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 widely throughout the formation as a whole, where some areas have no easily detectable fossils.
The visible fauna is mostly from two major kingdoms of life, Animalia and Plantae. There are likely examples of Fungi, and perhaps Protozoa and Bacteria, but I don’t possess the knowledge to find and identify these types. Animalia is grouped into two main types, vertebrates, and invertebrates. This is surprisingly 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)
- Bivalvia (Clams)
- Cephalopods (Squid)
- Gastropods (Snails)
- Plantae (Plants)
- Chondrichthyes (Cartilaginous fishes)
Anthozoa – Rugosa Corals
Horn corals are somewhat abundant in Brush Creek Limestone locally. The particular order is named Rugosa. Typically these are locked in limestone and can be difficult to remove cleanly. In the nearby Pine Creek limestone, these can be extracted by the handful.
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.
These are quite beautiful finds when they show up. They are likely common, however 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.
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 can be found. The following listing does not represent all species.
Brachiopod genera found include:
Clams can be identified as having a shell that is a mirror image across the two valves (shells). They are often found as a single valve, but some are more commonly 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. With Wilkingia, they bury themselves partially in sediment. However, I currently do not know why they are usually found with the valves closed.
Fossil bivalve genera include:
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 difficult to find one so large. The shell exteriors tend to adhere to the limestone they are encased in, leaving steinkerns more common to be recovered. Each chamber has a wall that attaches to the outer shell wall. This attachment is commonly seen in fossils preserved as steinkerns.
There are two base subclasses available. These are Nautiloid and Ammonoidea. Nautiloids are by far the most common to be recovered. Nautiloids can be recovered from the late Pennsylvanian, but their occurrence is rare in comparison. Nautilouds 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.
For comparisons sake, As of June of 2021, I have only recovered two confirmed Ammonoid specimens. They are:
- Order: Goniatitida? – A specimen with an Ammonoid pattern, but unlikely can be identified further.
- Genus: Schistoceras
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.
Gastropods are uniquely found in marine, freshwater, and land sediments. Not many creatures can bridge these realms, but gastropods are known to thrive in all of them. 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 genus of gastropods are available to find in Glenshaw rocks, and I suspect that number is more than double. The cataloged finds locally include:
Plants (Kingdom: Plantae)
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, nearly every town locally had at least one operating coal mine.
One of the most common featured 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 a very small one. The stems and larger pieces can leave deeper ones. The carbon films appear strikingly when freshly exposed, and can dull after exposure to air. They are also not always black in color, with examples of white, red, and other colors being found.
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.
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.
Chondrichthyes (Cartilaginous fishes)
Deltodus has been a very rare find, with only one recovered specimen in 3 years of searching. Petalodus are common to rare, with examples being found often if searched for aggressively. 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 6 of them could be said to have an entire crown.
Some Petalodus Background
All Petalodus are assigned to Petalodus ohioensis, the default species for North American Petalodus recoveries. While there are likely more than 1 distinct species, it’s difficult to find differences using the teeth. The teeth are considered homodont, which makes them all of the same type. Yet, their mouth positions determine the width and height ratio for each tooth. With an array of variation that extends from the front teeth to the back, no discernable difference can be reasonably made.
Also. Petalodus is a member of the Cartilaginous fishes, so they are assumed to have a skeleton made of cartilage, the same as modern sharks. These types of skeletons are rare to preserve, and despite being defined for 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.
- 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.