Abstract The Late Ordovician Epoch was marked by one of the two greatest global sea-level rises and inundations of the North American paleocontinent during the Phanerozoic (last 544 million years), accompanied by rapid diversification of invertebrate faunas in shallow, epicontinental seas. Toward the end of the Late Ordovician, continental glaciation in the southern hemisphere (Gondwana landmass) caused a major sea-level drawdown and marine regression from North America, bringing about one of the five major mass extinction events in life history. The diversity of marine life in the inland seas would be particularly sensitive to global sea-level fluctuations caused by the growth and decay of the Gondwana ice cap. This monograph is part of an ongoing comparative study of the biodiversity changes of the Late Ordovician – Early Silurian brachiopods (the most abundant and diverse group of shelly benthos at that time) in continental-margin basins and inland seas of Canada. Study of the brachiopod faunas helps us understand many aspects (duration, extent, intensity, and timing) of the climatic changes and their effects on marine environments far from the site of the glaciation. The Late Ordovician carbonate deposits now preserved in the Williston Basin contain a rich and diverse benthic shelly fauna that lived in the ancient equatorial epicontinental seas just before the Late Ordovician mass extinction event, and this work deals with the taxonomy, biostratigraphy, paleoecology, and paleobiogeography of the brachiopod fauna. The authors described a total of 16 genera and 22 species and discussed their ancient living environments and faunal provincialism.

Abstract The Late Ordovician Epoch was marked by one of the two greatest global sea-level rises and inundations of the North American paleocontinent during the Phanerozoic (last 544 million years), accompanied by rapid diversification of invertebrate faunas in shallow, epicontinental seas. Toward the end of the Late Ordovician, continental glaciation in the southern hemisphere (Gondwana landmass) caused a major sea-level drawdown and marine regression from North America, bringing about one of the five major mass extinction events in life history. The diversity of marine life in the inland seas would be particularly sensitive to global sea-level fluctuations caused by the growth and decay of the Gondwana ice cap. This monograph is part of an ongoing comparative study of the biodiversity changes of the Late Ordovician – Early Silurian brachiopods (the most abundant and diverse group of shelly benthos at that time) in continental-margin basins and inland seas of Canada. Study of the brachiopod faunas helps us understand many aspects (duration, extent, intensity, and timing) of the climatic changes and their effects on marine environments far from the site of the glaciation. The Late Ordovician carbonate deposits now preserved in the Williston Basin contain a rich and diverse benthic shelly fauna that lived in the ancient equatorial epicontinental seas just before the Late Ordovician mass extinction event, and this work deals with the taxonomy, biostratigraphy, paleoecology, and paleobiogeography of the brachiopod fauna. The authors described a total of 16 genera and 22 species and discussed their ancient living environments and faunal provincialism.

The Late Ordovician fauna of the northern Hudson Bay Lowland, Manitoba, Canada, consisting of three stromatoporoid species (1 new), 41 coral (11 new and 2 new genera), 8 gastropod (1 new), 56 cephalopod (21 new and 1 new genus), and 1 graptolite species are described and in part illustrated. Brachiopods are listed only. This fauna was obtained from five formations consisting mostly of fossiliferous dolomitic limestone 300–400 feet thick. In ascending order these are: the Portage Chute and Surprise Creek formations of the Bad Cache Rapids Group; the Caution Creek and Chasm Creek formations of the Churchill River Group; and the Red Head Rapids Formation. The Bad Cache Rapids Group, which rests on peneplaned Precambrian, is correlated with the Red River Formation of southern Manitoba, the Churchill River Group with the Stony Mountain Formation, and the Red Head Rapids Formation questionably with the Stonewall Formation. The faunas indicate a close temporal relationship between the Bad Cache Rapids and Churchill River groups. The latter is considered Richmondian and in part Gamachian. A Late Ordovician age is thus also suggested for the Bad Cache Rapids Group and hence for the coeval Red River Formation.