Ever since their discovery, flatfish have baffled scientists with their unique anatomy and lifestyle. They live as bottom feeders, lying flat on their side on the sea floor. For many types of flatfish, their top side is camouflaged to fit their surroundings while their bottom side is pale or has an underdeveloped fin. Another shocking component of the flatfish is that the hair cells in the inner ear, which are responsible for keeping balance, are rotated so that swimming sideways feels natural. The most shocking feature of flatfish though is their asymmetric eye structure. Young flatfish have normally placed eyes, on each side of their head but as they mature into adulthood, one eye migrates to the opposite side. As a result of this, they are among one of the few examples of asymmetry in vertebrates. All of these anatomical components are extremely advantageous to the fish’s lifestyle, aiding in their ability to catch smaller fish by blending easily into the deep sea environment.

Previously, no fish with an intermediate eye placement had been discovered, either alive or dead. Due to this, flatfish have fueled significant evolutionary debate. Creationists have insisted that the lack of an intermediary form is evidence against evolution and for intelligent design. They have used this example to insist that a higher power intentionally (and instantly) created flatfish.

Matt Friedman, a graduate student at the University of Chicago, has recently published an article in the journal Nature that possibly solves this evolutionary puzzle. While glancing through fossil records dating back 45 million years, he recognized early forms of the flatfish that had been previously overlooked (named Heteronectes and Amphistium). Using CT scanning technology, he scanned the bone structure around the eyes. Both fossils cited in the study had incomplete eye migration, so that one of the eyes had migrated but did not reach the opposite side of the head. The CT scans also confirmed the mature ages of the fish due to their size and bone density. The images showed an absence of damage or deformity, ruling them out as causes of the intermediary eye location. These fossils suggest a gradual evolutionary adaptation for the eye migration of the fish and are evidence against a sudden species appearance or change.

Famous creationist Frank Sherwin found this finding “underwhelming”.