The first discovery of a Cretaceous big Cycadeoidaceae (Bennettitales) trunk from Inner Mongolia

A well preserved big Cycadeoidea (Cycadeoidaceae, Bennettitales) fossil trunk has recently been found from the Cretaceous strata in Darhan Muminggan Joint Banner, Baotou City, Inner Mongolia. The trunk in columnar shape measures 56cm in height and 48cm in maximum diameter. It consists of central pith, peripheral xylem cylinder, petiole bases and cones from the central part to the outside. The dense rhombic bases of the petiole are helically arranged on the surface of the trunk. The petiole bases decrease in size from the base to the apex of the trunk, with cones unevenly scattered in between. This specimen is the first complete fossil trunk of Cycadeoidea found in China. The fossil wood of Xenoxylon latiporosum (Cramer) Gothan (Gymnosperm) is recognized near the fossil trunk. The trunk and other fossil woods are important materials for studying the evolution of Cycadeoidea and the composition of Cretaceous flora in northern China.