Ediacarans of the Land?

[shadron]

http://www.eurekalert.org/pub_releases/2012-12/uoo-aaf121012.php

So, were there entities (plants, animals, fungi? Only their hairdressers know for sure) on the land 100 million years before plants invaded the land in the Ordovician? How did they manage to brave the land before (I believe) the amount of oxygen got high enough to host an ozone layer?

You decide.

 

[BenBurch]

The supposed soil he finds seems doubtful to me. At least, insufficient by itself.

 

[Dinwar]

The supposed soil he finds seems doubtful to me. At least, insufficient by itself.

I haven't been able to access the original papers, but I agree. We have good evidence for microbial mats in the oceans during the Ediacaran, and I can easily see those looking like terrestrial soil. Also, we could be seeing near-shore environments that are periodically exposed for some reason. Finally, it's important to remember that we're seeing where these things wound up after they died, not necessarily where they lived. That's an important distinction--they certainly wouldn't be the only things that washed up onto shore in history.

Hopefully I'll be able to track down the papers and give a better critique soon. Unfortunately, they're behind a paywall right now.

 

[Floyt]

Interesting. Not a smash-bang argument as presented by that press release, but I'm looking forward to reading the paper once it becomes available for standard University access. One might have thought such a comparatively simple stratigraphic argument would have occurred to someone before now, if there was anything to it?

Note the important last paragraph on how Oregon Haz Cool Toys. Yay free PR!

 

[Dinwar]

One might have thought such a comparatively simple stratigraphic argument would have occurred to someone before now, if there was anything to it?

You'd be surprised. A lot of stratigraphers refer to paleontologists as "stamp collectors", and I have to admit there is some justification to that. As a field we are woefully lacking in stratigraphic knowledge. Historically, the focus has been on the fossils themselves--what animals they represent, how those animals fit together in ecosystems and evolution, etc. All worthy goals, but it's twisted the view of the fossil record many paleontologists have. Many have forgotten that ecosystems include both biotic AND ABIOTIC components--including the sediment.

I once read an article about some sediment near the Salton Sea. The whole point of the article was a long, detailed list showing all of the species that were found in one or two deposits, and the author made grand, sweaping claims about the ecology of the sea based on that alone. No discussion of the sediments the fossils were found in, no discussion of which bones were found, and no discussion of the condition of the bones. All of that is important, because it lets us know if they were transported by sedimentary processes or predators (owl pellets and canid and felid fecies, mostly). So in the end, the paper really was nothing more than a list of species names, of almost no utility to anyone doing a serious study of the region. But it's not atypical of paleontological thought.

(I, on the other hand, AM atypical, in that I was careful to study the stratigraphy of the region before I dove into the paleontology--which is how I caught the error. Everyone ELSE has the problem, obviously! )

Of course, to be fair, we ARE talking about stratigraphic processes on an alien planet here. You get earlier than the Cambrian and we can't really even pretend to know what the world was like in fine detail. And if you're not a stratigrapher it's not unreasonable to hold off on discussing stratigraphy until one shows up. It's been a tad too long, in my opinion, but then again the nature of the discussion of the Ediacaran fauna hasn't exactly been one of open acceptance and brotherly love.

 

[Soapy Sam]

If these were terrestrial, that would suggest they were even less likely to be ancestral to most modern forms than they are thought to be now.

Of course, to be fair, we ARE talking about stratigraphic processes on an alien planet here.

This is fair comment. We could be looking at an environment more Martian than Earthlike in some ways. You can only push uniformitarianism so far back.

I'll be intrigued to see the full paper too. I find it hard to believe it's right, but hey- that's where the fun comes into science, when you turn out to be wrong.

 

[Soapy Sam]

The supposed soil he finds seems doubtful to me. At least, insufficient by itself.

Indeed- but then we must define "soil". Most modern soil formation processes are biological in large part. Back then, we'd be talking about something very different- more inorganic / chemical in origin. Think ashfall / glacial / desert - those sort of rock decomposition processes. Not much vegetation to hold rock together back then ... unless we're wrong about that too?

 

[Dinwar]

Back then, we'd be talking about something very different- more inorganic / chemical in origin.

Would we, though? The requirements for algae and protists to live on land are less than those for animals and plants, meaning that we should expect to see organic material on land (and therefore impacting soil development) far earlier than we'd expect to see animals and plants. And then the fact that we're still talking near-shore environments is significant. If the authors are right there were organisms on land, and even if they themselves didn't contribute to soil development they certainly would after they died (organic compounds do all sorts of fun things to redox states, oxygen levels, pH, and other factors that control soil development).

I'm not necessarily disagreeing with you--pedogenesis isn't my strong suite, not by a long shot. I'm just trying to work through all the implications of this hypothesis.

Of course, all of this raises some other pretty serious questions. While there really aren't any truly uncollonized environments on Earth anymore, I find it really hard to believe that there was food without something eating it. What I mean is, if youv'e got enough food to support an Ediacaran faunal memeber you've got enough to support a large number of smaller things, and detritovores are the second-oldest ecological niche on Earth, after chemosynthetic organisms. I would be absolutely amazed if there weren't some in a soil where Ediacaran faunal members lived. And that of course implies bioturbation, something that we definitely don't see (if the authors are right) in these sediments. I'm not sure if we see it in other Ediacaran-age terrestrial sediments. I knew we do in marine sediments of that time--including some of the weirdest known, stuff were we're not sure if it's an animal that did it or just one large cell in some cases. But I'm not sure about the stuff on land.

 

[BenBurch]

Speaking of weird stuff; http://old.richarddawkins.net/articles/3361

That's what I was just reminded of by Dinwar's post.

 

[Dinwar]

That's good--because that's the article I was thinking about, and couldn't remember. Thanks for the link, and the reminder!

 

[Soapy Sam]

Hard to reconcile the Newfoundland sediments with a terrestrial environment.
As some of the same critters are in both the type location and here, they'd have to be both land and sea creatures.
Seems unlikely.
http://www.peripatus.gen.nz/paleontology/ediacara.html

 

[Soapy Sam]

I'm told the author has been pushing this idea since 1985.
Seems pretty improbable.

 

[Floyt]

Hard to reconcile the Newfoundland sediments with a terrestrial environment.
As some of the same critters are in both the type location and here, they'd have to be both land and sea creatures.
Seems unlikely.
http://www.peripatus.gen.nz/paleontology/ediacara.html

Good point (and nice review article).

 

[Dinwar]

Confusingly, the same term is also used in a biogenic sense, and in two different ways

The way I learned it, the biological definition came first.

Also, my 2009 GSA geologic timescale doesn't include a Vendian on it. There's the Neoproterozoic Era (1 ga to 542 ma), broken down into the Tonian (1 ga to 850 ma), Cryogenian (850 ma to 630 ma), and Ediacaran (630 ma to 542 ma).

Like Floyt said, that's an interesting article. Thank you for linking to it.

It spurred a few thoughts:

First, the Ediacaran fauna is diverse. We know that. It would seem likely, therefore, to expect to find them in a variety of environments. We see corals in everything from storm-surge to abysal plains, for example, and crabs live everywhere from land to open ocean to chemosynthetic ecosystems. And those aren't even phyla. So the more I think about it, the less surprised I'd be to find that these weirdest of creatures would have lived in a variety of settings. I'm not convinced they lived on land--I haven't read the paper, and the fact that the guy's been pushing it for decades makes me skeptical about it (he obviously hasn't convinced far more knowledgeable people than me)--but near-shore environments? Sure.

Which brings me to my other thought. A lot of these critters have holdfasts (or the equivalent). This seems to imply that they experienced some turbulence. You don't really need a strong grip on the ground when you're below storm-wave influence, since there's nothing that will really push you. That said, a lot of taxa have them (crinoids have holdfasts, for example), so this may not be the best line of reasoning.

 

[Soapy Sam]

I don't know if all Carboniferous crinoids were shallow marine beasts, but I think they were. These days, they have expanded (or been pushed) into deeper environs as well. They presumably took the anchors with them.

the fact that the guy's been pushing it for decades makes me skeptical about it (he obviously hasn't convinced far more knowledgeable people than me)

My thought exactly. I'm not fit to comment really, but I asked a couple of people who are. Not favourable.
Still. Doubtless time will tell.