| This work uses an analysis of morphology and morphological variation to investigate the nature of evolution, environment, life history, and life habit in three genera of orthidine brachiopods from the Upper Ordovician Richmond Group of the Cincinnati Arch: Hebertella, Glyptorthis, and Plaesiomys.; The first part is an analysis of size and shape variation in Hebertella, as correlated with stratigraphy. Significant size variation occurs in Hebertella that can be divided into three intervals based on the presence/absence of other orthidine species: (1) The Glyptorthis interval, containing Hebertella intermediate in size; (2) an interval in which Hebertella is the sole orthidine, containing particularly large Hebertella, and (3) the Plaesiomys interval, containing smaller Hebertella specimens. Bivariate and multivariate analyses of shape do not reveal significant differences correlated with these size changes. Competition is ruled out as a reason for the changes, with unobserved environmental factors being most likely. Shape change occurs with the introduction of a new species, H. alveata, in the Upper Whitewater, possibly associated with a sequence boundary.; The second part examines the Glyptorthis epibole at the base of the Liberty Formation. Morphological differences, degree of taphonomic degradation, frequency of epibiont encrustation, and the sedimentology and stratigraphy of the bed itself are examined in order to shed light on the origin and deposition of the bed. Shape analysis shows that no significant widespread regional variation takes place. Analysis of specimen completeness reveals a complex history of accumulation and burial. The Glyptorthis epibole most likely represents an unusual proliferation of Glyptorthis insculpta.; The final part is an analysis of growth pattern and functional morphology for the three brachiopods. Calculation of the allometric equation ( y = bxa) demonstrates that orthids show nearly isometric growth except for inflation of the brachial valve, which likely relates to the need for increased space for the lophophore. Close investigation of the shape of the three brachiopods indicates that Hebertella and Glyptorthis likely lived upright resting on their interareas, while Plaesiomys was convergent on a strophomenid lifestyle and lived free-lying, resting on its brachial valve. |
