Sunday, August 2, 2015

Orthis? sp. brachiopods from the Kalkberg formation of New York

I'm really torn on how to classify these next fossils from the Kalkberg formation. To my eye they look like Rhipidomella sp., which is very common in middle Devonian aged rocks, but I cannot find any literature that lists that genus as being found in the Kalkberg formation. What I have been able to find lists shells that look similar to these as belonging to the genus Orthis. Doing a little research on the website indicates that both Rhipidomella and Orthis are part of the same order, Orthida, but they diverge into separate families from there. It may be that minute details of the internal structure is what differentiates them from one another,

Here are two different specimens that show the size range of these brachiopods.

The smaller specimen is more complete so I will profile that for this post. This is the Brachial valve
Pedicle valve
Profile - note that in the profile, the anterior appears to be nearly flat. In some specimens of both Rhipidomella and Orthis, species can be differentiated if the pedicle valve sticks out beyond the margin.

These specimens were collected from the Kalkberg formation (Devonian, Lockhovian to Pragian stage) in a road cut near Schoharie, NY.

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