Official Penn Dixie Field Guide

Thanks to the New York State Geological Association, we’re pleased to offer a digital version of our definitive guide — Penn Dixie Fossil Park & Nature Reserve: A Window Into The Devonian Period of Western New York. The guide appears in the 89th Annual NYSGA Meeting Guidebook — print copies available here. You may download the Official Penn Dixie Field Guide for educational use only.

The guide was written by Executive Director Dr. Phil Stokes — a geologist — and Dr. Holly Schreiber — a paleontologist — and provides a broad introduction to the history and science of Penn Dixie. Topics in the 18-page paper include:

  • Geological setting of New York State in the Devonian Period
  • Plate tectonics affecting the Catskill Basin and WNY
  • Why many different types of fossils are found at Penn Dixie
  • An overview of the main types of fossils found, including brachiopods, bryozoans, trilobites, crinoids, bivalves, gastropods, cephalopods, plants, and fish
  • Images of our fossils with updated nomenclature
  • A discussion of the fossil-bearing layers at Penn Dixie
  • Our organization’s history, and how we ended up as Penn Dixie!

Banner Season for Rare Penn Dixie Trilobite

Three Partial Pseudodechenella rowi Specimens Uncovered

By Jay Wollin, Educator

Anyone who has ever visited Penn Dixie knows first-hand that trilobites, or at least “trilo-bits”, are a common occurrence at the site. Visitors flock from around the globe to try their luck at uncovering one of the site’s treasured complete trilobites. The most common of which by far is the Eldredgeops rana (Green, 1832) which is often still referred to, albeit erroneously, as Phacops rana (1). In addition to the abundant E. rana specimens, visitors are often fortunate enough to stumble across examples of the less common, and undescribed Greenops sp. It is even possible to find the even more uncommon Bellacartwrightia sp. (Lieberman & Kloc, 1997), which is frequently mistaken for a Greenops sp. based on similar features and overall appearance.

Pseudodechenella rowi
Pseudodechenella rowi, a rare Middle Devonian Trilobite found July 2017 by an unknown visitor in the Smoke Creek Trilobite bed.

This season has marked the beginning of a banner year with the uncovering of not just one, and not just two, but three of one of the site’s rarest and most sought after species. The Pseudodechenella rowi (Green, 1838) was first discovered in 1837 in Otsego county, New York by George L. Le Row, and is considered a rare trilobite in all but one locality where it is found (2).

Pseudodechenella_Jessica Laton
P. rowi found by Jessica Laton Hesske in June, 2017 in the Smoke Creek Trilobite bed.

Unlike the other trilobites at Penn Dixie, which are members of the order Phacopida, the P. rowi is a member of the order Proetida. From a cursory examination, it may be difficult to recognize any significant difference between the Phacopids and the Proetids, in fact they share many similarities.

Pseudodechenna_May visitor
P. rowi found by an unnamed visitor in May, 2017 in the Bayview Coral bed.

Trilobites in general were some of the first animals on Earth to develop eyes. The trilobites of the Cambrian period all exhibited advanced compound eye structures known as schizochroal eyes. In these trilobite eyes, up to 700 individual eye lenses with individual corneas separated by sclera are grouped together in rows and files creating compound eye surfaces. Later in the evolutionary timeline, many trilobites developed even more complex holochroal eyes. In these eye structures as many as 15,000 tiny lenses are combined without sclera under one cornea to create the eye surface.

eyeholochroal  eyeschizochroal
An example of holochroal eyes. (Clarkson, 1975) An example of schizochroal eyes. (Levi-Setti, 1993)

It is with these features that we can most easily differentiate the Phacopids from the Proetids. All members of the the order Proetida feature the more common holochroal eyes, whereas the Phacopida—which translates literally to “lens face”—all retained the more primitive schizochroal eyes (3).

While the Phacopids did not survive the end of the Devonian period, the Proetids managed to persist through the Carboniferous and Permian periods as the last remaining order of trilobites, finally going extinct during the great Permian extinction.

Like the Phacopid Greenops sp. and B. whitelyi, the cephalon, or head, features extended and tapered genal spines on either side. However, the P. rowi can be easily distinguished from these other species by its large, smooth, and laterally elongated glabella, or nose.

greenops bellacartwrightia-calliteles-2_pinboarditemoverlay-e1499374418902.jpg pseudodechenella-rowi.jpg
Greenops sp. (American Museum of Natural History) Bellacartwrightia whitelyi (American Museum of Natural History) Pseudodechenella rowi (American Museum of Natural History)

To easily distinguish between the P. rowi and the E. rana trilobites, the glabella can be compared when visible. The E. rana features a broad, stout glabella which is covered in small bumps, whereas the glabella of the P. rowi is elongated and very smooth. In the event that the cephalon is missing, damaged, or simply obscured from view, the pygidium can also be used for identification. The pygidium of the E. rana has pleural furrows that extend to the edge, while the P. rowi has a distinct margin or border between the ends of the pleural furrows and the edge.

57cdf1226778c_20160905_175903(Large).jpg.6f805b2f9abf4d7eabb2aeef7e6ade00-057  pseudodechenella-rowi
Eldredgeops rana (Jay Wollin) Pseudodechenella rowi (American Museum of Natural History)

The increasing number of P. rowi finds at the site has us hopeful that there are many more yet to be uncovered. If you happen to be among the fortunate few to find one of these rarities, we invite you to submit to us your photographs and information so that we can share your fantastic finds with our friends and trilobite fans around the world!

As always, happy hunting!

— Jay

Author’s notes: Special thanks to Gerald Kloc and Karl Wilson for their assistance! Karl Wilson’s book — Field Guide to Devonian Fossils of New York — includes a detailed listing of these trilobites and many other Penn Dixie fossils. The book is available for $18 through the Paleontological Research Institution and is in Penn Dixie’s gift shop.


(1) The Phacops rana classification was changed by Struve in 1990 after a morphologic study of differences between African and North American/Northern European Phacops examples. For further information see this article posted by trilobite expert Gerald Kloc.

(2) Hall, James. Paleontology of New York 7 (1888): 119-122.

(3) Additional information about trilobite eyes can be found here.

Pyritized Fossils at Penn Dixie

By Jay Wollin, Educator

While the Penn Dixie site is world renowned for its excellent trilobites, and perhaps even for its incredibly abundant corals, there are small, relatively underappreciated areas of the site which can offer unique and exciting treasures for those willing to take a closer look.

The site is broken up into several main areas which are frequented by our visitors. Among the most popular are our “trilobite beds” and the aptly-named “brachiopod pit”. Different areas of the site represent different exposures and layers of strata. While large portions of the 54-acre site are teeming with fossil horn corals, brachiopods, and trilobites, there are are other sections of the site which represent entirely different conditions.

This location, just to the left of the main parking lot entrance is home to some of Penn Dixie’s pyritized prizes.

During fossilization, there a process known as permineralization. During this process, empty spaces that were present in the living organisms are filled with groundwater, rich in minerals leached from the surrounding materials. This process can fill in very small spaces, even those within cell walls. Depending on the types of minerals present and the conditions during fossilization, this process can result in many interesting types of preservation. One of such types is known as pyritization.

An example of pure iron pyrite, or Fool’s Gold.

Pyrite is an iron sulphide and is often lustrous and gold in color, giving cause for its common name, Fool’s Gold. Under rather specific circumstances it can coat or fill gaps during the fossilization process. Typically, in order for pyritization to occur, organisms must be deposited in seawater areas that are low in both organic matter, and dissolved oxygen. This oxygen-deficient water create what is known as an anaerobic environment. In this environment, certain bacteria are able to survive and flourish. When combined with reactive iron, these bacteria convert the sulphates into sulphides which results in a pyrite mineralization in the remains.

At the Penn Dixie site it is possible to uncover beautiful, golden pyritized specimens, however, the vast majority have exhibit a higher iron content and have weathered out and oxidized to present with a metallic rust colored finish. These fossils are generally rather small in size—averaging roughly 5mm in diameter—and tend only to appear in the site’s “Pyrite Beds.”

Pyritized fossils and pyrite nodules in situ in the Penn Dixie Pyrite Beds.

To the untrained eye, these diminutive fossils could easily be mistaken for pebbles or debris. Upon closer examination however, one can find many interesting examples of Devonian critters. Pyritized goniatites, gastropods, brachiopods, ambocaelia and even trilobites can be found with some effort.

While the “Pyrite Bed” at Penn Dixie represents a rather small and unassuming portion of the site, those willing to spend the time and effort to examine the surface closely can find a veritable treasure-trove of unique and interesting fossils. Don’t be fooled, all that glitters is not gold… sometimes it’s pyritized fossils!

Clockwise from upper-left: Ambocaelia sp.; Greenops boothi; Goniatites sp., possibly G. uniangularis; Nuculites sp.; Loxonema sp.; and an unidentified brachiopod. Click fossils for larger images. All photos courtesy of Jay Wollin.

2017 Dig with the Experts Updates

Some general notes for those planning to attend:

  1. We will be open on Monday May 29 — Memorial Day. Admission on this day will be free for anyone who registered for the dig. Regular admission rates will be available for the general public. There is no need to sign up to visit on Monday. Penn Dixie will be open 9-4 on Memorial Day.
  2. For those who wish to arrive early on Saturday or Sunday: The gate will open at approximately 8 am and we will begin parking guests at that time. Please be advised that our staff will not be ready to handle check-ins until shortly before 9 am.
  3. The dig officially ends at 4 pm on Saturday and Sunday. However, the site remains open until 5 pm on both days. And, you are welcome to stay late if you’d like. We just ask that you move your vehicle outside the gate so that our staff can complete the process of closing for the evening.
  4. To our out of town visitors: welcome!! Here’s a link to the Hamburg Chamber visitor’s guide with some great suggestions for restaurants and attractions:
  5. Don’t forget that PaleoJoe Kchodl will present Trilobite Treasures: Arthropods of the Ancient Seas on Friday at 6:30 pm in the Gateway Auditorium at 3556 Lakeshore Road in Blasdell. Joe is a real treasure to the science education community and we are excited about having him back again this year.
  6. If you’re new to Penn Dixie, be sure to check out our FAQ.