First Early Cambrian Bryozoa Discovered

[Inyo]

Molecular clock analyses definitely suggest that Bryozoa (AKA, the
ectoprocts) should have been around during early Cambrian Explosion
times, though direct fossil evidence had long-constrained their first
geologic occurrence to the early Ordovician, with a hotly debated,
putative bryozoa example reported from the late Cambrian.

A paper just published online, and now available for pdf download (as of
October 27, 2021), describes what the authors call a potential
stem-group bryozoan, preserved as secondarily
mineralized--phosphatized--specimens from Cambrian Stages 4 and 3,
Australia (Wirrealpa Limestone) and South China (Dengying Formation),
respectively. They call it Protomelission gatehousei, whose original
unmineralized body plan shares traits with several Bryozoa classes,
including the soft-bodied Gymnolaemata (Ctenostomata).

By the way, the oldest bryozoans I've personally collected derives from
the lower Middle Ordovician Antelope Valley Limestone, Great Beatty
Mudmound, western Nevada. See a photograph of them over at
http://inyo.coffeecup.com/site/beatty/beatty15.html ,

Download the entire paper over at
https://www.nature.com/articles/s41586-021-04033-w .

The abstract:

Bryozoans (also known as ectoprocts or moss animals) are aquatic,
dominantly sessile, filter-feeding lophophorates that construct an
organic or calcareous modular colonial (clonal) exoskeleton1–3. The
presence of six major orders of bryozoans with\advanced polymorphisms in
lower Ordovician rocks strongly suggests a Cambrian origin for the
largest and most diverse lophophorate phylum2,4–8. However, a lack of
convincing bryozoan fossils from the Cambrian period has hampered
resolution of the true origins and character assembly of the earliest
members of the group. Here we interpret the millimetric, erect,
bilaminate, secondarily phosphatized fossil Protomelission gatehousei9
from the early Cambrian of Australia and South China as a potential
stem-group bryozoan. The monomorphic zooid capsules, modular
construction, organic composition and simple linear budding growth
geometry represent a mixture of organic Gymnolaemata and biomineralized
Stenolaemata character traits, with phylogenetic analyses identifying P.
gatehousei as a stem-group bryozoan. This aligns the origin of phylum
Bryozoa with all other skeletonized phyla in Cambrian Age 3, pushing
back its first occurrence by approximately 35 million years. It also
reconciles the fossil record with molecular clock estimations of an
early Cambrian origination and subsequent Ordovician radiation of
Bryozoa following the acquisition of a carbonate skeleton.

[erik simpson]

My first reaction is "how could I have missed this?", then I saw Oct. 27 2021!
Interesting find, confirming the molecular clock (and abundant and diverse Ordovician
forms) that the LCA must have been at least as far back as the early Cambrian. Good
catch!

[John Harshman]

This now places the first occurrences of all phyla (or their stem
groups) with (eventually, though not necessarily at the time)
mineralized skeletons at or before Cambrian stage 3. Makes the explosion
a little more explody.

[jillery]

Both the article, and what the article discusses are indeed
interesting finds. The discovery of a fossil bed that pushes the
origin of a phylum back over halfway across the Cambrian, is a
remarkable event indeed.

To refresh my understanding of Bryozoa, I looked up the Wikipedia
article. It mentions that it's unclear whether bryozoans should be
considered protostomes or deuterostomes. Dare I ask, could this
discovery settle that question? And if so, would that have any impact
on the overall understanding of the evolution of life on Earth?

[John Harshman]

I don't think it's unclear at all. Bryozoans are protostomes (in the
phylogenetic sense). But this discovery has no bearing on the question.
What it clarifies is a taphonomic issue: bryozoans didn't originate in
the Ordovician; that's just when some of them gained mineralized skeletons.

[erik simpson]

A similar situation of long standing is the "origins" or trilobites. Pre-calcification
identification has been very elusive. Even so, the Ordovician Bryozoans display much
more diversity than the earliest trilobites.

[John Harshman]

Naraoia is clearly closely related to trilobites, even if it isn't a
crown trilobite. So that's something.

[jillery]

Your absolute certainty on the point raises the question why anybody
ever thought differently.

>But this discovery has no bearing on the question.
>What it clarifies is a taphonomic issue: bryozoans didn't originate in
>the Ordovician; that's just when some of them gained mineralized skeletons.

I caught that from the cited article.

[John Harshman]

Simple enough: molecular data have greatly changed what we know and
don't know. Based purely on morphology, bryozoans are hard to figure
out. (So are brachiopods.) But the molecular data are clear.

[Trolidan7]

So based on the molecular data, is it clear that bilatera is
monophyletic?

Is there anything from it that could suggest that some animals
with taxonomic bilateral symmetry at some stage of their development
(including the echinoderms) could have separately arisen as offshoots
of the cnidarians in more than one branch?

Does the molecular evidence tend to indicate that animalia itself is
polyphyletic? In other words sponges, cnidarians, ctenophores, and
bilaterans all arose from eukaryotes separately and the nervous systems
of three of the four are the result of convergent evolution?

Is the least common ancestor of what is now called animalia not even
multicellular, and it is not just sponges that are that way? Thus
perhaps the only thing they have in common is cholesterol to make cell
membranes tough but flexible, and no cell walls?

You know, with every possibe branch, there is the possibility of
different interpretations.

What is the orthodox view on the formation of nervous systems?

Did they arise only once in the animal kingdom or did they
arise separately, once among the Cnidarians and a second
time among the Ctenophorans, with both of then having
similarities due to the functional nature of what nervous
systems do?

[John Harshman]

It is.

> Is there anything from it that could suggest that some animals
> with taxonomic bilateral symmetry at some stage of their development
> (including the echinoderms) could have separately arisen as offshoots
> of the cnidarians in more than one branch?

No, that doesn't happen. Cnidarians are monophyletic, ctenophores are
monophyletic, and bilaterians are monophyletic. However, there have at
times been some questions about whether sponges are, and the
relationships among cnidarians, ctenophores, and bilaterians can be
contentious.

> Does the molecular evidence tend to indicate that animalia itself is
> polyphyletic?  In other words sponges, cnidarians, ctenophores, and
> bilaterans all arose from eukaryotes separately and the nervous systems
> of three of the four are the result of convergent evolution?

Well, sponges don't have nervous systems. But there is some question
about whether some features of ctenophores arose independently of other
animals. Muscles, if I recall.

> Is the least common ancestor of what is now called animalia not even
> multicellular, and it is not just sponges that are that way?  Thus
> perhaps the only thing they have in common is cholesterol to make cell
> membranes tough but flexible, and no cell walls?

No, the ancestor was multicellular. There are also gap junctions.
Collagen too, I think.

> You know, with every possibe branch, there is the possibility of
> different interpretations.
>
> What is the orthodox view on the formation of nervous systems?
>
> Did they arise only once in the animal kingdom or did they
> arise separately, once among the Cnidarians and a second
> time among the Ctenophorans, with both of then having
> similarities due to the functional nature of what nervous
> systems do?

I believe the majority view is that it happened once.

[Inyo]

On the paleontological heels of discovering the earliest
non-mineralized, soft-bodied byrozoan in Earth history (described in the
link provided, above) we now have a published report of possibly the
oldest mineralized bryozoan colony yet recovered from the fossil
record--it's from the lower Cambrian (Stage 4) Harkless Formation of
Esmeralda County, Nevada, north of Death Valley National Park.

One caveat is that the investigators allow that confirmation of a
"palaeostomate bryozoan affinity," would certainly involve finding an
early growth stage, bearing the ancestrula with an associated
protoecium. Nevertheless, the morphologic and taphonomic evidence
already scrutinized does indeed point to fully mineralized bryozoans
already well established in early Cambrian Explosion times, pushing back
their first known mineralized occurrence in the geologic record by some
30 million years.

The abstract, from the full paper published online over at
https://www.science.org/doi/10.1126/sciadv.abm8465 :

"All skeletal marine invertebrate phyla appeared during the Cambrian
explosion, except for Bryozoa with mineralized skeletons, which first
appear in the Early Ordovician. However, the skeletal diversity of Early
Ordovician bryozoans suggests a preceding interval of diversification.
We report a possible earliest occurrence of palaeostomate bryozoans in
limestones of the Cambrian Age 4 Harkless Formation, western United
States. Following recent interpretations of the early Cambrian
Protomelission as a soft-bodied bryozoan, our findings add to the
evidence of early Cambrian roots for the Bryozoa. The Harkless fossils
resemble some esthonioporate and cystoporate bryozoans, showing a
radiating pattern of densely packed tubes of the same diameter and
cross-sectional shape. Further, they show partitioning of new
individuals from parent tubes through the formation of a separate wall,
a characteristic of interzooecial budding in bryozoans. If confirmed as
bryozoans, these fossils would push back the appearance of mineralized
skeletons in this phylum by ~30 million years and impact interpretations
of their evolution."

[John Harshman]

This goes to show the vagaries of preservation, even in Lagerstätten. If
it's a bryozoan, it also shows a 30-million-year gap in known
preservation of bryozoan fossils.

[erik simpson]

Thanks! I missed this, but I won't miss checking it out. It's only a couple of hours away.

[Peter Nyikos]

On Saturday, May 7, 2022 at 8:59:38 PM UTC-4, Inyo wrote:

Hi, Inyo! I returned yesterday from a half-year posting break, so I am only responding now.

I could kick myself for having missed your October post, well before my posting break began.
I've had lots of occasions to talk about the Cambrian explosion, and always I had to add "..except for Bryozoa..."
Now, no longer!

> On 10/27/2021 5:43 PM, Inyo wrote:
>
> > Molecular clock analyses definitely suggest that Bryozoa (AKA, the
> > ectoprocts) should have been around during early Cambrian Explosion
> > times, though direct fossil evidence had long-constrained their first
> > geologic occurrence to the early Ordovician, with a hotly debated,
> > putative bryozoa example reported from the late Cambrian.
> >
> > A paper just published online, and now available for pdf download (as of
> > October 27, 2021), describes what the authors call a potential
> > stem-group bryozoan, preserved as secondarily
> > mineralized--phosphatized--specimens from Cambrian Stages 4 and 3,
> > Australia (Wirrealpa Limestone) and South China (Dengying Formation),
> > respectively. They call it Protomelission gatehousei, whose original
> > unmineralized body plan shares traits with several Bryozoa classes,
> > including the soft-bodied Gymnolaemata (Ctenostomata).

Your new announcement is fascinating in the light of the following statement you made back in October:

> > By the way, the oldest bryozoans I've personally collected derives from
> > the lower Middle Ordovician Antelope Valley Limestone, Great Beatty
> > Mudmound, western Nevada. See a photograph of them over at
> > http://inyo.coffeecup.com/site/beatty/beatty15.html ,
> >
> > Download the entire paper over at
> > https://www.nature.com/articles/s41586-021-04033-w .

<skip to get to the fascinating feature of your new announcement>

> On the paleontological heels of discovering the earliest
> non-mineralized, soft-bodied byrozoan in Earth history (described in the
> link provided, above) we now have a published report of possibly the
> oldest mineralized bryozoan colony yet recovered from the fossil
> record--it's from the lower Cambrian (Stage 4) Harkless Formation of
> Esmeralda County, Nevada, north of Death Valley National Park.

Western Nevada again!! after the first discovery having been on the other side of our planet!
Will you be planning to go up there any time soon?

If you do, I'll be looking forward eagerly to your report about it.

> One caveat is that the investigators allow that confirmation of a
> "palaeostomate bryozoan affinity," would certainly involve finding an
> early growth stage, bearing the ancestrula with an associated
> protoecium. Nevertheless, the morphologic and taphonomic evidence
> already scrutinized does indeed point to fully mineralized bryozoans
> already well established in early Cambrian Explosion times, pushing back
> their first known mineralized occurrence in the geologic record by some
> 30 million years.

If these "bryomorphs" (as they are called in the article) are animals, then the evidence is strong that they are at least stem bryozoans,
meaning that they are closer phylogenetically to bryozoans than toany other living phylum.
It would be better, of course, if they were crown bryozoans, and that accounts for
the stress placed on finding an early growth stage as described.

> The abstract, from the full paper published online over at
> https://www.science.org/doi/10.1126/sciadv.abm8465 :

I wrote "if they are animals," because the paper dwells for a long time on two calcimicrobe genera,
one of which, *Bija*, has been assigned to cyanobacteria:

"There are varieties of calcimicrobial fossils that have similarities to the bryomorph fossils described here. Bija and Hedstroemia are two examples of Paleozoic calcimicrobes with structures reminiscent of the fossils described here (26–28). Originally, Bija was described from the Verkhneynyrga Formation of the Lebed’ River, Mountain Altay, southern Siberia, Russia (29). Bija has since been found from lower Cambrian (stages 2 to 4) carbonates of other Siberian areas and the South Urals, Russia (30–32) as well as from the Mackenzie Mountains of Canada (33), olistoliths associated with reefs in the Great Basin, Nevada, ..."

There we go again, Nevada! The term "calcimicrobe" was new to me, so I looked it up, and found this:

https://geologylearn.blogspot.com/2016/08/calcimicrobescyanobacteria-blue-green.html

In it, there is a microphotograph that very much reminded me of one of the bryomorphs.
It follows the paragraph,

"Lo. Cambrian (Tommotian) Pestrotsvet Fm., Siberian Platform, Russia
Dendritic growth forms of the widespread calcimicrobe or microproblematic organism, Epiphyton. This genus has distinctively thick, solid branches. It commonly forms unusually large growths that can be a substantial rockforming element in association with other framework organisms. Figure below

Comparing it with some photographs in your referenced article, Inyo,
I can understand the caveat I kept in above. There is at least a superficial resemblance
to Fig. 3 B in their article. Also, Fig. 5 in their article reminded me of
the one in the geologylearn webpage which comes after the following paragraph:

Up. Permian (Kazanian?) Karstryggen Fm., Jameson Land, East Greenland
Calcified. microproblematic, densely branching growths. Such calcified arborescent remains have been considered as microbial by some workers and as green algal by others. The examples shown here were formed and preserved in shallow-marine areas with exceptionally high rates of marine cementation. Figure below


Needless to say, I will be alert for any new developments about the affinities of
the bryomorphs of the Harkless Formation. Thank you for sharing this fascinating
find with us, Inyo.


Peter Nyikos
Professor, Department of Mathematics
University of South Carolina -- standard disclaimer --
https://people.math.sc.edu/nyikos/