Taxonomic Identification And Paleogeographic Migration Of The Late Miocene Anacardiaceae From Eastern Zhejiang And Comparative Study Of Monsoon Intensity

Plants play the role of producers in nature and are highly climate-dependent and environmentally sensitive to their growing environment.Understanding ancient plants provides an indirect understanding of the paleoclimate,paleoecology and paleogeography that correspond to them.The Shengxian Formation of the Late Miocene of eastern Zhejiang contains species-rich plant fossils with a long history of research and great research potential.Among them,there is a temporary gap in the study of Choerospondias and Rhus.Choerospondias(Anacardiaceae),characterized by radially arranged germination pores near the top,is a monotypic genus mainly distributed in subtropical and tropical eastern Asia,while fossil records indicate a wide distribution throughout Eurasia during the Cenozoic.There is no report of the fossil record in the late Miocene Shengxian Formation.In this paper,Micro-CT and epoxy resin embedding method were used to identify the endocarp of Choerospondias preserved in detail,and establish a new species,Choerospondias tiantaiensis sp.nov.Meanwhile,the associated compressed leaves were studied using traditional leaf macroscopic contrast and leaf epidermis microscopic and identified as a new species,Choerospondias mioaxillaris sp.nov.According to the Cenozoic fossil record and climatic fluctuations,we believe that Choerospondias may originate in the early Eocene Europe and spread to Asia along the coasts and island chains of the Tethys and Paratethys Oceans.The distribution position of the fossils in the current study is consistent with the northern boundary of the distribution of living Choerospondias plants in eastern China,suggesting that the distribution pattern of this genus in China formed no late than the late Miocene.The genus Rhus is the largest and most widespread genus in the Anacardiaceae,mainly in subtropical and warm temperate regions.The genus Rhus is only reported from Zhejiang Shengxian Formation.In this study,we found the leaf fossils of the Rhus in Shengxian Formation.According to the characteristics of leaf margin serrations,three veins of free branches,and combined with the fine structure of cuticle,3 leaf fossils were identified as the new species,Rhus miochinensis sp.nov.Molecular phylogenetic evidence and the fossil record suggest that the genus Rhus originated in western North America during the Early Eocene,spread to Asia via the Bering Land Bridge(BLB)and the North Atlantic Land Bridge(NALB)during the early Neogene,and distributed intermittently in Asia and North America during the Middle Eocene.Fossil evidence suggests that the fossil distribution of the genus Rhus is more widespread than its modern distribution.It is possible that the special topography and suitable climate in eastern Asia are conducive to the survival of the genus Rhus due to the contraction of its habitat as a result of climate change that occurred in the late Tertiary and Quaternary periods.In this paper,the endemic climate analysis(CAES)and coexistence analysis(CA)of eastern Zhejiang late Miocene reconstruction.The results showed that the late Miocene climate in Tiantai region of Zhejiang was warm and humid and generally similar to the modern climate in this region.The average annual precipitation is higher,which is warmer and wetter than modern times.At the same time,fossil flora sites located at four directions in the eastern monsoon region of China and controlled by the East Asian monsoon were selected,including southwestern(Kaiyuan,Yunnan),southern(Zhangpu,Fujian),southeastern(Tiantai,Zhejiang),and northeastern(Shanwang,Shandong)China.By comparing the climate conditions results of these fossil sites,we discuss the climate conditions of the late Miocene in the monsoon region of China.The results show that,except for Zhangpu(southern China),the other fossil sites were warm in the middle and late Miocene,and the monsoon intensity in the Miocene period was much less lower than that of the present.At the same time,the increased monsoon strength in the eastern Zhejiang Tiantai is also favorable for the survival of Choerospondias and Rhus,providing suitable climatic conditions for their survival and reproduction in the area.