Palms From The Oligocene Of Ningming,Guangxi And Their Biogeographical Implications

Palms are a monophyletic group with a dominantly tropical distribution;however,a general framework of palm evolution is still lacking and the biogeographic history of Arecaceae remains unclear.Palms are one of the most characteristic and ecologically important components of tropical rain forests worldwide.The stability of tropical rain forest ecosystem is related to the biodiversity of palms.So,understanding how the biodiversity of palms is shaped through time is fundamental in tracking rainforest evolution.The aims of this thesis are to seek evolutionary explanations for the geographical distribution of 6 palm lineages and the species diversity patterns at global and regional levels.This thesis describes fossil leaves,fruits,pollen of palms from the Oligocene Ningming Formation,outcropping in the Ningming basin,Guangxi.On the basis of leaf compressions with cuticular structure,eight new species are described as Calamus ningmingensis sp.nov.,Chuniophoenix slenderifolia sp.nov.,Livistona roundifolia sp.nov.,Livistona latipetiolus sp.nov.,Sabal guangxiensis sp.nov.,Sabal longiaxis sp.nov.,Trachycarpus formosa sp.nov.and Trachycarpustorchensis sp.nov.The fruit from the same layer is most similar to that of the extant Arenga and is described as Arenga sp.Besides,Arecaceae pollen are also found in the Ningming Formation and are described in four genera and 5 species:Arecipites sp.l,Arecipites sp.2,Dicolpopollis sp.,Monocolpopollenites sp.,Sabalpollenites sp.The fossils demonstrate that Arecaceae has exhibited certain diversity with costapalmate and pinnate species in a low-latitude locality-Ningming since at least the Oligocene,implying that the tropical zone of South China may represent one of the centres for early diversification of the family.Biogeographical evolutions of the five genera(Calamus,Chuniophoenix,Livistona,Sabal and Trachycarpus)are detailed analyzed based on the fossil record and the paleogeographic software ODSN.This thesis infers that(1)Calamus had a wide distribution across southern China during the Oligocene,ranging from southeastern Taiwan to southwestern Guangxi;(2)The fossil record and plant molecular data indicate that the crown node divergence of Chuniophoenix occurred during the Oligocene within southern China and northern Vietnam regions,resulting from the geographical environment and regional climate;(3)The morphological and anatomical analysis suggested that Livistona species from Ningming differ from all previously reported Livistona fossils from China and are new taxa;(4)The Sabal species from Ningming bear a close resemblance to the extant American species and provide new evidence for the floristic exchange of floras between eastern Asia and North America during the Oligocene;(5)Trachycarpus palms had migrated.to their present distributed regions,which core distribution is now in the Himalayan-Hengduan Mountains;(6)The Arenga fruit is the earliest unequivocal fossil record of this genus and indicates that Arenga has occurred in southern Asia since the Oligocene.The relationship between species diversity of extant palms in China(Y)and four climatic factors of their distributions,including mean annual temperature(x1),mean annual precipitation(x2),growing season precipitation(x3)and precipitation during the three consecutive driest months(x4),were analyzed using two techniques,Statistical Package for the Social Science(SPSS)and Excel.The two methods yield consistent results.The results show that an obvious correlation can be established between Y and x1 with a positive correlationship,a less obvious correlation between Y and x2 with a negative correlationship,and a low correlation between Y and x3 with a positive correlationship.Based on the correlation between Y and the three climatic factors,it indicates that palms prefer to live in warm and humid climate conditions.Because the Oligocene paleoclimate of Ningming is similar to that at present with mean annual temperature slightly higher,it suggests that the species diversity of palms in the Oligocene Ningming flora may be nearly equal to that in the present Ningming flora,with a few more species.Carbon isotope composition of fossil species(Chuniophoenix slenderifolia sp.nov.,Livistona roundifolia sp.nov.,Sabal guangxiensis sp.nov.,Trachycarpus formosa sp.nov.,Trachycarpus torchensis sp.nov.)and their nearest living relatives(NLRs)are also investigated.The water use efficiency of the fossil palms were calculated by the function WUE= Ca*(1-C1/Ca)/1.6.The carbon isotope discrimination of fossil palms is higher than that of their NLRs,whereas water use efficiencies of the fossils is lower than that of their NLRS,which confirm the Oligocene climate of China was more humid and wanner than it is now.Based on the fossil records of palms,the biodiversity of palms in China have been discussed.The fossils indicate the presence of nine palm taxa in China during the Eocene.However,during the Oligocene,palms in China had a higher diversity and included eight lineages:the genera Arecipites,Chuniophoenix,Livistona,Sabal,Trachycarpus and Arenga of the subfamily Coryphoideae,and the genera Calamus and Lepidocaryum of the subfamily Calamoideae.The fossils demonstrate the presence of at least sixteen taxa at the Oligocene of China,with nine new taxa emerging.Based on the paleogeographic distribution,the rich diversity of palms in China during the Oligocene is supposed to be related to a warm paleoclimate existed in southern China.Historical biogeographic analysis suggests that the change of the Miocene climate in China appears to have been the driving force in the loss of modern China palm diversity,which is low compared with other area outside of China.Besides,the distribution pattern of modern China palm is a result of the change of the Miocene climate,which is linked with the climatic pattern that southeastern China characterized by warm,humid climate,and northwestern China characterized by arid climate.