeth, you’d be forgiven for being a little confused. Was it some sort of toothy nautilus? A relic of a dinosaur’s carpentry shop?
When Helicoprion (meaning “spiral saw”) was first discovered in 1899, its whorl of teeth was one of the few things identified. Even though there were few skeletal clues, it was quickly decided that these teeth were from a cartilaginous fish. But where did these “teeth” fit in? On the body? Some freaky mouth appendage?
Over a century of confusion followed, but recent work using X-ray analysis of fossil specimens has all but confirmed that this fish used a spiral-fed whorl of teeth, constantly regrowing as today’s sharks do, to catch soft prey like squid, 270 million years ago. It’s actually not a shark at all, but a ratfish, a branch of cartilage-skeletoned fish that branched from sharks in prehistoric times.
Check out more great analysis by Brian Switek at Laelaps. He also features even more great art by Ray Troll, a Helicoprion aficionado who did the image at top.