Ancient sharks swam the seas during the Permian period. In classification, a phylum is a group of related or similar organisms. A phylum contains one or more classes. They eat stray bits of food left by the shark. They are carnivores that are distantly related to dogs and bears.
Many sharks eat pinnipeds, including the great white shark.
They diviersified and came to dominate the seas by the Devonian. They went extinct bout 355 million years ago. They had hinged bony armor on their head and thorax. They had no teeth, but did have bony reidges that acted like teeth. Placoderms were early fish, but not sharks.