Looking to how I can make Nagas and Mermaids able to exist and evolve in my story, I came across this post which explains how Nagas could evolve from humans: Anatomically Correct Naga
In the top answer by Renan, it mentions that the genes for sirenomelia could give Nagas an evolutionary advantage. Since they're close to each other, I was thinking that my Mer and Naga evolved from the same evolutionary line close to humans; the Mer staying in water, and Nagas evolving to climb trees and eventually live on land.
But regarding the Mermaids, I was wondering if they would also develop fins as well, if their sirenomelia didn't completely erase their feet. Would they be closer to cetacean fins, or seal fins? And how could this not change the appearance of the Naga?