Eusporangiate Ferns from the Dakota Formation, Minnesota, U.S.A.

Fossil records of the eusporangiate fern family Marattiaceae are common in Paleozoic and early Mesozoic sediments. However, whether this family occurred during the Cretaceous and Tertiary is unknown. Within the Marattiaceae, extant species of Marattia are distributed worldwide, while Danaea occurs only in the NewWorld, and Angiopteris and Christensenia show disjunct distributions throughout the Old World tropics, except in Africa. Two previously unknown marattioid ferns, Goolangia minnesotensis Hu, Dilcher, H. Schneid., et Jarzen gen. et sp. nov. and Mesozoisynangia trilobus Hu, Dilcher, H. Schneid., et Jarzen gen. et sp. nov. are described based on charcoalified isolated sporangia and synangia recovered from the Dakota Formation of the Courtland Clay Pit in south central Minnesota. These isolated sporangia and synangia have sessile, thick-walled sporangia and large spore output per sporangium, which is consistent with features of extant eusporangiate ferns. The spore wall ultrastructure of G. minnesotensis and M. trilobus supports affinities with extant Marattiaceae. These fossils provide evidence for the existence of marattioid ferns during the mid-Cretaceous in North America and present the first unequivocal documentation of the Marattiaceae in post-Jurassic times.