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When Cells Discovered Architecture

The views expressed are those of the author and are not necessarily those of Scientific American.


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In early 1997, while still a freshman in college pondering whether to study biology or archaeology, I opened up my copy of Discover Magazine to find an article that startled and captivated me. "When Life Was Odd", read the headline, and if that didn’t sell me, the photos did. They were of Ediacarans, creatures named after the stony hills in southeast Australia where they were first recognized in 1946, and their puffy, weirdo bodies were wonderful.  

There was the bilaterally radiating ovoid disk of Dickinsonia, the sea pen-like fronds of Rangea and Charniodiscus, the fruit loop embedded in a pineapple ring of Cyclomedusa, and the wickedly curved and utterly gorgeous vortex of Tribrachidium. Much later, I discovered the glorious shark tooth kebabs of Fractofusus from Mistaken Point, in Newfoundland, Canada. Imagine: a whole world of sea life that looked like almost nothing alive today that once briefly ruled the oceans – only to vanish forever. What an exciting thing!  

But what were these things? No one was really sure. They seemed somehow inflated, or pneumatic – a state that persists in few, if any, creatures alive today. They immediately pre-dated the Cambrian explosion – the sudden flowering of animals that produced the lineages that led to jellyfish, cockroaches, T. rexes, and giant sloths. Clearly, that was an important event, but what about this fascinating overture? Did us big bad higher animals wipe out the poor, defenseless, balloon animals? Or did we, at least in part, evolve from them? And where did they in turn come from — other than out of the blue?  

Scientists are still in the process of answering all these questions. But that last one got much more interesting after a paper in Nature published in February – to relatively little fanfare — debuted an entirely new group of Ediacarans, a group that predates classic Ediacarans by a good 20-40 million years. A group with a few members that look – surprisingly – like Stuff Alive Today. A group, it turns out, that might have evolved just after Earth emerged from the controversial cataclysm called "Snowball Earth" – and could perhaps even have been prodded to evolve by it. A group that, as far as we know, are the earliest surviving fossils of algae, plants, and possibly animals on Earth. They are called Lantians. And they are wonderful too.

Previously, the oldest known Ediacarans were about 580 million years old –  about 40 million years older than the Cambrian. In attempting to explain their pillowy appearance, scientists have speculated they may have had photosynthetic algae in their tissues, or have fed by absorbing nutrients across their thin bodies. They seem to have lived in tidal mudflats or shallow tidal pools and were preserved when they were covered by sediment, though some, like the Avalon group, were abyssal creatures eking out a living by osmotically absorbing dissolved nutrients.

Until the discovery of the Lantians, the only recognized pre-Ediacaran massively multicellular fossils were stromatolites, blue-green algal high-rises of limited morphological sophistication: they are simply the left-behind houses of cyanobacterial biofilms stacked layer upon layer. They’ve been around for at least 3 billion years. And after they evolved . . . not much happened. Life barely changed, at least in terms of shape and size, for a really long time. Until something really big did happen: Earth froze solid. Or slushy. Or possibly with a band of water around the equator, or in some other odd configuration. Or maybe not at all. However it may have been, based on a near-worldwide appearance of glacial deposits, some geologists think our planet iced up.  

Those who say that it did believe the planet froze three times for millions of years each in the late Proterozoic, in the aptly named Cryogenian period. This age was followed by the last period of the Proterozoic: the Ediacaran, which stretched from 635 to 542 million years ago. The Cambrian, in turn, followed that. Until now, the oldest known Ediacaran fossil group was called the Avalon, and first appeared about 575-580 million years ago.  

But in eastern China, north of Nanjing, lies a layer of rock called the Lantian formation made of a flaky mudstone called shale. Inside are fossils – the newest, and earliest Ediacarans, scientists now report. Though many were discovered, described, and named over 10 years ago, they were misdated to 551 million years old. In the Nature paper, scientists at the Chinese Academy of Sciences and Northwest University in China and at Virginia Polytechnic Institute correct this, estimating their age at 607 to 635 million years.  

The shale lacks any cross-banding or wave or current induced structure. These rocks formed in quiet water.  Most of the fossils appear to have been attached to the seabed. And the fossils found inside are randomly oriented and not folded or broken. They weren’t swept there by currents or deposited from above. They seem to have died, quietly, where they lived. The authors suggest that was a muddy bottom below the base of storm waves but still within reach of the sun.  

Together, they form a buffet of biodiversity. Unlike other Ediacarans, some of these fossils stun by their sameness, not their eccentricity. One dichotomously branching form(see photo at top) looks very much like modern algae (scroll down to photos here). One fossil (see photo at left) resembles resembles the modern sea palm, Postelsia palmaeformis..

 

 

 

 

But others remain enigmatic. One may be a polyp-like creature. The axial traces of others [right] might be the digestive tract of worm-like organisms with "probosci", or alternatively, another alga with "holdfast" and "stalk". This strange chain could be anything [below, left].

All told, the scientists estimate the Lantian fauna consists of about 15 types of mostly complex form. They could be 15 different species, or some could be different developmental stages of others. Strikingly, there seems to be no species overlap – perhaps even at the kingdom level, according to Guy Narbonne in a commentary accompanying the Nature paper — with the abyssal Avalon biota, the previous record-holder for oldest big life. Avalon is filled with "traditional" pneumatic Ediacarans. Lantian is populated by large algae. That has both to do with the differences in habitat, but also the details of the different preservations (Avalon is sandstone).  

And here’s the truly intriguing bit. The layer containing the fossils lies directly on top of (conformably, for the geologists in the crowd) the rock layer with the deposits from what we think was the last glaciation of Snowball Earth. Thus it may well be that oxygenation of seawater and other changes in ocean chemistry spurred by the massive global glaciation pulled the trigger on the development of "big life". 

Of course, the Lantian holds the current record for oldest Ediacaran fossils, but that does not mean they were, and they almost certainly were not. As with all of the fossil record, some life was preserved by chance but most wasn’t. And of that that was preserved, much may have eroded out and thus lost over the last 600 million years, while much may still lie exposed unseen or buried deeply across and within the planet.  

And there remains one discrepancy. Early organisms – photosynthetic or not — are thought to have had a strict “no oxygen, no respiration, no life”  policy. But the rocks these fossils lie in say the Lantian oceans were devoid of oxygen. To account for this, the authors believe that the oceans were in the process of oxygenating, and that for short periods of time – too short to have been properly sampled and detected so far — the normally stifling Lantian seabeds lay under oxygen-rich water. These new life forms, not knowing any better, snuck in to take advantage of prime uninhabited real estate. But the oxygen soon vanished, suffocating, preserving and consigning them to muddy graves. Graves from which we have finally retrieved them, 600 million years later. If they truly were algae, they would be glad to finally again see the light of day.  

Sources:

An early Ediacaran assemblage of macroscopic and morphologically differentiated eukaryotes .

Evolutionary biology: When life got big .

"Prehistoric Life"

 

About the author: Jennifer Frazer is a AAAS Science Journalism Award-winning science writer who lives in Boulder, Colorado. She has degrees in biology, plant pathology/mycology, and science writing, and has spent many happy hours studying life in situ. Read her blog The Artful Amoeba and find her on Twitter at @JenniferFrazer.

The views expressed are those of the author and are not necessarily those of Scientific American.






Comments 10 Comments

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  1. 1. HubertB 8:03 pm 06/13/2011

    Interesting article. I would like to know the size of the fossils but do not understand the scale used in the pictures.

    Link to this
  2. 2. Jennifer Frazer 12:42 am 06/14/2011

    Hi Hubert,
    Sorry for that omission. The scale bars are all 5 mm long with the exception of the possible worm-like creature with the "proboscis", in which it’s 2 mm. Hope that helps!

    Link to this
  3. 3. Cesar Sanchez 3:12 am 06/14/2011

    Great post, Jennifer. However, as a microbiologist, I just freak out every time I read things like "Stromatolites (…) They’ve been around for at least 3 billion years. And after they evolved . . . not much happened. Life barely changed, at least in terms of shape and size, for a really long time."

    "Life barely changed" for almost a couple of billion years??? You must be kidding. Life kept changing, including shape and size, and keeps changing all the time. A different issue is that most people (including biologists, unfortunately) do not appreciate the evolution of organisms (such as microbes or tiny soft-body living beings) that didn’t leave any clear fossil evidence inside hard rocks. That’s our fault, for not trying hard enough to make people aware that "life" is not just the animals and plants that we can see with our naked eye. Life was, and still is, mostly microbial.

    (Sorry, I had to write this. But I did enjoy reading your post!)

    Link to this
  4. 4. Lc5827carter 11:33 am 06/14/2011

    I first encountered a report about these in an article written by Gonzalo Vidal "The oldest eukaryotic cells" in Scientific American, February, 1984 referring to the first convincing evidence of pre-Cambrian life and the discoveries of C. Spriggs in 1945 in the Edicara hills in southern Australia.

    Link to this
  5. 5. Jennifer Frazer 12:07 pm 06/14/2011

    Hi Cesar,
    Thanks for pointing that out. You’re right to point out that microbial life did, of course, change and evolve during that time.

    I was thinking broadly, in terms of large, morphologically complex life — and the diversification within the Ediacaran definitely has no precedent, or if it does, we haven’t found the fossils. But eukaryotic cells, multicellularity (things like chains of bacteria) and even simple multicellular algae all evolved in that time between the evolution of stromatolites and the Ediacaran. As I was just doing a little research on this subject, I found this paper (http://paleobiol.geoscienceworld.org/cgi/content/abstract/26/3/386) on a red alga fossil dated to 1.2 billion years ago that possibly represents the first evidence of a sexually reproducing creature. Name: Bangiomorpha pubescens(!) This paper (http://www.vend.paleo.ru/pub/Fedonkin_2003.pdf also has some great photos of possible animal life older than 1 billion years. I didn’t know about any of this before so it is great to see!

    And certainly bacteria and protists were evolving and differentiating morphologically just like eukaryotes, and don’t fossililize well. So I agree microbes don’t get enough respect, so I apologize if I was perpetuating microbial stereotypes! : )

    I definitely could have worded it better. Thanks for the reminder (and for a little foray into a sector of life I hadn’t explored yet!)

    Jennifer

    Link to this
  6. 6. Cesar Sanchez 4:44 pm 06/14/2011

    Thank you again for writing the post, Jennifer, and for the links to those articles. Fascinating topic!

    Link to this
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  8. 8. seo experts academy review 1:18 am 10/17/2011

    interesting post! i really admire the study of fossils… scientific contribution for everybody.

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  9. 9. seo experts academy review 1:21 am 10/17/2011

    this is amazing. our cells are also works of architecture.
    http://www.seoexpertsacademy.net/seo-experts-academy-review

    Link to this
  10. 10. Charles Hollahan 1:37 pm 10/17/2012

    The specimen with the “probosci” or stalk that was found in quiet water probably would not have needed a holdfast. I’ve held onto a lot of holdfasts like the palm seaweeds and they are really good at that. So while they would have needed to evolve more, maybe – maybe not- it does look more like a proboscis than a holdfast.

    If it had been an anchor then I think it would have been larger at the base. Mostly this is for organisms in calm waters.

    I hope to see more on this in the near future (2012).

    Link to this

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