Atargatis

And when you search for the oldest origin of this whole gallery, The trail recedes to Syria, centuries before classical Greece.

There, a goddess was worshipped named Atargatis, represented with the torso of a woman and the tail of a fish, probably the oldest recorded form of what we would come to call a mermaid.

The accounts of her come from the same band of the world where Genesis anchors its first chapters, the same neighborhood as Mesopotamia and its Apkallu.

It isn't the edge of the map inventing a fable.