Well, what the documentary suggests is that the apes' legs and feet are what evolved into the tail and like they joined together at some point, kind of like how whales

and dophins' flippers evolved from the legs and paws of wolf-like animals. I'm guessing they went in that direction because they still wanted the creatures

to be somewhat recognizable as mermaids to the viewers watching at home, and they probably wanted the viewers to easily recognize them as a more intelligent

species that could forge and use tools, because it's supposed to be a speculative docufiction which explores the idea of mermaids being real animals that diverged

from humans and evolved alongside us, without us knowing.



Your design doesn't really look an intelligent species that could use tools like chimps or humans do, and that's because as you said, yours is based on tailless primates

(apes don't have tails, only monkeys do) and those types aren't as interest as tool-making apes tend to be. Lastly, the reason I made that comparison is because of the basic concept.

The idea of creating a realistic, or plausible, mermaid by making an evolved aquatic primate. The execution of that idea may be different and you took this in a completely different direction

than the makers of the "Mermaids: The Body Found" documentary, but the basic concept, the basic idea is very similar.