It is implied that the Tall Ones took the physical bodies of animal-headed humanoids before the Godslayer killed them and corrupted their spirits, as evidenced by some stele text and the giant fucking skeletons that are revealed after one completes the different plateaus. Or they were never human in the first place and just lived alongside the Isle humans for a while before they were ousted.
THE PATHLESS SHELLS HOW TO
Somehow the Godslayer managed to grow twice the height of a normal person and attained a tail and claws, so I don’t think its a stretch that a society might develop where the people figured out how to give themselves gills or something. Than again, magic is a thing in-universe, or at least a rather unusual form of it. It doesn’t quite make a ton of sense, given how the architecture in Abzu is rather amphibious (yes, there are stairs underwater that would imply they used to be above water, but also, the more “urban” areas (such as the area where you find the bird mural) seem built specifically for exploration above and below water, implying the inhabitants could travel both ways). Jumping off that point, it does kind of weird me out that the ancestors from Abzu appear to be human, at least to some extent. Either way I’m not 100% convinced they’re normal humans. Maybe the developers borrowed from the Diver’s model, or they’re wearing masks. The eye sockets are small and the rest of the face looks blank. Also, though I couldn’t get a super long look at the faces of their skeletons, they look.