Phylogenetic revision of the Late Ordovician orthid brachiopod generaPlaesiomysandHebertellafrom Laurentia

Abstract

The orthidine brachiopod generaPlaesiomysandHebertellaare significant constituents of Late Ordovician benthic marine communities throughout Laurentia. Species-level phylogenetic analyses were conducted on both genera to inform systematic revisions and document evolutionary relationships. Phylogenetic analyses combined discrete and continuous characters, from which character states were determined using a statistical approach, and utilized both cladistic and Bayesian methodologies.Plaesiomys cutterensis,P. idahoensis, andP. occidentalisare herein recognized as distinct species rather than subspecies ofP. subquadratus. Similarly,Hebertella montoyensisandH. prestonensisare recognized as distinct species separate fromH. occidentalis, andH. richmondensisis recognized as a distinct species rather than a geographical variant ofH. alveata.Hebertella subjugatais removed from its tentative synonymy withH. occidentalisand revalidated.The development of species-level evolutionary hypotheses forPlaesiomysandHebertellaprovides a detailed framework for assessing evolutionary and paleobiogeographic patterns of Late Ordovician brachiopods from Laurentia. The geographic range ofHebertellaexpanded throughout Laurentia during the Richmondian into both intracratonic and marginal basins.Plaesiomys subquadratusparticipated in the Late Ordovician Richmondian Invasion. The recovered phylogenetic topology forPlaesiomyssuggests thatP. subquadratusmay have migrated into the Cincinnati region from a basin situated to the paleo-northeast.