Zhao et al.—New Jurassic Nilssoniopteris species from Xinjiang of China


543


Figure 13. Jurassic stratigraphic and geographical distribution of Nilssoniopteris (base maps are from Boucot et al., 2009): (1) one species; (2) two or three species; (3) four to five species; (4) more than six species.


Northern Hemisphere (Nathorst, 1897) and in India in the Southern Hemisphere (Bose and Baneriji, 1984), with the number of species dramatically decreased to only two. In general, from the Early to Middle Jurassic, the number of


species of Nilssoniopteris rose and the distribution range expanded; while entering into the Late Jurassic, both the number of species and distribution areas remarkably declined. Vakhrameev (1991) divided the Jurassic climatic zones into


Hami, Xinjiang shows that the flora belongs to the Conioperis- Phoenicopsis flora, with Filicopsida and Ginkgoposida as the dominating components, Cycadopsida and Coniferopsida next most abundant, and Sphenophyllales, Lycophyta, and Bryophyta least dominant (Deng et al., 2010). In the flora, deciduous plants


the moderate-warm climate belt of the Northern Hemisphere (Siberian region), the subtropical belt of theNorthernHemisphere (Euro–Sinian region), the tropical belt (Equatorial region), and the subtropical belt of the Southern Hemisphere (Austral region) on the basis of global phytogeographic regions. Accordingly, phy- togeographic regions of the Early–Middle Jurassic in China have been divided into the North China Phytogeographical Region and the South China Phytogeographical Region, the former of which belongs to Vakhrameev’s Siberian region and the latter to Vakh- rameev’s Euro–Sinian region (Wu, 1983; S.-E. Wang et al., 1994; Deng et al., 2012, 2017a). The above-mentioned geographical analysis of Nilssoniopteris confirmed that plants of this genus not only grew in subtropical regions as living cycads do, but alsowere abundant in warm climatic regions. The species list of the Middle Jurassic flora fromSandaoling in


(e.g., Ginkgoales, Czekanowskiales, and Pinaceae) as indicators of seasonal warm climate and Osmundaceae as an indicator of humid warm climate occupied dominant positions, indicating a warm and humid climate in general (Deng et al., 2010, 2017a). Lacustrine bivalves discovered from the same stratigraphic layer are composed of Ferganoconcha and Unio, which are adaptive to warm and cool climates (Yu et al., 1993; Chen, 2003; Deng et al., 2017a). In addition, the presently studied strata are mainly characterized by fluvial, lacustrine, and swamp facies sandstone–mudstone, with developed coal beds and dark mudstones, which also indicate a humid climate. As a result, the paleoclimatic condition of the two newNilssoniopteris species in the present flora further corroborates the conclusion that Nilssoniopteris can flourish in awarm temperate zone in addition to subtropical–tropical zones. The presence and density of trichome bases have long been


used to indicate a dry and hot climate (Watson and Alvin, 1996). Interestingly, because the abaxial surface of some of our current specimens of Nilssoniopteris has abundant trichome bases, it may suggest that there existed dry and hot microenvironments within the generally humid and warm climate. The wide range of stomatal density of variously shaped leaves of the species N. hamiensis n. sp. can be viewed as additional evidence in support of various microenvironments in one flora.


Conclusions


We describe two new Nilssoniopteris species, N. hamiensis Zhao and Deng, n. sp. and N. crassiaxis Zhao and Deng, n. sp.,


Figure 12. Nilssoniopteris crassiaxis Zhao and Deng, n. sp. from the Xishanyao Formation of the Sandaoling Coal Mine, Xinjiang Uygur Autonomous Region, China. (1) Reconstruction of a whole leaf based on Figure 9.1, 9.3, 9.6, 9.10, 9.11, and 9.13; scale bar=5cm; (2) details of veins; scale bar=1cm; (3)1mm2 abaxial epidermis of the leaf shown in Figure 9.13 (right), showing orientation of stomata (“ø”); (4)1mm2 abaxial epidermis of the leaf shown in Figure 9.3, showing orientation of stomata (“ø”); (5)1mm2 abaxial epidermis of the leaf shown in Figure 9.13 (right), showing distribution of trichome bases (“x”).


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