He looks almost identical to the modern-day Gary, but he is much more larger. The only real differences are that Prehistoric Gary has eight light green spikes coming out from his shell like how a gigantspinosaurus has spines coming from its back, has three Stegosaurus-like tail spikes, the ones on the left and right have the same size while the one in the middle is the shortest, and he sports a large thick black unibrow.
Role in episode
He first appears when SpongeGar leaves and says, "Bunooga ready! Tabunga, Gary." Gary does not move. SpongeGar then 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.
Role in Lights, Camera, Pants!
He is not a huge monster. Also, when the mouse rolls over him, captions are not seen.
Prehistoric Gary does not like Squog, similar to how Gary does not like Squidward.