It is said that the kaiju lived in the Jurassic period. It adeptly uses both tails for pounding attacks and to constrict enemies.

Its fossil-like egg is found by Jiro Sakata as he walks by near a construction site of a shopping mall. MAT Member Fumio Kishida decides that it is just a normal rock, and the egg is buried underground again. However, moments later the egg turns giant and appears above-ground. MAT attempts to set the egg on fire with their MN bomb, but the egg hatches before the operation and thus Twintail is born.

After Ultraman Jack arrives, Twintail fights him, later joined by Gudon, the Subterranean Monster, which appears from underground, and the two monsters overpower him. Twintail then runs away towards the sea to escape from Gudon, who is actually its natural enemy.

Later, Twintail reappears in Tokyo, but MAT uses their anesthetizing shots to blind both of its eyes. The weakened Twintail is then bitten and killed by Gudon appearing from behind.