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January 5, 2012
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Eldonia ludwigi by NocturnalSea Eldonia ludwigi by NocturnalSea
a somewhat enigmatic creature from the Cambrian-era Burgess Shale. When originally discovered, Eldonia was interpreted as a sea cucumber with an odd, circular mantle around its body. Later, it was thought to be some sort of jellyfish or maybe a lophophore. Now it's believed to be a primitive deuterostome-- the group of animals that includes echinoderms, chordates and hemichordates. Its closest relative is believed to be another Cambrian animal called Herpetogaster-- nicknamed the Parsley-Penis Worm (google Herpetogaster, you'll understand).

In the past Eldonia was thought to be a pelagic swimmer, due to its jellyfish-like shape. More recent reconstructions portray it as a benthic animal like a bowl with a plume of tentacles sticking out of the top-- even the model in the Field Museum looks that way. But.... I don't know, something just never looked right about that to me.
Here I've split the difference and reconstructed Eldonia as a kind of prehistoric Enypniastes, spending most of its time on the ground grubbing around in the mud, but with the ability to make short, jerky swims if it needs to. It swims by scrunching up its C-shaped body, which contracts the flexible gelatinous mantle.
Also featured here is a small school of Odaraia and a couple of Hallucigenia poking around for food that the Eldonia are stiring up.
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:iconherofan135:
herofan135 Featured By Owner May 21, 2012  Hobbyist Traditional Artist
Great job on these! Many of the cambrian life-forms are so strange! :wow:
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:icontarturus:
Tarturus Featured By Owner Mar 22, 2012  Hobbyist Digital Artist
This sounds like quite an interesting creature.
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:iconamnioticoef:
AmnioticOef Featured By Owner Jan 6, 2012
I like it, but it's a little hard to make out the form of the Eldonias(ae?).
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:iconnocturnalsea:
NocturnalSea Featured By Owner Jan 6, 2012  Professional Traditional Artist
Yeah, I know. I struggled a bit since no one angle properly conveys what the whole animal looks like. That's why I tried to show them from four different perspectives. Even the fossils are hard to figure out. It's kind of like looking at a picture of a ctenophore or an Enypniastes for the first time-- a lot of cool curves, but no clue how it all fits together exactly.
Basically Eldonia looks like a sea cucumbers curled into a C-shape floating inside jellyfish bells with its tentacles sticking out the bottom.
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:iconamnioticoef:
AmnioticOef Featured By Owner Jan 7, 2012
I think I understand. Very cool tentacles, by the way.
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:iconbanvivirie:
Banvivirie Featured By Owner Jan 5, 2012  Professional Traditional Artist
I like the little hallucigenia walking around.
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:iconnocturnalsea:
NocturnalSea Featured By Owner Jan 5, 2012  Professional Traditional Artist
thanks. I'm not sure if I got their heads totally right. There seems to be some disagreement in the reconstructions I found.
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:iconderoagent73:
DeroAgent73 Featured By Owner Jan 6, 2012
"disagreement in the reconstructions" is Hallucigenia in a nutshell, I think.
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:iconavancna:
avancna Featured By Owner Jan 5, 2012  Hobbyist Traditional Artist
While your reconstruction is elegant, the benthic mode of life is based on several lines of evidence, the first being the pattern of epibionts being closest to the rim, rather than scattered randomly, the second being evidence of the carapace being a firm, keratinous material (especially apparent in its close relative, Velumbrella), and third being how would a jellyfish-shaped organism pulsate jellyfish style if its organs surrounded a not-hollow center?
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:iconnocturnalsea:
NocturnalSea Featured By Owner Jan 5, 2012  Professional Traditional Artist
Yeah, it probably was a benthic critter-- I just can't shake the feeling that it looks too much like a swimming animal. I think it's because of the big, perfectly circular carapace-- why is it so much bigger than the main body? Seems like a lot of wasted energy.
I've read Dzik's paper about the epibionts, but I haven't been able to find any good information about the hard carapace (that paper does mention growth rings indicatig a hard shell, but I don't think that's necessary true-- it could have just been a semi-solid, but still flexible mantle that grew in noticeable stages).
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