User blog comment:Kogath/Monster Hunter X Discussion/@comment-25083735-20150710192336/@comment-6050823-20150711002920

@Strikerhunter and some others.

Akantor and Ukanlos were classified as Elder Dragons due to their sheer strength being beyond any near Flying Wyvern. After they did more research on the two, they found their skeletons were much closer to some ancient species of Flying Wyverns.

Leviathans(/Sea Wyverns) are a species that are able to swim in just about anything, depending on the environment they are adapted for. For all we know, Bubbles maybe able to swim in the ground/water/even in the sky because I remember seeing on Bubbles' concept art it was floating on the bubbles.

Fanged Wyverns are Fanged Beast-like Wyverns. Zinogre has characteristics of a Fanged Beast(In this case, a wolf) but is still considered wyvern due to it sharing more with wyverns rather than a Fanged Beast.