University of Nebraska-Lincoln, United States

Recent studies of Santonian and Campanian sediments from several sites in northern Canada identified two new silicoflagellate genera, many new and unusual species, a Santonian assemblage of Variramus and abundant specimens of the poorly known genus Cornua. This allowed a reassessment of Variramus with information from three new species, and transfer of V. loperi into the new genus Schulzyocha, along with five new species that form an unusual assemblage in the early Campanian. A second new and unusual genus, Umpiocha, and two new species of Cornua provide knowledge of a previously unknown diversity of silicoflagellates in the Santonian. The first appearance of Lyramula is now dated as early Campanian. The occurrence of C. poretzkajae in early Campanian offers new information on the early history and timing of the transition from Cornua to Corbisema. Sediments from higher in the Campanian show development of Corbisema apical plates, and unusual new skeletal morphologies of Arctyocha. These and other discoveries present an improved understanding of early silicoflagellate evolution. Most of the recently described species lack a basal ring, though many of the skeletal morphologies allow for interpretation of a basal plane. Variramus lacks an obvious basal plane, suggesting a more primitive skeletal symmetry, which is interpreted to have given rise to Lyramula (also lacking an apparent basal plane and not known to produce double skeletons). Recent discoveries of rare double skeletons for Corbisema, Schulzyocha and Vallacerta show the skeletons rotated with respect to known Cenozoic configurations. This information, along with a better understanding of Cornua and knowledge of the enigmatic Umpiocha, provides an opportunity to fill part of the 35-40 million year gap between the previously known Albian and late Campanian/Maastrichtian silicoflagellate occurrences. These new interpretations of early silicoflagellate evolution are presented in the context of studies by Deflandre, Gleser and other previous research. Abstract Copyright (2010) Elsevier, B.V.