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Earth Science Frontiers, Vol. 17, Special Issue, Aug. 2010 ISSN 1005-2321 secta). Australian Journal of Zoology and Supple- ment, 1956, 4: 165-238. Menon F., Heads S.W., Martil D.M. New Palaeon- tinidae (Insecta: Cicadomorpha) from the Lower Cretaceous Crato Formation of Brazil. Cretaceous Research, 2005, 26: 837-844. Wang B., Zhang H.C., Fang Y. Gansucossus, a replace- ment name for Yumenia Hong, 1982 (Insecta, Hemiptera, Palaeontinidae), with description of a new genus. Zootaxa, 2006a, 1268: 59-68. Wang B., Zhang H.C. , Fang Y., et al. A new genus and species of Palaeontinidae (Insecta: Hemiptera) from the Middle Jurassic of Daohougou. Annales Zoologici (Warszawa), 2006b, 56(4): 757-762. Wang B., Zhang H.C., Fang Y. Middle Jurassic Palaeo- ntinidae (Insecta, Hemiptera) from Daohugou of China. Alavesia, 2007, 1: 89-104. Wang Y., Ren D., Shih C. K. New discovery of palaeo- ntinid fossils from the Middle Jurassic in Dao- hugou, Inner Mongolia (Homoptera, Palaeon- tinidae). Science in China Series D: Earth Sciences, 2007a, 50(4): 481-486. 160 Wang Y., Ren D., Shih C. K. Discovery of Middle Jurassic palaeontinids from Inner Mongolia, China (Homoptera: Palaeontinidae). Progress in Natural Science, 2007b, 17(1): 112-116. Wang Y., Ren D. Two new genera of fossil palaeontinids from the Middle Jurassic in Daohugou, Inner Mongolia, China (Hemiptera, Palaeon- tinidae). Zootaxa, 2007, 1390: 41-49. Wang Y., Ren D. New fossil palaeontinids from the Middle Jurassic of Daohugou, Inner Mongolia, China (Insecta, Hemiptera). Acta Geologica Sini- ca: English Edition, 2009, 83(1): 33-38. Xu Z.Z. Mesozoic volcanism and volcanogenic iron-ore deposits in eastern China. Geological Society of America Special Paper, 1990, 237: 46. Zherikhin V.V., Kalugina N. S. Landscapes and com- munities. In: Rasnitsyn A.P. (ed). Yurskie con- tinental ‘nye biotsenozy Yuzhnoy Sibiri I sopredel’ nykh territoriy (Jurassic Non-marine Biocoenoses of South Siberia and adjacent territories). Trudy Paleontol. Inst. Akad. Nauk SSSR 213. Moscow: Nauka, 1985: 137-183 (in Russian).
Earth Science Frontiers, Vol. 17, Special Issue, Aug. 2010 ISSN 1005-2321 A Jurassic Angiosperm and Its Implications for Seed Plant Systematics Xin Wang Nanjing Institute of Geology and Palaeontology, Nanjing 210008, China (E-mail: brandonhuijunwang@gmail.com ) Among the current ecosystem seed plants are the structure defining group. Among seed plants angiosperms are the dominating ones. However, the origin of such an important group and its phylogenetic relation- ships with other peers have been mysterious for long time. The current widely accepted angiosperm fossils are restricted to the Early Cretaceous and younger strata while their peer gymnosperms are dated back to the Devonian. How did the plants evolve the angiospermy? From which group did angiosperms arise? How do the earliest angiosperms look? These have been lasting and vexing problems for botanists. With more and more discoveries of early angiosperms, the general pattern of early angiosperm evolution is now emerging. In this talk I will focus on one of the recent discoveries: Xingxueanthus sinensis, which potentially undermines the foundation for the traditional perspective on angiosperms. The fossil was found in the stratum of the Haifanggou Formation (160 Ma, Middle Jurassic) in western Liaoning, China. The fossil is a catkin-like female inflorescence, about 23 mm long, with more than 20 flowers. Bracts are helically arranged alone the inflorescence axis, each subtending a pistil in its axil. The pistil is composed of a sub-spherical ovary and an apical style. There is a vertical column bearing numerous ovules in the ovary. This kind of ovule arrangement and enclosure are hard to be distinguished from free central placentation in living angiosperms. Apparently, the occurrence of Xingxueanthus in the Jurassic contradicts the current doctrines on origin and evolution of angiosperms. However, this new fossil evidence and evidence from other fields converge to the same conclusion. First, the developmental genetics of model plant, Arabidopsis, indicates that carpel and placenta are controlled by different sets of genes, suggesting that they are two separate organs, namely, the carpel is, like other lateral floral parts, equivalent to a leaf while the placenta is equivalent to a shoot bearing ovules. Second, floral morphology, development and anatomy indicate that many ovules in Caryophyllales are borne on the periphery of the floral axis, subtended and enclosed by carpels from bottom up, and that sometimes the ovules are completely independent of the carpels. These phenomena suggest that early ovules in angiosperms may be borne on shoot and independent of the carpels. Third, vascular anatomy proves that the distribution of vascular bundles, which is thought more conservative, may provide implications on the history of the organs. The comparative floral anatomy indicates that carpel and ovules have independent vascular supplies in flowers, implying that ovule/placenta is independent from carpel in early angiosperms. Fourth, the evolutionary trend in Cactaceae suggests that the highly specialized inferior ovary in Cactaceae, in which carpels have little to do with ovules but covering the latters, is derived from ovary with protruding basal placentation, implying that earlier ovules are borne on a shoot, and carpels are foliar accessories covering the ovules. Fifth, outgroup comparison based on molecular systematics confirms the conclusion in the above implications. Protulaccaceae, the closest sister of Cactaceae, has the ovules clustered on a basal protrusion on the ovary bottom, very similar to the above inferred primitive ovary in Cactaceae. All these evidences concurringly suggest that carpels in angiosperms are foliar accessories, and placentae are ovule-bearing shoots independent of carpels. This conclusion based on comparative morphology, development and anatomy of living angiosperms, which are from the same time level and thus bears only weak historic hints, is further confirmed by the information residing in Xingxueanthus, a fossil angiosperm from the Middle Jurassic. Following this guidance, searching for archetype angiosperms suggests that Cordaitales or its close relatives in the Palaeozoic are very informative worthy of further studying because their ovules and megasporophylls are borne on the secondary shoots in axils of bracts. Interestingly, this hypothesis is supported by cladistics, and when Caryophyllales is taken as the representative of angiosperms, the systematics for seed plants becomes well-resolved and stable. Key words: Angiosperms; Jurassic; Systematics; Flowers References: Wang X., Wang S. Xingxueanthus: An enigmatic Jurassic seed plant and its implications for the origin of angiospermy. Acta Geologica Sinica: English Version, 2010, 84(1): 47-55. 161
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