The very first time you fight the V-Rexes, there is a ledge which you can climb onto so they cannot attack. However, once you are up there, you will be attacked by the flying dinosaurs. They are not hard to defeat. When you are up there, go into Fury mode by repeatedly tapping Triangle until Kong smacks the ground. While in Fury mode, attack the V-Rexes one at a time. After you have hit one of them three times with X, they will be temporarily knocked out. You can then perform a finishing move by repeatedly tapping Circle or X. If done correctly, Kong will snap the V-Rex's jaw in two or throw it.