Dear Dr. Guy Narbonne,
I want to share with the Paleonet group some of my observations and
reflections made on the field trip to Mistaken Point Ecological Reserve
this last weekend, perhaps to enhance discussion at the upcoming
Denver conference (which I unfortunately cannot attend).
Firstly, let me say thank you for conducting a most enjoyable field
trip. I truly admired the energy and obvious motivation you and the
other organizers expended to share your dedicated research efforts and
knowledge with us. I don't know if there will be future
trips to Mistaken Point, but for anyone interested in the origins of
eukaryotic morphogenesis, I can certainly recommend a visit there as very
worthwhile. The Avalon in Newfoundland is a fantastic place,
especially well appreciated when the weather cooperates!
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 seems unacceptably illogical to me for the paleobiology community to argue, on the one hand, that the volcanic ash of the Ediacaran at Mistaken Point was the key for the outstanding preservation of lifeforms on bedding planes, and on the other that the same ash destroyed every bit of the stalks and fronds of organisms envisaged to project upward from the seafloor. The absence of any evidence in the volcanic tuff beds (some quite thick) for the fossils, and the presence of an abundance of non-stalked species -- such as the spindles -- leads me to consider that the majority of the fossils when living were actually either swimmers or at least buoyant well above the bottom. Could it not be that instead of being seafloor dwellers, they were killed in surface water by the shock of volcanic explosion (just as fish are today) whereupon they settled flat to the bottom and were buried beneath the ash? (Incidentally, cellulose and other plant polysaccharides have densities near 1.6 g/cm3, much denser than water.)
Having seen what I did on the Mistaken Point trip, I see no reason for anyone taking a dogmatic stance about those organisms necessarily having a holdfast. Certainly there was a circular structure associated with many of the fossils that could be (evidently has been extensively) interpreted as the base of a holdfast. However, within an animal kingdom scenario, that structure might equally be interpreted as an early form of cephalization, with a long neck (rather than a "stalk") connecting the feeding 'head' to the swimming part. In some of my photos there does appear to be a mouth-like opening in the circular structure, but none are fully persuasive because of the quality of preservation. Within a plant kingdom scenario, morphogenesis as we understand it today is incredibly plastic. That more or less spherical object at the end of the stalk could be a swelling created in response to polar transport of nutriment and growth regulators, at a time before genetic competence for either root or holdfast development had been attained. It is reminiscent of the ball of callus cells that not uncommonly develops at the base of many species of plant cuttings after they've stood in water for a few weeks.
These considerations take me back to what motivated me to participate in the field trip. It seems to me that the uncertainties about Edicaran biota can only be resolved if specimens having excellent preservation, sufficient for microscopy, are found. Unfortunately, Mistaken Point does not appear to be a source of such specimens, although it clearly is an outstanding site for both stratigraphic and paleoecological investigation, particularly as it is within an ecological reserve and protected by law.
with best wishes,
Rod Savidge, PhD
Professor, Physiology/Biochemistry
Forestry & Environmental Management
University of New Brunswick
Fredericton, NB E3B 6C2
tel. (506) 453 4919
fax (506) 453 3538