Devonian Leptaena

These pictures of maroon colored brachiopods are from the Middle Devonian Period Silver Creek Limestone of Clark County, Indiana.  I believe the identification of this brachiopod is Leptaena rhomboidalis. 

Mi amigo, Señor Herb, provided some images of fossils he photographed from Benton County, Tennessee.  These brachiopods are called Leptaena acuticuspidata of the Lower Devonian Period (Birdsong Formation). After getting the images it inspired me to find the local brachiopods and put the images together for this post.

Update: Here is a picture of a Silurian Period Leptaena waldonensis from the Waldron Shale of Clark County, Indiana.

Classification:
Phylum: Brachiopoda
Class: Articulata
Order: Strophomenida
Family: Rafinesquinidae
Genus: Leptaena

The Fossil Clock

The Falls of the Ohio State Park located on the bank of the Ohio River in Clarksville, Indiana, has an interesting display called Fossil Clocks.  A picture below shows the text hanging on the wall in their interpretive center.  Basically, it informs the reader that corals produce bands or growth lines of calcium carbonate to form their skeleton.  Looking at the fossils one can see ridges showing annual growth with finely spaced lines recording daily growth.  Researchers determined these clusters of these lines represent lunar months.  They found out a Devonian year had 13 lunar months that added up to 400 days.  This information tells us that friction maybe slowing the Earth's rotation giving us a current year with approximately 364 days.

Picture above is of an Siphonophrentis elongata horn coral fossil fragment from the Jeffersonville Limestone.  It existed in the Devonian Period and was found in Clark County, Indiana.  This horn could grow to over 60 cm long.

Here is another side of the horn coral pictured earlier.  When I saw this cross-section of growth lines, it reminded me of the state park display.

This is a picture of the horn coral cross section on display at the Falls of the Ohio State Park.  Obviously, it has been cut and polished to highlight the growth segments.  The genus and species were not listed for this fossil.

The last two pictures show the outer wall of the S. elongata horn coral shown earlier and the last picture is of the bottom of the fragment showing part of the septa.

Mystery Devonian Rock

Mystery rock picked up in an area with Jeffersonville Limestone Devonian Period fossils. When I picked up the rock I assumed it was the inside of brachiopod. The inner part has a blue appearance. It reminds me of some of the crinoid stems found at Lake Cumberland, Kentucky. At one time, I thought it might be agate but there are no layer lines. Could it be some sort of blue opaque quartz or blue chalcedony? Then there is the crystal area, that I guess is calcite.

The area surrounding the nodule shape has a lot of dendrite patterns. I did not test the rest of the stone but I assume it is limestone.  Found in Clark County, Indiana.  I only found one half, not sure where the other part is.

What the nodule looks like from the back.