Abstract

Specimens of the well known and distinctive Jurassic (typically Oxfordian) dinoflagellate cystspecies Scriniodinium crystallinum from Australia and New Zealand vary from being nonparatabulate to paratabulate. Where present, the paratabulation, which is manifested by low parasutural ridges on the periphragm, shows a clear dextral torsion, indicating affinity with the gonyaulacacean subfamily Cribroperidinioideae. Other species of Scriniodinium, such as S. pharo and S. playfordii confirm that this genus unequivocally belongs in the subfamily Cribroperidinioideae. Scriniodinium and S. crystallinum are both emended in order to note the cribroperidinioid paratabulation. Endoscrinium, however, exhibits neutral torsion and thus belongs in the subfamily Leptodinioideae. Endoscrinium and its type, E. galeritum, are emended to note this paratabulation style. On the basis of this clear paratabulation difference between Scriniodinium and Endoscrinium, ten species are transferred to the most appropriate genus. Endoscrinium anceps is transferred to Scriniodinium as it has dextral torsion. Endoscrinium acroferum, E. attadalense, E? hauterivianum, E. heikeae, E. indicum, E. irregulare, E? novissimum, E. obscurum and E. reticulatum are all new combinations of taxa with neutral torsion which were previously placed in Scriniodinium. Additionally, Aldorfia warringtonii is transferred to Apteodinium because it displays dextral torsion. Scriniodinium and Endoscrinium peaked worldwide during the late Callovian to early Kimmeridgian. There are differences in the stratigraphical ranges of species of Scriniodinium and Endoscrinium between the Northern and Southern hemispheres. For example, Scriniodinium crystallinum has a younger range top in Australasia than in Europe. However, there are many strong global consistencies with these two important genera and some potential evolutionary trends have been discerned. Endoscrinium has the older range base and this is consistent with the phylogeny of the subfamilies Leptodinioideae and Cribroperidinioideae.

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