Prehistoric Gary is a huge version of Gary only seen in the episode "Ugh." He is extremely large with spikes on his shell. He is owned by SpongeGar. He is first seen when SpongeGar leaves and says, "Bunooga ready! Tabunga, Gary." Gary doesn't move. SpongeGar says more sternly, "Gary, tabunga!" Gary finally obeys. He knows Squog is very afraid of him, although it seems Squog is afraid of Prehistoric Gary as well, due to his size. Prehistoric Gary leaves slime trails everywhere, which annoys Squog. His slime trails is commonly known as "tabunga" among the trio. Prehistoric Gary also appears in Lights, Camera, Pants!, but wasn't a huge monster. Also, when the mouse rolls over him, captions aren't seen.
Prehistoric Gary basically looks the same as Gary, but is larger. The only real differences are that Prehistoric Gary has light green spikes coming out from his shell like how a gigantspinosaurus has spines from it's back, has a Stegosaurus-like tail, and sports a thick unibrow that almost resembles Squilliam's.