User blog comment:Kogath/Monster Hunter: World Discussion/@comment-33384696-20170919110416/@comment-25275196-20170920000330

There's no way that Nergigante is a Flying Wyvern. Every wyvern in the series shares one characteristic, and that is that they all have four limbs. The only creatures with six limbs are Elder Dragons, Carapacions, Neopterons, and Temnocerans. Nergigante certainly doesn't look like a crab, bug, or spider, so it's definitely an Elder Dragon.

Otherwise, I think that our Ferret monster is indeed a new Fanged Wyvern, the new raptor is another Bird Wyvern, and the white flying creature is another Flying Wyvern. As for Pukei-Pukei or whatever it's called, I have no idea. It could fit into either the bird or the flying wyvern class.