Origin of Flatfishes: The Eyes Have It!

Flatfishes (Pleuronectiformes) are unusual in that they are asymmetrical, having both eyes on the same side of the head. The placement of eyes in young flatfishes is symmetrical, and the origin of this bizarre morphology has puzzled evolutionary biologists dating back to Charles Darwin. Unfortunately, the apparent lack of flatfish species that exhibit an intermediate morphology with regard to the placement of eyes has been a favorite of creationists as yet another example of "no intermediate form. " A paper published yesterday in Nature by Matt Friedman, a graduate student at the University of Chicago, blows this creationist example away by showing that fossil flatfish species dating from the Eocene (approx. 50 Ma) have an intermediate placement of the eyes on the head. Another important aspect of this study is that the evolution of this was not saltatory, but gradual. The work presented in this paper is an outstanding example of integrating fossil and extant lineages to discover the course of diversification in a trait, and how information from fossil lineages can inform phylogeny. There is some news buzz about this paper, and I was interviewed by the Chicago Tribune (my home town paper). Philippe Janvier wrote a very nice News & Views for this paper in Nature.