Late Ordovician solitary rugose corals of the Stony Mountain Formation, Southern Manitoba, and its equivalents

Two large cratonic interior basins, the Williston and Hudson, were situated within the Red River-Stony Mountain Solitary Coral Province, which occupied most of North America during Late Ordovician time. Helicelasma selectum (Billings, 1865), Deiracorallium angulatum gunni n. subsp., Lobocorallium trilobatum trilobatum (Whiteaves, 1895), and Bighornia cf. B. patella (Wilson, 1926) are known from the Stony Mountain Formation of southern Manitoba. The presence of identical species in Saskatchewan and Wyoming suggests that one assemblage inhabited the Williston Basin. The Hudson Basin assemblage comprises species that also occur in the Williston Basin, species closely resembling Williston Basin forms, and taxa that do not occur in the Williston Basin. Solitary Rugosa within the Red River-Stony Mountain Province in eastern North America are most closely related to those of the Williston Basin. The eastern cratonic margin assemblage includes species that were introduced from the continental interior, species not found in the interior, and the genera Streptelasma and Bodophyllum, which were restricted to cratonic margin areas of the province. Taxa in western Canada and northern North America appear to be most closely related to those of the Hudson Basin. Assemblages in the southwestern United States are not known at the specific level, but the presence of Bighornia, Deiracorallium, and triangulate to trilobate species of Grewingkia and possibly Lobocorallium indicates that they belong to the Red River Stony Mountain Province. Studies of Ordovician solitary Rugosa suggest that cratonic interior basins were centers of evolution, diversification, and dispersion. The Middle to Late Ordovician diversification of Paleozoic corals coincided with the Tippecanoe transgression, which was the most extensive in the Phanerozoic, and with the initial development of cratonic interior basins, which were characteristic of much of the Paleozoic. These factors may have been important in the Ordovician radiation of the "Paleozoic fauna" in general.