Quetzalcoatlus is proved to be one of the biggest creatures to fly. They said that Quetzalcoatlus is an adpotable animal. It is said to be in the Up coming expansion pack " Weird creatures " Possibly made out of Pteranodon. There is also a version downloadable from Zoo Tycoon Volcano, but this quetzy is made from the Masai Giraffe and as such it can't fly. This animal was likely chosen because when it was on the ground, Quetzalcoatlus would have resembled a reptilian giraffe due to its quadrupedal gait and long neck.
Another version is at Caldera Unlimited but it is an ambient.