Evolving Flatfish

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Evolving flatfish found, according to articles in New Scientist, 13 July 2008, p11, and Nature, vol 454, p209, 10 July 2008. Flatfish, such as the sole and flounder, have both their eyes on one side of their body. This means they can lie on their sides on the bottom of the sea and watch what’s going on above them with both eyes. When they are hatched they have eyes on the opposite sides of the head, just like any other fish, but as they mature and take up their adult habit of lying on their side on the sea bottom, one eye migrates to “up-side” of the head. There has been much speculation as to how this could evolve from a fish with eyes on opposite sides of its head.

Matt Friedman of the University of Chicago has found two fossil fish that have one eye in the normal position in the skull and the other closer to the midline, although still on the opposite side of the skull. The fish are of adult size, so are not juveniles whose eyes have not finished migrating. According to the Nature editor’s summary: “This is a graphic example of a transitional form spotted in the fossil record, confirming that the evolution of the specialized flatfish body plan was a gradual process.” Friedman suggests the fish lived on the sea bottom and propped themselves up with their fins, like living flatfish do, so that “a small asymmetry is better than none to see the water column above you”. The asymmetrical fossil fish lived alongside the oldest known sole (a still living flat fish) for several million years, before becoming extinct.

Freidman commented in his article in Nature: “The sudden appearance of anatomically modern pleuronectiform groups in the Palaeogene period matches the pattern repeated by many acanthomorph clades. Inferring interrelationships between higher groups in this explosive radiation has proved difficult, and an unresolved bush persists.” (“Pleuronectiform” is the scientific name for flat fish.)

Editorial Comment: If these fossil fish lived alongside the oldest sole, this only proves there were once more varieties of flat fish than there are now. Freidman’s comment that “anatomically modern” fish of this group appear suddenly in the fossil record is an admission that the fossils he describes are not the ancestors of flat fish, and no other fossils show signs of evolving into flatfish either.

If Friedman is right about these fishes’ habit of lying propped up on one side then these fish are fully functioning fish, not half-evolved flat fish. The claim that these fish fossils, or any other fossils, are transitional forms is futile because transition is an active process and cannot be proven from fossils. To prove a transition you must observe the change actually happening. This cannot happen with fossils because they are dead and not doing anything. Acanthomorphs are all the spiny-rayed fish, including most of the familiar sea and freshwater fishes, such as trout, perch, cod, tuna, etc. and Freidman’s statement about them means that other fish beside flat fish also appear as fully formed fish and stay that way. This is exactly what you would predict if fish were created as separate kinds and have reproduced after their kinds ever since. (Ref. vertebrates, ichthyology)

Evidence News 24 Sept 2008

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