I'm guessing the changing of the elf's name has become an in-joke or something as now it is changing within the chapter itself.
Anyway... they're just fighting Remobras. It isn't like they've encountered real wyverns yet. They'd be pissing themselves if a Rathalos showed up.
@relic626 : The traditional chimera has a goat head, a lion head and a snake head. Body less set. Chimera as a term now just indicates different animal parts generally.
Wyverns though... strictly they're like dragons but with two fewer limbs. Whereas dragons have 4 legs and 2 wings usually, wyverns traditionally have 2 legs and 2 wings in a more bird-like arrangement. O'course I've adapted to the notion of wyvern's limbs being a bit more variable courtesy of a certain source... but yeah. Also it seems to be a recurring theme in Japan for wyverns to be poisonous, but that is neither here nor there.
Anyway... these wyverns are basically just Remobras.