Late Carboniferous Fossils from the Glenshaw Formation in Armstrong County, Pennsylvania » Preface

This publication is a photo book and an inventory of the fossil fauna available in Armstrong County, Pennsylvania. Each section contains information on Late Pennsylvanian fossil groups recoverable from these locations. While I am still learning new things through research, my skills in digital photography are well refined, which I spent over a decade improving on as a hobby.

In the late summer of 2018, I found seashell fossils in the rocks behind my house. The hillside is a tall, eroding shale face, dug out a few times by the previous homeowners to enlarge the yard and to provide walking space at the edge of the forest. Ignoring my father’s advice, I carelessly split a mudstone with a pocket knife, with the blade facing me. The knife’s blade skipped across the rock, and its point sunk into my left hand. I loudly swore off fossils as I traveled to the urgent care to get stitches. I declared that trying to find them was silly and would only cause me more pain.

By winter, my curiosity got the better of me again, and I started to walk the local stream in the evenings. The numerous water-eroded rocks have many interesting shapes. I soon found black rocks with circular surface depressions. One rock had a sizeable cylindrical fossil with a central depression. The fossil fell from the stone and landed in my hand as I stood in the stream in the pitch darkness, wearing rubberized wading boots and juggling a flashlight.

I did not know what I had found; it was a fossil of something and seemed interesting. The identity became apparent after using Google to search for terms relating to the shape; it was a fossilized crinoid, or sea lily, whose descendants are still alive today. See page X for more on fossil crinoids.

Again, I became enamored with fossils and soon sought every piece of the black rock in the stream. I learned that the rock was limestone and that there must be a source for it somewhere near the creek. I brought home these small boulders using five-gallon buckets, placed pieces under a stereo-inspection microscope, and dug out all the fossils using needles and scribes. Plenty of crinoids, brachiopods, clams, horn corals, and cephalopod pieces existed. I learned my lesson with the pocket knife and bought a rock hammer and a chisel.

My limited geology knowledge started to expand; I already knew that (non-avian) dinosaurs had gone extinct 66 million years ago. Still, I was unaware of the implications of the Permian (252 mya) extinction that set the stage for their emergence. Enormous amounts of sediment settled in Pennsylvania during the age of the dinosaurs, but most of it has since eroded. In northern Pennsylvania, massive glaciers further eroded the surface rocks during the deeper cooling periods of the current ice age. Many people may be unaware that we are in a period of glaciation today, dating back 2.58 million years; the most recent interglacial period began 11,700 years ago, a time of warming and reduced ice. In popular culture, an ice age is a glacial period with cold temperatures and massive continental glaciers.

I read all I could find on local fossils. The Pennsylvania Department of Conservation and Natural Resources has published many helpful resources over the past half-century. I started with Common Fossils of Pennsylvania (Hoskins et al., 1983) and moved on to Pennsylvania Geology, a quarterly magazine. It occasionally featured articles by John A. Harper, someone I consider my mentor for local fossils and geology.

I found a pentagon-shaped fossil in one of the limestone rocks I had brought home that looked like a tooth. Harper (2016) wrote a detailed article about a Pennsylvanian “shark” Petalodus ohioensis that I thought had teeth similar to what I had found. I sent him photos of my specimen. I was dead wrong; I had a crinoid calyx piece, but he provided me with several more resources, including information about the geological formations that make up local rocks in the area. Later, John became a mentor and friend.

Discovering the local limestone.

The Brush Creek limestone should have cropped out somewhere on the hillside, so I started to dig and explore. Soon, I found it and discovered several additional limestone locations using its vertical position on the hill. The bedrock in Armstrong County is not parallel with global sea levels. Instead, it dips and rises. The low point of a dip is a syncline, and the high point is an anticline. Most of these dips and rises are named. They occur due to the horizontal compression and lifting of the bedrock during past geological events, such as the Alleghanian orogeny. The Duquesne – Fairmont Syncline runs through both the Parks Township and the Kittanning locales written about in this book.

This folding event happened during the formation of the supercontinent Pangea, which created the modern Allegheny Mountains over 65 million years ago. These mountains were once like the Rocky Mountains or the Alps of modern times but have since eroded to the rolling, rounded Allegheny Mountains that exist today. Armstrong County sits on a geographic area known as the Allegheny Plateau, a raised dissected plateau. These types of plateaus appear mountainous but are the result of deep erosion. Instead of cutting a cake by forcing the knife down, you lift the cake upwards into the blade. Proper mountains built by a continental collision will have folded bedrock, many faults, metamorphic rock, and evidence of igneous rocks.

Once I found the limestone, I started collecting larger pieces and several more from the stream beds. The location in Parks Township (SL 6533) has many miles of streams running through it. The shales erode quickly, sandstones last longer, and the limestones remain the longest. The limestone crops out on steep, eroded hills and is easy to spot. Using heavy sledge hammers, I broke large pieces into smaller ones and carted the pieces home for further study.

At SL 6533, the limestone is approximately one foot thick. The slabs are often segmented with stress fractures where they crop out. The shale above and below the limestone can be fossil-rich, but thus far, it has produced few fossils more than a few inches above the limestone. The shale under the limestone does not have any noticeable macrofossils. The bottoms of the limestone boulders often have extensive burrows, which are trace fossils.

A second place to collect: The Pine Creek limestone.

In 2020, the United States locked down due to the COVID-19 pandemic. I discovered and visited another location in central Armstrong County during the lockdowns. The Carnegie Museum of Natural History in Pittsburgh refers to it as SL 6445. A deep road cut at the intersection of PA 28 and US 422 exposes a prominent face of bedrock, with the Pine Creek limestone sitting at road level and up to several tens of feet off the roadway. The Pine Creek limestone is younger and was laid down during similar environmental conditions that created the Brush Creek limestone. The Brush Creek limestone is also here but is only exposed in a few places.

The Pine Creek limestone in Kittanning (SL 6445) is a few inches thicker and fissile than the Brush Creek limestone in Parks Township. This creates different collecting opportunities. There is a notable difference in fossil fauna between the two locations. For example, in Parks Township, the limestone has many visible pointed oval-shaped shell outlines on the top of the rocks. These are fossil traces of pinnids in life positions. None of these exist at SL 6445. What does exist is a vibrant horizon of fossil gastropods, much more than in Parks Township.

Each location has provided me with a good collection of a particular type of fossil; SL 6533 produces pinnids, and SL 6445 is a prolific producer of gastropods. Using these specimens, I have attempted to understand the individual species better, and both have provided me an opportunity to assist with or conduct new research that is currently ongoing.

Why I authored this publication.

This book introduces the reader to the Late Pennsylvanian fauna that once lived in an area known today as Armstrong County, Pennsylvania. Rocks exposed in Pennsylvania represent the type section of the Pennsylvanian Subperiod. Many excellent publications are available for the Pennsylvanian, including several publications from the State of Ohio. I will list them later in this book.

Regionally, the Pennsylvanian has a few state publications and is often featured in research manuscripts. The fossil-rich rocks offer plenty of opportunities for paleontological study. During the Pennsylvanian, the global paleoclimate frequently fluctuated between cold and warmer temperatures, locking and releasing ice. Temperature swings affect sea water levels on scales fast for geological time. There is an excellent variety of marine fossil-producing strata in these deposits. The rocks between them offer additional types, such as plants, insects, and, if you are fortunate, tetrapods.

Some tens of feet below the Brush Creek limestone at SL 6533, a shale layer has produced many fossil plant specimens. Plants often fossilize by leaving a thin carbon film, but at SL 6533, they also survive as impressions. This book includes several photos of plant specimens. Plants can be difficult to identify using modern taxonomy, as several form genera exist. Instead of describing a genus or species, the name can represent the part of the plant. Examples include a name for a part, such as tree roots, or a name for what is unknown, like Welchia. I am still looking for a reliable source of plant fossils at SL 6445. Therefore, most of the plants in this publication are from the SL 6533 locale.

Inspiration for this book comes from the many regional fossil publications focusing on the Late Pennsylvanian fossil fauna. Armstrong County has seen little paleontological publication, but many geological studies mention and sample from the city of Kittanning, the county seat adjacent to SL 6445. In Parks Township, there are only a few paleontological and geological reports. H.H. Hughes showcased the Freeport Quadrangle in a publication for the Geological Survey of Pennsylvania Fourth Series. Hughes reported on the geology throughout the quadrangle, which includes all but the northeastern corner of Parks Township. The most recent report is likely by J.J. Burke, who named the Carnahan Run shale and the Nadine Limestone in 1958. He also named many fossil genera from his Carnahan Run shale, including Lophophyllidium, Pharkidonotus, Meekispira, Juresania, and Amphiscapha. Today, we know this stratum as a shale facies of the Woods Run limestone (Wells 1983).

Meeting Experts Along The Way

Another surprising aspect of independent paleontology is the character of the people you meet. I’ve made several connections along the way. I’ve mentioned John Harper, whom I consider my mentor and a Paleozoic Gastropod expert. Thomas Yancey was the first to visit me and wrote a manuscript to name a new species of Pinnid from my backyard. He also encouraged me to publish online and gave great paleontology advice. Ben Neuman—who studies viruses by day and brachiopods by night—has spent considerable time conversing with me over various paleo topics. Nicholas Gardner helped me get my first publishing credits and belongs to a group of paleoworkers who focus on vertebrates, primarily sharks. Last is the late Bob Peck (July 2022), who exchanged many emails with me. I’ll never forget his line: “When I get money, I buy books. If I have any left, I buy food and clothing.”

Over the years, I’ve received replies from many collection managers. When I started out, I never thought I could get a reply from Yale, but they reply often and have provided great access to their collections. The Carnegie Museum, the Field Museum, the Natural History Museum in London, and many others have communicated well.

Many of the fossils in this book have type specimens. Holotypes are the sole representative of a species. Without them, that designation falls to a designated replacement—a neotype—or several paratypes and syntypes. Some fossils have type specimens well over 125 years old, and their last published image was a hand drawing. Collection managers have sent me modern photos of several types and helped confirm the loss of others.

This book will detail much of the available fossil fauna of the Brush Creek limestone in Parks Township (SL 6533) and provide a clear picture—and clear pictures—of the fauna from the Pine Creek limestone in Central Armstrong County (SL 6445). In addition, I have included supplementary text to provide additional insights on each locality, fossil hunting safety, tools, and more. Finally, I hope to shed some light on what kind of fossils exist and pass on some advice to keep the reader from having the same knife blade accident I had.