Careful study of the Heteronectes chaneti fossil found that it represents a new genus. The genus name is derived from the Greek Heteros (different) and nectri (swimmer). The species, chaneti, honors Bruno Chanet, a pioneer in the study of fossil flatfish.
The two fossil sets "deliver the first clear picture of flatfish origins," said Friedman, "a hotly contested issue in debates on the mode and tempo of evolution."
Charles Darwin was baffled by what he referred to as the "remarkable peculiarity" of flatfish anatomy. "During early youth," he noted, the eyes "stand opposite to each other...Soon the eye proper to the lower side begins to glide slowly round the head to the upper side...The chief advantages thus gained seem to be protection from their enemies, and a facility for feeding on the ground."
Although the survival advantages of such asymmetry were clear, Darwin, when challenged, was unable to explain the mechanism of what appeared to be a rather sudden and radical change in morphology and suggested a Lamarckian adaptation in which the fish, through "muscular action," slowly pulled the down-side eye toward the upper side. The resulting distortion, he suggested, "would no doubt be increased through the principle of inheritance."
Darwin's explanation, which relied on the inheritance of acquired traits, preceded the discovery of genes, but geneticist Robert Goldschmidt, tackling the same flatfish issue in the 1930s, came up with a genetic explanation. He argued that such a sudden drastic change could be triggered by a single fortuitous mutation that triggered a deformity, which in some environments would prove beneficial--and then get passed on. He termed these sudden accidental evolutionary leaps "hopeful monsters," and made the mysterious origin of flatfishes the centerpiece of his argument.
Friedman's discovery eliminates the need for such optimistic accidents. It "refutes these claims of radical sudden change" he said, "and demonstrates that the assembly of the flatfish body plan occurred in a gradual, stepwise fashion."
The research was supported by grants from the Lerner-Grey Fund for Marine Research, the Hinds Fund, the Evolving Earth Fund, the National Science Foundation and the Environmental Protection Agency.
--------------------------------------------------------------------------------
Adapted from materials provided by University of Chicago Medical Center, via EurekAlert!, a service of AAAS.
Email or share this story: Need to cite this story in your essay, paper, or report? Use one of the following formats:
APA
MLA University of Chicago Medical Center (2008, July 10). Flatfish Fossils Fill In Evolutionary Missing Link. ScienceDaily. Retrieved May 8, 2009, from
http://www.sciencedaily.com /releases/2008/07/080709144213.htm
