Late Pennsylvanian Trilobites consist of only a tiny handful of species. Trilobites were still 50 million years from extinction but were far from their previous size and diversity. Fossil Trilobite finds from this geologic age are tiny, often only 4-6mm in width. Compare that to the largest, 450mm long and weighing over 4 kilograms. So far, I’ve mostly found pygidium specimens, also known as the tail section. The cephalon, or head, appears to be harder to track down. However, I did recover a specimen of the left side of one in 2020.

If you are looking for trilobites in Pennsylvania, the further East you go, the larger the finds tend to be. This is due to the older rocks in the East from when trilobites were in their prime. These western Pennsylvania specimens exist but can be challenging to find due to their tiny size.

Late Pennsylvanian Trilobites next to a number 2 pencil eraser.
Tiny Trilobites. Some late Pennsylvanian Trilobite pygidiums next to the end of a standard Number 2 pencil.

The general distributions of Trilobites in Pennsylvanian rocks, as it pertains to stratigraphy and paleoecology, are not well known (Brezinski 1989). They are a rare find, and I can attest to that. I’ve only found about a half dozen examples over the past two years of searching through local rocks.

Two Late Pennsylvanian Trilobite Species of Interest

GenusSpeciesDescribed byStrata Found In
Ameuramissouriensis(Shumard)Brush Creek / Pine Creek
Ditomopygescitula(Meek & Worthen)Brush Creek / Pine Creek
Ditomopygedecurtata(Gheyselinck)Ames Limestone

Ameura missouriensis and Ditomopyge scitula are the two species that I have focused on, as they are the only two known to exist where I search. Both extend back in time through the Allegheny and Pottsville formations in Ohio. The state of Ohio is often referenced in research here as the Ohio Geological Survey has spent far more resources researching and writing about paleontology than Pennsylvania.

Morphological Variation

One of the fascinating facts presented in Pennsylvanian Trilobites of Ohio (Report of Investigations No. 142) by D. Brezinski et al. is that Ditomopyge scitula exhibits proven morphological variation across the strata. From the Pottsville Formation through the Allegheny Formation until the later Conemaugh Formation, the average width of the Pygidal drops from nearly 8mm to below 6mm. This width also drops by 2mm.

Trilobite Temporal Range

Temporal range of the class Trilobita
The illustration above shows the temporal range of the class Trilobita. The entire class died out at the end of the Permian Triassic Extinction. They existed for over a quarter of a billion years.
Temporal range of the Late Pennsylvanian Trilobite genus Ditomopyge
Ditomopyge temporal range. The genus persisted for 90 million years.

Carboniferous / Permian Trilobite Anatomy

Late Pennsylvanian Trilobite Diagram

Carboniferous Trilobite Specimens

Below are several specimens I have collected locally in the Brush Creek limestone and the Pine Creek limestone. The Pine Creek specimens tend to be more complete; however, the free/fixed cheek that I found was from Brush Creek limestone.

CG-0386 - Ditomopyge scitula. Scale bar = 5 mm. The topmost shell covering of this pygidium is removed, exposing some of the inner shell structure.
CG-0386 – Ditomopyge scitula. Scale bar = 5 mm. The topmost shell covering of this pygidium is removed, exposing some of the inner shell structure. From the Pine Creek limestone.
CG-0386 - Ditomopyge scitula. Scale bar = 5 mm.
CG-0386 – Ditomopyge scitula. Scale bar = 5 mm. From the Pine Creek limestone.
CG-0385 - Ditomopyge scitula. Scale bar = 5 mm.
CG-0385 – Ditomopyge scitula. Scale bar = 5 mm. From the Pine Creek limestone.
Tail mold
Specimen CG-0040
Entire specimen: Trilobite Free Cheek Genal Spine with metric scale
Trilobite free cheek

Late Pennsylvanian Trilobites Specimen Posts

More Pennsylvanian Trilobite Information Online

References