" Mermaids weren't mammalian. They couldn't be. Too many sightings focused on their 'slender backs' and 'narrow waists'--features that seemed reasonable to modern readers with modern beauty standards, but which made no sense for an Italian fisherman during the plague years, or a Puerto Rican swimmer in the 1920s. If the mermaid had been an idealized projection of a human woman onto a marine mammal, she would have looked different every time, fat during some eras, thin during others, not consistently slim to the point of freezing in oceanic waters. The people who described mermaids were describing a real creature, something that wasn't mammalian, but looked mammalian enough to make a tempting lure. And why would anything lure sailors, if not as a form of sustenance? "

― Mira Grant , Into the Drowning Deep (Rolling in the Deep, #1)