As babies, flatfishes like plaice and flounders look like every other fish. But as they grow up, one of their eyes moves to the other side of their heads. This allows the adults to lie flat on their sides without getting an eyeful of sand. The evolution of these grotesque fish is beautifully captured by a fossil called Heteronectes. It’s a half-committed flatfish. One of its eyes has begun migrating to the other side of its head but hasn’t made it all the way – it stops at the midline. We couldn’t have wished for a better intermediate form – it’s half-way between the standard fish body plan and the distorted visages of flounders and soles.
Read more: Early flatfish has eye that’s moved halfway across its head