Paleosaurus

The Paleosaurus was a creature which appeared in the low-budget 1959 creature-feature The Giant Behemoth.

Description
A colossal quadrupedal dinosaur, the Paleosaurus was a dark green in colour, covered in thick scales, and with a mouthful of viciously sharp teeth. Due to having been irradiated by some unknown method, it emitted a constant aura of radioactivity which was lethal to living beings and interfered with electrical equipment. It was also able to discharge bolts of electricity in a manner similar to that of an electric eel, and the radiation which saturated its form was transmitted through these blasts. It was also invisible to radar tracking.

History
After a series of deaths involving both humans and marine creatures, along with the discovery of an enormous dinosaurian footprint, scientists uncovered the existence of the Paleosaurus. Theorising that the beast was also dying of the massive dose of radiation which was killing all those around it, but that it would travel up the River Thames to perish in fresh water whilst devastating London en route, the group devised a way to deliver an even higher dosage of radiation which would hasten its demise.

Whilst constructing their weapon, authorities discovered the Paleosaurus’ radar transparency, and had to rely on helicopter surveillance. However, the radiation emitted by the creature caused the helicopters to crash, and the Paleosaurus subsequently embarked on a rampage through central London.

Finally finishing the weapon, the remaining scientists loaded their radium-filled torpedo aboard a miniature submersible and destroyed the beast in the River Thames after sustaining heavy damage.

However, news reports of shoals of dead fish at the end of the film suggest that a second Paleosaurus may have made landfall in the United States. ..

Trivia

 * Although the Paleosaurus is apparently named after a real dinosaur, Palaeosaurus, little is known of this creature, and it likely bears no resemblance to the monster seen in the movie.
 * The roars of the Paleosaurus are recycled sounds from the brontosaurus from the movie King Kong