Ediacara is weird

I am giving a presentation in my Invertebrate Paleontology class on the Ediacara fauna. For the presentation, I need an abstract, which you can see below, and a slide show. The thing is, I'm completely stumped by what the things represent. The traditional interpretation is ok for only a few of the fossils, but the newer interpretation is completely absurd. Single celled organisms with quilted skin textures living on the sea floor growing to gigantic sizes (up to 1 meter diameter)! Or alternately, colonial cell sheets with weird cell growth patterns creating bilateral, trilateral, and pentaradial forms, and a coelom that's most similar to an inflatable air mattress.....

Anyway, here's the abstract:

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ABSTRACT—The Late Precambrian fossils of the Ediacara Hills in South Australia represent some of the oldest known body fossils of multicellular organisms. The fossils are preserved as imprints in sandstone, and it is thought that thick microbial mats, as well as a lack of bioturbators and collagen consuming bacteria, led to their exceptional preservation. Two theories of evolutionary relationships have been proposed for Ediacaran fossils. One theory states that most members of the fauna represent organisms belonging to, or ancestral to, known metazoan clades. The second theory suggests that most members of the fauna belong to an extinct clade, known as Vendozoa or Vendobionta, which are thought of as infaunal or epifaunal organisms with a “quilted” body plan of consisting of series of water-filled tubes resembling an inflatable air mattress. The vendobiontan theory also suggests that they possessed symbiotic photosynthetic organisms in their tissues, a unique manner of cell division creating bilateral, trilateral, or pentaradial symmetry; or alternatively, were giant single celled eukaryotes. The vendobiontan theory, although interesting, is not found to be parsimonious, as many Ediacaran fossils such as Charnia, Kimberella, and Arkarua can be assigned to the modern clades Cnideria, Mollusca, and Echinodermata respectively; although some such as Tribrachidium, are genuinely unique with no modern counterparts.

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This fossil is Dickensonia, which has been interpretted as a segmented worm, or alternatively, as the archetypical vendobiontan air mattress:


This is Charnia, which has been interpretted as a sea pen, and I think that's a rather sane interpretation. This also has been thought of as an air mattress:


This is Kimberella, which has been recently identified as a mullusc, although it's been thought of as a jellyfish, or, you guessed it, a vendobiont air mattress:



This is Spriggina, which looks a lot like some sort of basal arthropod, as it has a definate head region, and serial segmentation towards the tail. You guessed it though, it's an air mattress according to some....:



This lovely is known as Arkarua, which is probably the earliest known echinoderm, quite similar to edrioasterozoans, which were like sand dollar equivalents of barnicles:




This one is weird, Tribrachidium, it has no modern or fossil relatives, and I'm at a loss. Unfortunately though, this fossil, like Arkarua, although they've been interpreted as vendobiontans, they have nothing close to a quilted air mattress form:

:kick:

;-)

Since you're stumped by what they represent, I'll offer my assistance. I'm pretty good at this.

Dickensonia: You will find difficulty sleeping while your stars are in cusp.

Charnia: Be careful, or you may cook your burgers too long on the grill. Especially bad for Tofurgers or Boca Burgers.

Kimberella: You will meet a dark and mysterious woman, who you will travel with. You will give her your bus token and she will take you someplace down the street.

Spriggina: Ah, a stroke of luck to draw this invertebrate. It may fend off Dickensonia, and help you to sleep better.

Arkarua: Don't make any pecuniary investments for a while, at least until your sleep troubles are over.

Tribrachidium: Indeed weird. It has different meanings if drawn upside-down. Problem is, no one knows which side is up. :shrug:

Tribrachidium: Indeed weird. It has different meanings if drawn upside-down. Problem is, no one knows which side is up. :shrug:

You don't know how true this is LOL

Could it be, well, you know, three separate little wormy things, all like, you know, "spending quality time together". Nudge nudge nod nod wink wink say no more?

but there are multiple specimens, so, uh... unless they were pathological fornicators :-)

I actually think that it's an echinoderm. Echinoderms (starfish, urchins, sea cucumbers, crinoids) have a five-part symmetry in living forms (although there are four and six armed starfish).

There are fossils forms known as helicoplacoids which look like footballs that stuck their ends in the ground and mouths up top and filter fed with three tube feet rows, ie, triradial symmetry.

Also, there is embriological and genetic evidence that echinoderms aren't really as weird as they appear and they have an anterior end, a posterior end, and a dorsal and ventral end, and a left and right side. IIRC, HOX genes show that out of the left, right and dorsal ends, the arms are serially repeated in a 2-1-2 pattern, and only appear to be pentaradial, but could be triradial also if it was 1-1-1.

Or it could be an alien space ship.

I'm bringing a chisel, so I can carve odd shapes into the rocks that mess with you. Be sure to look out for the rectangular echinoderm with the letters S-E-R-T-A carved in the corner. ;-)

just so long as it's quilted and thin, you'd make Adolf Seilacher very happy :-)

How could one cell grow to be 1m long? I would think the surface area to volume ratio would hinder that sort of thing?
Weird is right!

The story is this:

Foraminifera, which are shelled planktonic amoebae, have grown to sizes of 3 cm in the past. They did this by changing the archetecture of their shells so that the struts are wavey, and can withstand greater pressures both from being in deep water, and from being large.

For organisms like Dickensonia..... they propose that the quilting created structural support, and that there were many hydrostatic tubes (the lobes or segments) holding the cell relatively stiffly. Supposedly the cell would be almost one meter in diameter, but only 4 or 5 millimeters thick.

It's a pretty big jump from 3 cm with a calcite skeleton for support, to 100 cm without any mineralized support.

I am not sure if it came through quite clearly in the first post, but I find this idea completely absurd. The vendobiontan idea is unsupported AFAIAC, but the megacell hypothesis for Vendobionta is complete crap!

Now that's weird.

:kick:

We need to have a weird science thread. I live for this kind of thing.

i love reading about it -- though my knowledge is thin at best. but i still love reading about it.

p.s. eddie munster is pretty weird too.

feel free to ask, although I may answer with "I don't know" quite frequently.