Semester
Spring
Date of Graduation
2024
Document Type
Thesis
Degree Type
MS
College
Eberly College of Arts and Sciences
Department
Geology and Geography
Committee Chair
James Lamsdell
Committee Member
Dorothy Vesper
Committee Member
Charles Shobe
Abstract
Chasmataspidids are a group of Early Paleozoic (Middle Ordovician-Middle Devonian) chelicerates with an unclear phylogenetic placement. Though recent phylogenetic tests that include chasmataspidids support a monophyletic Chasmataspidida as sister to a Sclerophorata (Eurypterida+Arachnida) clade, very few previous phylogenetic analyses have sampled more than three of the fourteen currently recognized species. Without a robustly tested phylogenetic hypothesis, understanding macroevolutionary and biogeographic trends within chasmataspidids is difficult. Chasmataspidids also represent the earliest preserved euchelicerate in the fossil record, with Chasmataspis laurencii Caster and Brooks, 1956, dated to approximately 478 million years ago, and the group’s relationship to other euchelicerates has implications on divergence times of other clades.
I present two phylogenetic analyses (a maximum parsimony analysis and a Bayesian Inference) that present very similar results for the placement of Chasmataspidida that indicates that Xiphosura separated from euchelicerates prior to the Middle Ordovician, followed by the separation of Chasmataspidida by the Middle Ordovician, and that Sclerophorata existed by the Middle Ordovician. This analysis also supports a taxonomic revision of Chasmataspidida, with the clade divided between two superfamilies, four families, and two subfamilies. Loganamaraspis dunlopi Tetlie and Braddy, 2004 was reevaluated for this analysis and found that the original fossil does not preserve any form of limbs, but its phylogenetic placement indicates an interpretation that includes swimming paddles. The resulting phylogeny has implications on previous morphological hypotheses about the morphological evolution of Chasmataspidida, some biogeographic interpretation of the clade’s origination in Laurentia and dispersal through Laurussia and Siberia, and provides a framework for future discussions of early chelicerate evolution and phylogenetic analyses involving chasmataspidids.
Recommended Citation
Voss, B.D., "The phylogeny of Chasmataspidida" (2024). Graduate Theses, Dissertations, and Problem Reports. 12475.
https://researchrepository.wvu.edu/etd/12475
Embargo Reason
Publication Pending