Getter Robo (1974)

Mankind is threatened by the Megasaur Empire, an advanced civilization of dinosaurs that survived extinction by living underground. In response, Prof. Saotome develops Getta Robo, a 3-in-1 robot formed by three separate vehicles (Getta Machines Eagle, Jaguar, and Bear). Powered by cosmic/getta rays, Getta Robo battles the army of Mechasauruses unleashed by the Empire.