Digital Digital Burgess Conference Follow-up:
Stefan Bengtson
Conference was held August 29-September 1 1997, Banff Alberta, Canada

Re: the Cambrian flipflop,
or Inertial Interchange True Polar Wander Event, proposed by Kirschvink's group

A fascinating story that may well be true. My problem is with its proposed role as trigger for the Cambrian Explosion - it comes too late. Given that evolutionary radiation is not instantaneous but rather follows an exponential growth curve, you would expect any environmental trigger to occur before the start of the growth curve, i.e. before the appearance of various various shelly fossils, etc. in the Manykaian ("Nemakit-Daldynian") or perhaps even before the appearance of the Ediacaran biota, well before the flipflop.

Kirschvink et al. instead argue that the event coincided with the period of fastest growth of the diversity curve. If so, it may have helped boost things, but it wouldn't have been necessary. The curve would have gone up anyway.

That said, I think Kirschvink et al. have written a great paper. Not only would it explain the very rapid dance of the continents in the Lower-Middle Cambrian, but it also would help us take the bearings on the continents from radically different polar positions over a short period of time (normally, you get only latitudes from paleomagnetic measurements and have to fix up the longitudes by other means). And it would certainly have had some profound influences on life, though hardly as a trigger for the Cambrian Explosion.

Stefan Bengtson

Senior Curator (invertebrate fossils)
Swedish Museum of Natural History
Department of Palaeozoology
Box 50007v S-104 05 Stockholm

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