Friday, February 28, 2014

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.

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.
Brachical valve side that is also crushed and does not retain the shape of the shell very well.
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
Brachial valve
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).

Monday, February 24, 2014

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.

Saturday, February 22, 2014

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).

Thursday, February 20, 2014

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.

Tuesday, February 18, 2014

Platyostoma gastropod and Stereolasma coral from the Mahantago

As I'm parsing through my findings and cataloging the pieces I want to keep, two new species will joining my collection of fossils from the Mahantango Formation of Pennsylvania.

The first is this internal mold from the gastropod Platyostoma (Nanticonema) lineata. It is somewhat intact and free of any distortion unlike some fossils found in nearby exposures in the same pit.

...and this partial rugose coral that I think is Stereolasma rectum. All that I found is this little stump with septa converging on the interior

and what may be septal grooves on the exterior. I wish I could have found the rest of this guy as rugose corals are somewhat rare in the Mahantango.

Both of these specimens came from an exposure of the Mahantango Formation (Devonian, Givetian stage) near Liverpool, PA.

Sunday, February 16, 2014

Chonetes sp. brachiopod with spines from the Mahantango formation

Chonetid type brachiopods are fairly common in the Mahantango formation on Pennsylvania but a recent find deserves a little more notice. It's a shell with small spines preserved coming off the posterior hinge. Only three are visible, the yellow iron staining helps set them off, but this is a somewhat unusual occurance based on my experience. Most all the fossils found in the Mahantango are the results of storm deposits, very few are "smothered bottom" type. As such delicate details like the spines are often lost when the original shell is tossed in the waves.

I collected the above specimen was collected near Seven Stars, PA from the Mahantango formation (Devonian, Givetian stage).

Friday, February 14, 2014

Modiomorpha pelecypod from the Mahantango

I have posted some specimens of Modiomorpha from the Mahantango formation before but this specimen is different in that there is some shell material preserved. It's not the original shell but more likely a replacement by Calcite.

The shell cast is not complete but this is still an uncommon occurrence from the Mahantango formation (Devonian, Givetian stage) since I often find the weathered, leached molds of pelecypods. This specimen came from near Liverpool, PA.

Wednesday, February 12, 2014

Some gastropods from the Mahantango formation

I'm going through some boxes of findings from the Mahantango formation (Devonian, Givetian stage) and came across some decent gastropod fossils that I found at Liverpool, PA.

This is a Cyclonema mold in matrix with a little bit of the exterior shell cast intact. There is also a Nucula varicosa pelecypod just above and to the right of it.

Then there is this mold from the internal chamber of a gastropod. It's tightly coiled and the whorls stack internally rather than rise up like most snails fossils I've seen. It seems to be a fairly wide living chamber and the width of the whorls increases rapidly unlike the Goniatites of the era.

Here you can see the groove where the whorl pressed against the previous shell area.

Maybe this is a Straparoullus or Tropidodiscus? With the small amount of info that I can find online I'm leaning towards Tropidodiscus.

Monday, February 10, 2014

Fossil branch from the Mahantango

Being that the Mahantango formation is Devonian in age, more specifically Givetian stage, it is not uncommon to find pieces of pyritized branches. Sometimes they can be a bit difficult to ID as fossil wood because they are thin and often could be confused with worm burrows. On a recent trip to Deer Lake, PA I found a piece with what I believe is unmistakably a fossil branch. On the specimen below you can see the brown-orange staining from the breakdown of the pyrite which is the first clue.

Next is this closeup which shows a branching structure that could be the remains of a rachis (central vein to which the pinnules of leaflets were attached in tree ferns).
Lastly is the patten of the preserved structure which is entirely different from the surrounding rock. It looks striated and rough where as the rock is smooth and homogenous.
I could still be wrong and this is actually a worm burrow. There are no other preserved "rachis" which should be regularly spaced along a main branch. On the other hand the fossil is very straight with no obvious undulations that might be the result of the worm moving through the sediment.

No matter what this is an interesting specimen and makes one think about the paleoenvironment that it was deposited in.