This brings up the preservation question in the discussion of the pattern
of evolution of new taxa. Many living phyla are represented by soft bodied
forms (nearly half are "worms") that have very poor preservation potential
and very poor or non-existent fossil records. Thus, when writers declare
that the fossil record shows that all living phyla appeared at the
beginning of the Cambrian they are making an _interpretation_ of the fossil
record. They are assuming the presence of phyla that have no fossil record
in the Cambrian.
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Keith, I thought that the discoveries of many soft-bodied forms in the Burgess
shale supported the concept of the "Cambrian explosion". Lots
of weird phyla such as Opabinia and Hallucinogenia were found which have no
clear relationship to later forms. The mud of this shale was favorable to
preservation of lots of soft bodied organisms. If this outcrop were located
closer to civilization, say in New York, I suspect that even more work would
have been done on it.
Your point is still valid, that earth history has a 'discovery history', and I
suspect that the latter history is still very 'young' -- we have only been
skimming the surface, so to speak. One thing we can be sure of is that new
forms will continue to be discovered; gaps will continue to be filled.
Paul Arveson, Research Physicist
Code 724, NSWC, Bethesda, MD 20084
73367.1236@compuserve.com arveson@oasys.dt.navy.mil
(301) 227-3831 (W) (301) 227-1914 (FAX) (301) 816-9459 (H)