Palaeobiology,palaeoecology And Stratigraphic Correlation Of Brachiopods From The Lower Cambrian Across South China,laurentia,and Baltica

The Cambrian Explosion represents the geologically abrupt appearance and diversification of nearly all major metazoan phyla,which provides an excellent window for exploring the early origination and evolution of metazoans.Brachiopods first appeared during early Cambrian(Stage 2),and rapidly became one of the most important components of Cambrian and Paleozoic Evolutionary Fauna.The excellent fossil records of brachiopods highlight their diversity,abundance and long evolutionary history,making them one of the most important fossils in the fossil record.The research of Cambrian brachiopods firstly started from Laurentia and Baltica continents.Many type genera and type species of Cambrian brachiopods were derived and named from these areas.In this context,it becomes necessary to conduct a global comparative study across these continents in order to better understand the early radiation and evolution of brachiopods during the Cambrian Explosion.Based on recent extensive research of Cambrian brachiopods from South China,this dissertation focused on the comparative study of the contemporaneous material from the Laurentia and Baltica continents in terms of brachiopods’ faunal composition,preservation type and radiation pattern,in order to improve our understanding of the taxonomy,anatomy,morphology,ecology,early evolution and radiation of Cambrian brachiopods.The poorly studied brachiopods species from early Cambrian Chengjiang and Guanshan Lagerst?tten were systematically analyzed.The taxonomic and systematic position of Heliomedusa orienta(the most abundant brachiopod species from Chengjiang Lagerst?tte)remains unsolved.New material reveals their shell structure,ornamentation,and shell penetrating setae,which indicate that Heliomedusa orienta is a stem group brachiopod closely related to Mickwitziidae.A large number of exceptionally preserved brachiopods allows for a comprehensive study of the complexity of the Cambrian benthic ecosystem.Apart from parasitism and mimicry,possible borings by annelids were found on the shells of brachiopods from Chengjiang Lagerst?tten,providing more information on the diversity and complexity of the Cambrian benthic ecosystem.Laurentia brachiopods fauna from the Cambrian Latham Shale(Series 2,Stage 4)and Cadiz Formation(Miaolingian,Wuliuan),California were systematically investigated.This fauna includes both linguliform and rhynchonelliform brachiopods—Hadrotreta primaea,Paterina prospectensis,Dictyonina pannula,Mickwitzia occidens,Nisusia fulleri and Wimanella highlandensis,together with olenellid trilobites and hyolithids.The fauna differs from other Cambrian Lagerst?tten(notably Cambrian Series 2 Chengjiang and Guanshan Lagerst?tten,eastern Yunnan)in that brachiopod shell valves in many cases are still preserved with their original mineralization.In addition,both Mickwitzia occidens and Paterina prospectensis preserved soft-bodied setae,representing the first report of soft tissue preservation from this fauna.The fauna also represents the earliest onset of the transition from the Cambrian Evolutionary Fauna to the Paleozoic Evolutionary Fauna.Baltica brachiopods from early Cambrian Mickwitzia Sandstone and Lingulid Sandstone,V?sterg?tland,Sweden were comprehensively studied.Mickwitzia monilifera preserved their phosphatic shell exhibiting detailed shell structure and ornamentation.The combination of the three-dimensionally preserved Mickwitzia monilifera and soft tissue preservation from Heliomedusa orienta allows us to better understand these enigmatic stem group brachiopods.The Lingulid Sandstone yielded at least two species of lingulid brachiopods,belonging to Obolidae and Botsfordiidae,repectively.In addition,the lower Cambrian strata in the Bothnian Sea,Sweden not only yielded abundant small carbonaceous fossils including ecdysozoan and lophotrochozoan elements,but also an enigmatic fossil taxon Wimanigma soderarmensis.Detailed research on its shell morphology,composition,structure and ornamentation indicates it is a stem group brachiopod closely related to Mickwitzia.Comparison of early Cambrian brachiopods from South China,Laurentia and Baltica were conducted in terms of the preservation type,faunal composition,and radiation pattern.Stem group brachiopod Mickwitzia were yielded from these continents,a stratigraphic correlation based on trilobite biozonation suggests that the first appearance datum of mickwitziids in different continents may be diachronous.A global-scale biogeographical analysis of early and middle Cambrian brachiopod distribution was conducted based on cluster analyses for two time slices(Stages 4 and Wuliuan Stage),indicating a transition from Botsfordiidae(Botsfordia,Schizopholis)to Acrothelidae(Eothele,Acrothele).Moreover,brachiopods from these continents exhibit differences in the preservation type both on the shell and soft tissue.Baltica brachiopods all preserved phosphatic shells,even the soft-bodied setae were mineralized and preserved as calcium phosphate.Laurentia brachiopods present both phosphatization and pyritization(typical Chengjiang preservation).The unusual preservation of Nisusia fulleri provides important clues to the ancestral composition of the brachiopod shell.Lingulid(Order Lingulida)brachiopods are diverse and abundant during the early Palaeozoic,but decrease in diversity over time,with only a few genera of linguloids and discinoids present in modern marine ecosystems.The dynamics that drove this decline remain uncertain and it has not been determined if there is an associated impact on morphological and ecological diversity.Here we apply geometric morphometrics to reconstruct global morphospace occupation for lingulid brachiopods through the Phanerozoic,with results showing that almost all of the total morphospace was occupied by the Early Ordovician.At this time of peak diversity,linguloids with sub-rectangular shell shape possessed most of the evolutionary features necessary for an infaunal lifestyle,as evidenced by the rearrangement of mantle canals and reduction of the pseudointerarea.The end Ordovician mass extinction has a differential effect on linguloids,disproportionally wiping out those forms with a rounded shell shape,whilst forms with sub-rectangular shells survived both the end Ordovician mass extinction and the Permian-Triassic mass extinction,leaving a fauna predominantly composed of infaunal forms.For discinoids,both morphospace occupation and life strategies(epi-benthic lifestyles)remain consistent through the Phanerozoic.Morphospace occupation over time for Lingulids,when considered in light of anatomical,ecological and genomic analyses,suggests the limited morphological and ecological diversity of modern lingulid brachiopods reflects contingent events rather than evolutionary limitations.