Friday, September 23, 2011

Diplotrypa franklini

As I've said before many times, Bryozoans are very hard to ID down to the species level. Even to get to the genera level is tough unless there is some readily identifiable physical feature. So how can I say with any confidence that the Bryozoan specimens below are likely Diplotrypa franklini? Simple, I read about it.

Here are a couple of specimens, note the rounded shape and layered structure. The shape is due to the colonies being overturned during storm events and the bryozoan growing back around to the newly upturned surface. The layering is the result of annual growths and is highlighted by the selective preservation of some layers by Silica while other remain Calcite.

You can make out the pore structure very well on weathered specimens.

These are a couple of specimens that I etched out of the limestone with acid.

The locality I found these at near the Juniata River in Juniata county, PA. There is a small borrow pit and railroad cut that slice through layers of rock from the Silurian aged Keyser formation. I found out about this exposure by reading an issue of Pennsylvania Geology, the official publication of the Pennsylvania Geological Survey, which discussed the paleoenvironment that these Bryozoans came from. Here is a link to a .pdf of the issue. Within the article they note that there are nine different species of Bryozoan that can be found at the site but the most prevalent is Diplotrypa franklini. So while I can't examine the micropores with an electron microscope or thin slice a colony I can say, with a fair amount of certainty, that the specimens I found are likely to be from the most common and abundant species present.

A piece of advise from me to anyone who wants to seek out the site, stay off the railroad tracks as they can be dangerous because of train traffic. 

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