Early Cretaceous Nilssoniopteris In Yanbian Region,Jilin,China And Its Geological Distribution

Yanbian Korean Autonomous Region is located in the eastern of Jilin Province,China,adjacent to Russia in the north,and to Democratic People's Republic of Korea in the east.The Mesozoic terrestrial strata are well developed in Yanji Basin,and rich in coal and oil shale.It is also one of the hot spots on researching the Early Cretaceous terrestrial strata,vegetation and environmental changes in Northeast China.Abundant fossil plants are yielded in the Changcai Formation.Research team in Jilin University has recorded quite a number of fossils from Lower Cretaceous Changcai Formation in this area since 2005.The fossil flora is composed of 63 species of 29 genera,including ferns?23 species of 10 genera?,Bennettitales?5 species of 2 genera?,Cycadales?6species of 2 genera?,Ginkgoales?7 species of 3 genera?,Czekanowskiales?3 species of 2 genera?and conifers?19 species of 10 genera?.In order to determin the geological ages of the fossiliferous Changcai Formation,an andesite sample for isotopic dating was taken from the base of the Quanshuicun Formation?formerly named as Fudong Formation by Zhou in 1980?at Fudong Town of Helong,Yanbian area of Jilin Province,giving a weighted mean age of 115.0±1.7 Ma,about the late Aptian in age.Considering other isotopic dating on the uppermost part of the Tuntianying Formation?125.1±2.7Ma??Yin et al.,2008?and the basal part of the Quanshuicun Formation?116.8 ±1.4 Ma??Sun et al.,2010,2016?,and the fossil animals,mega-fossil plants and pollen assemblages,the Changcai Formation is confined to early and middle Aptian in age.Abundant bennettialean fossils were founded in the Lower Cretaceous Changcai Formation in Yanbian area,Jilin Province.Some of them described in this thesis were collected from the Changcai Coal-mine,Chundong Coal-mine,Nanyang Coal-mines and Chunyang Coal-mines in Helong City,Yanbian area.Based on the examine of fossil cuticles,four species of Nilssoniopteris are recognized including a new species.They are Nilssoniopteris changcaiensis Sun et Li?sp.nov.?,Nilssoniopteris longifolia Doludenko,Nilssoniopteris prynadae Samylina,Nilssoniopteris platyrachis?Samylina?Wei et Sun.The new species,Nilssoniopteris changcaiensis Sun et Li?sp.nov.?can be recognized by its strip-shaped foliage,fine and dense veins,smaller stomatal density,large stomata and short aperture.Bennettites is an abundant and frequently well-preserved component among Mesozoic fossil floras.Nilssoniopteris genus has been reported from East Greenland,America,Russia,Japan,China and so on,and it is a major component in the mid Jurassic and early Cretaceous.In total 37 Mesozoic species have been discribed at present.These Nilssoniopteris fossils,except for a few fossils that are unknown in cuticle details,most of the plants can be confirmed.In order to find out the geographical distribution of Nilssoniopteris,each period and points were plotted on the paleogeographic map.This study indicate that Nilssoniopteris moved away from lowlatitude tropic-zone and expanded to the mid-latitude warm-temperate-zone from late Triassic to early Cretaceous.The northern migration of the genus is related to the overall warming from the Late Triassic to Early Cretaceous.A large number of Nilssoniopteris plants appear in the humid climate zone,others exist in the arid belt.With the decline of temperature in the late Cretaceous,the genus gradually decreases,remant in the low latitudes of the Czech Republic,and finally extincted in the end of Cretaceous.Stomata control the exchange of gases between the interior of the leaf and the atmosphere,and also occupy a central position in the pathways for both photosynthesis and respiration.In this capacity they make major contributions to the ability of the plant to gain atmospheric CO₂ for photosynthesis.Therefore,the stomatal parametersare considered as the sensitive part which can response to the change of atmospheric CO₂ concentration,and has been widely uesd in recent years to reconstruct past p CO₂ levels.In the present study,the stomatal method has been applied,and the cuticles of conifers,ginkgoales and angiosperms were studies as potencial indicators of the atmospheric CO₂ content.This method requires the stomatal parameters of a Nearest Living Relative?NLR?.The stomatal index of Cycas guizhouensis as NLR was obtained by averaging the stomatal parameters of 67 fragment of 8 leaves.The stomatal density?SD 80.58 ± 7.56?and non-stomatal epidermal cell density?ED1112.52±119.92?was counted,then stomatal indices was calculated as 6.84±0.83.On the basis of that,three fossils of Nilssoniopteris longifolia Doludenko and Nilssoniopteris prynadae Samylina from three places were selected for cuticle preparation.The stomatal indices were respectively obtained by 7.20±0.77,12.06±0.63,15.11 ± 1.79,stomatal ratios are 0.956 ± 0.078,0.632 ± 0.093,0.457 ± 0.046.Contrast with the data of CO₂ concentrations that was estimated a pCO₂ of the ginkgo from the same bed,we attempt to use SR=4RCO₂=1200ppmv in this experiment.The paleo-CO₂ concentration for the samples from the Changcai Formation are estimated to be 548.6±55.0 ppmv¹147.6±94.0 ppmv.It provides a new material and ideas for the reconstruction of paleoclimate.Systematic Description:Order: BennettitalesGenus: Nilssoniopteris Nathorst,1909Species: Nilssoniopteris changcaiensis Sun et Li?sp.nov.?Holotype: JLC0718049?pl.1,fig.1;pl.2,figs.1-6?Repository: the Research Center of Paleonology and Stratigraphy,Jilin University,China.Type locality: Chundong Coal mine,Helong Country,Jilin Province.Type Horizon: Changcai Formation,Lower Cretaceous?Aptian?.Etymology: Changcai refers to the stratigraphic horizon,the Lower CretaceousChangcai Formation in Yanbian area,Jilin Province.Diagnosis: Leaf liner,margin entire,gradually narrowing toward the base and apex.Fine veins,30 lateral veins/cm.Smaller stomata density and large stomatal,as well as short aperture.Description: Leaf strap,margin entire.The leaf observed is 220 mm long and 22 mm wide in the middle widest part of the leaf,gradually narrowing toward the base and the apex.The apex is blunt.The slender midrib is 1mm wide.Membrane of lamina thick.The lateral veins arise at angle of 80°-90°to rachis.Simple veins are fine and parallel to each other,and there are 30 lateral veins per cm.The stratum corneum is well preserved.The leaf is hypostomatic.Upper cuticle is thinner and fragile.Internal view showing the part of adaxial surface.Cells of adaxial epidermis have sinuous anticlinal walls,consisting of irregular cells.The outside surface is rough and honeycomb.Diffrent between costal and intercostal zones is obvious on the abaxial epidermis.The abaxial epidermis is divided into costal and intercostal zones in terms of distribution of stomata.Costal zone 124?m wide,cells rectangular,70?m long and30?m wide.Anticlinal cell wall ? shape of undulation,with small knotlike protuberance.Width of intercostal zone over 270?m,the cells are irrigularly in shape.Anticlinal cell wall intensely curve,cutinized.Stomatal apparatus Bennettitalean,irregularly in arrangement,at a concentration of 25-35/mm2.Stomatal oval,about?40-50??m ×?20-28??m in size.Stomatal aperture variably oriented,about 16-21?m long.Guard cells oval or semicircle,19.2?m×12.5 ?m in size.Subsidiary cells width 2times of guard cells,square-circle,outer margin cutinized.Suface of external flatter,cavitys and pits also present.Midrib cells are rectangula.The epidermal cells are 20-60?m long and 20?m wide.The epidermal cells have papillae,the anticlinal walls slightly sinuous.The outer surface is slightly smoother than that of the abaxial surface,but with irregular pits.Disscusion: In China,foliage with exactly the same external morphology as our specimen,i.e.,N.angustiflia Wang of Middle Jurassic from the Mentougou Formationin Hebei,N.beyrichii of Lower Cretaceous from Qingshilazi Formation in Hebei,N.vittata?Brongn.?Florin of Middle Jurassic from the Xiangxi Formation in Hubei,N.aniana Li,Ye et Zhou of Lower Cretaceous from Jilin,N.bolei Barale,Thevenard et Zhou of Middle Jurassic from the Yima Formation in Henan,and N.Wei et Sun of Lower Cretaceous from Changcai Formation in Jilin,as well as N.binggouensis Na,Sun,Dilcher et Wang of Lower Cretaceous from Binggou Formation in Liaoning.But widest part of the N.angustiflia leaf is near the top and suddenly shrink to the apex.Stomatal more dense?50-60/mm2?and perpendicular to the veins.The veins of N.vittata and N.beyrichii are sparse?10-20 per cm?.N.vittata differ from the new species by dense stomatal and fine vertical ridge on the rhachis.The leaf of N.aniana Li,Ye et Zhou suddenly shrink to the base.The veins of N.bolei Barale,Thevenard et Zhou forked once.The width of nonstomatal and stomatal zones of N.Wei et Sun are basically same.N.Wei et Sun and N.binggouensis Na,Sun,Dilcher et Wang have more dense stomatal and regular epidermal cells.On a global scale,the current material is somewhat similar to many species,such as N.haidingeri?Stur ex Krasser?nov.comb in Austria,N.oishii T.Yamada,J.Legrand et H.Nishida in Japan,N.corrugata Ray,Rothwell,and Stockey in Canada.However,The leaf lamina of N.haidingeri?Stur ex Krasser?nov.comb is amphistomatic.The lamina of N.oishii T.Yamada,with larger stomatal.The midrib of N.corrugata Ray is very wide.Based on the morphology and epidermal tectonic characteristics,the species is undoubtedly assigned to genus Nilssoniopteris.The new species is established on the basis of the following features: strap-shaped leaf,fine veins,smaller stomata density,large stomatal,short aperture,so named as Nilssoniopteris changcaiensis Sun et Li?sp.nov.?.Locality & Horizon: Chundong coal mine,Lower Cretaceous Changcai Formation.