Using morphometric analysis to determine patterns of evolution in the Upper Ordovician brachiopod Sowerbyella rugosa from the Kope Formation of northern Kentucky
Levy, Gayle M
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This study examines patterns of evolution in the Upper Ordovician brachiopod Sowerbyella rugosa from the Kope Formation using morphometric analysis. Landmark analysis was used to determine centroid size and shape coordinates, which were then tested against stratigraphic position, environment and a random walk. Neither centroid size nor any of the shape coordinates show correlation with stratigraphic position or environment. Centroid size and one shape coordinate exhibit stasis, while the other shape coordinates follow a random walk. Centroid size and shape coordinates were also measured for Eochonetes clarksvillensis, another Upper Ordovician brachiopod from the Liberty Formation, a descendant of S. rugosa. S. rugosa has a smaller centroid size but has a longer hingeline than E. clarksvillensis. The change in morphologies between S. rugosa and E. clarksvillensis may have resulted from punctuated equilibrium or may be attributable to very gradual evolution that cannot be seen at the resolution of a million years.