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Animals Before the Ediacaran?
The Ediacaran Environment
The Embryos of Doushantuo
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 Actually not so well-known after all. Recent abstracts suggests that the genus Rangea is a nomen dubium. In any event, the more inclusive taxon is, formally, Rangeomorpha Pflug, 1972; and the original citation is: Pflug HD (1972), Zur fauna der Nama-Schichten in Südwest-Afrika, III. Erniettomorpha, Bau und systematische Zugehörigkeit. Palaeontographica A, 139: 134-170.
 There is a considerable literature on the fractal growth of fungal hyphae. Our math is not up to it. However, it is plain that the fungal pattern is different, in that it lacks the long-range order seen in vendobionts. This is a critical difference, because long-range order suggests that transcription factors may be at work. On a related subject, students often make the assumption that the observed pattern in a body plan is the result of selective growth. That may be the case. However, the morphology may also be explained by a pattern of selective cell death.
 瓮安 is pronounced Weng-an, rather than Wen-gan.
 Someone always wants the math. To be precise: δ34S = (((34S/32S)sample/(34S/32S)standard) - 1) × 1000, where the standard is usually a particular meteoric sulfur ("CDT") with a composition 95.040% 32S, 0.749% 33S, 4.197% 34S, and 0.015% 36S.
 In case you have zoned out completely, we repeat that these are stable isotopes. This discussion has nothing whatsoever to do with carbon dating or radioactivity. Carbon dating uses an unstable isotope of carbon, 14C and a completely different set of analytical techniques.
 The mutations involved in the biochemical shift probably occurred in the Paleocene, or even earlier; but grasses started off slowly. It was only in the Miocene that they began to grow, so to speak, like weeds.
 Once upon a time, in our distant youth, we attended a school almost unbelievably similar to Hogwarts, where we received the relatively serious discipline of 10 demerits for "cynicism" from one of the masters, a Snape anlage named Mr. Wischert. We have never forgotten or forgiven this monstrous injustice.
 Maybe not so unshakable, after all. Peterson et al. (2008) may signal that that molecular clock-making has finally come of age.
 Solely for our own benefit we include notes on the following scenario, with facts taken from abstracts and other uncitable stuff. It actually looks as if a triple conjunction was required.
One of the few bacteria with only a photosystem II ("PSII")-like complex is Rhodobacter. Assume the primitive state is a bacterium like Rhodobacter, but having a PSI system as well. Interestingly, it is unclear whether the Rhodobacter PSII complex uses manganese at all. If it does, the metal specificity is low and the oxidation is only from MnII to MnIII. Mating this kind of reaction system with PSI would accomplish nothing. However Rhodobacter does possess an enzyme which can do the MnII to MnIV oxidation: superoxide dismutase ("SOD"). This enzyme is one of the scavenger enzymes which removes toxic high-energy oxygen free radicals (or their precursors -- I can't recall which). These free radical agents are, in turn, produced when Ribulose-1,5-bisphosphate carboxylase/oxygenase ("Rubisco") makes a mistake. Rubisco frequently makes mistakes because it has low substrate specificity. Since Rubisco is the key carbon-fixing enzyme in photosynthesis, it follows that SOD would coordinate with PS I, which contains the rubisco.
SOD normally returns its excess redox potential to general cell metabolism via some shunt into the shikimate(?) pathway. The shunt is weird and cumbersome. It seems natural that it would find some other way to blow off excess steam. On the other hand, it is unclear why it would evolve a partnership with PSII, rather than PSI. The answer may have to do with the effect of pH on the redox potential of the MnII/MnIV couple. An increase of pH from 7 to 8 reduces the redox potential of Mn oxidation by a full 25%. PSII is normally in the business of pumping protons across membranes, thus creating a transmembrane pH differential. Thus, evolution has an opportunity to fine-tune the SOD reaction by associating it with PSII as well as PSI.
There is a considerable literature on the effects of ultraviolet light and temperature on both photosystems and on SOD which might be used to elaborate this hypothesis and coordinate it with the geochemical record. It would also be useful to look at the several bacterial taxa which have PSI only. Is there coordination with SOD, as expected? Are there other common enzymes which use the MnII/MnIV couple. Kopp et al. (2005) don't think so. Are there any cases in which SOD uses some other unconventional pathway to recycle superoxides? Probably: see fungal lignin digestion materials. Finally, we should look at the effects of methane haze on UV and visible sunlight. At a guess, a significant drawdown of methane would be necessary before any of this would work well enough to be worth evolving. Note the remarks on the pre-GOE "methane greenhouse" by Kopp et al. (2005). Indeed the increased mass-independent sulfur fractionation in the Siderian may represent increased penetration of solar UV, as suggested by Farquhar et al. (2007). This would be a natural result of a (latest Archean?) methane drawdown. ATW 090118.
We were shocked and delighted to find that Kirschvink & Kopp (2008) recently published a somewhat similar hypothesis, even using some of the same arguments, plus a pile of new molecular fossil data we haven't had a chance to work through. Every once in a while, it seems, we inadvertently stumble on something plausible. ATW090223.
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