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A Fossil Hunt in the Mahantango Formation

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A Hunt for Dipleura Trilobites in the Mahantango of Central PA

Our first fossil hunting trip of the year was to an outcropping that exposes one of the largest Devonian formations in Pennsylvania, the Mahantango formation. To learn about the Mahantango formation, go to the Mahantango page. The Mahantango covers about half of Pennslyvania, but it is usually deeply buried under younger sediments. However, in central pa it is often exposed in roadcuts and quarries. We took a trip with the DVPS to one of these places where the Mahantango is exposed.

One interesting aspect of this particular Mahantango exposure is the layers show evidence of a more silty bottom; ideal habitat for the large Dipleura trilobites. So instead of the usual Eldredgeops (Phacops) and Greenops trilobites, this site has Dipleura as the most common trilobite. Unfortunately, the Mahantango shale and siltsones are very fissile, meaning the rock tends to shatter into many small shards. Extracting whole specimens is very difficult.

Hoping the incredibly harsh winter and ensusing freeze thaw cycle eroded specimens out, we started the day surface hunting. We found a mangled pygydium and a few thorax segments of a large Dipleura, and some broken up brachiopods. After having little success, we hunkered down and tried to pry out large chunks of the Mahantango, which, as stated before, is very difficult. After doing this for a couple hours and still not finding much, we decided to try and surface hunt again. We managed to find a section with lots of Dipleura bits and pieces. Deciding this was a good spot, we chiseled through some of the larger rocks in search of a whole fossil specimen. In the end I managed to find a really beat up and small enrolled Dipleura. However, it was complete (although part of the head is chipped off). We also ended up with an assortment of brachiopods and bivalves, including these neat looking bivalves called Orthonota that look like modern day razor clams.

Overall it was great to go out and collect with the nice fossil hunters that make up the DVPS!

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Below are pictures and fossils from the Devonian Mahantango fossil hunt:

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Recommended Books for Devonian Fossils:

Fossil Collecting in the Mid-Atlantic States: With Localities, Collecting Tips, and Illustrations of More than 450 Fossil Specimens
This book is a must for West Virginia! It's also a classic!
Out of the 45 fossil collecting sites, 22 are from West Virginia, and another 10 or so are just across the border! Although the book is getting old, many of the sites are roadcuts and are still accessable. Many of these sites are roadcuts that expose the Mahantango Formation.

What makes this book a classic is Jasper Burns incredible sketches of the locations and the fossils found at each location. It is a very descriptive and useful guide book. Even after all these years, I still find myself referencing it!

Fossil Collecting Locations in this book are from Virginia, West Virginia, Pennsylvania, Maryland, and Delaware.

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Trilobites: Common Trilobites of North America (A NatureGuide Book)
by Jasper Burns, 2000

I love Jasper Burns. His Fossil Collecting in the Mid-Atlantic book is still one of my favorite fossil books. His drawings are spectacular and the books are well laid out. This book serves as a field guide and identification guide to North American trilobites. If you fossil hunt for trilobites in North America, you should have this book!

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