Wednesday, February 26, 2014

Crushed/warped Spirifer fossils from the Mahantango Formation

Below are some specimens of a Spirifer type brachiopod that I am tentatively calling Spinocyrtina granulosa.

Specimen #1 is crushed but retains details of the exterior of the shell.



Specimen #2 is a partial internal mold. Here you can see the striations where the pedicle muscle was attached.
Anterior
Brachical valve side that is also crushed and does not retain the shape of the shell very well.
Anterior
Left profile
Right profile
This is an isometric view of the posterior that shows a mold of the delthyrial cavity (the tongue like extension) where the pedicle muscle would have extended from.

Specimen #3 is another internal mold that has some distortion as well as crushing. The distortion is likely a reflection of the strain the fossil experienced as the rock around it was deformed during the building of the Appalachian mountains.

Pedicle valve
Anterior
Brachial valve
Posterior
Left profile
Right profile

After reviewing Plate 11 in "Stratigraphy and Paleontology of the Mahantango Formation in South-central Pennsylvania" (Ellison, 1965), I'm convinced that what I found can be called Spinocyrtina granulosa.

All three specimens were collected from a site near Liverpool, PA from the Mahantango Formation (Devonian, Givetian stage).

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