Early Silurian Atrypoids from Manitoulin Island and Bruce Peninsula, Ontario

Silicified atrypoid brachiopods are common at two levels in the early Silurian sequence of the Bruce Peninsula and Manitoulin Island. The Manitoulin Dolomite (Llandoverian: Rhuddanian) contains Zygospiraella planoconvexa (Hall), Spirigerina (Eospirigerina) parksi (Williams) and Sypharatrypa honora n. gen., n. sp. in decreasing order of abundance, and ecologically sortedinto interreef, peri-reef and mud-mound habitats respectively. This establishes the importance of carbonate environments in the early speciation of some atrypoids. The late Llandoverian (Telychian) Fossil Hill Formation contains Atrypa (Gotatrypa) gibbosa Hall and rare Limbatrypa leptostriata n. gen., n. sp., members of the shelly Pentameroides community. Both new atrypoid genera display innovative morphological developments, such as the growth of frills, and spacing and arrangements of ribbs and growth lamellae, of significance in determining the evolutionary record of atrypoids.