178-15 Recurrence of Eldredgeops in the Upper Devonian of New York, and its Implications for Trilobite Systematics and Punctuated Equilibria

Session: Paleontology, Diversity, Extinction, Origination

Presenting Author:

Authors:

Abstract:

A newly discovered locality in the upper Devonian Ithaca Formation of Central New York has yielded several cephala and pygidia of the charismatic and well-known trilobite genus Eldredgeops. This discovery indicates a recurrence of the genus, which was generally considered to have gone extinct at the end of the middle Devonian Taghanic Biocrisis (upper Tully Limestone). Eldredgeops, previously known as Phacops, is primarily known for being a “type case” in the theory of punctuated equilibria, and the focus of the work of its namesake, Niles Eldredge. This study aims to understand the taxonomic significance and placement of these newly-discovered specimens, while quantifying the morphological change of Eldredgeops throughout the middle and upper Devonian, beyond the usage of dorso-ventral eye lens files, which was the focus of Eldredge’s previous work. 

We reexamined Eldredge’s original thesis material, which spanned the Appalachian and Michigan basin at multiple horizons, in addition to several upper Devonian specimens discovered at the new locality. To quantify morphological change, 2-dimensional geometric morphometrics of cephalic characteristics were conducted on Eldredgeops specimens from throughout the middle and upper Devonian of central New York, Pennsylvania, Ohio, Michigan, and Indiana. Dorso-ventral file count, the species-delimiting character that was previously shown to demonstrate stasis and rapid morphological change in Eldredgeops, was also examined in all specimens. Our results show that while dorso-ventral file count demonstrates a pattern of punctuated equilibria throughout the middle Devonian, the character becomes polymorphic in the upper Devonian assemblages, bringing their use as a species-delimiting character into question. We argue that punctuated equilibrium in its “type case” is still valid. The intraspecific dorso-ventral file variation observed in upper Devonian Eldredgeops assemblages may be explained by geographic isolation and a genetic bottleneck following the Taghanic Biocrisis.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-7922

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