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Oh no, not another transitional fossil...
Jul. 10th, 2008 02:18 pmUp until now flatfish have been been a bit of a problem. They're very weird, going through a metamorphosis so that both eyes end up on the same side of the head. The patterns of development are well understood, (though not at a genetic level) but their early evolution is not well understood. The lack of intermediate fossils has lead to workers such as Goldschmidt proposing "hopeful monsters" and others, like St. George Jackson Mivart doubting natural selection.
However Matt Friedman, a doctoral student in Chicago, has found the first fossils illustrating this change. Matt found the fossils in a drawer of indeterminate fish remains in Vienna, and re-examined two species of a similar genus Amphistium. Matt Freidman prepared the rediscovered specimen, recognised it as a new genus and species, Heteronectes chaneti, and has a paper in Nature for his trouble.
The three species show incomplete migration of the eyes, having one on each side of the head, but displaced, and the skulls are clearly asymmetric, rather than distorted during fossilisation as had been thought. Another fact indicating the primitive nature of these fishes is that Amphistium is known from several specimens, and they are both left and right-handed, a character seen in the primitive living Psettodes (Spiny Turbots), but not in the more derived forms.
Another feature from the point of view of evolution is that these animals were clearly successful predators, as stomach contents are known from one specimen, so the intermediate condition was clearly not maladaptive as creationists like to suggest these things are.
Incidentally Friedman seems to be making a career out of re-examining neglected and ignored specimens. I met him at SVPCA last year, when he presented a talk on the "Cretaceous Swordfish" "Protosphyraena" gladius, which turns out not to be a Protosphyraena at all, but a something else entirely, and is closely related to the giant filter-feeder Leedsichthys.
However Matt Friedman, a doctoral student in Chicago, has found the first fossils illustrating this change. Matt found the fossils in a drawer of indeterminate fish remains in Vienna, and re-examined two species of a similar genus Amphistium. Matt Freidman prepared the rediscovered specimen, recognised it as a new genus and species, Heteronectes chaneti, and has a paper in Nature for his trouble.
The three species show incomplete migration of the eyes, having one on each side of the head, but displaced, and the skulls are clearly asymmetric, rather than distorted during fossilisation as had been thought. Another fact indicating the primitive nature of these fishes is that Amphistium is known from several specimens, and they are both left and right-handed, a character seen in the primitive living Psettodes (Spiny Turbots), but not in the more derived forms.
Another feature from the point of view of evolution is that these animals were clearly successful predators, as stomach contents are known from one specimen, so the intermediate condition was clearly not maladaptive as creationists like to suggest these things are.
Incidentally Friedman seems to be making a career out of re-examining neglected and ignored specimens. I met him at SVPCA last year, when he presented a talk on the "Cretaceous Swordfish" "Protosphyraena" gladius, which turns out not to be a Protosphyraena at all, but a something else entirely, and is closely related to the giant filter-feeder Leedsichthys.
