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Species definition in heliolitine corals of the lower Douro Formation (Upper Silurian), Canadian Arctic
Published online by Cambridge University Press: 19 May 2016
Abstract
Specimens representing Heliolites diligens Bondarenko, 1966, H. aff. H. luxarboreus Yang, 1978, and H. tchernyshevi Bondarenko, 1966, are common and Heliolites sp. and Stelliporella sp. 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 diligens is 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.
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