fossils, worms, and Metazoan evolution

[Ken Kinman]

    I personally believe that we cannot possibly evaluate Precambrian
metazoans properly until we get past the notion that Vendobionts are some
kind of weird non-Metazoans:  Seilacher's quilted organism theory is
probably the best-known (but probably least likely to be true), and the
lichen hypothesis, etc.
    Not that I believe Dickinsonia is a giant annelid either.  The truth
probably lies somewhere between the extreme shoe-horning on the one hand,
and the weird-wonders of the Precambrian on the other hand.  We are
beginning to realize that the Cambrian fauna is not quite as full of
"weird-wonders" as Gould once would have had us believe.  The same thing
will undoubtedly happen with Precambrian fossils as well.  Only then will we
clearly see that Metazoan phyla radiated more slowly in the Precambrian, and
in retrospect see that the Cambrian "explosion" of hard parts is far from
being the fast radiation of metazoan phyla that it has been made out to be.
     My best advice would be to get past this simplistic notion that things
like worms or "worm" tracks will tell us anything about the origins of
Metazoa (or even Bilateria).  Generations of biologists have been taught
that flatworms and the like are extremely primitive, so much so that some
twist genetic data (presumably subconsciously) to fit that longheld
preconception.  Some, like Rieger, are challenging such outdated notions,
but they are still swimming against the inertia of tradition.  For some
peculiar reason, many find the wilder notions like "quilted organisms"  to
be more worthy of their attention.  I love brainstorming and scientific
speculation, but some of these "sea-monsters" need to be interpreted more
realistically and speculations rejected more expeditiously.  It really is a
shame that Metazoan phylogeny is still so poorly understood, and those who
would blame it on a fast radiation of phyla are probably deluding
themselves.
                     ------Ken Kinman
P.S.  For starters, I would recommend the 1991 paper by Rieger et al. in the
book "The early evolution of Metazoa and the significance of problematic
taxa" (Simonetta and Conway Morris, editors).
*****************************************************
>From: John Bruner <jbruner at GPU.SRV.UALBERTA.CA>
>Reply-To: John Bruner <jbruner at GPU.SRV.UALBERTA.CA>
>To: TAXACOM at USOBI.ORG
>Subject: Oldest known fossil metazoans?
>Date: Wed, 1 Sep 1999 19:16:11 -0600
>
>With Adolph Seilacher's worm tracks from the Vindhyam Basin, India, shown
>to be only 600 my old rather than 1,100,000,000 years old, I am wondering
>what is the age of the oldest known fossil metazoans (Kerr, 1999)?  Would
>it be the paper by Breyer et ali (1995) of the sediment-filled tubes from
>the Allamoore Formation of Texas, USA?  These were reported to be 1.4 to 1
>Ga (1.4 to 1 billion years old).
>
>Breyer, John A., Busbey, Arthur B., Hanson, Richard E., Roy, III Edward C.
>1995.  Possible new evidence for the origin of metazoans prior to 1 Ga:
>Sediment-filled tubes from the Mesoproterozoic Allamoore Formation,
>Trans-Pecos Texas.  Geology.  Vol. 23(3):269-272.
>
>Kerr, Richard A.  1999.  Earliest animals growing younger? Science Vol.
>284(5413):412.
>
>         John
>******************************************************
>* Mr. John C. Bruner                                 *
>* Department of Biological Sciences                  *
>* Unviersity of Alberta                              *
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