Revision of the Cambro-Ordovician acritarch genus Vulcanisphaera Deunff, 1961

After its first description in Cambrian–Ordovician boundary strata from Gondwana, the acritarch genus Vulcanisphaera Deunff, 1961 has been found subsequently on most other paleocontinents, with a total of 32 species assigned to this genus. A comprehensive revision of the published literature indicates that the genus contains only three species that are easily differentiable: (1) V. africana Deunff, 1961; (2) V. mougnoana Martin, 1973; and (3) V. simplex Jardiné et al., 1974. The other species are either synonymous with these three or must be excluded from the genus. The generic and specific diagnoses of Vulcanisphaera are emended herein. The new classification scheme is tested and validated by using quantitative multivariate analyses based on morphometric studies on abundant material from England, Algeria and Iran. The species show large morphological variability, and transitional forms between V. africana and V. mougnoana are observed. The stratigraphic ranges of the species have been determined. V. mougnoana occurs from the Miaolingian to the Early Ordovician, V. africana is found with certainty from the Furongian to the Floian and V. simplex is recorded in the latest Furongian and throughout the Tremadocian. The genus Vulcanisphaera shows a cosmopolitan paleogeographic distribution with most occurrences recorded in higher paleolatitudes.