Cosmopolitanism in Northern Hemisphere Cretaceous Charophyta (Clavatoroidae)

Three pulses of migration and biogeographic range expansion are recognized in Clavatoroidae. The first, late Berriasian to Early Valanginian pulse occurred in an Early period of the subfamily's evolution and involved one species, Clavator grovesii grovesii, which extended across Eurasia and North America, reaching full cosmopolitanism in a latitudinal belt. The second pulse, late Hauterivian to Barremian, involved the four species in Eurasia, i.e. C. grovesii jiuquanensis, Clavator harrisii, Clavator calcitrapus and Hemiclavator neimongolensis. The third migration pulse occurred in the Aptian and involved two species, C. grovesii corrugatus in Laurasia and C. harrisii, which reached full cosmopolitanism in the Northern hemisphere. These migration pulses lasted from 2.2 to 5 million years and are hypothesized to have been controlled by the paleogeographic connection of Early Cretaceous wetlands in Eurasia and by the adaptation of these species to a wide range of paleoenvironments. The influence of animal dispersal on the cosmopolitanism of species with a conjoint arrangement of gametangia, which is the rule in extant Chara, cannot be proposed as a testable hypothesis in Clavatoroidae, due to the lack of information about their male gametangia.