What it was
An animal from about 270 million years ago with a spiral of 117 teeth, 23 centimeters across. It looks like a shark, and it was not one. On the family tree it sits closer to the ratfish.
Where the spiral went
For a century nobody could place it. People drew the spiral on the snout, on the back, even on the tail. Then a scan in 2013 settled it. The spiral sat inside the lower jaw, filling the whole of it.
Every tooth it ever grew
Helicoprion never shed a single tooth. It kept every one, curling back into the coil.