If we chose to take every paleolithic painting literally - lots of things are real. :) But this is pretty cool - though by the look, this mermaid/man would have to swim sideways. They would've been smarter to go with a dolphin, seal or manatee lower half.
Mermaids are mythical and legendary sea-dwelling creatures of European & Asian folklore, resembling a woman, with a human torso, but having a fishtail or tails instead of legs. Mermen are also heard of, but have a secondary role in the lore of the sea. Other similar water spirits include nymphs, dryads, oceanids, hamadryads, naiads, nerieds, oreads, and undines. Mermaids are supposed to be able to lure imaginative, amorous men to destruction by enticing them into the depths .