PALEOECOLOGICAL AND PHYLOGENETIC IMPLICATIONS OF SAXICAULIS MECKERTII GEN. ET SP. NOV.: A BENNETTITALEAN STEM FROM THE UPPER CRETACEOUS OF WESTERN NORTH AMERICA

A new anatomically preserved bennettitalean stem has been recovered from the Upper Cretaceous (Coniacian) Eden Main locality on Vancouver Island, British Columbia, Canada. The fossil, described as Saxicaulis meckertii gen. et sp. nov., is permineralized and consists of a eustelic stem with diverging non-girdling leaf traces, a narrow zone of dense wood, primary cortex, and adventitious roots. Important vegetative characters that differentiate bennettitalean stems from cycad stems are reviewed, and while the anatomy of the stem conforms to Bennettitales, it is not consistent with either the Williamsoniaceae or the Cycadeoidaceae as they are currently understood. This fossil documents greater structural diversity among Cretaceous bennettitaleans than previously known and tentatively documents an additional growth habit (underground stem). Co-occurring fossils and plant structure suggest this plant may have inhabited an environment prone to fires. Additionally, there is evidence for two forms of plant-animal interaction in the fossil. The first is a large gallery in the pith lined with wound reaction tissue and accessed through a 3-mm hole on the surface of the stem that represents a new type of herbivore damage for Bennettitales. Reaction tissue occurs in rings and plates throughout the plant body. Smaller galleries containing coprolites of oribatid mites and lacking wound reaction tissue are present in the cortex. The complexity of Upper Cretaceous bennettitalean plant-animal interactions through herbivory and detritivory is evaluated.