A pod of Liopleurodon appear in Episode 5.2 when the team are sucked into the past as the Liopleurodon's damage the outside of the Nuclear Submarine.
It is seen attacking the sonar reader cable and smashing the sub. It then follows it thru the anomaly. A while later, in the Jurassic, a pod of 3 Liopleurodons appear and start ramming the sub. Near the end of the episode, the pod attacks one more time, but the team make it thru there attacks.