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In Xanadu did Matthew E Clapham a stately e-mail message write: > At 11:04 10/8/02 -0300, Rod Savidge wrote: <snip> > As an amateur, one of the things that puzzles me about > paleobiology in general is the preoccupation with animals at > and just prior to the so-called Cambrian explosion, despite > the general acknowledgement that algae had appeared on earth > about a billion years earlier. There seems to be an > attitude that complex animals had the wherewithal to evolve > whereas plants did not. It doesn't make a whole lot of > sense (at least to me), and I therefore participated in this > field trip with the idea that maybe some of the Mistaken > Point 'animals" in fact were plants. As I now understand, > the tendency has been to see the Mistaken Point biota as > early complex animals primarily on the assumption that the > lifeforms were positioned too deep to be able to > photosynthesize. Recall that we discussed non-green plants > in relation to the fossils there! An example of Monotropa > uniflora can be found at > http://www.rook.org/earl/bwca/nature/herbs/monotropa.htmla > (I have my own photos if you would like to show one at a > conference). It is a common flowering (tracheophyte) > species found in forests throughout North America. There > are various other species, all non-photosynthesizers, within > that genus, and there are a great many other non-green > species of vascular plant that are very well documented. > Every one that has been investigated biochemically has been > found to have dark CO2 fixation capability (i.e., no > requirement for photosynthesis), and most if not all also > take up carbon skeletons from other organisms. Thus, > nature shows us that it is possible for higher plants to > exist despite lacking intrinsic capability for > photosynthesis. Conceivably, the same was true in the > Neoproterozoic. > > It is possible that there are non-photosynthetic vascular plants in > the fossil record, but I don't think there were any at Mistaken Point > - simply because vascular plants did not evolve until ~150 million > years after the Mistaken Point biota (in the Silurian/Devonian). I > don't know if there are any instances of algae that can live > non-photosynthetically (if there are I would be interested...) The only examples I'm aware of are some nonphotosynthetic red algae, which happen to be parasitic on photosynthetic red algae -- you won't find those below the photic zone because their hosts wouldn't be there. Non-photosynthetic plants certainly do exist, but they're all secondarily derived from photosynthetic ancestors -- all the outgroups to the Plantae for many and many a node are themselves photosynthetic. The upshot is that, if the Mistaken Point things were secondarily non-photsynthetic plants, or complex algae, etc., we'd expect to see something that looked very much like them, but that was photosynthetic, in older deposits that were laid down within the photic zone. Analogy: if I found a fossil Monotropa and could somehow tell from the fossil that it wasn't photosynthetic, I'd expect to find similar fossils that were photosynthetic in older rocks (e.g., almost any other fossil flowering plant). There's a fair number of well-preserved fossil algae now known from rocks about the same age as Mistaken Point (the Doushantuo biota of China) -- some of which can be classified as red, green, and brown algae with a fair amouint of confidence. Many of these are preserved down to the cellular level of detail. As far as I know, none of them look anything like the Mistaken Point fossils. If someone does find a fossil alga in, say, the Doushantuo that looks a lot like a "spindle", that would support your hypothesis -- but unless that happens, I agree with Matt that your idea's a bit of a stretch. . . -- Ben Waggoner Department of Biology University of Central Arkansas Conway, AR 72035-5003 benw@mail.uca.edu
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