Abstract

Crassiangulina variacornuta sp. nov., a new distinctive species of acritarch, with a short stratigraphical range within the Telychian (Silurian), is recorded from low latitude areas of Balonia (Belgium, England and Sweden) and from high latitude areas of Gondwana (Algeria, Brazil, Libya and Saudi Arabia). Therefore, the new species has good potential to be an international biostratigraphic marker for the Upper Llandovery. It has so far only been recorded in depositional environments where the sediments settled below storm wave base. The genus Crassiangulina Jardineet al., 1972 is emended to incorporate the new species and to include triangular and other polygonal acritarchs with solid processes. The emended genus includes the type species Crassiangulina tesselita Jardineet al., 1972 emend., C. grotesca Crameret al. 1976 comb. nov. et emend. and C. variacornuta sp. nov. A biometric study of 138 specimens of C. variacornuta sp. nov. from two sections in England and one section in Belgium and its statistical treatment show the biological consistency of the studied population and point to differences between the mean measurements between the sections, because of taphonomic or environmental factors. This emphasises the need to unravel the morphological variations of acritarch species along the genotypic, ecophenotypic, chronotypic and taphonotypic axes of morphological variability.

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