If you’ve ever wondered how the eyes of flatfish like flounder and sole ended up on one side of the head, you should take a closer look at a newly published article by Dr Matt Friedman.

Dr Friedman, who recently took up a post at Oxford University, has been investigating this mysterious eye migration using 50-million-year-old fossilized Acanthomorph fishes from Italy and France, and has managed to show that the change was slow and gradual rather than abrupt. Over millions of years, the positions of the flatfish eyes have gradually changed, little by little.

Addressing the Society of Vertebrate Palaeontologists’ (SVP) annual meeting at the University of Bristol today, Dr Friedman said: ”Flatfishes and their profoundly asymmetrical skulls have been enlisted in many arguments against gradual evolutionary change, precisely because it is difficult to imagine how intermediate forms might have been adaptive. My work provides clear evidence of the kinds of intermediates deemed ‘impossible’ by earlier workers and answers this long-standing riddle in vertebrate evolution.”

The most ancient Acanthomorph fishes had asymmetrical skulls, but the eyes were still located on both sides of the head. From these foregoers, intermediate species evolved and one of the eyes gradually moved across the head until both eyes ended up on the same side – millions of years later.

The flatfish group puzzled 19th century scientists trying to grasp the new Darwinian ideas, because during that epoch, the group’s fossil record was incomplete and it was unclear how the gradual migration of one eye could have come about. Today, a much broader range of fossil fish is available to science and Dr Friedman’s study included over 1,200 fossil specimens belonging to over 600 different species.