Cosmopolitanism in Northern Hemisphere Cretaceous Charophyta (Clavatoroidae)

Clavatoroidae were dominant charophytes in Early Cretaceous lakes and ponds of the Central Tethyan Archipelago and a significant contributor to the coeval non-marine floras of Asia and North America. From the 17 clavatoroidean evolutionary species reported, only four extended to reach a cosmopolitan or subcosmopolitan range. These species were originally limited in their biogeographic range to the islands of the Central Tethys, which were an active area of speciation for the whole family Clavatoraceae. In addition, most of them evolved from endemic Tethyan ancestors, suggesting that the ancestral biogeographic condition was one of range restriction rather than cosmopolitanism. 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. grovesiijiuquanensis, 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. (C) 2015 The Author. Published by Elsevier B.V.