Early Cretaceous angiosperm leaves from the Dakota Formation, Braun Ranch locality, Kansas, USA.(With 13 plates, 13 text-figures and 3 tables)

An examination of about 1,100 impressions of fossil angiosperm leaves from the Dakota Formation of Early Cretaceous (Albian) age at the Braun Ranch locality, eastern Kansas, USA disclosed 21 species. Fifteen of them are assignable to the modern orders Magnoliales, Laurales, Proteales, and Saxifragales. One species, Eoplatanus serrata SCHWARZWALDER & DILCHER, is assigned to the modern family Platanaceae and one other species, Trochodendroides elliptica DILcHER & WANG may be related to Trochodendraceae. Comparisons with ocher Cretaceous angiosperm leaf floras, e.g., the Rose Creek flora from the Dakota Formarion in Nebraska and the Potomac flora from the eastern United States indicates that the Braun Ranch assemblage is archaic. The small species overlap between the two Dakota localities and the high diversiry of angiosperms at each single locality is best interpreted as the result of different environments, i. e., a tidaJly influenced distributary margin at the Rose Creek locality and a marshy lakeside on an alluvial floodplain at the Braun Ranch locality. The high diversity of angiosperms at each Dakota locality suggests the successful local competition of angiosperms over gymnosperms and ferns during the Early Cretaceous. This research represents one of a series of careful revisions of the Dakota flora from different localities in Kansas, Nebraska, Iowa, and Minnesota by the authors of this report. Furthermore, it provides important new information that clarifies the early diversity and evolution of the angiosperms during the Early Cretaceous, a critical time during which angiosperms began rapid adaptive radiation.