A review of the enigmatic microalga Tetranguladinium Yu et al. 1983 ex Chen et al. 1988; palaeoecology, stratigraphy and palaeogeographical distribution

The probable zygnematacean zygospore Tetranguladinium is recorded in Mesozoic strata from southern Scandinavia for the first time. Tetranguladinium, which exhibits morphological similarities to the extant filamentous green alga Mougeotia, occurs in Jurassic–Cretaceous (J/K) boundary (latest Tithonian–Early Berriasian) assemblages from the Vomb Trough, southern Sweden and on the Danish island of Bornholm. The J/K boundary strata of southern Scandinavia were deposited in marginal marine settings, varying from freshwater marshes, lakes and flood plains, to lagoons, shoreface, and shallow marine to fully marine environments. The assemblages containing Tetranguladinium are diverse, consisting of spores and pollen, the colonial green alga Botryococcus, various other zygnematacean zygospores e.g. Ovoidites, Schizosporis and Tetraporina, and rare marine dinoflagellate cysts.

 A review of published fossil occurrences of Tetranguladinium reveals that its stratigraphical range extends at least from the Late Guadalupian (Mid Permian) to the Holocene. It has been recorded from Africa (Tanzania), Asia (China, Korea), Australia, northwest Europe (Denmark, Great Britain, Sweden), North America (Canada, USA), and South America (Argentina). Depositional and palaeoclimatological data for the known localities of Tetranguladinium confirm a preference for freshwater settings in a humid warm temperate to subtropical–tropical climate, often with a pronounced dry season. The palaeogeographical positions of all the known Tetranguladinium localities indicate that it is has stayed restricted within narrow belts between 30–40 south and 30–60 north of the palaeoequator since the Late Jurassic.