For almost 50 million years, there was nothing around to eat the sharks.
— Allen
in Big Blue Killer Whale

Physogaleus was a very small species of prehistoric shark from the Eocene period. These sharks hunted fish in the open ocean and also often lived in mangroves, where they ate Apidium, but were too small to attack creatures like a Moeritherium. These sharks though were small fry compared to Basilosaurus and are often preyed upon by these whales.