Late Pennsylvanian Trilobites consist of only a small handful of species. Trilobites were still 50 million years from extinction, but they were far from their previous size and diversity. They are tiny, often being only 4-6mm in width.Compare that to the largest known, which was 450mm long and weighed over 4 kilograms. So far I’ve only found the pygidium, or tail section. The cephalon, or head, appears to be harder to track down.

The general distributions of Trilobites in Pennsylvanian rocks, as it pertains to stratigraphy and paleoecology, are not well known (Brezinski 1989). They are described as 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 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 of these 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 into researching and writing about paleontology than Pennsylvania.

Morphological Variation

One of the highly interesting 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
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 Trilobite genus Ditomopyge
Ditomopyge temporal range. The genus persisted for 90 million years.

Carboniferous / Permian Trilobite Anatomy

Pennsylvanian Trilobite Diagram

Carboniferous Trilobite Specimens

References

  • Brezinski, D.K., Sturgeon, M.T., Hoare, R.D., 1989, Pennsylvanian Trilobites of Ohio, Report on Investigations No. 142
  • Shimer, H.W, Shrock, R.R., 1944, Index Fossils of North America, P. 637, 645, 648