Monday, January 2, 2012

Megastrophia (?) internal cast from the Mahantango fm.

This is the last of my posts regarding the fossils I found in the quarry at Roseburg, Pennsylvania. It's a large internal mold of the pedicle valve from what I believe is a Megastrophia. I base this ID on the sheer size of the fossil as there are not many other genera that attained the size that Megastrophia did.

A closer view of the fossil. You can see the beak like area where the muscles for the pedicle were attached. The pedicle muscles were what the brachiopod used to anchor itself to the sea floor

The muscle scars are well detailed and you can see what looks like a worm tube or bryozoan that grew on the interior surface of the shell as it laid on the sea floor. This implies that the shell was exposed on the surface of the sea bed before being completely buried. You can also see small stipples or pits all over the fossil. Presumably these were attachment points for other muscles in the shell.

I've written about Megastrophia before that I found in the Silica Shale near Sylvania, OH. The specimen in this post came from the Mahantango formation which is from the middle Devonian (Givetian stage).


  1. Dave - I'm thinking this brachiopod is "Subrensselandia claypolii". The general obovate outline and strong muscle scar is a give away on the ID. A typical Mahantango Subrensselandia measures: length 38 mm and width 28 mm. In the Mahantango, "Megastrophia concava" measures: length 42 mm and width 60 mm. The Megastrophia is aways much wider that it is long. Check "Stratigrophy and Paleontology of the Mahantango Formation in South-Central PA" see pp 68 for more detail. I await your thoughts. Jack K

  2. Jack - I see what you mean when you reference size and shape. I measured the specimen yesterday and it's roughly 50mm by 50mm which would put it more in the range for a Megastrophia. Also, the obovate outline that the fossil shows I think is the result of the distortion that is present in many of the fossils due to the regional syncline. Another issue are the adductor scars which, in the description on pg. 68 of "Stratigraphy and Paleontology of the Mahantango Formation", should be "narrow, elongate and bounded by diductor scars; Diductor scars small, deeply excavated, 'snow-shoe-shaped'". I don't see that in this specimen nor do the scars seem to match the illustrations on plate 6, #28-31, which show a very sharp and pointed beak that rapidly flares out towards the edges of the shell. What do you think? - Dave

  3. That sure is a Megastrophia. Nice find!