The metamorphosis of dragons was in the first encyclopedia.

We've seen dragons of Bahamut and Tiamat's brood in Coil and Aszys Lla, they follow the same morphology we've seen in Hraesvelgr and Nidhogg with the one possible exception of the 'Coeurl' Dragons which are land-bound dragons that develop agility rather than heavy defensive shells. The metamorphosis chart says the Brobinyak which we see among Nidhogg's brood is the stage before that, though.

"Her remaining brood can still be seen soaring through the skies, the wanderlust of their progenitor flowing strong through their veins."

Bahamut and Tiamat do feel like the most obvious draw because of titles, but they don't hold exclusive claim to day/night dichotomies and to our knowledge they'd only ever lived in Meracydia, and the Au'ra had lived on the Othardian continent since at least the time of Allag. There's also a pretty fundamental gap in the whole idea in that dragons came to the world after the sundering, and au'ra have counterparts on the reflections indicating the race was present before it.