ALBERT

Description: Conoidal shells of Cornulites celatus n. sp. occur commonly within host coralla of Propora conferta Milne-Edwards and Haime, 1851, sensu lato, from the Laframboise Member of the Ellis Bay Formation (Ashgill: Upper Ordovician) at Pointe Laframboise on western Anticosti Island. Examples have also been found at the same locality in the tabulate corals Paleofavosites sp., Acidolites arctatus Dixon, 1986, and A. compactus Dixon, 1986, and the stromatoporoid Ecclimadictyon sp., but not in other associated tabulate coral species. Growth interference between the shells and their hosts indicates a commensal relationship. C.celatus apparently had a more limited paleoenvironmental range than its principal coral host species, which occurs abundantly elsewhere on the island without its endobiotic partner. The diagnosis of Cornulites is emended to include forms having a two-layered shell wall with a distinctive outer layer consistently preserved as prismatic calcite. This new species extends the known stratigraphic range of cornulitids in commensal relationships with corals and stromatoporoids from the Silurian back to the Upper Ordovician.

Description: Heliolitine corals occur in Upper Silurian strata of the topmost Douro, lower Barlow Inlet, and lower Somerset Island formations in the Boothia Uplift region. The fauna includesHeliolites(nine species),Propora(two species), the stelliporellid generaPodollites(three species) andStelliporella(one species), and the plasmoporidSquameolites(one species). Species present but not previously reported from the region includeHeliolites arcuatusBondarenko,Heliolites uksunayensisMironova,Stelliporella ilensisBondarenko,Podollites assitusnew species,Podollites parryinew species,Podollites plectilisnew species,Propora tubulata(Lonsdale) and an unidentified species ofPropora.All species occur in reef and reef-associated facies of open carbonate shelf and ramp settings. In restricted nonreefal carbonate shelf settings, diversity attenuates to a minimum, exemplified by numerically abundant monospecific assemblages ofHeliolites uksunayensis.Six of the 16 morphotaxonomic units recognized compare with species reported previously in Silurian faunas of Kazakhstan and Mongolia. Combinations of characters in the species attributed toPodollitessupport revision of the genus, possibly to includeDerivatolitesandTarbagatailites, in a group morphologically intermediate betweenStelliporellaandHeliolites.

Description: Heliolitine corals are closely associated with lithistid sponge-dominated reef mounds in Ludlow carbonate ramp facies on Somerset Island. The corals occur abundantly in argillaceous, fossiliferous wackestone immediately flanking and capping the reef mounds, less commonly in calcilutite mudstone within the reef mounds, and with sharply decreasing abundance in nodular argillaceous wackestone to mudstone away from the reef mounds. Exhaustive field collection, and systematic study that included biometric analysis of collected assemblages, indicates that ten heliolitine species are present, including the new species Heliolites furyi, H. garnieri, and H. greineri, and two unidentified species, Heliolites sp. A, and Podollites? sp. The occurrence of H. subdecipiens Klaamann, 1984, H. tchernyshevi Bondarenko, 1966, H. cf. H. rariformis Tchi, 1976, Stelliporella cf. S. podolica Bondarenko, 1971, and Squameolites anomalus Tchi, 1976 indicates an affinity with Eurasian rather than North American faunas of equivalent age. Many new species have been ascribed to Stelliporella since the mid-1970s; most lack the diagnostic axial structures of the genus and are more appropriately regarded as belonging to Heliolites. Newly defined structures termed septal florets occur commonly in H. garnieri and very rarely in three other species of Heliolites. Effective taxonomic use of septal development requires very careful study because of the degree of intraspecific and intracolony variation in some species.

Description: 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.

Description: Specimens representingHeliolites diligensBondarenko, 1966,H.aff.H. luxarboreusYang, 1978, andH. tchernysheviBondarenko, 1966, are common andHeliolitessp. andStelliporellasp. are rare in diverse coral assemblages associated with lithistid sponge reefs in deep shelf or ramp limestone facies of the Douro Formation.Heliolites diligens, a more widely adapted, possibly “opportunist” species, occurs abundantly in lower diversity stromatoporoid/coral assemblages from nonreefal, shallower shelf limestone facies. Detailed systematic study of approximately contemporaneous populations of these Ludlovian heliolitid species shows that all are morphologically variable; assessment of this variability qualitatively and quantitatively is critical to species definition and recognition.Heliolites diligensis the most variable, with wide intercolony variation in septal development, corallite wall configuration, and spacing of horizontal skeletal elements. This apparently represents morphological plasticity rather than differences that can be ascribed to distinct species. Conspecificity of the more extreme and dissimilar variants can be inferred from study of large assemblages of coeval specimens. The other species, with more narrowly defined, discrete variation fields, are more readily distinguished from each other.