Chapter Four sees a second wave of predators close in, as mosasaurs and plesiosaurs follow the herd as it makes its way along a beach near the ocean. A baby sauropod which had been trapped in the river onto the corpse of a hadrosaur is washed along towards the beach by the tide; as a group of mosasaurs attacks the corpse, it is forced to make a break for the shore. One mosasaur spots it and tries to move in for the kill; by sheer luck, the baby sauropod makes it onto land just as the two baby tyrannosaurs are passing nearby. The mosasaur lunges out of the surf, but the parent tyrannosaur comes rushing to the rescue, fearing for the safety of its young; a massive battle ensues. After a tough fight, both predators ultimately decide to withdraw, with the mosasaur slinking back to the deep and the tyrannosaurs sharing a moment.