User blog comment:Mckrongs/Ecological Tree Plots/@comment-5043481-20140303123517/@comment-4009941-20140303163724

Like I said earlier 古龍目/Elder Dragon Order = Unknown Origin

Plesioths most ancient ancestor is "Ancient Fish" you know that fish you find at the Tower, Gorge and other places who according to picture of it look a lot like Coelacanth, at one point maybe some stayed more fish like or stayed fish all together with minor changes and split into 古魚亜目/Ancient Fish Sub Order.

I wanna note that it says nothing about Wyverns in this name 古魚亜目 < No wyvern in name at all it just says Ancient Fish.

And this 古蛇下目 < Says Ancient Serpent also has no Wyvern in it to be clear but may be one that has gone partly reptile on its own path.