This is Liopleurodon. Even though it was smaller than megalodon it was still a giant is was an efficient hunter, attacking in packs to take down large pods of whales. This powerful beast was one of megalodon's only rivals for food.
This one is Tylosaurus also a giant but smaller than liopleurodon and megalodon but bigger than the plesiosaurs this was another one of megalodon's rivals for food.
This is the plesiosaur there were several different kinds, the largest probably being elasmosaurus. They had long powerful necks and jagged strong teeth for catching prey. Like liopleurodon they hunted in packs.