Abstract
AbstractTwo new species ofNilssoniopterisof the order Bennettitales,Nilssoniopteris hamiensisZhao and Deng, new species andNilssoniopteris crassiaxisZhao and Deng, new species, are established from the Xishanyao Formation (Middle Jurassic) of Sandaoling Coal Mine in Hami, Xinjiang, China, based on leaf macromorphology and cuticular features.Nilssoniopteris hamiensisn. sp. is characterized by its varied leaf shapes and trichome bases of 1–4 cells on the abaxial epidermis.Nilssoniopteris crassiaxisn. sp. is characterized by its broad midrib (especially near the leaf base) and trichome bases of 1–3 cells on the abaxial epidermis. Both species possess unique venation patterns that are not only simple and free, but also forked and merged to form closed loops. These anastomosing veins are even more complicated inN.crassiaxisn. sp. in that the veins can fork once, twice, or even three times, the forked veins can later merge with each other or with an adjacent vein to form a closed loop, which may later further disjoin. The generic diagnosis ofNilssoniopterisis thus accordingly emended, particularly in the venation pattern. In addition, the stratigraphic and geographical distributions of all 45 JurassicNilssoniopterisspecies worldwide have been summarized and analyzed to better understand their brief evolutionary history, indicating thatNilssoniopterismight be able to grow not only in subtropical regions as the living cycads are, but also in warm climatic regions.
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