Anatomically Preserved Williamsonia (Williamsoniaceae): Evidence for Bennettitalean Reproduction in the Late Cretaceous of Western North America

Abstract

An anatomically preserved ovulate cycadeoid cone has been discovered in Upper Cretaceous (Campanian) sediments of Vancouver Island, British Columbia, Canada. The specimen is preserved by calcareous cellular permineralization and displays diagnostic features of the genus Williamsonia Carruthers. The cone consists of a receptacle from which tightly packed interseminal scales and ovulate sporophylls with terminal ovules diverge over an arc of ca. 300°. Adjacent interseminal scales interdigitate and form a continuous tissue. Seeds are erect and more or less round in cross sections at all levels, and a cupule is not produced. The sarcotesta consists of multicellular peglike projections. The nucellus is attached to the integument only at the chalaza and is vascularized by a shallow cup of tracheids. Apically, the nucellus narrows to a solid finger‐like projection that fits tightly into the base of the micropylar canal. A pollen chamber is not produced. Nucellar cells are often separated from each other and are associated with large, hollow structures that represent pollen tubes similar to those in living conifers. Cellular megagametophytes and immature embryos are also preserved in some seeds. Williamsonia bockii sp. nov. represents the most recent seed cone of the Williamsoniaceae and is the first anatomically preserved reproductive structure of this family to be discovered in western North America. It reveals new features for the family Williamsoniaceae and allows for the interpretation of several additional facets of reproductive biology in the Bennettitales, particularly pollen tube production, pollination biology, and mode of fertilization.