The final one! I tried giving them the skin texture of a dolphin.

Their wings aren't really wings - they're more like overgrown flippers with the 'finger' digits still prominently shown. Sort of the halfway point in their evolution as their wings turn to flippers, much like penguins have flippers instead of wings. Sea Wyvern wings are also really fleshy, the membrane not so much membrane but a thin bunch of boneless flesh, like your tongue.