This week's Friday Fossil is Helicoprion.
What can I say. This is one weird bastard. And it used to look even weirder,
The story is like this. At the turn of the last century, people started to find these strange dinner plate sized fossils that look superficially like ammonites,
But then, on closer inspection, they look uncannily like shark teeth...
It became part of the life's work of a russian paleontologist named Andrzej P. Karpinski to reconstruct this beast. He tried it on the dorsal fin, like a windmill. He tried it on the tail, like a piglet. He even tried it on the tip of its nose, like an evil elephant. But, his contemporary, a Russian paleoichthyologist called Dimitri Obruchev, decided that a location in the lower jaw "would only prevent the fish from feeding" an placed the whorl in the upper jaw, thinking that it could act as a shock absorber for the animal's head.
Today, however, we generally agree that the helical structure must have been part of the lower jaw, based on the skull of a relative, Ornithoprion. But then, we still have this enormous problem of how a reconstruct a shark that apparenly had a 3 foot wide buzz saw for a lower jaw.
The interesting thing is that its teeth are all remarkably perfect. Considering that paleozoic sharks shed their teeth even more slowly than modern sharks, this probably means that they weren't even used for biting.
