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660 Views 10 Replies Last post: Dec 31, 2013 10:24 AM by Dan RSS
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Dec 26, 2013 9:15 PM

Crinoid Head?

Hi

Found this Crinoid on the Holderness coast a long time ago and was wondering if the crown was inside of the rock.

Don't know wether to have a go at prepping it because all of the arms seem to be going to the center after i removed some of the outer matrix.

 

Tabfish

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  • Currently Being Moderated
    Dec 26, 2013 9:37 PM (in response to Tabfish)
    Re: Crinoid Head?

    That's a tough one, Tabfish.

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        • Currently Being Moderated
          Dec 27, 2013 11:19 PM (in response to Tabfish)
          Re: Crinoid Head?

          Tabfish,

           

          ...I suggest not!

          If you work in from the other side, and if there is not much fossil, by the time you have prepped it, there won't be enough stone left to support it - it will be very likely to break.

           

          Personally, I'd work from the side you started, and see (test first) if you can get any differential action with acids applied to both fossil and matrix, and/or paint acid carefully only on the matrix to weaken it, and/or abrade the matrix away with a dental drill.

           

          Good luck,

          Mike

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  • Currently Being Moderated
    Dec 28, 2013 5:42 PM (in response to Tabfish)
    Re: Crinoid Head?

    Hi Tabfish,

     

    Interesting - I am having trouble viewing the details of the arms, so cannot be absolutely certain from the photograph there may be another possibility. Perhaps a more detailed photograph might help - however, it seems very likely you have a crinoid crown. Crinoids are found in similar orientation from two possible forms:

     

    1. Crinoids are often found with the cup in an upturned position, with arms splayed out, branching and dividing. If your specimen is a crinoid crown (head) then is is upturned and you are looking at a weathered, upturned cup - the stem would have broken off. There would be no point in trying to prepare it out further. Can you see any details on the large mass in the middle as this is the cup (Calyx or theca), if you can -  we might be able to identify it further from the features of the cup and the branching arms (brachials). A clearer photo, with higher magnification on the arm in clear focus on the arms?

     

    Other possibilities are ....

    2. Crinoid attachment structures or holdfasts are found and look like miniature tree-roots.Crinoids anchor or attach themselves to the seafloor, bryozoans or substrate by a number of different mechanisms such as:

     

    • radicular holdfast (rootlets which help to maintain balance and keep it upright in much the same way that a tree has roots. The large central mass could well be the remains of the lower part of the crinoid stem which has broken off at some time.
    • loose coiling e,g, around bryozoan or shell
    • grapnel-like structure like an anchor
    • cemented discs to a brachiopod (or any hard substrate they land on)

     

    You can find more about the different structures of crinoid attachments structurs on page 51 of the online paper I wrote, published in Scripta Geologica 136 which you can find by copying the title below in google search.

     

    Towards a systematic standard approach to describing fossil crinoids, illustrated by the redescription of a Scottish Silurian Pisocrinus de Koninck -

    F.E. Fearnhead

     

    I hope this has been interesting to you.

     

    Happy New Year!

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    • Currently Being Moderated
      Dec 28, 2013 7:20 PM (in response to Fiona - Museum ID team)
      Re: Crinoid Head?

      Fiona,

       

      Great comment; I knew there was something different about those 'arms' - holdfasts - of course!

       

      Also, nice to hear from you!

       

      Mike

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  • Currently Being Moderated
    Dec 31, 2013 10:24 AM (in response to Tabfish)
    Re: Crinoid Head?

    I think it's either a Crinoid head or a coral.

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