EVOLUTION AND BIOGEOGRAPHIC PATTERNS OF LATE ORDOVICIAN BRACHIOPOD EOCHONETES CLARKSVILLENSIS

The Late Ordovician strata of the Cincinnati region are characterized by a large cross-faunal invasion termed the Richmondian Invasion. The ecological impact of the invasion on Cincinnatian paleocommunities has been well studied, but the ultimate geographic source of invaders remains unclear. One was to identify biogeographic source(s) of the invaders is by examining biogeographic patterns within a phylogenetic framework. This study focuses on determining the pathway of invasion of the strophomenid brachiopod Eochonetes clarksvillensis (Foerste, 1912) within the context of a species-level phylogenetic revision of the entire genus.

Prior to phylogenetic analysis, character-based multivariate statistical analyses were conducted to determine generic and species validity. A well-resolved phylogenetic hypothesis was generated using 16 species of Eochonetes Reed, 1917. An area cladogram was constructed and speciation mode was analyzed using Fitch Optimization. Within the area cladogram, speciation mode could be resolved for 24 speciation events; 75% were characterized as vicariance and the remaining 25% as dispersal events. Dispersal occurred between Laurentia and the Baltic region multiple times during the evolution of the clade.

Eochonetes clarksvillensis apparently originated west of the Transcontinental Arch and subsequently underwent further dispersion to reach the Cincinnati Basin. Previous studies have uncovered pathways of invasion that include the southern midcontinent, Anticosti Island, and western Canada. Eochonetes clarksvillensis utilized the pathway from western Canada during the Late Ordovician.