Giant Ancyrocrinus spinosus crinoid anchor from the Mahantango Formation

A recent trip to an exposure of the Mahantango Formation near Seven Stars, PA yielded this giant Ancyrocrinus spinosus anchor. It's still embedded in the rock but you can see four spikes emerge from the bulb like base.

This is by far the largest specimen of this genera that I have ever found and only the second that I've found in the Mahantango Formation. The total length of the exposed bulb and spikes is about 4cm.

I posted a few years ago about some small anchors I found in a different part of the Mahantango Formation in Montour County, PA Here and a specimen that I found in the Windom Shale along Lake Erie in NY Here.

Crushed/warped Spirifer fossils from the Mahantango Formation

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

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

Traces of epibonts colonizing a pelecypod from the Mahantango Fm.

One of my favorite fossils to find in the Mahantango formation are large pelecypods that have epibonts that grew on them. Sadly I don't find the casts of those fossils but rather the molds so it takes a little interpretation to figure out what you are looking at. Below is one such fossil that I recently found in Central Pennsylvania. It is the mold of one valve from a Leioptera sp. pelecypod. Decorating the mold are traces of the coral Pleurodictyum americanum and and a bryozoan called Ascodictyon fusiforme.

A closer view of the Pleurodictyum molds. What you see are the molds of the internal living spaces where the animal once lived. It looks like fingers because each individual corallite grew up and out from the Pelecypod shell it was attached to. The little tiny bits that run in between the larger "fingers" are infilled septal spines that the animal used to help support it's body.

These are the traces of Ascodictyon fusiforme which was a bryozoan that formed widely scattered colonoies that sort of resembled teardrops connected by thin strings. A better example is shown in the first picture on this page from Karl Wilson's New York Paleontology web site. Since I only have the molds of their exteriors, I have to instead recognize the shape and growth pattern.

I may not find the most beautiful fossils in the Mahantango Fm. but you can still tease information out of them. The Mahantango Formation is middle Devonian (Givetian stage). I suspect the location that I found these fossils in is roughly equivalent to the upper Windom Shale of the Moscow Formation in New York.

Pleurodictyum styloporum coral from the Mahantango formation

I've blogged about Pleurodictyum fossils from the Mahantango Formation before, in this post, but this specimen that I recently found is kind of neat. It's a pair of Pleuordictyum styloporum colonies where there is some detail preserved of the external surface as well as molds of the internal surface.

 Here is the anterior view where you can see the rounded, golf ball like mounds. There is a bit of shale still covering the surface of the coral that obscures some of the detail.

This is the posterior view where you can see the internal mold details.

This specimen was collected near Seven Stars, PA from the Mahantango Formation (Devonian, Givetian stage).

Palaeoneilo emarginata pelecypod from the Mahantango formation

Just a simple one picture post today. It's a Palaeoneilo emarginata pelecypod mold that I found in the Mahantango Formation (Devonian, Givetian stage) near Liverpool, PA.

There are some other shells on the same piece such as the Chonetes sp. just above the P. emarginata and possibly an Atyrpa sp. below it.