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.

Mucrospirifer mucronatus Brachiopod

Pictures of a sampling of small brachiopods (1.5-3.0 cm wide) found in the Jeffersonville Limestone (Devonian Period). Using the Fossils of Ohio book and Index Fossils of North America this brachiopod is a Mucrospirifer mucronatus. The Ohio book says they are found in the Columbus Limestone which I think is similar to the Jeffersonville Limestone this was found in. Looking at Nettelroth's book Kentucky Fossil Shells (1889) this brachiopod seems to closely match images on Plate XII figures 14-15 of Spirifera arctisegmenta (1889 name) or today's Spirifer arctisegmenta (Hall, 1857).

Another document I have entitled Middle Devonian Type Jeffersonville Limestone at the Falls of the Ohio by James E. Conkin, Barbara Conkin, and Larry Steinrock on page 8, figure 5 labeled Diagnostic fossils of the Jeffersonville Limestone shows it as "Spirifer duodenarius" in the Paraspirifer acuminatus Zone.

So confusing but all the names seem to have spirifer in them.

All brachiopods found in Clark County, Indiana.