Dinosaurs are an extinct group of prehistoric reptiles that roamed the Earth mostly between the Mesozoic and Late-Cretaceous periods approximately 252 million and 66 million years ago before suffering a hotly debated unknown apocalyptic event.[1] In GTA, sightings are reportedly almost exclusively in San Andreas and GTA V.
San Andreas
Reports of Dinosaurs are primarily within forested areas of the state with some claiming herbivorous dinosaurs appear docile, while carnivores are hostile and will attack CJ. While ample video evidence has been produced, all examples so far have been thought to be medications. The most damning evidence of this is the lack of consistency between texture resolutions when compared to the other textures in the game. Additionally, while Rockstar are fans of zany parody, it is reasonable to conclude that placing Dinosaurs in their games would be a stretch too far. Dinosaurs are mentioned in San Andreas by members of Epsilon Program, who consider them a lie fabricated by scientists to fool weak-minded people. This is likely a reference to real-world conspiracy theories that claim dinosaurs are an elaborate hoax.
GTA IV
GTA IV is unique in that it is the only GTA game where Dinosaurs have been confirmed to be present. Somewhat anti-climatically, this is of course in the form of a Tyrannosaurus Rex and a Triceratops skeletal fossil on display at The Libertonian museum in downtown Algonquin. The location is prominently featured in the missions Museum Piece, Collector's Item and Not So Fast in GTA IV and both of it's expansion packs.
GTA V
Accounts of Dinosaurs in GTA V become somewhat absurd, with alleged lone Tyrannosaurs patrolling Raton Canyon and large plesiosaur type aquatic leviathans roaming the oceans. So far no compelling evidence has yet been produced and all reported sightings are thought to be modifications. Interestingly, GTA V is the only game in the series with a verifiable dinosaur texture and model in the game files in the form of the large purple mascot of Rex's Diner in Blaine County. It is likely this dinosaur is a reference to Barney the Dinosaur.