Tuesday, March 22, 2016

Actinopteria sp. pelecypods from the Bois d'Arc formation

I found a few pelecypod mold and casts during my hunt among the rocks of the Bois d'Arc formation in Oklahoma. All are without shell material and some have little detail with which to help identify them. One group of specimens does have some detail and appears to belong to the genus Actinopteria and may be A. textilis. The fossils I found are all of single valves but show impressions of the interior or exterior of the left or right valves. The shells have an overall rectangular outline with a central lobe that starts in one corner and widens as it extends diagonally to another corner.There is a small, short ear that extends along the hinge line and connects to the body of the shell for a short distance. Preserved impressions of the shell surface decoration shown radiating ribs that are crossed with concentric growth lines. Both features have some relief to them to that the shell surface looked a little like a checker board.

Specimen 1 - External mold

Specimen 2 - Internal cast

This may be a different species from the two specimens shown above. The ear is much longer and connects with the body of the shell for a greater distance as well. It could be an Actinopteria communis as that has features that appear to fit this fossil. I made this ID after viewing plate 76, fig. 2-4 in "Devonian Plates". Maryland Geological Survey. Johns Hopkins Press, 1913

I found the specimens shown on this page in the Bois d'Arc formation (Cravatt Member) near Clarita, OK which is Devonian in age (Lockhovian stage). The Bois d'Arc overlies the Haragan formation but both are the same age (Devonian, Lockhovian stage). They are both roughly correlative to the Helderberg fauna of New York and thus are contemporaneous with the Coyemans, Kalkberg and New Scotland formations.

I used the book "Palaeontology of New York". Hall, James, George Bancroft Simpson, and John Mason Clarke. Vol. 3. C. van Benthuysen, 1859. Part 2, pl. 53. to help ID the first two specimens as I can't locate any references for pelecypods from the lower Devonian of Oklahoma.

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