Dickensonia in India?

[erik simpson]

https://www.sciencedirect.com/science/article/abs/pii/S1342937X20303038#:~:text=The%20discovery%20of%20Dickinsonia%20in,reconstructions%20for%20the%20late%20Ediacaran.&text=Cloudina%20and%20other%20small%20shelly,at%20temperate%20to%20subtropical%20latitudes (unfortunately paywalled)

I just encountered this link in a nearly incomprehensible pop article, that
seemed to be conflating an Ediacaran fossil with cave paintings known
previously from the Bhimbetka Rock Shelters, a well-known Mesolithic
cave art site near Bhopal. It's Dickensonia, all right. The lead author,
Greg Retallack is slightly notorious for his theory that some Ediacaran organisms were fungi, and living on land, but he's not a crank. The
Dickensonia found in the cave are indistinguishable from those found in the
Flinders range in Australia, and even the sandstone beds are similar as well.

[Glenn]

Of course anyone who sees the obvious, a plant leaf, would have to be considered a crank.

[jillery]

You didn't cite the pop article, so I did a Google search, and I got a
link to the full pdf:

<https://cpb-us-e1.wpmucdn.com/blogs.uoregon.edu/dist/d/3735/files/2020/12/Retallack-et-al.-2021-Dickinsonia-India.pdf>

<https://tinyurl.com/m4f69wfx>

The conflation to which you refer is because the impression is on the
roof of a tall cave, which made it difficult to determine if its a
true fossil or merely painted on the rock. IIUC the article
establishes it as a true fossil.

As to whether Dickinsonia was an animal, I recall seeing images of
these fossils associated with traces of their moving along the ocean
floor.

[erik simpson]

Also see https://science.sciencemag.org/content/361/6408/1246/tab-figures-data
"Ancient steroids establish the Ediacaran fossil Dickinsonia as one of the earliest animals"

Even open access.

BTW, I mispoke Retallack's suggestion of Ediacaran "fungi". He actually sugggests lichens,
maintaining that the fossils appear in what look (to him) like paleolsols (fossil soils).

[jillery]

On Mon, 22 Mar 2021 21:17:44 -0700 (PDT), erik simpson

Retallack disagrees with Bobrovskiy's conclusions:

<https://science.sciencemag.org/content/re-dickinsonia-steroids-not-unique-animals>

My impression is Ediacaran lichens would be as likely as pre-Cambrian
rabbits.

[erik simpson]

Indeed he does. There's plenty of room in paleontology for disagreements, especially in regards to
Precambrian organisms and ecology. Paleontolgy needs unusual ideas more than most empirical
sciences. Most Ediacaran workers disagree with Retallack, but as I remarked, he's no crank, even
though the idea of Precambrian lichens is "out there".

> <https://science.sciencemag.org/content/re-dickinsonia-steroids-not-unique-animals>
>
> My impression is Ediacaran lichens would be as likely as pre-Cambrian
> rabbits.

Motile lichens especially.

[erik simpson]

Further reading in Ediacaran bio- geo- chemistry:

https://www.nature.com/articles/s41467-020-15063-9
"Food sources for the Ediacara biota communities" (Bobrovskiy, et al.)

https://www.nature.com/articles/s41559-020-01334-7?proof=t (paywalled)
"Algal origin of sponge sterane biomarkers negates the oldest evidence for animals in the rock record" (Bobrovskiy, et al.)

Abstract:

"The earliest fossils of animal-like organisms occur in Ediacaran rocks that are approximately 571 million years old. Yet 24-isopropylcholestanes and other C30 fossil sterol molecules have been suggested to reflect an important ecological role of demosponges as the first abundant animals by the end of the Cryogenian period (>635 million years ago). Here, we demonstrate that C30 24-isopropylcholestane is not diagnostic for sponges and probably formed in Neoproterozoic sediments through the geological methylation of C29 sterols of chlorophyte algae, the dominant eukaryotes at that time. These findings reconcile biomarker evidence with the geological record and revert the oldest evidence for animals back into the latest Ediacaran."

So the sterane evidence for animal affinities of Dickensonia appear to be still "up in the air", or better "down under water".

[John Harshman]

There's nothing odd about the idea of Precambrian lichen. Why shouldn't
there be terrestrial fungi long ago, and why shouldn't some of them have
symbiotic algae? What's odd is the identification of Ediacaran fauna as
lichens. If I recall, it was all about their perceived lack of
compressibility.

[erik simpson]

I believe this is the best summary of Retallack's thinking. Compressibility is a major
argument.

https://www.tandfonline.com/doi/full/10.1080/03115510701484705

See in particular his Table 5.

[jillery]

On Tue, 23 Mar 2021 10:29:15 -0700 (PDT), erik simpson

>"The earliest fossils of animal-like organisms occur in Ediacaran rocks that are approximately 571 million years old. Yet 24-isopropylcholestanes and other C30 fossil sterol molecules have been suggested to reflect an important ecological role of demosponges as the first abundant animals by the end of the Cryogenian period (>635?million years ago). Here, we demonstrate that C30 24-isopropylcholestane is not diagnostic for sponges and probably formed in Neoproterozoic sediments through the geological methylation of C29 sterols of chlorophyte algae, the dominant eukaryotes at that time. These findings reconcile biomarker evidence with the geological record and revert the oldest evidence for animals back into the latest Ediacaran."

>
>So the sterane evidence for animal affinities of Dickensonia appear to be still "up in the air", or better "down under water".

<https://science.sciencemag.org/content/361/6408/1246>
****************************
Bobrovskiy et al. conducted an analysis using lipid biomarkers
obtained from Dickinsonia fossils and found that the fossils contained
almost exclusively cholesteroids, a marker found only in animals (see
the Perspective by Summons and Erwin). Thus, Dickinsonia were basal
animals. This supports the idea that the Ediacaran biota may have been
a precursor to the explosion of animal forms later observed in the
Cambrian, about 500 million years ago.
****************************

IIUC, although lots of organisms form steranes, only animals form
cholesteroids. This is the basis for Bobrovskiy's animal conclusion.

Here's a short PBS Eons video which provides a short summary
<https://www.youtube.com/watch?v=PGBf4Q2XWZo>

[jillery]

Nothing above suggests Precambrian lichens being odd.

But since you did, my understanding is fossil-bearing Ediacaran
sandstones are exclusively marine deposits. So if Dickinsonia were
lichens, they would not have been terrestrial, but marine. To the
best of my knowledge, marine lichens don't exist. Also, the first
lichens appeared around 250 mya.

[jillery]

On Tue, 23 Mar 2021 16:32:46 -0400, jillery <69jp...@gmail.com>
wrote:

Replace "marine" with "aquatic" as there are some lacustrine deposits
as well:
<https://www.nature.com/articles/s41598-019-46304-7>

[erik simpson]

jillery? Where does that come from? I don't see her contribution here.

[Glenn]

Nah. Only the Sith deal in absolutes.

"Finally, cholesterol even occurs in plants (Behrman & Gopalan 2005), of which some (e.g., canola) can have more than 70 percent of cholesterol in the sterol fraction of their surface."

https://evolutionnews.org/2018/09/why-dickinsonia-was-most-probably-not-an-ediacaran-animal/

[John Harshman]

If you will note, Retallack claims that the deposits are terrestrial,
being paleosols.

[jillery]

On Wed, 24 Mar 2021 15:51:49 -0700, John Harshman

My understanding is Retallack makes 3 extraordinary claims:

1. That algae and fungi formed a symbiotic relationship millions of
years before the existence of any terrestrial plants,

2. and hundreds of millions of years before lichens are thought to
have originated,

3. and geologists can't tell the difference between aquatic and
terrestrial deposits.

Extraordinary claims require extraordinary evidence.

The following describes Dickinsonia in association with numerous other
Ediacaran taxa, all part of a larger marine community found at the
National Heritage Site, Nilpena Station, west of the Flinders Ranges,
South Australia. Unless Retallack claims all these taxa are
terrestrial lichens, this is extraordinary evidence against his
extraordinary claims.

<https://escholarship.org/uc/item/0gm5k164>

[John Harshman]

I don't find that to be extraordinary.

> 2. and hundreds of millions of years before lichens are thought to
> have originated,

That's the same claim, isn't it?

> 3. and geologists can't tell the difference between aquatic and
> terrestrial deposits.

That's more broad than his claim, but it is extraordinary.

You omit his most extraordinary claim: that Ediacaran fossils are lichen.

> Extraordinary claims require extraordinary evidence.
>
> The following describes Dickinsonia in association with numerous other
> Ediacaran taxa, all part of a larger marine community found at the
> National Heritage Site, Nilpena Station, west of the Flinders Ranges,
> South Australia. Unless Retallack claims all these taxa are
> terrestrial lichens, this is extraordinary evidence against his
> extraordinary claims.
>
> <https://escholarship.org/uc/item/0gm5k164>

I believe that's exactly what he claims.

[jillery]

On Wed, 24 Mar 2021 21:25:28 -0700, John Harshman

Our opinions on what is extraordinary are equally authoritative.

>> 2. and hundreds of millions of years before lichens are thought to
>> have originated,
>
>That's the same claim, isn't it?

No. Lichen may have originated before terrestrial animals or before
terrestrial plants. My understanding is there was no multicellular
terrestrial life during Cambrian, nevermind during Ediacaran.
Retallack's claim makes lichen an extraordinary outlier... IMO.

>> 3. and geologists can't tell the difference between aquatic and
>> terrestrial deposits.
>
>That's more broad than his claim, but it is extraordinary.

It is corollary. If Dickinsonia is terrestrial lichen, then the
deposits its found in are necessarily terrestrial. Or do you suppose
Dickinsonia transplanted from land to water unbroken?

>You omit his most extraordinary claim: that Ediacaran fossils are lichen.

I omitted what was previously explicitly stated multiple times, a
nitpick at best.

>> Extraordinary claims require extraordinary evidence.
>>
>> The following describes Dickinsonia in association with numerous other
>> Ediacaran taxa, all part of a larger marine community found at the
>> National Heritage Site, Nilpena Station, west of the Flinders Ranges,
>> South Australia. Unless Retallack claims all these taxa are
>> terrestrial lichens, this is extraordinary evidence against his
>> extraordinary claims.
>>
>> <https://escholarship.org/uc/item/0gm5k164>
>
>I believe that's exactly what he claims.

That all are terrestrial lichens is a far more broad claim than
Dickinsonia is a terrestrial lichen. Cite evidence to support your
expressed belief.

[erik simpson]

Abstract

Ediacaran (635–542 million years ago) fossils have been regarded as early animal ancestors of the Cambrian evolutionary explosion of marine invertebrate phyla1, as giant marine protists2 and as lichenized fungi3. Recent documentation of palaeosols in the Ediacara Member of the Rawnsley Quartzite of South Australia4 confirms past interpretations of lagoonal–aeolian deposition based on synsedimentary ferruginization and loessic texture5,6. Further evidence for palaeosols comes from non-marine facies, dilation cracks, soil nodules, sand crystals, stable isotopic data and mass balance geochemistry4. Here I show that the uppermost surfaces of the palaeosols have a variety of fossils in growth position, including Charniodiscus, Dickinsonia, Hallidaya, Parvancorina, Phyllozoon, Praecambridium, Rugoconites, Tribrachidium and ‘old-elephant skin’ (ichnogenus Rivularites7). These fossils were preserved as ferruginous impressions, like plant fossils8, and biological soil crusts9,10 of Phanerozoic eon sandy palaeosols. Sand crystals after gypsum11 and nodules of carbonate12 are shallow within the palaeosols4, even after correcting for burial compaction13. Periglacial involutions and modest geochemical differentiation of the palaeosols are evidence of a dry, cold temperate Ediacaran palaeoclimate in South Australia4. This new interpretation of some Ediacaran fossils as large sessile organisms of cool, dry soils, is compatible with observations that Ediacaran fossils were similar in appearance and preservation to lichens and other microbial colonies of biological soil crusts3, rather than marine animals1, or protists2.

https://www.nature.com/articles/nature11777

[John Harshman]

This all goes back to his original publication of this theory in
Paleobiology, almost 30 years ago:

Retallack, G.J., 1994b. Were the Ediacaran fossils lichens?
Paleobiology, 20, 523-544.

Dickinsonia is mentioned, but so are many other Ediacaran "vendobionts".

[erik simpson]

Here's a more recent reference:

https://cpb-us-e1.wpmucdn.com/blogs.uoregon.edu/dist/d/3735/files/2013/07/Retallack-2018-interflag-laminae-1dl9df5.pdf

His opinions have been pretty stable for a long time. As far as "extraordinary" is concerned, nearly everything about
the Ediacaran is extraordinary.

[jillery]

On Thu, 25 Mar 2021 08:57:41 -0700 (PDT), erik simpson

>Ediacaran (635–542?million years ago) fossils have been regarded as early animal ancestors of the Cambrian evolutionary explosion of marine invertebrate phyla1, as giant marine protists2 and as lichenized fungi3. Recent documentation of palaeosols in the Ediacara Member of the Rawnsley Quartzite of South Australia4 confirms past interpretations of lagoonal–aeolian deposition based on synsedimentary ferruginization and loessic texture5,6. Further evidence for palaeosols comes from non-marine facies, dilation cracks, soil nodules, sand crystals, stable isotopic data and mass balance geochemistry4. Here I show that the uppermost surfaces of the palaeosols have a variety of fossils in growth position, including Charniodiscus, Dickinsonia, Hallidaya, Parvancorina, Phyllozoon, Praecambridium, Rugoconites, Tribrachidium and ‘old-elephant skin’ (ichnogenus Rivularites7). These fossils were preserved as ferruginous impressions, like plant fossils8, and biological soil crusts9,10 of

>Phanerozoic eon sandy palaeosols. Sand crystals after gypsum11 and nodules of carbonate12 are shallow within the palaeosols4, even after correcting for burial compaction13. Periglacial involutions and modest geochemical differentiation of the palaeosols are evidence of a dry, cold temperate Ediacaran palaeoclimate in South Australia4. This new interpretation of some Ediacaran fossils as large sessile organisms of cool, dry soils, is compatible with observations that Ediacaran fossils were similar in appearance and preservation to lichens and other microbial colonies of biological soil crusts3, rather than marine animals1, or protists2.
>
>https://www.nature.com/articles/nature11777

You and Harshman make a good team. I acknowledge I didn't recognize
the implication of your statements wrt "fossil soils" being
necessarily terrestrial. But since this thread has finally arrived at
the heart of the matter:
<https://astrobiology.nasa.gov/nai/media/medialibrary/2015/07/tarhanetal2015_pcubed_ediacaranissue.pdf>

<https://tinyurl.com/ydhn6ed4>
*******************************
A careful assessment of paleoenvironmental parameters is essential to
the reconstruction of the depositional and early diagenetic history of
the Ediacara Biota and thus the physical, chemical and biological
factors that shaped the development and the fossilization of these
earliest examples of complex life. We find no compelling evidence for
a terrestrial setting for the Ediacara Member and strong support
for a shallow marine depositional environment.
*******************************

IIUC the consensus is the evidence Retallack describes in your cite is
consistent with shallow marine pools which repeatedly dried up and
refilled.

Also, my understanding is these taxa disappeared from the fossil
record during the Cambrian, even as these types of paleosols continued
through time. This suggests to me these taxa were aquatic organisms
which went extinct as newer lifeforms evolved. This explanation
doesn't work if these were terrestrial lichens, which had no known
competition during the Ediacaran and the Cambrian.

Also, I don't know if these taxa are found only in this particular
strata, or how many different types of Ediacaran strata exist. If
these taxa are found in other Ediacaran strata, this would be evidence
against their terrestrial origin.

[jillery]

On Thu, 25 Mar 2021 09:31:47 -0700, John Harshman

>> Ediacaran (635–542?million years ago) fossils have been regarded as early animal ancestors of the Cambrian evolutionary explosion of marine invertebrate phyla1, as giant marine protists2 and as lichenized fungi3. Recent documentation of palaeosols in the Ediacara Member of the Rawnsley Quartzite of South Australia4 confirms past interpretations of lagoonal–aeolian deposition based on synsedimentary ferruginization and loessic texture5,6. Further evidence for palaeosols comes from non-marine facies, dilation cracks, soil nodules, sand crystals, stable isotopic data and mass balance geochemistry4. Here I show that the uppermost surfaces of the palaeosols have a variety of fossils in growth position, including Charniodiscus, Dickinsonia, Hallidaya, Parvancorina, Phyllozoon, Praecambridium, Rugoconites, Tribrachidium and ‘old-elephant skin’ (ichnogenus Rivularites7). These fossils were preserved as ferruginous impressions, like plant fossils8, and biological soil crusts9,10 of

>Phanerozoic eon sandy palaeosols. Sand crystals after gypsum11 and nodules of carbonate12 are shallow within the palaeosols4, even after correcting for burial compaction13. Periglacial involutions and modest geochemical differentiation of the palaeosols are evidence of a dry, cold temperate Ediacaran palaeoclimate in South Australia4. This new interpretation of some Ediacaran fossils as large sessile organisms of cool, dry soils, is compatible with observations that Ediacaran fossils were similar in appearance and preservation to lichens and other microbial colonies of biological soil crusts3, rather than marine animals1, or protists2.
>>
>> https://www.nature.com/articles/nature11777
>>
>This all goes back to his original publication of this theory in
>Paleobiology, almost 30 years ago:
>
>Retallack, G.J., 1994b. Were the Ediacaran fossils lichens?
>Paleobiology, 20, 523-544.
>
>Dickinsonia is mentioned, but so are many other Ediacaran "vendobionts".

So how well does Retallack's hypothesis apply to the Dickinsonia
fossil on the roof of Auditorium Cave at Bhimbetka Rock Shelter?

[erik simpson]

The rock at Bhimbetka are quite similar to those in the Flinders Range. The main point
of the original paper is the evident proximilty of India and Australia. From that paper,

"There remains controversy about whether vendobionts ofsiliciclastic facies,Ernietta,Dickinsonia,andArumberiaare shallow-marine or non-marine (Retallack, 2016), but either way, there are deep ocean separations of Erniettain Namibia and Nevada (Smithet al., 2017), and of Dickinsoniain Australian-India compared withBaltica (Fig. 5). Strong clustering of Baltic and Australian Ediacaran as-semblages, which shareDickinsonia(Retallack, 2007;Ivantsov, 2007;Retallack and Broz, 2020), may thus reflect similar paleoenvironmentsrather than a single biogeographic province (Muscente et al., 2019)."

[John Harshman]

Specifically, it's the origin of macropredation that is said to have
done in the Ediacarans, either directly or as a result of destabilizing
the microbial mats on which they might have fed (if they were
metazoans). And there's no evidence of terrestrial predators until the
Ordovician at the very earliest.

> Also, I don't know if these taxa are found only in this particular
> strata, or how many different types of Ediacaran strata exist. If
> these taxa are found in other Ediacaran strata, this would be evidence
> against their terrestrial origin.

Some Ediacaran faunas are in clearly deep water environments, e.g.
rangeomorphs, the Mistaken Point assemblage, and such. So at least those
can't be lichens. I don't know what Retallack has written about them.

[jillery]

On Thu, 25 Mar 2021 15:49:32 -0700, John Harshman

Specifically, these taxa were not terrestrial lichens.

[jillery]

On Thu, 25 Mar 2021 12:26:14 -0700 (PDT), erik simpson

Correct. So Retallack's history of pushing this trope, and the trope
itself, are not especially relevant to that main point and your OP.

[erik simpson]

That's right.

[John Harshman]

Sorry, not clear what point you're trying to make. What do you refer to
as "these taxa"?