The local section, the Glenshaw Formation, is home to many different phylum or classes of Marine and Plant fossil fauna. This formation is late Pennsylvanian in age. The different classes are not equally represented in each area. Rocks from one hillside may be diverse, whereas rocks from the opposite hillside may have only a few species. This varies throughout the formation as a whole, where some areas have no detectable fossils.

The visible fauna is from two major kingdoms of life, Animalia and Plantae. There are likely examples of Fungi, and perhaps Protozoa and Bacteria, but I do not have the knowledge to find and identify these types. Animalia is grouped into two main types, vertebrates, and invertebrates. This is not something always written in scientific classification. Meanwhile, it is widely known which type belongs to which. For example, Petalodus belongs to the subphylum Vertebrata.

Classes or Phylum of life found locally

The following types of life by scientific name are available locally:

  • Anthozoa (Rugosa Corals)
  • Bryozoa
  • Brachiopoda
  • Mollusca
    • Bivalvia (Clams)
    • Cephalopods (Squid)
    • Gastropods (Snails)
  • Plantae (Plants)
  • Trilobita
  • Crinoidea
  • Chondrichthyes (Cartilaginous fishes)

Anthozoa – Rugosa Corals

Horn corals are somewhat abundant in Brush Creek Limestone locally. The particular order is Rugosa. It is common to find these locked in limestone and they are difficult to remove cleanly. In contrast, horn corals from the nearby Pine Creek limestone are simple to extract.

One of the more interesting things about these is their use as evidence for the rate of spin for the Earth. In modern corals, there are approximately 365 growth lines generated per year. Every day the coral adds a little bit of material and creates a growth line. Once a year there is also a thickening of these lines, likely due to changing temperatures or environment. In Carboniferous Rugose corals, the growth line count was 385 to 390 lines. This correlates with the known phenom of the Earth’s rate of spin slowing as the Moon exerts tidal drag. In conclusion, the length of a day was shorter back in the Pennsylvanian period. A shorter length of the day means more days in a year, which was around 387.

Rugose Coral Specimen
Pine Creek Rugose coral with a smooth appearance. The growth lines, or rugae, are visible.
Rugosan coral
A Rugose coral from above, with matrix filling the cavities in a cross-section.
Rugose Coral Specimen
A Rugose coral with visible costae


These are quite beautiful finds when they show up. They are common, but, I often find them broken up into pieces. The net-like matrix of openings were the living chambers of the animal. Each chamber holds between two to eight individuals. The number is known as each individual leaves two small rimmed pores in the front of each branch.

Fenestella Under Microscope
CG-0011, Fenestella
Fenestellidae Temporal Range 449.5 to 252.3 Million years ago
The temporal range of the family Fenestellidae


Brachiopods are a very common find in the limestone stratum. While clams have a mirrored appearance between two shells, brachiopods have a mirrored appearance across each individual shell. If you look at a particular shell from above, the left and right will be a mirror of each other. In clams, they will not be, with the left differing from the right most of the time.

Several different genera are available. The following listing does not represent all species.

Brachiopod genera found include:

Pulchratia, a brachiopod
CG-0105, Pulchratia
Neospirifer, a brachiopod
CG-0103, Neospirifer


Bivalvia (Clams)

Clams have a shell that is a mirror image across the two valves (shells). They are often found as a single valve, but some are found with both valves, still together. These include Wilkingia and Meekopinna. In the case of Meekopinna, they are buried upright in the ocean sediment and usually die in the same position. Some genera such as Wilkingia bury themselves partially in sediment. Shells recovered with both valves together likely buried themselves during life.

Fossil bivalve genera include:

CG-0157, Astartella
CG-0112, Meekopinna. Two values, one destroyed.
CG-0054, Wilkingia

Cephalopoda (Squid)

Cephalopod shells are an enjoyable find. These shells are one of the larger invertebrate fossils that can be recovered. Some species have shells as large as a soccer ball, but it’s rare and difficult to find one so large. The shell exteriors in the Brush Creek limestone tend to adhere to the rock, often leaving a steinkern form. Each chamber has a wall that attaches to the outer shell wall. This attachment is commonly seen in fossils preserved as steinkerns.

CG-0021, Metacoceras. Chamber wall attachment marks (vertical dark lines in the center) are visible along the venter.

There are two base subclasses available. These are Nautiloid and Ammonoidea. Nautiloids are by far the most common. Ammonoids are found in the late Pennsylvanian, but their occurrence is rare in comparison. Nautiloids typically have straight-walled chambers, while Ammonoids have more intricate patterns. To further complicate things, Ammonoids divide into a number of different orders that typically differ with pattern complexity.


Nautiloid genera found are:

Specimen CG-0071, Metacoceras.
Specimen CG-0071, Metacoceras. An example of one and a half complete whorls. A find this complete is rare.
CG-0056, Metacoceras at the top, Solenochilus at the bottom. A rare pairing of two different genera.


For comparison’s sake, As of December of 2021, I have only recovered a handful of confirmed Ammonoid specimens. There is also one additional piece that is unconfirmed. They are:

  • Two from the order: Goniatitida? – A specimen with an Ammonoid pattern, but unlikely can be identified further.
  • Three from the genus: Schistoceras
CG-0167, an Ammonoid, likely from the order Goniatitida.
CG-0167, an Ammonoid, likely from the order Goniatitida.
Schistoceras, an ammonoid
CG-0091, Schistoceras. This was considered to be a gastropod at first, as certain gastropods and cephalopod shells can have similar shapes.
Schistoceras, an carboniferous ammonoid
CG-0283, Schistoceras. Found in the Pine Creek limestone, Kittanning, PA

Cephalopod Shell Morphology

Shell terminology for descriptions of recovered fossils can take a while to memorize. There are several terms available for the different parts of each shell. The outside wall is the venter and the sides are considered the flank. The number of whorls is commonly reported.

Cephalopod Shell Morphology

Gastropods (Snails)

Gastropods are found in marine, freshwater, and land sediments. Few creatures can bridge these realms, but gastropods can thrive in all. Even here in Parks Township, you can find late Pennsylvanian fossilized marine gastropods on rocks that have living land gastropods attached to them. In local lakes, large gastropods feed within the muddy sediments of the lake shorelines.

At least a dozen unique genera of gastropods are available to find in Glenshaw rocks, and I suspect that number is more than double. The cataloged finds locally include:

Shansiella carbonaria group, gastropod fossil

Plants (Kingdom: Plantae)

Illustrated fern frond.

Plants are another very large group that exists in all known common environments. From the sea to lakes, to the land, plant fossils can exist in several different places. Carboniferous rocks are famous for large coal deposits, which came from large areas of swampy land that were full of plant material. Coal strata were one of the major named things in most early geology literature. They were commercially important for producing heat and energy for industrial processes, and for heating homes. An early geologic map of the Freeport quadrangle featured locations of current and former coal mining operations. At some point, many western Pennsylvania towns had one or more operating coal mines.

One of the most common plant fossils is fern fronds. These are preserved as thin carbon film often in shales. In my observations, they also can leave an impression on the rock, albeit it is a very small one. The stems and larger pieces can leave deeper ones. The carbon films are striking when first exposed, and can dull after exposure to air. They are also not always black in color, with recovered examples of white, red, and other colors.

Fern leaves with veins and lamina visible.
Fern leaves with veins and lamina visible.

Plant identification

Identification of fossil plants can be difficult, as many different parts of the plant can have unique names. The roots, the trunk, the branches, lower leaves, mid leaves, upper leaves, seeds, and spores can all possibly have a name. The majority of specimens are found disarticulated, with no reference to the complete lifeform. Only when they are found together can these gaps be corrected and names synonymized.

Leaves are pretty simple to catalog, as they have identifiable markings. Different types of bark can also help with the identification of large tree trunks.

CG-0152, Taproot
CG-0152, Taproot. Genus identification is not possible without thin section and cellular identification.

Plant preservation in different environments

Plants are preserved commonly in three places. The most common and easy to recover is in shale. These recoveries are typically from a deposit of mud and silt that buried some sort of plant remains. Perhaps parts that washed away in a river, or settled in the bottom of a lake.

The second more common location is in sandstone deposits. Locally, larger pieces of plants are seen in sandstone deposits. These are difficult to recover, as the larger grains of sandstone break easily and often don’t allow recovery of a specimen using common tools.

The third is in limestone, however, this is a rare occurrence. Often when I find bits of plants in limestone, they are fossilized and replaced as pyrite. Another excellent find was a mass of plants preserved as a wavy surface with fine lines. When looking at it with a microscope, you can see bits of preserved carbon. While plant material certainly gets washed out to sea, the plant surviving and sinking into the sediment is much less common than say a marine shell.

CG-0153, Petrified wood.
CG-0153, Petrified wood. This small piece was recovered from the talus immediately below a section of Pine Creek limestone.
CG-0093, Pecopteris
Specimen CG-0093, Pecopteris. An example of preservation as a carbon firm, but also leaving an impression in the rock.
Lepidodendron close-up. Specimen CG-0009.
CG-0009, Lepidodendron. The bark of what was called a scale tree. Specimen preserved in sandstone.

Chondrichthyes (Cartilaginous fishes)


There are several types of fish teeth available to find in the Glenshaw Formation. To date, I have found two genera. Several specimens of Petalodus and a single example of Deltodus.

Deltodus has been a very rare find, with only one recovered specimen in three years of searching. Petalodus teeth are uncommon to rare. These teeth can be fragile and whole examples are hard to come by. Of the fourteen specimens in the catalog as of June 2021, only six of them have an entire crown.

Some Background on Petalodus

All Petalodus specimens are of the species Petalodus ohioensis, the default for North American Petalodus recoveries. While there are likely more than one distinct species, it’s difficult to find differences using the teeth. The teeth are homodont, which means they all have the same function. Yet, each tooth’s position in the mouth determines the width and height ratio for each tooth. With an array of variations that extends from the front teeth to the back, no discernable difference can be made.

Also, Petalodus is a member of the Cartilaginous fishes, so they should have a skeleton made of cartilage, the same as modern sharks. These types of skeletons are rare to preserve, and despite a known existence of 185 years, nobody has recovered a fossil of the body or even a jaw containing any teeth. The closest are two recovered specimens from a sibling genus.

CG-0055, Petalodus ohioensis
CG-0055, Petalodus ohioensis. Common shape and size of a mid to front position tooth.
Specimen CG-0015
Specimen CG-0015, Petalodus ohioensis. This is likely a tooth from the back of the jaw.
CG-0101, Detalodus
CG-0101, Detalodus. The only tooth recovered of this genus thus far. These were flat crushing teeth.


  • Fenestella (bryozoan) – Wikipedia
  • 1966, Wells, J. W., Paleontological evidence of the rate of the Earth’s rotation. pp. 70-81, in: B. G. Marsden and A. G. W. Cameron (eds.), The Earth-Moon System, Springer.