|This article is about a/an kaijin in Kamen Rider, the original series.|
- "The only place you'll be getting off this bus is in hell!"
- ―Phirasaurus before releasing his Death Fog.[src]
The first Phirasaurus Human (人間ピラザウルス Ningen Pirazaurusu, 16), also simply known as Phirasaurus (ピラザウルス Pirazaurusu) after the prehistoric creature he was modified from, was a piranha-dinosaur Shocker cyborg.
He had the human guise of a bus driver, and after using his "Death Fog" ability to kill a group of humans in a bus it was discovered his poison was so potent it killed him as well. Phirasaurus was a project from Shocker commander Maya (マヤ Maya), and she quickly looked for a stronger person to be altered.
The Phirasaurus Human's main ability, engineered from the prehistoric Phirasaurus, was releasing a poisonous breath. Appearing as a powerful mist, the Phirasaurus' poison was said to be able to kill a dinosaur in seconds. During its test run the poison of the Phirasaurus Human was able to kill a bus full of humans. However the poison was so potent it killed the Phirasaurus Human itself immediately after, thus a stronger human was needed to create a Phirasaurus Human that could survive the use of its power.