Middle silurian ludlovian and wenlockian sponges from Baillie-Hamilton and Cornwallis islands, Arctic Canada

Abstract

The Silurian sponge fauna described here from Baillie-Hamilton and Cornwalls islands is one of the most diverse known from North America. The fossils are from Wenlockian-Ludlovian age deposits of the Cape Phillips Formation, which accumulated on the slope and in the basin of the Franklinian Geosyncline. The Cape Phillips Formation consists of interbedded shale, calcareous shale, and limestone, and most of the fossils are found in allochthonous limestone beds, mass movements having transported much of the fossil material downslope. Silurian sponges described here are representative of a distinct sponge biogeographic province that occurs north and northwest of a line along the Transcontinental Arch and contrasts with one to the southeast where sphaerocladine lithistid and heteractinid calcareous sponges are dominant. New genera within the demosponges include the rhizomorine Parodospongia and the orchocladines Antrospongia and Cauliculospongia. New hexactinellid genera include Corticulospongia and Lumectospongia. New species described here include the rhizomorines Haplistion frustrum and Parodospongia euhydra and the extensive orchocladines Antrospongia aberans, Aulocopium nana, Calycocoelia micropora, Cauliculospongia solida, Dunhillia fistulosa, D. megaporata, D. pluraliporosa, Patellispongia alternata, Perissocoelia (?) gelasinina, Perissocoelia (?) spinosa, Psarodictyum attenuatum, and Somersetella amplia. Astylospongiella (?) lutera and Astylospongiella striola are the only new representatives of the Sphaerocladina. The hexactinellid Amphidiscosa are represented by Lumectospongia uncinata n. gen. et sp. and the Lyssacinosa by the new Corticulospongia floccosa n. gen. et sp. and Dictyospongia apache n. sp. Carpospongia globosa (Eichwald, 1830) is reported here from North America for the first time. The broadly distributed Archaeoscyphia minganensis (Billings, 1859), Hindia sphaeroidalis (Duncan, 1879), and species of Patellispongia and Psarodictyum add "universal" elements to the assemblage.