Morphology And Ultrastructure Of The Late Palaeozoic Dispersed Megaspores From South And North China Blocks

Purpose of the present thesis is to display the morphological and ultrastructural features of the late Palaeozoic megaspores from North and South China blocks by using standard palynological maceration methods and the latest microscopic imaging techniques.147 rock samples in total were collected from the Early-Middle Devonian Longhuashan section in Zhanyi County,Yunnan Province and the Pennsylvanian-Lopingian Palougou section in Baode County,Shanxi Province.Four dispersed megaspore species of four genera were obtained from the Givetian Shangshuanghe Formation at the Longhuashan section.For the Pennsylvanian to Guadalupian strata of the Palougou section,eight megaspore species of seven genera were recovered.Two endemic megaspores were acquired from the Givetian deposits in the Longhuashan section.Amongst,Cereusisporites mirabilis Lu et Ouyang,1978 is decorated with long fused biform processes.Each process of C.mirabilis has a candle-flame-like apex.The exine of C.mirabilis is composed of four regions:the innermost region is a thin basal lamina with a high density of sporopollenin units;the second region is a solid region with few tiny voids;the third region is an irregular spongy region with different shapes of voids;the outer region is a solid region with some processes.Besides,a large cavity usually occurs in the inner part of each biform process.Longhuashanispora reticuloides Lu et Ouyang,1978 is ornamented by biform processes.Each process of L.reticuloides has a swollen base and a mucronate apex.The exine of L.reticuloides is composed outwardly by the innermost multilamellate interradial zones,the basal lamina,the spongy region and the solid region.Moreover,each biform process of L.reticuloides usually has a relevant large cavity inside the exine.Other two cosmopolitan megaspores were macerated from the Shangshuanghe Formation.One is the Ocksisporites maclarenii Chaloner,1959 which is covered by biform sculptures.Each process has a long spine with a swollen base.The swollen base of each process can be fused with others,which forms sheath-like ornamentation capping the distal surface.The proximal exine of O.maclarenii consists of the basal lamina and the solid region,while the distal exine is made up of the basal lamina and the outer spongy region.The other one is Hystricosporites grandis Owens,1971 which is azonate and ornamented by anchor-shaped processes on the equator and distal surface.The solid region dominates the exine of H.grandis.Four endemic megaspores were recovered from the Pennsylvanian to Guadalupian coal-series strata of the Palougou section.Amongst,Laevigatisporites cf.subhorridus Playford,1986 has short and straight trilete laesurae with outer smooth surface.The exine of L.cf.subhorridus is composed by a single solid layer.Banksisporites cf.sinuosus(Dettmann)Glasspool,2003 has laevigate surface and sinuous trilete laesurae which extend to the margin of the equator.The exine of B.cf.sinuosus also consists of a single solid region.Biharisporites grosstriletus Liu et al.,2011 has membranous trilete laesurae extending to the equator.The surface of B.grosstriletus is covered by firmly and evenly spaced coni which are usually fused at their bases to form rugulae.The exine of B.grosstriletus can be devided into the basal lamina and the solid region with few tiny voids.Telocystes sinica Pierart,1961a is decorated by the robust and dense filamentous processes.The exine of T.sinica comprises the discontinuous basal lamina,the spongy region and the solid region,outwardly.In addition,Other four widely distributed megaspores had been collected from the same section.Amongst,Laevigatisporites reinschii Ibrahim,1932 shows the dehiscent trilete laesurae and sparse coni on the proximal surface.The exine of L.reinschii consists of the solid region with compact sporopollenin units.Sublagenicula nuda(Nowak et Zerndt)Dybova-Jachowicz et al.,1979 has robust and elevated trilete laesurae which elevate to form a prominent subgula.The surface of the gula sometimes is covered with dense spherical starch grains.The exine of S.nuda is composed of the basal lamina,the spongy region and the solid region.Bentzisporites margaritatus Bhardwaj,1 957 shows special three papillae on interradial surfaces and the radially ranged spines on the zona.The exine of B.margaritatus comprises the basal lamina,the spongy region,and the solid region from the inside out.Spencerisporites radiatus(Ibrahim)Winslow,1959 is bizonate and is ornamented by three small radially ranged striates on interradial surfaces and a large one on the distal surface.The exine of S.radiatus consists of the basal lamina and the solid region.Based on the comprehensive study about the morphology and ultrastructure of the present dispersed megaspores,we suggest that the evolution trendy of the morphology of megaspore is similar to that of the microspore.The trendy of the evolution of the morphology and wall structure of spores is mainly from simple to sophisticated,which may indicate that the terrestrial plants should form special reproductive organs in various shapes to adapt the intricate land environment.Comparing the characters of the exine ultrastructure of fossil megaspores with the layered pattern of the modern pollen wall,we think that the discordance and complexity of the wall ultrastructure of the present fossil megaspores shows a huge structural difference of exine exists between the late Palaeozoic megaspores and the modern pollen.However,the ultrastructure of the megaspore plays a crucial role in the comparison and discussion with the megaspore species of the same genus.Comparing with in situ megaspores from their parent plants,the regional plant community could be recovered or reconstructed.The fossil plants preserved in the coeval or neighboring horizons in the Longhuashan section mainly include Drepanophycus spinaeformis Goppert,1852,Eocladoxylon minutum(Halle)Koidzumi,1 943 and Minarodendron cathaysiense(Schweitzer et Cai)Li,1 990.By comparing and analyzing the previous records of those fossil plants,we deduce that the parent plant of the Middle Devonian dispersed megaspore Longhuashanispora reticuloides from the Longhuashan section shows the closest affinity with the fossil homosporous plant Leclercqia complexa by the similar spinous-verrucate biform processes and multilamellate interradial zones under the labra of in situ spores of L.complexa.However,the affinities of other three megaspore species from the Longhuashan section remain unclear.Thus,we speculate that their parent plants may belong to herbaceous lycopsids which are hard to be preserved as fossils.By comparisons with the reported in situ megaspores from the Palougou section,we conclude that the Pennsylvanian to Lopingian palynoflora in North China is mainly composed of arboreal,sub-arboreal and herbaceous lycopsids.Amongst,Laevigatisporites reinschii and Sublagenicula nuda are similar to in situ megaspores from fossil strobili of Sigillaria.The parent plants of L.reinschii may belong to the species which bear Mazocarpon bensonii cones,while the mother plants of S.nuda are very likely to form the strobili of Nudasporestrobus ningxicus.Surprisingly,some megaspores of S.nuda from the lower part of the Lower Shihhotse Formation in the Palougou section have dense outer coatings of conspicuous granular starch grains.By analogy to elaiosomes on seeds of some zoochorous plants today,we come up with that these starches may serve as food rewards to attract animals,possibly terrestrial arthropods or gastropods,to realize the dispersal of these megaspores.This study offers a rare glimpse into early stage of plant-animal co-evolution in Permian swamp-forest ecosystems.The parent plant of Spencerisporites radiatus is most likely to be the sub-arboreal lycopsid Spencerites havlenae.The mother plant of Telocystes sinica may be some kind of the Lepidocarpon which bears the Porostrobus cones.The parent plants of the Banksisporites cf.sinuosus share some similar features with the Pleuromeia which generates the strobili of Cylostrobus sydneyensis.The plants which produce the megaspores of Bentzisporites margaritatus show some affinities to the Lepidodendrid plants which form the strobili of Lepidostrobus goldenburgii.The parent plant of the Biharisporites grosstriletus shows some characters of Archaeopteris.Although we found out that most Pennsylvanian to Guadalupian megaspores obtained from the Palougou section have some affinities with the sub-arboreal or herbaceous lycopsids,the investigation of the plant fossils in the equivalent horizons suggests that about 45%of the total plant community reconstructed from the Palougou section is dominated by arboreal and woody Filicophytina and Pteridosperm,only with rare occurrence of Lepidondendrales.However,sub-arboreal or herbaceous lycopsids have not been reported from the same Palougou section.These prominent biases further demonstrate that a comprehensive reconstruction of the plant community in geological time should be based on a joint study of palaeobotany and palynology.The palynological evidences of Middle Devonian dispersed megaspores Hystricosporites grandis,Longhuashanispora reticuloides and Ocksisporites maclarenii from the Longhuashan section demonstrate that the existence of the evolution of heterospory in the same epoch.Moreover,megaspores cannot undergo long-distance dispersal from their parent plants and are also unable to cross the vast stretches of the open marine.Thus,the palaeogeographic distribution of the cosmopolitan megaspores can provide palynological evidences for discussing the existence of the land connection among different plates or blocks.Furthermore,based on the comprehensive analysis of the sediment structures and the animal and plant fossils collected from the co-eval and neighboring beds which bear the fossil megaspores,we propose that all the late Palaeozoic megaspores collected from the strata in the Shangshuanghe Formation at the Longhuashan section and the coal layers at the Palougou section were buried in the paralic faces.