Additional evidence for the Mesozoic diversification of conifers: Pollen cone of Chimaerostrobus minutus gen. et sp. nov. (Coniferales), from the Lower Jurassic of Antarctica

Paleontological data indicates that the Late Triassic-Early Jurassic was a critical time interval for the phylogenetic and morphological diversification of conifers, especially modern families. In this study a new genus and species, Chimaerostrobus minutus, is characterized based on an anatomically preserved pollen cone from the Lower Jurassic of Antarctica. The cone was prepared using the cellulose acetate peel technique and studied using light and scanning electron microscopy. The pollen cone of Chimaerostrobus is subspheroidal with tightly imbricate microsporophylls. Microsporophylls contain a single vascular bundle and abundant transfusion tissue. There are 22 pollen sacs per microsporophyll that are both abaxially and adaxially attached to the stalk and distal laminar head. In situ pollen grains are oblate, 15-20 μm in equatorial diameter, and asaccate. Chimaerostrobus has a combination of characters indicative of Araucariaceae and extinct conifers such as voltzialeans and Kobalostrobus; however, due to its unique character mosaic it cannot be assigned to an established group. This new species sheds light on the complexity of pollen cone evolution and the diversity of conifers that were evolving during the Late Triassic and Early Jurassic.