Mystery of the Flatfish Head Solved

ScienceDaily (June 25, 2012) — Those delicious flatfishes, like halibut and sole, are also evolutionary puzzles. Their profoundly asymmetrical heads have one of the most unusual body plans among all backboned animals (vertebrates) but the evolution of their bizarre anatomy has long been a mystery. How did flatfishes, with both of their eyes on one side of their head, evolve? So puzzling was the anatomy of flounders and their kin that they were used in early arguments against Darwin and his theory of natural selection. Skeptics wondered how such unusual features could have slowly evolved whilst remaining advantageous for the fishes' survival.

A new fossil discovery described in the latest issue of the Journal of Vertebrate Paleontology by Oxford University researcher Dr Matt Friedman finally solves the mystery. Friedman's fossil fish, named Heteronectes (meaning 'different swimmer'), was found in 50 million year old marine rocks from northern Italy. This study provides the first detailed description of a primitive flatfish, revealing that the migrated eye had not yet crossed to the opposite side of the skull in early members of this group. Heteronectes, with its flattened form, shows the perfect intermediate stage between most fish with eyes on each side of the head and specialized flatfishes where both eyes are on the same side.


Continued:  http://www.sciencedaily.com/releases/2012/06/120625160358.htm