A review of Scriniodinium Klement 1957 and Endoscrinium (Klement 1960) Vozzhennikova 1967 and related dinoflagellate cyst taxa

Specimens of the well known and distinctive Jurassic (typically Oxfordian) dinoflagellate cyst species Scriniodinium crystallinum from Australia and New Zealand vary from being nonparatabulate to paratabulate. Where present, the paratabulation, which is 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. The morphologically similar genus 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, nine species are transferred to the most appropriate genus. Endoscrinium anceps is transferred to Scriniodinium as it has dextral torsion. Endoscrinium acroferum, E. attadalense, 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 some stratigraphical range differences of species of Scriniodinium and Endoscrinium between the Northern and Southern hemispheres. For example, in Europe, Scriniodinium crystallinum ranges from the late Callovian to the earliest Kimmeridgian and is a reliable marker species. However, in the Southern Hemisphere, the species has a significantly younger range. It is present consistently from the early Oxfordian to the mid Tithonian and occurs in low numbers to the late Berriasian. However, there are many strong global consistencies with these two important genera. Notably, Endoscrinium has the older range base and this is consistent with the phylogeny of the subfamilies Leptodinioideae and Cribroperidinioideae. Some potential evolutionary trends have been noted; these include Endoscrinium asymmetricum and E. acroferum (late Bajocian to Callovian) possibly being precursors to E. luridum (Oxfordian-Kimmeridgian) in Europe.