| The late Middle Devonian (Givetian) Hamilton Group of southwestern Ontario is well known worldwide for its diverse, abundant and well-preserved brachiopod fauna. Yet, despite their undoubted value as a paleontological resource, the Hamilton Group brachiopods have been largely ignored over the past few decades in terms of their systematics and potential biostratigraphic value.;A quantitative study of 38 brachiopod associations from the Hamilton Group of southwestern Ontario and equivalent strata in the Appalachian and the Michigan basins, using Q-mode (taxa as variables) and R-mode (localities/ages as variables) cluster analyses, principal component analysis, and four faunal similarity analyses (i.e., Jaccard similarity, Dice similarity, Simpson's coefficient of similarity, and Raup-Crick similarity indices), has revealed that the late Middle Devonian (Givetian) brachiopod faunas from time-equivalent strata of the Michigan and Appalachian are distinct, allowing identification of two separate faunal subprovinces.;In spite of its present-day position in the southeastern part of the Michigan Basin, southwestern Ontario had brachiopod associations which were more similar to those in contemporaneous strata of the Appalachian Basin during the deposition of the lower and middle Hamilton sediments. This may have been related to the absence of a topographic high in the present-day Findlay Arch area that would have otherwise prevented immigration of Appalachian Basin fauna into the study area. During the deposition of the upper Hamilton strata, the southwestern Ontario brachiopod associations developed a closer affinity to those of the Michigan Basin, suggesting that the immigration of brachiopod faunas from the Appalachian Basin into the study area was impeded. This change in faunal affinity may have been related to the formation of a local arch at present-day Cleveland area of Ohio that blocked the immigration of Appalachian Basin taxa into the study area.;Keywords: brachiopods, Hamilton Group, Middle Devonian, southwestern Ontario, Arkona-Thedford-Ipperwash area, taxonomy, biogeographic investigations, brachiopod association, cluster analysis, principal component analysis.;A detailed systematic study of brachiopods collected from exposed strata of the Hamilton Group in the Arkona-Thedford-Ipperwash area of southwestern Ontario has led to the recognition of 50 species assigned to 34 genera, among which one species, Devonochonetes arkonensis n. sp., has been newly defined. |
