Alright, so ZUN has confirmed that Ariya's avian aspect is based on the Archaeopteryx – iconically the earliest known bird in the world.
An alternative name for this is Urvogel, which is literally "proto-bird" in German, and it's actually translated just like that for the Japanese equivalent – shisochou.
And since the name in Japanese is so simple, the bird actually shows up in school tests a lot. And so in all likelihood, ZUN probably got the image of the bird while reading through his kids' homework or something.
