Time magazine article & metazoans (posted for D. Erwin)

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Date:         Tue, 16 Jan 96  17:58:57 EST
From: Doug Erwin <MNHPB028@SIVM.SI.EDU>
Subject:      Time magazine article & metazoans (posted for A. Martin)
To: <paleonet-owner@NHM.AC.UK>
Status: O

Actually, the point of the Time article, and the Grotzinger et al. paper
in Science upon which it was based, is that the Ediacaran faunas DO NOT
preceed the Burgess by 100 million years, or more.  Rather, the Ediacaran
faunas have now been tightly constrained by Grotzinger, Bowring, Saylor
and Kaufman to 565-543 (the pC/C boundary) with the Burgess and about 520.
The old gap between the Ediacaran and the onset of the Cambrian small
shellies (now in the Earliest Cambrian Manykaian Stage - see Knoll et al
in the Dec. 1995 GEology) has virtually vanished.
   The oldest metazoans remains a contentious issue, with no clear
resolution.  Mitch Sogin's molecular data would suggest the higher eukaryote
radiation (which preceeded the origin of metazoa) occurred somewhere from
1200 mya to 800 mya, but the dates could be way off.  Trace fossil evidence
is unconvincing, so the earliest good metazoans are probably the Twichia
disks from the MacKenzie Mtns of Canada at about 610 mya.
   As with the Ediacaran fauna and the early Cambrian, we are probably
a long way from pinning down the earliest metazoans.  And if Davidson
et al are correct (Science 1995 v. 270, pp1319-1325) we wouldn't find the
earliest metazoans anyway.  There are substanitive difficulties with their
arguments, however.