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David Marjanovic wrote:
Replace the taxon names with any taxon names and the time with any time,
and I think you have the story of evolution in a nutshell. :-)
I'm not sure I agree. The kind of transformations we see in the
fish-amphibian and theropod-bird transitions each involve a major change in
body plan. These macroevolutionary events only happen relatively rarely.
For the fish-amphibian and theropod-bird transitions, this change is
associated with a major shift in locomotion: water-to-land, or land-to-air.
Thus, taxa like _Archaeopteryx_ and _Tiktaalik_ represent snapshots of
macroevolutionary change. So we see an opportunity for mosaic evolution
when a major changeover in body plan occurs - as in basal tetrapods and
basal avians. Certain anatomical features show a much more rapid rate of
evolutionary change than others. The result is a great deal of
experimentation in transitional body plans, with mosaic evolution usually
being the rule. There may also be some U-turns (reversals) along the way.
This experimentation lasts until an evolutionary "tipping point" is reached,
when the body plan becomes committed to a given ecomorphology (locomotory
style, in these cases), and there's no way back.