Mutant Chickens, also known as Animo's Pterodactyls, are Pterodactyls hatched from de-evolved chickens created by Dr. Animo. They first appeared in The Eggman Cometh, where Animo was trying to use them to take over the world. They were created by de-evolving chicken eggs with a devolutionary ray, and were then sent to stores to be distributed to customers. They were turned back to normal when Ben as Jury Rigg, reversed the polarity of the devolutionary ray and then flew over Bellwood as Jetray, evolving them back into chickens. They resembled Pterodactyls.
The mutated chickens were strong, fast, and able to fly. They grew very quickly, as seen when a baby hatchling came out of a chicken egg and grew from being small enough to fit in it to being a bit taller than a human.
They could also sense heat and were attracted to it, they swarmed around Swampfire as he gave off great amounts of heat.
At least one of them, their leader, was able to speak, and was intelligent, asking to be given a name.
The mutated chickens need heat to survive, and cannot stand cold temperatures. They can be taken out by freezing them. Once devolved back into chickens, they become ordinary birds and have no abilities.
Animo was concerned that an experimental balloon that could end global warming could be a threat to the mutated chickens, as that would make the planet colder, and thus a harder place for the heat loving mutated chickens to take over. He destroyed the balloon to prevent this from happening.