Re: Cambrian Explosion

From: Keith B Miller (
Date: Fri Mar 23 2001 - 23:14:05 EST

  • Next message: Tim Ikeda: "RE: Fw: Arkansas Anti-Science Bill"

    >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

    * 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 B. Miller
    Department of Geology
    Kansas State University
    Manhattan, KS 66506

    This archive was generated by hypermail 2b29 : Fri Mar 23 2001 - 23:13:55 EST