Instructions
Press the "R2" button on your controller. This will pull up your on-screen character's V.A.T.S. screen. The V.A.T.S. is a computer guidance system that helps with aiming and that also displays information about allies and enemies in your general area.
Move the right joystick on the controller to the left or right to change the target that you currently have selected. Select as your target the mutated animal about which you want more information.
Look at the name of the mutated animal on screen. The name will tell you what the animal used to be prior to the nuclear holocaust. For example, the "Mutated Rat" used to just be a regular rat prior to absorbing nuclear radiation.