Re: transitional fossils

From: Dr. David Campbell <>
Date: Tue Dec 06 2005 - 12:40:42 EST

> No, that is not what the evidence is telling us. The fossil record
> sometimes shows us minor morphological change for long time periods.

And sometimes it shows us major morphological change in short time

> In other words, the fossil record is giving us the kind of resolution
> we would need to test evolution. What we see is little or no change
> for long periods, even 500 million years in the case of, say,
> sipunculan worms.

Sipunculans are practically unknown as fossils-there are some burrows
probably attributable to them. You may be thinking of priapulids,
which are common in the Burgess Shale. However, there are significant
differences between the Cambrian priapulids and the modern ones.
There are a few things with little change over very long periods of
time; however, they are exceptional. In most cases there is quite a
lot of change over time.

My undergrad honors thesis, MS, and PhD all dealt with invertebrate
paleontology and evolution. To the extent that we have looked, the
patterns from paleontology fit evolutionary expectations. We can
trace mollusks from a rather generic Precambrian form through a
Cambrian diversification of basic body plans, Paleozoic
diversification of major groups, various turnovers in form with
extinctions and radiations, and eventually the modern diversity. We
can trace from primitive chordates in the Cambrian to jawed fish to
amphibians to reptiles to birds and mammals. The fossil record
supports evolution. We don't have detailed explanations for the
evolution of everything that has been seriously examined, much less
for the vast majority of organisms that have not even been examined
evolutionarily, but the patterns so far as we know them fit
evolutionary expectations. We see fewer, simpler things giving rise
to more, more complex things. Basic patterns are established, and
then the range of available options within these patterns are
established. Situations with little competition (invasion of new
habitat, major morphological/behavioral innovation, vacancies created
by mass extinction, etc.) lead to radiations.

Dr. David Campbell
425 Scientific Collections Building
Department of Biological Sciences
Biodiversity and Systematics
University of Alabama, Box 870345
Tuscaloosa AL 35487-0345  USA
Received on Tue Dec 6 12:41:44 2005

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