Permineralized Cycad Stem From The Late Permian Of Qujing,Yunnan Province And It's Palaeoecological Study

As an ancient phyto-group,the cycads lived on earth since the Late Paleozoic at least and are known as living fossils.Therefore,a detailed study of Late Paleozoic cycads will be crucial to study the origin and evolution of them.Up to now,although the researches on cycads fossils are mainly about impression and compression,showing the external morphological characteristics,few studies have involved the preservation of permineralized fossils with internal anatomical structures of cycads.In this paper,a permineralized cycad stem from the Xuanwei formation of the Late Permian in Qujing,Yunnan province,are studied in details by using the method of cellulose acetate peel technique,establishing a new genus called Shuichengopitys gen.nov.and a new species called Shuichengopitys enhongensis gen.et sp.nov.and enriching our knowledge about the anatomical characteristics and taxonomical diversity of cycads plants of the Late Permian.In addition,the evolutionary and paleoecological implications are discussed.Shuichengopitys enhongensis gen.et sp.nov.which has the typical characteristics of cycads,is a tree-like plant.The most important feature of S.enhongensis is that the rays of the species are dense,high and wide,and leaf traces appear in broad rays,with each containing only one leaf trace.The leaf trace of S.enhongensis has both the axisymmetric(bilaterally symmetric)leaf trace of cycads and the centrosymmetric(radiosymmetric)leaf trace of cordaitopsids,indicating that it may be a transitional type between cycads and cordaitopsids.What's more,a large number of growth interruptions developed in the S.enhongensis suggests that the species may live in an unstable environment with fewer changes in the seasonal climates but with the distinctions of drought and moisture.S.enhongensis contains a large number of borings and coprolites.According to the shapes and distributions of borings and the size,morphology,and inclusions of coprolites,three types of borings and one type of coprolites were identified.Borings are decayed by parasitic or saprophytic beetles and saprophytic Oribatida mites,and coprolites are produced by Oribatida mites.Furthermore,fungal hyphae and spores and a large number of corrosion marks were found in S.enhongensis.Probably,spores belong to the Chytridiomycota or Glomeromycota,hyphae are Zygomycota or Glomeromycota,and the white-rot fungi causing corrosion marks the secondary xylem of stem.The presence of hyphae in the plant cells around the borings in S.enhongensis is the evidence that the beetles use symbiotic fungi to damage the stem.The co-existence of consumers(beetles)and decomposers(fungi)in S.enhongensis is a form of fungi-plant-arthropod interaction and a manifestation of the complexity and diversity of terrestrial ecosystems during the Late Permian.