Unidentified Fossil, Whistable Beach, Uk

[Otto Sump]

Hi there,

This might not be the most impressive post, but it's my first here and not identifying this is really bugging me!

General description:

Discoid/flattened ovoid ~30 mm diameter, ~10 mm Z axis.

There is a regular undulate indentation that appears to extend around most if not all of the lateral edge.

Best guesses right now are some kind of seed, or the soft parts of a bivalve (although it is harder to believe that these may have been preserved), or the body of an echinoderm, although there are no visible mouthparts.

The exterior appears to be chert, while damage to the edges reveal a darker flint or quartz interior, suggesting that it was once embedded in limestone (which is consistent with the local geology).

Picked up from the pebble beach at Whistable, UK.

Thanks for your help!

[painshill]

Hi Otto and welcome to the forum.

I wonder if we're looking at the crenellated toothed areas around the edge of an eroded crab carapace. Crab nodules are fairly common in that area.

[Kosmoceras]

It is a flint sponge. I could find some photos for reference later if needed.

[Otto Sump]

Thanks for your help!

I thought crab at first becuase of the shape, but there are no markings where the coxa would have attached and although it doesn't show very well in the photos, the crenulations extend all the way around the fossil.

Any idea of the spp. of sponge out of interest (I'd like to find out what the crenulations are for), and does this flattened morphology represent their usual appearance?

[Kosmoceras]

I have seen some identified as Ventriculites, one looks identical in one of my books but I cannot find any source on the internet. Here are a couple of examples showing the marks in my collection.

Regards,

[Otto Sump]

That's great! And thanks for the pics.