ORIGIN OF THE FUSULINID PROFUSULINELLA IN EURASIA AND NORTH AMERICA

The fusulinid genus Profusulinella appeared in sub-Arctic North America in Medial Atokan (= Early Moscovian) time, roughly 4 to 5 My later than its oldest known occurrence in the Eurasian-Arctic province. The genus originated in the latter area in late Early Bashkirian time and then underwent significant diversification, so that by Early Moscovian time a variety of shell morphologies existed. The first sub-Arctic North American species in the genus are interpreted as immigrants from Eurasia, with their migration through the Franklinian corridor having been facilitated by generally east-to-west currents during a glacio-eustatic flooding event. Previous work suggested that North American Profusulinella spp. may have derived from a local ancestor such as Eoschubertella. This possibility seems unlikely given that early North American species in Profusulinella are very similar to age-equivalent Eurasian forms, that they differ in a number of morphologic features from Eoschubertella, and that there are no known North American intermediates between Eoschubertella and Profusulinella. Fusulinoidean faunas apparently migrated from Eurasia to North America on multiple occasions during Pennsylvanian time. These migrations were an important source of North American diversity, and their recurrence is a dominant theme in fusulinoidean biogeography.