Dry Dredgers Field Trip
May 27, 2017
Ponderosa Ranch, Ohio
Bellevue Formation

Photos by Bill Heimbrock

We gathered at a rest stop in large numbers for an opportunity to go to the famous Mount Orab trilobite farm to collect unprecedented numbers of Flexicalymene and Isotelus trilobites.

 Bob Bross, our field trip chair, arrived early to check out the site. We had lots and lots of rain in May 2017, as well as the night before the field trip. We didn't know whether the site would be flooded. Bob returned with a sad face and unfortunately, it would be impossible because it was impassable.

Fortunately, fossil hunting in the tristate area is ubiquitous. We quickly came up with an alternate site, less than a half-hour away from where we were.

The Ohio site we code named "Ponderosa Ranch" was not flooded. It had been a popular site in past years for finding the large brachiopods Vinlandostrophia (Platystrophia) ponderosa and Rafinesquina ponderosa. The site exposes the Bellevue Formation of the Cincinnatian Series. These rocks and fossils are from the Late Ordovician Period and are about 445 million years old.

 This was also not a sure thing because the Ponderosa Ranch site had been flooded out in the past, as well.  Here are some photos of us hunting brachiopods that day. For most, it was much fun as hunting trilobites.

Fossils Found That Day

Best Find of the Day

Trilobites were still the theme of the day, even at our brachiopod site. The best find of the day was made by a family of fossil fans who were examining the ground after spotting some trilobite fragments. They found an impressive spiny trilobite called Acidaspis cincinnatiensis!  Awesome! Congratulations.

As you can see from the photo below, this Acidaspis cincinnatiensis trilobite specimen is small and hard to see but really a decent size specimen.

What we really wanted to find was a complete specimen of the very large trilobite Isotelus sp. But one member did find a very nice fragment. Shown below, this is the underside of an Isotelus sp. trilobite and remarkably, it has the Hypostome (mouth place) in place! This is probably the second best find of the day.

And someone did find a somewhat decent prone and potentially complete Flexicalymene sp. just waiting to be "prepped out" of the matrix.

There were at least a couple of nearly complete Flexicalymene sp. trilobites found. These were inverted, meaning we are looking at the underside of the trilobite in the Ordovician mud.

Here are a couple of pygidia (tails) of Flexicalymene sp. trilobites people found.

Trilobite fragments were everywhere, as this slab below illustrates.

Here's a really nice shale slab covered in the tracks of creepy-crawlies from the late Ordovician Period. Some of these tracks might be trilobites.

Brachiopods Found That Day

Only modest quantities of the large brachiopod Vinlandostrophia ponderosa were found.

A smaller species of the same brachiopod genera was found in greater numbers. This one is likely to be Vinlandostrophia laticosta.

Another common brachiopod found in good condition was Rafinesquina ponderosa.

Here are a couple of slabs of rock randomly picked up to show you the abundance of brachiopods on this fossil site. (next 2 pics)

Nautiloid Cephalopods

In the Corryville and Bellevue formations exposed on this site, orthocone (straight-shelled) nautiloid cephalopods are one of the largest fossils. These are the internal molds of animals with spear-like shells that spanned as long as 14 feet and were feared by trilobites and others. They are abundant fossils but highly collectable for obvious reasons.  

Here's a close-up of a nautiloid cephalopod specimen with a few chambers represented as internal molds. Note also that a small tube, called the Siphuncle, runs down the center or the off-center interior of the chambers. (next 2 pics)


Here's an interesting ramose (branching) bryozoan. It's still articulated. Many fossil hunters spend hours gluing fragments of bryozoans together for exhibition. With this specimen, only a little cleaning is needed. Cool!


Among the Pelecypods we saw, also known as bivalves or clams, almost all were internal molds. The shell of these clams are typically not preserved. Here's a specimen of what is probably Ambonychia sp..


One of the snail fossils that had shell details preserved was Cyclonema sp.

Many of our local fossils are hollow. In the hollowed out portion, water over time deposits minerals that form calcite crystals, as if the fossil were a geode. This first picture shows a nice "cathedral" made of calcite. The second is a brachiopod filled with warmly colored calcite crystals.

That's all for this field trip. Now lets see the photo from our September 2017 field trip.

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