Titanosaurus is a fictional kaiju featured in the 1975 Showa film Terror of Mechagodzilla, the fifteenth Godzilla film to be produced by Toho.
An amphibious dinosaur found in the Pacific Ocean, the character appeared only once, as one of two antagonists in the film Terror of Mechagodzilla. Characters in the film state that the Titanosaurus was originally a gentle creature, not aggressive by nature; it was only under mind control that it became hostile. Titanosaurus shares its name with a real dinosaur species, though they do not share much beyond nomenclature. Titanosaurus more closely resembles a Spinosaurus or a Suchomimus than a real Titanosaurus. Toho's Titanosaurus is more like a Japanese version of the British giant movie monster Gorgo, sporting the same webbed ear-like appendages, and has a dorsal sail like that of Spinosaurus. Originally, Titanosaurus was going to be two separate monsters that would eventually form into one, but due to budget restraints, only one Titanosaurus suit was made.
In Terror of Mechagodzilla, a mad scientist named Shinji Mafune becomes so obsessed with studying the brain patterns of marine life that he loses his academic credentials and is cast out from the scientific community. Quickly descending into madness, Mafune is able to gain control of Titanosaurus and joins forces with the Black Hole Aliens; the monster is used as the guardian of the destroyed Mechagodzilla's remains; an attack by Titanosaurus on a submarine sent to investigate the remains opens up the film. Dr. Mafune aids in the rebuilding and reconstruction of Mechagodzilla, and with both monsters under control, begins his revenge on humanity. After a lengthy battle in Tokyo, Mechagodzilla is destroyed by Godzilla, who then hits Titanosaurus with a blast of atomic ray. Titanosaurus then falls off a cliff into the ocean. Whether or not he survived is unknown.
Titanosaurus has not appeared in any films since, although he briefly appeared as stock footage in the opening credits of the 2004 Millennium film Godzilla: Final Wars as one of many monsters that arose from the devastation brought by the World Wars, along with Varan, Gezora, Baragon, Gaira, and Megaguirus.