How flatfish evolved

A new look at the fossils of primitive flatfish offer evidence that these fish — well-known for having both eyes on one side of their head — started out symmetrical and gradually evolved their one-sided trait...

Fossil evidence had already shown that flatfish ancestors had one eye on each side of the head. But no evidence had existed for a transition between a symmetrical skull and one-sided skull. Matt Friedman, a graduate student at the University of Chicago, looked more closely at 45-million-year-old fossils of primitive flatfish and found the transition species: One eye had moved, but it had not crossed the midline of the fish’s body, as seen in today’s flatfish, Friedman reports...

(Image and text from Science News. Further discussion here.)