Triassic Period: Mostly reptiles, small mammals, and the first few dinosaurs.

Jurassic Period: It is here that the first dragon species began to form. Though smaller and weaker compared to their future descendants and lacking fire breath, they were one of the top predators of this time. Modern dragons refer to these ancestors as wyverns

Wyverns often compete with Allosaurs and many of the various Pterosaurs for hunting grounds.

Cretaceous Period: It is here that the dragon species had begun to hit its stride. Along with the Tyranosaurus Rex, the Prehistoric Dragon was one of the top predator of this era. Still bearing more similarities to the wyverns of the Jurassic, the Prehistoric Dragon had developed the ability to breath out quick bursts of flame, which would soon give way to true fire breathing.

The only predator that posed any major threat to the Prehistoric Dragon was the gigantic Quetzalcoatlus.

1625084 Again, I like to point to the permian era for exotic ancient reptiles.

1625084 That is pretty cool.