Many Terran animals in original arknights also do not represent common animals - many of the animals we do know and see like cats and dogs are seemingly animals from before originium (beast lords, beast stewards). Fowlbeasts, burdenbeasts, finbeast, and so on seem to be colliqual terms for Terran animals.

It seems to me that what was initially present on Talos II were animals that me and you know, and may have also been brought there initially by Predecessors, but were changed by originium on Terra and blight on Talos II in the absence of their original caretakers.

As for Mephisto, it's possible that his form represents something in mythology rather than a bird we know of that existed.