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kerouac22

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Hi esteemed forum members,

I have several finds I need help identifying, but I'm going to do them in separate posts/threads/topics/whatever.

I found this one in some Burlington Limestone in central Missouri. It's super brittle. You can see areas where pieces have just flaked off. The lines you see going across the front of it are raised.

The leading theory on this so far is that it's a Rhodocrinites calyx that flattened during diagenesis. I've also attached an image of the small matrix it came off of (I found the calyx, if that's what it is, in situ unattached, just laying there on top of the matrix).

Let me know. And stay tuned for other, and probably less exciting, ID requests. Thanks!

post-20368-0-71790200-1451583513_thumb.jpg

post-20368-0-36187200-1451583514_thumb.jpg

Edited by kerouac22
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I agree with the holdfast suggestion. The arrangement of plates is irregular, typical of root/holdfast structures, the number of "arms" is not a multiple of 5 (no pentameral symmetry), and the pattern of division of the "arms" is completely irregular. Even if this were a flattened calyx the basic arrangement of calyx plates (infrabasals, basals, radials, interradials) should be apparent, and it is decidedly not. There should be 5 arms, or some multiple of 5 as the arms bifurcate. Close to the calyx, at least, the arms should divide at regular intervals so the pattern of division will look symmetrical, and this is not the case.

Don

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I agree with the holdfast suggestion. The arrangement of plates is irregular, typical of root/holdfast structures, the number of "arms" is not a multiple of 5 (no pentameral symmetry), and the pattern of division of the "arms" is completely irregular. Even if this were a flattened calyx the basic arrangement of calyx plates (infrabasals, basals, radials, interradials) should be apparent, and it is decidedly not. There should be 5 arms, or some multiple of 5 as the arms bifurcate. Close to the calyx, at least, the arms should divide at regular intervals so the pattern of division will look symmetrical, and this is not the case.

Don

Thanks guys. Interesting. So I'm assuming there's not a great way to ID a crinoid by a holdfast?

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I would love to see some larger photos of it to see the detail. Something up near the 2 meg limit. It is very interesting.

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I would love to see some larger photos of it to see the detail. Something up near the 2 meg limit. It is very interesting.

Agreed. VERY interesting specimen. I've never seen a holdfast with that much of a spread and that many individual plates. I'm not familiar with the Burlington but it would be a great specimen in any collection, with an ID or not.

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I would love to see some larger photos of it to see the detail. Something up near the 2 meg limit. It is very interesting.

Agreed. VERY interesting specimen. I've never seen a holdfast with that much of a spread and that many individual plates. I'm not familiar with the Burlington but it would be a great specimen in any collection, with an ID or not.

Thanks! Here's a 1.82 MB image.

post-20368-0-69764500-1451602639_thumb.jpg

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It is odd looking. I'm thinking it is a steinkern of a crinoid crown, maybe Physetocrinus.

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It is odd looking. I'm thinking it is a steinkern of a crinoid crown, maybe Physetocrinus.

Oh, good guess. I've found plenty of Physetocrinus stuff at that site.

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I'm in the camp of crinoid crown.

The holdfasts are more irregular in crinoids, almost in every species. In the picture above I recognise the pattern of five-fold (pentaradial) symmetry of the echinoderms, in this case the bifurcated five arms and so on, wich I propose to compare with the schematic morphology of the crinoid crown shown here: post-17588-0-78767300-1451748445_thumb.jpg

Edited by abyssunder
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I agree with crinoid crown, beautiful specimen.

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It is odd looking. I'm thinking it is a steinkern of a crinoid crown, maybe Physetocrinus.

Bingo! Correct on both the general ID and on the genus.

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