Thursday, December 16, 2010

Crinoid bits

Recently I took a trip up into Schuylkill County to check out a new (to me) pit that exposes the Mahantango formation. The fossils were somewhat sparse and seemed to be concentrated in thin layers or lenses. I was pleasantly surprised to find some interesting Crinoid specimens.

These are a couple of Crinoid arms. You can see the segmentation of the arms and some of the pinnules. This piece also shows the typical preservation for the Mahantago formation with the specimen being merely an impression of the fossil as the mineralization (likely Calcite) has been dissolved away by ground water.

On another chunk of rock I found this which looks like it might also be a Crinoid arm. It needs a little prepping to tell for sure but sadly I didn't find any evidence in the field of a Calyx or body of the crinoid that belonged to this arm.

Yet another potential arm was found on yet another rock chunk.

There is good news and bad news that can be gleaned from these bits and pieces of Crinoids. On the one hand there is good evidence for a potential complete Crinoid. On the other is that the Mahantango formation tends to splinter easily and not form clean flat pieces. The three pieces shown above came from three different rocks in three different places. Maybe they are from the same layer or lens and it could be found again.

One last piece to show from this site was this neat cast of a large Crinoid segment. Check out the cool patterns, originally on the exterior of the stem, that have been preserved by the cast.

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