Study Of Ningxiaites From The Sun-Jiagou Formation In The NW Ordos Basin And Its Palaeoecological Implications

The study of fossil woods is an integral part of Palaeobotany.Specimens with pith,primary xylem,and bark,with associated branches are crucial in fossil plant systematics and phylogenetics.Remains and traces of arthropods and fungi preserved in fossil woods are one of the most direct evidence of the ecosystem during the geological history.Forty-five fossil stems have been collected from the upper Permian Sunjiagou Formation of Shitanjing,northwestern Ordos Basin,Ningxia Hui Autonomous Region,North China.This desertation is focused on an enigmatic coniferous plant Ningxiaites Feng.Based on the anatomy of stems,including the pith,primary xylem,secondary xylem,and bark,and associated leaves,seven species of Ningxiaites have been described.Six new species,including N.shitanjingensis Wei et Feng,N.boligouensis Wei sp.nov.,N.szei Wei sp.nov.,N.circlea Wei sp.nov.,N.changii Wei sp.nov.,and N.sinensis Wei sp.nov.are established.It provides additional knowledge on the composition,diversity,and disparity of conifers in North China during the latest Permian.In addition,anatomical features of the branch of Ningxiaites specialis Feng are described for the first time.They are different from those of the stem.The anatomy and emission pattern of leaf traces of N.shitanjingensis,N.szei sp.nov.,and N.specialis are studied in detail.The leaf traces in each cluster can be divided into upper,middle and lower portions,and initiate at the pith periphery and cross the wood horizontally.The upper leaf trace increases its diameter during the first growth increment and then diminishes completely,which indicates leaf abscission at the end of the first year.The middle trace immediately bifurcates once or twice to form two or three vascular bundles.The lower trace persists as a single bundle during its entire length.The intricate leaf trace dynamics indicates this fossil plant had a novel evolutionary habit by promoting photosynthetic capability in matured plant.Secondary phloem N.sinensis sp.nov.and N.specialis consist of sieve cells and ray parenchyma.Each associated leave of N.sinensis sp.nov.and N.specialis contains a single vascular bundle,large numbers of transfusion cells.The mesophyll is composed of palisade and spongy tissues.Haplocheilic stomata present on the adaxial epidermis.The relatively primitive secondary phloem and single-veined leaves indicate that the species Ningxiaites are of a coniferous affinity.Extensive coprolites,borings,and galleries occurred in the pith,xylem,and bark demonstrate diverse arthropod-plant interactions in the community.According to the size-ranges,morphologies,and contents of the coprolites,it is proposed that at least three types of arthropods,including beetles,oribatid mites,and millipedes,are the major culprits.Furthermore,fungal hyphae are present in pith parenchyma,tracheids of xylems,and ray cells.Considering the occurrence of white-pocket rot structures in the wood of Ningxiaites shitanjingensis,these fungi are hypothesized to be members of basidiomycetes,playing roles of decomposers.In summary,the seven species of Ningxiaites reveal conifers were one of the major components of the late Permian Cathaysia Flora in North China.The diversity of conifers during this time interval was underestimated only according to compressions.The interactions among plants,arthropods,and fungi suggest an extremely complex terrestrial ecosystem and nutrition network in the late Permian.