The Early Silurian brachiopod Eocoelia from the Hudson Bay Basin, Canada

Abstract

Eocoelia akimiskii sp. nov. from the Lower Silurian (upper Telychian) Attawapiskat Formation of Akimiski Island, James Bay, Nunavut, is the first and oldest Eocoelia to be described from the Hudson Bay Basin, one of three largest inland basins of North America. The new species lacks dental plates, dental cavities, and marginal deflection or lip, which indicates a post‐Aeronian form of the well‐known Eocoelia lineage. In rib numbers, Eocoelia akimiskii falls between E. curtisi and E. sulcata, being closer to E. sulcata. In rib strength, however, the new species is more closely allied to E. curtisi. Although Eocoelia is currently assigned to the Rhynchonellida because of its lack of spiralia, several features (particularly the lack of a septalium, the presence of a unique notothyrial platform and cardinal process, and dense, free‐hanging fibrous growth frills) of the genus and other leptocoeliids are distinctly atypical of the rhynchonellides. The new species occurs in an inter‐reef, shelly packstone facies within the Attawapiskat Formation, which is characterized by coral‐stromatoporoid reefs with abundant, diverse, reef‐dwelling brachiopods and other shelly organisms. The close association of Eocoelia akimiskii with the Attawapiskat reefs supports a shallow subtidal (BA2) setting generally assigned to the Eocoelia Community. The reefs themselves, however, host an extremely abundant brachiopod fauna dominated by Pentameroides, Trimerella, Septatrypa, and Gypidula. Four species of Clorinda are also common elements of the reef‐dwelling brachiopods. This demonstrates that the concept of the classic Early Silurian level‐bottom brachiopod communities cannot be directly applied to reef‐dwelling brachiopod communities.