Lots was happening on land in the Carboniferous Period, but in the sea, it was the golden age of sharks and their kin. More types of these fearsome fishes existed than at any other time in Earth’s history. They may have had few competitors for food and few predators (placoderms went extinct about 345 million years ago). Like today’s sharks and their relatives, Carboniferous species had skeletons made of flexible cartilage, but they showed notable differences. Some sported a weird whorl of teeth at the front of the jaw. Others had odd-shaped heads and long snouts. Sharks like those in today’s oceans didn’t arise until much later, during the Cretaceous Period.

Peaking during the Permian Period, the whorl-toothed “shark” Helicoprion, actually a ratfish relative, had a bizarre buzz-saw blade of teeth whose fit and function have puzzled paleontologists.

The strange, anvil-shaped brush of calcified cartilage behind the head of Akmonistion zangerli (from today’s Scotland) may have identified this fish to others of its species.

The odd-looking shark relative Edestus heinrichsii had a curled mouth full of curving teeth.