Friday, June 24, 2011

Large gastropod from the Upper Devonian

While exploring some rock dumps from a road project just above the PA/NY border I found a large fossil snail. This comes from Upper Devonian aged rocks that are within the Wiscoy formation (equivalent to the Lockatong formation in PA).

It's not the best preservation but still shows some detail. I believe it's a snail since the coil is offset it gets larger rather than being overlapped concentrically as Ammonoids (Ammonites don't yet exist in the Devonian) and Nautiloids often are.
As for the genera, that is something of a mystery to me yet. I am not familiar with upper Devonian fauna but it looks similar to Platystoma which is known from middle Devonian rocks.

The rock is a mudstone shale which was part of a sequence of rocks that record a series of transgressive and regressive (rising and falling) sea level events. As such the formation of rocks fines upwards from sandstone through shale and mudstone to limestone and then back to sandstone.

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