>I accept that you criticize the ID for their view of God's intervention
>and eg creation of new species seen in the Cambridge explosion. BUT how
>do you as a Christian geologist explain the Camridan explosion and the
>lack of intermediate varieties or transition forms?
It is important first to know what exactly the "Cambrian explosion" is. It
is not the appearance of all, or even nearly all living phyla within a ten
or twenty million year window.
The claim that all major body plans appear in the early Cambrian is simply
NOT an objective reading of the fossil record.
A few major points to be made:
* Several modern animal phyla do appear in the fossil record before the
Cambrian. These include sponges, cnidarians, mollusks, and possibly
echinoderms and chaetognaths. In addition, there were burrow-forming worms
of uncertain affinity in the late Precambrian (Ediacaran) that increased in
diversity toward the Cambrian.
* Only about 7 modern animal phyla (out of a total of 29) are currently
known to first appear as fossils in the Cambrian.
* Most of the living phyla are "worms" and other small or soft-bodied forms
that have a very poor fossil record. There are likely at least six modern
phyla that have no known fossil record at all.
* The early Cambrian explosion was primarily a rapid diversification within
a relatively few skeleton-bearing phyla - particularly the arthropods and
molluscs.
* There are early Cambrian fossils that are transitional between phyla.
One example is the transition between lobopods and arthropods. There are
some species with anatomies that are beautifully tansitional between
lobopods and peculiar arthopods such as Opabinia and Anomolocaris. I have
posted on this previously. A group of scale, plate and conical shell
bearing slug-like animals includes specimens that share similarities with
both mollusks and annelids, and with both mollusks and brachiopods.
Genetic data also suggests cloase relationships between these threee phyla.
* There are many complex taxonomic issues involved in the definition and
recognition of phyla.
There are many unaswered questions regarding relationships between major
groups and the evolutionary steps and mechanisms involved. But great
advances have been made within the last decade both in genetics and in our
knowledge of the fossil record. This is one of the most exciting times to
be a paleontologist. There is so much going on in the field that it is
virtually impossible to stay on top of the developments.
Keith
Keith B. Miller
Department of Geology
Kansas State University
Manhattan, KS 66506
kbmill@ksu.edu
http://www-personal.ksu.edu/~kbmill/
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