Looks great so far. Really detailed. I'll add in a few notes:

1. All higher sentient dragons are extinct. Only the feral ones remain.
2. Dragons have evolved to become smaller than they were in the past due to a huge reduction in prey.
3. The Ancient are traditionally dragon slayers. The tradition still exists today but not many have actual experience slaying a dragon, only in practice.
4. Elves have a natural affinity towards dragons as they do with most natural wildlife. One of the Gods from their religion can actually take the form of a great dragon that protects all the forests of Terrene (he's doing a bad job at it).
5. Sand Wurms are not true dragons but they have a common ancestor link. Wyverns are closer to dragons genetically than Sand Wurms even though they are not considered true dragons themselves.