The betasaur.

The Betasaur was a giant reptilian animal native to the planet Beta II. It had scaly skin which was resistant to phaser fire, a spiky back and sharp teeth and claws.

In 2266, Spock and other members of a USS Enterprise landing party discovered a Betasaur approaching the bodies of Captain James T. Kirk (actually a Klingon duplicate) and two other crewmembers. After firing their phasers at its hide proved ineffective, they instead fired at its mouth, killing it. (TOS comic: "The Enterprise Mutiny")

The Betasaur had red skin on the comic's cover, but green skin in the interior art.
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