Wednesday, November 25, 2009

Pterotrigonia thoracica Pelecypod

The Pterotrigonia thoracica (Morton 1834) pelecypod is the official state fossil of Tennessee. It existed during the Cretaceous Period (about 70 million years ago - Maastrichtian). This fossil was found in McNairy County, Tennessee (Coon Creek Formation).

It became state fossil in 1998.

This creature might be related to the Myophorella ("Trigonia") of the Jurassic Period which has the modern relative of the Australian Broach Clam (Neotrigonia margaritacea). Learn more at this British website: Fossils of the Kimmeridge Clay (Southern England) by Ian West.

The genus was named by van Hoepen in 1929.

Thanks to Herb for allowing me to photograph it.

Update: August 2010, here is a picture of two Trigonia on display at the Smithsonian Museum of Natural History in Washington, D.C. The ones on the top are Trigonia thoracica (Late Cretaceous Period, Tennessee) and the bottom one is Trigonia moorei (Middle Jurassic Period, Australia).

Brevispirifer gregarius Brachiopod

It has taken a while to find an intact specimen of this brachiopod. It has special significance in the Louisville area. The fossil marks a zone of the Jeffersonville Limestone. The small book entitled Middle Devonian Type Jeffersonville Limestone at the Falls of the Ohio by James E. Conkin, Barbara Conkin, and Larry Steinrock refers to this fossil quite a bit. The book and the Internet do not have good images for identification. Recently, I was lucky to find several complete ones. In the past, I have found the shells in rock plates, just one half, or fragments.

These specimens were found in Jeffersonville Limestone and existed in the Middle Devonian Period.

This brachiopod is known as the Brevispirifer gregarius and the ones in this picture range in size of 1-1.5 cm wide, 1-2 cm tall. It was named by Clapp in 1857 as Spirifera gregaria. The brachiopod is also found in Ohio in the Columbus Limestone.

Now that I have found some good specimens, I need to get a good photo of the Devonian Period horn coral Bordenia knappi.