>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.
Such soft-bodied preservation is exceptional. Such localities are
extremely valuable for understanding the history of life because they are
so rare. They provide widely spaced snap shots of the history of life.
Also, even these exceptional localities are selective in their
preservation. The fossil record of soft bodied forms is largely restricted
to trace fossils (burrows and trails) which can rarely be associated with
particular trace making species.
A second comment is that the weird organisms you mention have now been
grouped into living phyla (The view presented in Gould's book "Wonderful
Life" is out of date). Hallucigenia is now recognized as a member of a
group of organisms called the lobopods which includes the modern
onychophorans, and that was very diverse and abundant in the Cambrian.
Opabinia, together with Anomalocaris, have been recently placed within the
arthropods and recognized as closely related to the lobopods. These forms
are transitional in morphology between the lobopods and arthropods. The
Cambrian fauna is no longer viewed as representing a collection of phyla
unrelated to modern forms.
Keith
Keith B. Miller
Department of Geology
Kansas State University
Manhattan, KS 66506
kbmill@ksu.ksu.edu
http://www.ksu.edu/~kbmill/