Once upon this same Earth, beneath this same sun, long before you, before the ape and the elephant, there were dinosaurs. Some had flat teeth, and ate the leaves of trees while others had sharp teeth for eating meat, and they preyed upon the leaf-eaters. The two lived in harmony, but then everything changed when the fire nation attacked. Since then, the dinosaurs were thought to have been long since extinct... until now that is!
eh, close enough.