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609 Views 7 Replies Last post: Jun 17, 2014 9:16 PM by MikeHardman RSS
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Jun 16, 2014 8:06 PM

Found in South Devon Tide Pool - Fossil?

I found this today while wandering through tidal pools in South Devon, and would love any info on what it might be.

 

Thank you in advance!

 

photo 1(7).JPG

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    Jun 16, 2014 9:17 PM (in response to e f a)
    Re: Found in South Devon Tide Pool - Fossil?

    Yes, fossil - crinoid ossicles.

     

    There is a slight anomaly in that they look like moulds, yet they seem to have the vacant central canal as if they were the originals. I think that they may be the acutal fossils, just partly eroded around the edges, though I'm not sure why that might happen.

     

    Note that the specimen also has modern borings, mainly top-left and middle-right. They account for the extra two or three holes near the middle of the upper ossicle.

     

    Mike

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        Jun 17, 2014 10:18 AM (in response to e f a)
        Re: Found in South Devon Tide Pool - Fossil?

        I can give you an idea of the age, if you can tell in more detail where you found it.

         

        'Modern borings':

        There are many modern organisms that make borings into substrates. Shipworm (Teredo) is a bivalve that bores into wood. Other bivalves, various worms, etc. bore into rock; some bore into sea shells. The 'boring' may be accomplished by various methods: some bivalves have rasping exteriors to their shells, other organisms dissolve rock. Seaweeds and sea lilies have holdfasts, which can also make depressed marks on their anchoring rocks. (Other creatures use natural adhesive to hold themselves in place, eg. barnacles and limpets.)

        The same sorts of creatures that make borings today, used to make them in the geological past. So, we also find fossil borings. Because these are traces made by organisms (rather than the organisms themselves), they come under the broad heading of trace fossils (ichnology). Simple, unbranched, cylindrical borings (like those in your specimen) can be called Trypanites.

        With trace fossils, it is important to understand that the genus names (such as Trypanites) don't generally refer to particular organisms. That's because in most cases, we can't be sure what creature made the trace, and it is perfectly possible for multiple creatures to create trace fossils that are indistinguishable from each other.

        Trace fossils are fascinating.

         

        Mike

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            Jun 17, 2014 12:29 PM (in response to e f a)
            Re: Found in South Devon Tide Pool - Fossil?

            Most of the rocks around Thurlestone are (yes) Devonian.

            They are mostly in the Meadfoot Group (a stratigraphic part of the Devonian in SW England). They comprise slate, siltstone and sandstone, formed from mud, silt, sand and gravel laid down in shallow seas about 398-411 million years ago. (There is a small exposure of Beeson Grits Formation on that part of the coast; that is of similar age. But chances are, your specimen is from the Meadfoot Group.)

             

            Yes, there are two distinct types of organic markings: fossil sea lily stem fragments and modern borings.

             

            New and strange info is best digested slowly - otherwise there's a risk of indigestion!

             

            Mike

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