On Wednesday, June 2, 2021 at 7:13:58 PM UTC-4, erik simpson wrote:
> On Wednesday, June 2, 2021 at 3:01:16 PM UTC-7, Peter Nyikos wrote:
> > On Tuesday, June 1, 2021 at 8:04:07 PM UTC-4, erik simpson wrote:
> > > On Tuesday, June 1, 2021 at 3:52:28 PM UTC-7, nyik...@gmail.com wrote:
> > > > On Tuesday, June 1, 2021 at 2:02:59 PM UTC-4, John Harshman wrote:
> > > > > On 6/1/21 10:12 AM, Peter Nyikos wrote:
> > > > > > On Saturday, May 29, 2021 at 9:16:28 AM UTC-4, John Harshman wrote:
> > > > > >> On 5/28/21 7:07 PM, Peter Nyikos wrote:
> > > > > >>> Over in talk.origins, there was a brief discussion of some fascinating fossils of first rate importance. Except for stromatolites, they are one of only a handful of fossil organisms from a gigayear or more ago. Named *Bicellum* *brasieri,* it possesses two distinct cell types, and AFAIK this sets it apart from all fossil species from more than 600 million years ago.
> > > > > >>>
> > > > > >>> It was described scientifically here:
> > > > > >>>
> > > > > >>> "A possible billion-year-old holozoan with differentiated multicellularity,"
> > > > > >>> by Paul K. Strother, Martin D. Brasier, David Wacey, Leslie Timpe,
> > > > > >>> Martin Saunders, Charles H. Wellman,
> > > > > >>> Current Biology 31, 1--8 June 21, 2021
> > > > > >>>
> > > > > >>> https://www.cell.com/action/showPdf?pii=S0960-9822%2821%2900424-3
> > > > > >>>
> > > > > >>> The article is free access. It includes many detailed photographs of a high magnification.
> > > > > >>>
> > > > > >>> The title is guardedly optimistic about it being an animal. It does try to narrow it down somewhat:
> > > > > >>>
> > > > > >>> "It seems reasonable to assume that Bicellum falls within one of
> > > > > >>> the lineages leading to one of the six clades that possess complex multicellularity today: animals, plants, florideophyte algae,
> > > > > >>> brown algae, ascomycete fungi, and basidiomycete fungi."
> > > > > >>>
> > > > > >>> The words "of eukaryotes" should have been inserted after "six clades".
> > > > > >> "complex" would seem to rule out any of the various multicellular
> > > > > >> prokaryotes.
> > > > > >>> They do try to rule out prokaryotes with:
> > > > > >>>
> > > > > >>> "... these cells probably lacked rigid cell walls. This eliminates both cyanobacteria and the eukaryotic chlorophyte algae as likely homologs, because multicellular form in these taxa is strongly influenced by their
> > > > > >>> possession of rigid cell walls."
> > > > > >>>
> > > > > >>> This reliance on a single feature of *extant* cyanobacteria (some of which do have two very distinct kinds of cells)
> > > > > >>> is a weakness which calls for independent corroboration, provided by more characteristically
> > > > > >>> eukaryotic features.
> > > > > >
> > > > > > My first response to this post ended with my answer to the following question:
> > > > > >
> > > > > >> How big are these cells?
> > > > > >
> > > > > > I looked up a cyanobacterium with two very different kinds of cells, one with which I have an intimate acquaintance: *Anabaena*.
> > > > > > Its cells are just about the same size as the ones of *Bicellum* *brasieri.* So the following was a false lead:
> > > > > >
> > > > > >> That could be a good clue. Of course one might
> > > > > >> postulate giant cyanobacteria, I suppose.
> > > > > >
> > > > > >
> > > > > > We are in full agreement about the following:
> > > > > >
> > > > > >> Of course what they would need
> > > > > >> would be some character or other unique to animals. Perhaps something
> > > > > >> molecular, if they can find any traces. Or it would be nice to find
> > > > > >> collar cells or something similar.
> > > > > >
> > > > > > No such luck as collar cells with these organisms . Haven't you looked at the paper yet?
> > > > > > You did not answer this question in your reply to my first reply.
> > > > You seem uninterested in this whole discovery, John. This is the second time you've failed
> > > > to answer this simple question.
> > > >
> > > > <snip for focus>
> > > > > >>> The cyanobacteria of today may only represent the hardiest kinds that survived this ordeal by ice.
> > > > > >
> > > > > >> Still, cells similar to the cyanobacteria of today are the only ones we
> > > > > >> have fossil evidence of before or after the Cryogenian.
> > > > > >
> > > > > > Can you give me a good source for them, apart from the ones (if any) found in stromatolites?
> > > >
> > > > > Those are the ones.
> > > > Do you know of any articles or books that go into the exterior covering? Do we have any evidence that they
> > > > were made of peptidoglycan, as is the case with modern cyanobacteria?

> > > Here's the most recent comprehensive review of Cyanobacteria fossils:
> > >
> > > https://www.sciencedirect.com/science/article/pii/S0891584918324845?via%3Dihub
> > Cyanobacteria evolution: Insight from the fossil record
> > Catherine F.Demoulin, Yannick J.Lara, Luc Cornet, CamilleFrançois, DenisBaurain, AnnickWilmotte, Emmanuelle J.Javaux,
> > Free Radical Biology and Medicine Volume 140, 20 August 2019, Pages 206-223
> >
> > Thank you very much, Erik. It does look like a very valuable resource on the subject.
> > > Chemical remains are important information, but peptidoglycan (mentioned in the review) isn't discussed as
> > > present in the fossils (no surprise there).
> > >
> > > I haven't read all of it yet, but I intend to. Considerable info is new to me.
> > For me too. A quick skim fails to provide answers to the two questions that interest me most at the present time:
> > (1) are cyanobacteria fossils from a billion or more years ago exclusively from stromatolites and
> > (2) are they all thick-walled?
> >
> >
> > I'll be looking at it off and on for about a week before posting on it. Mostly off: for the better part
> > of this past academic year, my family has had to ration their time with me due to the tremendous burden
> > of online teaching -- almost three times as time-consuming as in-person teaching. I've decided to give
> > them some real quality and quantity time, so I'm going on a posting break until next Tuesday.
> >
> > Meanwhile, here's something y'all might think about: how rare is it to have fossils of any organisms which,
> > like *Bicellum* *brasieri,* are from a billion or more years ago and are NOT from stromatolites?
> >
> >

> I believe most of the cyanobacterial fossils are derived from stromatolites, but some are found in other
> "microbially induced sedimentary structures (MISS)".
>
> Unsheathed cyanobacteria are known in the fossil record, but the majority of fossils are thick-walled, probably
> due to tophonomy favoring the thick-walled specimens.

There is also what might be called "identification bias": there are lots of different microorganisms in
stromatolites, but the article you showed us judges whether a microorganism is a cyanobacterium
based on its resemblance to extant cyanobacteria.

https://www.sciencedirect.com/science/article/pii/S0891584918324845?via%3Dihub

Its criteria are sufficiently stringent so that "only three taxa are unambiguously identified as cyanobacteria." [p. 209] Earlier on that page we see:

"In this section, we discuss a selection of (1) unambiguous cyanobacteria microfossils for which morphological features and habitats coincide strikingly with modern lineages, (2) probable and possible cyanobacteria microfossils that share morphological similarities both with a taxon belonging to the cyanobacterial phylum and with other lineages belonging to another phylum or domain of life. The limited number of preservable characters, along with their taphonomic alteration, and possible morphological convergence, limits the interpretation of the fossil record."

Criteria like these can also be responsible for putting the "first known cyanobacterium" a billion or
more years later than the first photosynthetic autotroph on a direct line to the "first known." This
autotroph might well qualify as a "cyanobacterium" if we knew it as intimately as we know extant ones.

There is plenty of evidence, in the form of stromatolites and banded iron formations, of the action of
photosynthetic autotrophs, going to maybe as billion years before the Great Oxidation Event (GOE).
This article places the beginning of the GOE at 2.4 Ga, which itself is half a billion years before
the "unambiguous" 1.9 Ga. for "the first known..."

The 2.4 Ga dating seems to be "settled science":

https://en.wikipedia.org/wiki/Great_Oxidation_Event

Peter Nyikos
Professor, Dept. of Mathematics -- standard disclaimer--
U. of South Carolina at Columbia
http://people.math.sc.edu/nyikos