Corals of the Advance Formation (upper Middle Ordovician), northern Rocky Mountains of British Columbia

Abstract

All corals known from slope deposits of the Advance Formation are solitary rugosans. Paliphyllum norfordi n. sp., represented by a single specimen, and Grewingkia burdenensis n. sp., which is more common, are the only identifiable species. Diversity and abundance are low compared with the taxonomically different coral fauna in approximately coeval shelf deposits of the Johnson Spring Formation, California. Grewingkia burdenensis is considered to be the ancestor of Grewingkia robusta, a Late Ordovician species that was widely distributed within the Red RiverþStony Mountain Province of cratonic North America. Paliphyllum norfordi is the earliest paliphyllid worldwide, and the only rugosan with dissepiments known from the Middle Ordovician of North America. It appears to be most similar to some representatives of Paliphyllum in the Dolbor Formation (uppermost Caradocþlowermost Ashgill), Siberian Platform. Coralla of G. burdenensis were subject to little current action or transportation. This species generally lived freely on soft substrates; sediment cohesion may have been low. In one stratigraphic interval, the presence of specimens with attachment structures suggests that the substrate may have been unfavourable for the coral's normal mode of life, or that more objects suitable for attachment were available than usual. The corallum of P. norfordi was subject to higher current energy and possibly transportation, and/or longer exposure before final burial. This coral was overturned, possibly due to current activity or substrate instability or both, and redirected its growth upward several times during life. It is the earliest North American solitary rugosan that had the ability to resume upward growth after being fully overturned.