It appears that the sea to land
transition took place on the flood plains choked with organic debris. It would be slow enough to actually make
sense. An opportunity recognized and an
opportunity realized. That happens to
also be a far better description of the evolutionary process in any event.
It is always nice to see an old
idea modified out of recognition.
Somehow, I doubt if our old friend coelacanth had any part whatsoever to
play in this story at all. In fact, it
sort of looks like the domain of a few trash fish. After all, all fish were genetically
predisposed to make the necessary changes.
This also supports similar
transitions arising on land in which the potential for an expanded habitat was
exploited.
new theory emerges for where
some fish became 4-limbed creatures
by Staff Writers
Eugene OR (SPX) Dec 30, 2011
A small fish crawling on stumpy limbs from a shrinking desert pond is
an icon of
can-do spirit, emblematic of a leading theory for the evolutionary transition
between fish and amphibians. This theorized image of such a drastic adaptation
to changing environmental conditions, however, may, itself, be evolving into a
new picture.
University of Oregon scientist Gregory J. Retallack, professor of
geological sciences, says that his discoveries at numerous sites in Maryland,
New York and Pennsylvania suggests that "such a plucky hypothetical
ancestor of ours probably could not have survived the overwhelming odds of
perishing in a trek to another shrinking pond."
This scenario comes from the late Devonian, about 390 million years ago
to roughly 360 million years ago. Paleontologist Alfred
Romer, who died in 1973 after serving on the faculties at the University of
Chicago and Harvard University, saw this time as a period of struggle and
escape - and important in fish-tetrapod transition - to ensure survival.
Reporting in the May 2011 issue of the Journal of Geology, Retallack,
who also is co-director of paleontological collections at the UO's Museum of
Natural and Cultural History, argues for a very different explanation.
He examined numerous buried soils in rocks yielding footprints and
bones of early transitional fossils between fish and amphibians of Devonian and
Carboniferous geological age. What he found raises a major challenge to Romer's
theory.
"These transitional fossils were not associated with drying
ponds or deserts, but consistently were found with humid woodland soils,"
he said.
"Remains of drying ponds and desert soils also are known and are
littered with fossil fish, but none of our distant ancestors. Judging from
where their fossils were found, transitional forms between fish and amphibians
lived in wooded floodplains. Our distant ancestors were not so much foolhardy,
as opportunistic, taking advantage of floodplains and lakes choked with roots
and logs for the first time in geological history."
Limbs proved handy for negotiating woody obstacles, and flexible
necks allowed for feeding in shallow water, Retallack said. By this new
woodland hypothesis, the limbs and necks, which distinguish salamanders from
fish, did not arise from reckless adventure in
deserts, but rather were nurtured by a newly evolved habitat of humid, wooded
floodplains.
The findings, he said, dampen both the desert hypothesis of Romer and a
newer inter-tidal theory put forth by Grzegorz Niedbwiedzki and colleagues at
the University of
Warsaw
In 2010, they published their discovery of eight-foot-long,
395-million-year-old tetrapods in ancient lagoonal mud in southeastern Poland
"Ancient soils and sediments at sites for transitional fossils
around the world are critical for understanding when and under what conditions
fish first walked," Retallack said. "The Darwin
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