The Dave-o-saurus Rex (simply reffered to as Dave-o-saurus) is a dinosaur that lives in the past, at the same time as Caveman Charlie and Caveman Max, and another version of Dave. He goes around the forest destroying things as he walks. Caveman Charlie and Max devote their lives to defeating him. His weakness is vegetables (a kind of food Dave hates), so the cavemen throw vegetables at him.
In the events of Charlie's Time Machine, Oobi threw a carrot in the Dave-o-saurus' mouth, which caused him to fall to the ground. It is unknown if he is now living or dead. He is portrayed by Buckteeth.
The dinosaur has orange eyes with black pupils like the original Dave. he also has a large muzzle with sharp, yellow teeth in them (they are really made of paper). He is very tall like most dinosaurs.