Sauron could shapeshift

Therefore he took upon himself the form of a werewolf, and made himself the mightiest that had yet walked the world.....


Then Sauron shifted shape, from wolf to serpent, and from monster to his own accustomed form;.............


And immediately he took the form of a vampire, great as a dark cloud across the moon...............

The Silmarillion: "Of Beren and Luthien"