Upper Silurian heliolitine corals, Canadian Arctic: Taxonomic method, keys to identification, and biogeographic relationships

Abstract

Taxonomy of heliolitine corals, and tabulate corals in general, benefits from analysis of larger assemblages of coralla that approximate populations. Quantitative data derived from such assemblages allow intraspecific variation to be tested rigorously and illustrated, and similar, co-occurring species to be discriminated using normal patterns of continuous population variation. Field collection and analysis necessarily involve recording and comparing assemblages from the full spectrum of sedimentary facies available at any one stratigraphic level and from the maximum available stratigraphic range. The large published taxonomic literature on heliolitine corals is a daunting obstacle to identification at the species level because a substantial part appears to involve taxonomic splitting to a degree inconsistent with variation known in modern coral species. The heliolitine corals studied occur in Ludlow-age ramp and shelf carbonate facies in the Boothia Uplift region in the southern Arctic archipelago of Canada. The “population” approach resulted in discrimination of 18 morphotaxonomic species, belonging to five genera and four families. A few select morphologic characters, incorporated in simple identification keys, are particularly helpful in distinguishing the 11 heliolitid and four stelliporellid species present, and are useful in screening the voluminous literature on species of Heliolites. Six of the species compare closely to Silurian species reported from central Kazakhstan, West Siberia, and North China; few are shared with other regions. The principal affinities are consistent with occurrence in the Uralian-Cordilleran paleogeographic region in the Silurian northern hemisphere. Eight species do not appear to be recorded in published literature elsewhere and are apparently endemic.