Study On Sigillarian Strobili From The Asselian Wuda Tuff Flora,Inner Mongolia

Sigillaria Brongniart is a fossil genus of arborescent lycopsids.As one of the dominant components in the Carboniferous-Permian Euramerican swamps,Sigillaria possesses abundant fossil records and there are lots of comprehensive researches on its reproductive organs.However,its fossil records in Cathaysian floras,especially reproductive organs,are relatively rare.This research systematically investigates the well preserved specimens of sigillarian strobili in the autochthonous peat-forming forest(Wuda Tuff Flora,"vegetational Pompeii")from the Asselian Taiyuan Formation of Wuda Coalfield,Inner Mongolia.The current research describes a new genus and species of bisporangiate strobilus named Bisigillariostrobus prolificus gen.et sp.nov.This type of bisporangiate strobilus is cylindrical with a slender peduncle.Sporophylls are arranged in helix,with a horizontal pedicel as the proximal part,an upturned lamina as the distal part,and an abaxial heel in the transitional part between the proximal and distal parts of sporophyll.Sporangia are borne on adaxial surface of the pedicel.Megasporangia are located in the basal portion of the strobili and microsporangia in the apical portion.This is the first record of bisexual strobili with evidence of organic connection to Sigillaria cf.S.ichthyolepis(Presl)Corda,the upper-canopy tree of peat-forming forest.In addition,there are two other slender arborescent lycopsids,S.wudensis D'Antonio et al.and S.pfefferkornii D'Antonio et al.in Wuda Tuff Flora.Their reproductive organs are yet not certain.It is possibile that these three species of sigillarian stems are likely to share the same type of reproductive organ,but more and better preserved strobili are needed to be examined in this swamp forest.Sigillaria so far known only produces monosporangiate strobili.The new bisporangiate strobili indicate a higher diversity and more complexity on the reproductive strategy of sigillarians than previously understood.Based on previous studies,this research discusses the systematic and reproductive characteristics of sigillarian strobili.Bisigillariostrobus prolificus gen.et sp.nov.presents many primitive features and tends to be r-selection strategy.These basic structures are vital for Sigillaria cf.S.ichthyolepis to occupy an important ecological niche in Wuda Tuff Flora,and provide significant information for further study on the evolution and ecology of sigillarians.