Mark McMenamin Unveils New Theory with Profound Evolutionary Implications
<<< An evolutionary new
idea--Geologist Mark McMenamin's new theory posits that
organisms from the Ediacaran period (now preserved in these fossils)
were neither plant nor animal, but an entirely new type of life.
He'll present his evidence at a major conference this week.
In 1995, geologist Mark McMenamin found in Mexico what were then thought to be the earliest fossil records of animal life. Now he believes these fossils, dating from the Ediacaran period, are neither plant nor animal, but are instead a record of a failed evolutionary experiment. McMenamin will detail his findings on October 20 before the Geological Society of America in Salt Lake City. Here is an overview of his latest work.
The Ediacaran organisms are a curious group of thousands of fossil specimens, known from rocks over a half billion years old located throughout the world. For many years they were considered to be the remains of the earliest animals. This interpretation, however, has been questioned since the 1970s, and a scientific battle has been waged between scientists who see these forms as animals and those who see these fossils as something entirely different. In the 1980s scientist Adolf Seilacher considered these forms to be so unusual as to merit the creation of a whole new category. Seilacher labeled the Ediacarans an entirely new (but now extinct) division of life or kingdom, like plants, animals, and fungi.
Paleontologist Mark McMenamin believes he has definitive evidence indicating the Ediacarans were not animals. Using his specimens from Mexico (which include the oldest Ediacarans known), McMenamin is now able to organize all known Ediacaran fossils based on the number of early cell divisions seen in each type of organism. He hypothesizes that, unlike animals, Ediacarans never went through a blastula stage (an embryonic hollow ball of cells), but rather went directly from a one-, two-, three-, four-, or five-cell stage to a larger size. These results are in direct contradiction to a recent, controversial proposal that one type of Ediacaran was a mollusk.
McMenamin says some of the Ediacarans appear to have head-like structures, although no eyes or mouths can be confidently identified. He interprets these structures as the functional equivalent of heads, with concentrations of nervous tissue and sensory equipment. McMenamin believes the heads evolved independently from animals through a process known as convergent evolution.
The implications of this hypothesis for contemporary evolutionary theory are profound; they suggest that nervous systems evolved more than once in Earth history. Like the development of life itself, the evolution of central nervous systems can happen any time conditions are appropriate, McMenamin argues. He notes that the development of brains, and ultimately human-like intelligence, is therefore not likely to be a unique occurrence in our universe.
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