Author ORCID Identifier

https://orcid.org/0009-0001-2117-2819

Semester

Spring

Date of Graduation

2025

Document Type

Thesis

Degree Type

MS

College

Eberly College of Arts and Sciences

Department

Geology and Geography

Committee Chair

James Lamsdell

Committee Co-Chair

Kathleen Benison

Committee Member

Kathleen Benison

Committee Member

Martha Gibson

Abstract

Eurypterids are a group of diverse chelicerates that first appeared during the Middle Ordovician (467.3 Ma) and went extinct at the end of the Permian (251.9 Ma). The fossil record of eurypterids during the Ordovician is relatively sparce, comprising only 12 species representing the Megalograptidae, a ‘waeringopterid’ clade, Rhenopteridae, Onychopterellidae, Adelophthalmoidea, and Eurypteroidea clades. This study describes early eurypterids from the Katian aged (~452 Ma) Big Hill Lagerstätte of Michigan. The described material represents two new species, herein named Machipterus margaritae sp. nov. (based on 21 specimens preserving the ventral prosoma and prosomal appendages, and opisthosoma) and Dikranopterus lysinae sp. nov. (based on 10 specimens preserving a prosomal appendage, paddle, genital appendages, and pretelson with telson). Phylogenetic analysis resolves Machipterus margaritae as a sister taxon to the Mixopteridae and Carcinosomatidae, providing insight into the ground pattern of the two groups; the prosomal appendages are short and robust, the preabdomen is moderately expanded, and the telson is lanceolate. Dikranopterus lysinae resolves within Dolichopteridae based on the angle between podomeres VI-3 and VI-4 being greater than 180º. This work fills in the ghost ranges of carcinosomatoids and dolichopterids and assists in ascertaining the tempo and mode of eurypterid evolution before the end-Ordovician mass extinction event.

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