Flounder's missing link


It's a strange, strange sea down there — four-legged fish, firefly squid, giant tube worms. But with both eyes on the same side of its head, the flounder ranks high as an oddity of the ocean.

The fish has puzzled science for years. As larvae, flounder have one eye on one side and one eye on the other. They swim straight up, like any normal, self-respecting fish. But as the larva develops, one of the eyes shifts to the other side and the fish turns to lie flat on its side. Everybody knows why — so it can stay camouflaged on the bottom and ambush prey.

But nobody could really say how the eyes got that way until Matt Friedman had to write a doctoral paper.

By the rules of evolution, flounder and other flatfish couldn't just suddenly have both eyes on one side of the head. A succession of creatures would have had to evolve the feature. But there were none, it seemed. It was the missing link in a very fine line of seafood.

"You do question how. It certainly is an oddity from a fish standpoint," said Denise Sanger, assistant research director of the S.C. Sea Grant Consortium.

The answer is even stranger.

"Imagine taking a normal fish skull and twisting it around so both eyes are on the same side," Friedman said. That's pretty much what happened.

Searching for a paper topic, Friedman, a graduate student at the University of Chicago, came across a series of photos of fossil fish and noticed that one of the them looked like a flounder, even though it wasn't considered a flatfish.

When he got a look at the skeleton on display, he did the archive-incorrect thing: He picked it up to look at it from the top down.

There was a space near the very top of the skull that could have held an eye.

"You've got one eye moving all the way up to the top of the head but not crossing over it," he said. The missing link. Those primitive fish had asymmetrical skulls, essentially twisted heads, that allowed the eye to gradually move.

It's like they were craning their heads up so much to find prey, the bones just started forming that way.

Also, Friedman found that some flatfish skulls were "left-eyed" and some were "right-eyed."

"As a project I thought it would be fun or something more exciting," Friedman said. Little did he know. His paper gets published today in Nature magazine.