Asplenium From The Early Cretaceous Xishanping Formation In Yanbian Area, Jilin

The early Cretaceous coal-bearing strata overlying on Tuntianying Formation in Yanbian region of eastern Jilin are composed of two sedimentation cycles, and can be divided into two formations, i.e. Xishangping Formation and Changcai Fomation. The lower sedimentary cycle is named as Xishanping Formation, bearing thin coal seams, while the upper one is called Changcai Formation, bearing thick coal beds. The two formations are divided by the sandy conglomerate on the bottom of the Changcai Formation which shows parallel unconformable contact relationships between them. This suit of coal-bearing strata is distributed mainly in Laotougou and Tuntianying of Yanji County; Changcai, Fudong, Nanyang, Tushanzi, Songxiaping and Dajinchang of Helong County in the eastern Jilin. It is an important coal-bearing strata consisting mainly of array sandstone, sandy conglomerate and gray-green conglomerate intercalated with black shale, carbonaceous mudstone and coal beds, yielding abundant fossil plants.Since 1950's, 42 species of 11 genera of ferns have been recorded from the Changcai and Xishanping formations inYanbian region (Yang, 1959; Zhou, et al., 1980; Shang, 1992; Li, 1995, etc.), based on the gross morphology. The present paper deals mainly with the fossil Asplenium found from the Lower Cretaceous Xishanping Formation in Yanbian area.Based on the gross morphology and the fertile organ and spores in situ which plays an important role in identification and phylogeny, three species of Asplenium, i.e. Asplenium changcaium Sun et Liu (sp. nov.), Asplenium tiefanum Deng and Asplenium popovii Samylina and are recognized for the first time. On the sterile fronds, the present new species of Asplenium, Asplenium changcaium Sun et Liu (sp. nov.) is different from the known species of fossil Asplenium by having the specialized oval segments on acroscopic side of pinnule and 2-3 times forking lateral veins. For the fertile fronds, Asplenium changcaium Sun et Liu (sp. nov.) is also distinguishing from the known fossil Asplenium by the small elliptical sori attached longintudinally at the middle part of veins on every segments of the pinnules. With regard to the monolete spores in situ, Asplenium changcaium Sun et Liu (sp. nov.) is characterized by having short polar axies and fabaceous shape (lateral view) which is quite different from the spores in situ of Asplenium tiefanum Deng and A. popovii Samylina.Based upon studies of fossil records of Asplenium and the distribution of fossil and living Asplenium, the place and time of origin and the migration route of Asplenium are discussed preliminarily, concerning on phylogeny, the paleoclimatology and plate tectonic theory. This provides a new basement for the further researches on Asplenium.The lowest horizon of reliable appearance of Asplenium in the world might be the middle part of the early Cretaceous (i.e. Hauterivian, Barremian and Aptian) in NE China, Siberian and central Honshu of Japan. During that time, the Northeast Asia was in the warm and humid climate zone and might be the original places of Asplenium in the middle of early Cretaceous. Later on, Asplenium dispersed widely on the Eurasian. During the late Cretaceous, Asplenium was already living on the middle Europe, accompanied by the northward migration of warm and humid climate zone. At the same time, the Asplenium occupied the high altitude region of North American (warm and humid climate in the Cretaceous and early Tertiary) via Bering Land Bridge. In the early late Cretaceous, Asplenium might spread to the South Hemisphere due to global climate cooling and the extension of warm and humid climate zone. With the radiation and dispersal, Asplenium diversified, adaped to different environmentsits, and gradually distributed worldwide.Systemic comparision between the fossil Asplenium changcaium, A. popovii and the living Asplenium is done in the aspects of shape and size of spores in situ and the gross morphology of leaves.For the shape and size of spores in situ, A. changcaium is resembled to the living Ser. Trichomanoidea of Sect. Asplenium, the length of polar axis changes little, while the equatorial axis varied greatly with the maturity of fossil and living ones. The spores of A. popovii is slightly bigger than those of the living Asplenium and close to those of the living Sect. Holophyllum and Ser. Falcata of Sect. Asplenium in size. On the gross morphology of fronds, A. changcaium is similar to the living Ser. Falcata and Ser. Variantia of Sect. Asplenium, while the only analogue of A. popovii is Asplenium castaneoviride of Ser. Trichomanoidea. This might indicate that the living Sect. Asplenium is close related to A. changcaium and A. popovii.