Titanosaurus was a shy, aquatic dinosaur that was discovered by Doctor Shinji Mafune. When he informed his colleagues about his remarkable discovery and revealed to them that he could control the dinosaur, they thought he was mad. He was shunned from the scientific community, for they didn't believe him... but the scientific community was wrong.
Dr. Mafune's daughter, Katsura, was badly injured in a lab experiment soon after. When the ruthless Black Hole aliens revived her as a cyborg, they asked for one thing in return. They wanted Dr. Mafune to assist them in their plot to dominate Earth. Mafune agreed, seeing it as a opportunity to strike back at those who had shunned him from his own field of work.
However, as the aliens prepared Mechagodzilla for operation, Dr. Mafune went against his orders and released Titanosaurus upon a coastal city prematurely. Titanosaurus marched through the city and caused massive destruction until Godzilla appeared. The two monsters exchanged physical blows. The vile, vermilion monster started to gain an advantage when he used his tail fin to create a powerful wind, which knocked Godzilla off balance. The two titans' confrontation was cut short, though, when a group of Interpol agents shot Katsura off a nearby cliff, causing Mafune to order Titanosaurus into retreat in order to save her. The injured Katsura was brought back to the Black Hole Alien's base, and, again, they saved the young girl's life. Mafune assured them of his allegiance this time, after saving the life of his daughter twice, and that he would deploy Titanosaurus at their will from then on.
The Black Hole Aliens and an alterative motive in saving Katsura the second time, though, as they later revealed to Mafune that they had inserted Mechagodzilla's control unit into the girl, putting the Doctor's own emphasis on the importance of living brain tissue to task. With final preparations made on the robot monster, Mechagodzilla and Titanosaurus were sent to attack Tokyo, but Godzilla came to face the duo. Godzilla first engaged in a fierce battle with the crimson creature. Titanosaurus seemingly defeated Godzilla by burying him in a ditch, but he quickly lost the upper hand. The humans managed to exploit Titanosaurus' one weakness: sonic waves. A sonic waves gun was created in order to deal with deadly dinosaur. The weapon was unleashed, and it effectively stunned Titanosaurus. Godzilla emerged from the ditch and began to attack Mechagodzilla. After a fierce battle, which included the removal of Mechagodzilla's head, Godzilla finally destroyed his robotic double once and for all. With the mechanical menace finally defeated, Godzilla turned his attention to the weakened Titanosaurus. Godzilla fired his radioactive ray and sent his final opponent tumbling off of a cliff back to its watery home.
Titanosaurus was defeated, and whether or not he was ever seen or heard from again is a complete mystery...