Prehistoric Gary looks almost identical to the modern-day Gary, but he is much larger. The only real differences are that Prehistoric Gary has light green spikes coming out from his shell like how a gigantspinosaurus has spines coming from its back, has three Stegosaurus-like tails, and sports a thick black unibrow.
He first appears when SpongeGar leaves and says, "Bunooga ready! Tabunga, Gary." Gary does not move. SpongeGar says more sternly, "Gary, tabunga!" Gary finally obeys. He knows Squog is very afraid of him due to his size. Prehistoric Gary leaves slime trails everywhere, which annoys Squog. His slime trails are commonly known as "tabunga" among the trio.
Prehistoric Gary also appears in Lights, Camera, Pants!, but is not a huge monster. Also, when the mouse rolls over him, captions are not seen.