Brachyceran Flies(Diptera)in Mid-cretaceous Burmese Amber:Systematics And Palaeoecology

The Mid-Cretaceous Burmese amber(about 100 Ma)preserves one of the most diverse amber inclusions all over the world,and this biota provides a significant window to the ancient world.The Diptera(true flies)is one of the most diverse and species-abundant orders of Insecta.Brachycera is an important component of Diptera,with very diverse habits.Abundant brachyceran flies are preserved in Burmese amber,and they provide important clues to understanding the early evolution and palaeoecology of this group.Based on a huge collection of Burmese amber kept at the Nanjing Institute of Geology and Palaeontology,Chinese Academy of Sciences and previous studies,some progresses have been achieved in some important brachyceran families and overall features of the brachyceran fauna.Totally 2000 pieces of amber with dipteran flies are recorded from the collection and classified into 42 families or superfamilies,among them,including 600 pieces with brachyceran flies.Based on these brachyceran flies,8 genera and 9 species in 5 families are erected,including:Zhenia xiai Zhang et al.,2016 and Zhenia burmensis sp.nov.in Eremochaetidae;Burmomyia rossi Zhang and Wang,2019 and Cratomyia zhuoi Zhang and Wang,2019 in Zhangsolvidae;Myanmarapsilocephala grimaldii Zhang et al.,201 8 and Irwinimyia spinosa Zhang et al.,2018 in Apsilocephalidae;Mesonemestrius caii Zhang,Zhang and Wang,2017 in Nemestrinidae;2 new genera and species Burminemestrinus qiyani gen.et sp.nov.and Viriosinemestrius mai gen.et sp.nov.in Rhagionemestriidae.Based on the species Jurassinemestrinus euremus(Grimaldi,2016)in Rhagionemestriidae ereceted a new genus Cretinemestrimus gen.nov..The morphological phylogenetic result based on Apioceridae,.Mydidae and relacted Mesozoic fossil records together new materials from Burmese amber,indicates that Protapioceridae might be a junior synonym for Mydidae and the fossil group in Burmese amber should be a stem group of the lineage Apioceridae+ Mydidae.Fossil records of brachyceran flies from major Cretaceous insect localities are summarized,including Lebanese amber,Spanish amber,New Jersey amber,Jehol biota and Crato biota.The brachyceran assemblages reveal that Burmese amber biota is distinctly younger than the Jehol biota.In addition,many endemic families in brachyceran flies indicate that the Burmese amber fauna might be isolated from other continent biotas for a long period before mid-Cretaceous.The fossil records of some brchyceran flies are reviewed in detail,including flower-visiting flies Tabanidae,Nemestrinidae,Bombyliidae,Zhangsolvidae,endoparasitoid Eremochaetidae,and the flower-visiting Kalligrammatids of Neuroptera.The fossil records reveal that some flower-visiting groups had diversified during the mid-Cretaceous,consistent with the rise of angiosperms to widespread floristic dominance,and suggest that the high niche diversity of pollinating insects are present during the Mesozoic.The earliest definite record of endoparasitoid brachyceran flies is described and represents the unexpected morphological specialization of the specialized flies.Asiloidea is among the most predominant group of brachyceran flies in Burmese amber,andacanthophorite spines are present in many female species.This result shows that there might be arid or subarid environment in the tropical Burmese amber rainforest.The detailed photonic structures of wing scales from Jurassic lepidopterans and Cretaceous tarachopterans from Burmese amber are revealed with the application of SEM,TEM,CLSM.The results provide the earliest evidence for structural coloration in fossil lepidopterans and support the hypothesis that fused wing scales and the type 1 bilayer covering are groundplan features of Lepidoptera.To summarize,this dissertation enriches the fossil record of brachyceran flies in mid-Cretaceous Burmese amber,summarizes the fauna of Diptera in Burmese amber,and reveals the palaeoecology in mid-Cretaceous Burmese amber.