Saturday, August 22, 2020

Possible Atrypidae type brachiopod from the Louisville formation

The single specimen below is the only one I have found from the sediments near Louisville. I believe that it is an member of the family Atrypidae and may in fact be a member of the genera Atrypa. It looks very similar with a rounded outline to the shell, a more deeply curved brachial valve than pedicle valve, and has radial ribs that look typical. However the anterior margin has a sulcus that is confined to the forward 1/3 of the two valves. It does not continue all the way to the beak on the pedicle valve.  I have seen examples of Atrypa with a similar feature but generally the pedicle valve is much flatter than in this specimen.

Brachial Valve
Pedicle valve (the broken section does not help with the ID)
Left profile
Right profile

This specimen was found in an area that had mixed residual soils from the Jeffersonville limestone (Devonian) and Louisville limestone (Silurian) formations near Louisville, KY.  Based on my experience with the preservation styles of the two formations, I think this came from the Lousiville limestone (Homerian to Gorstian stage of the Silurian).

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