Fossil Liverworts From The Late Triassic Of Baojishan Basin,gansu Province And Its Geological Significance

Liverworts are considered to be the earliest terrestrial plants,which played an important role in terrestrial ecosystems.They distributed widely in geological time and were the oldest atmospheric CO₂ recorders.Among the living liverworts,except for a few types grow in a cold and drought environment,most of the living genus and species grow in a warm and humid environment.The liverworts are very sensitive to changes in climate and environment because of their special physiological mechanism,which is widely used in indicating the environmental change.Compared with the vascular plant fossils,fossil liverworts are small in shape and neglected easily.Their fossil records are relatively rare and the research of fossil liverworts is not enough.The fossil liverworts which were reported in China were mostly found in Jurassic and Cretaceous strata.The Mesozoic strata in the Baojishan Basin of Baiyin City,Gansu Province,China,were relatively developed,such as the Late Triassic Nanying'er Formation.Abundant plant fossils were preserved in Nanying'er Formation.Fossil liverworts in this paper were collected from the Late Triassic Nanying'er Formation.They were assigned to 6 species belong to 5 genera according to the general morphology and micro characteristics:Marchantites baojishanensis Han et Yan sp.nov.,Ricciopsis sp.,Metzgerites baojishanensis Han et Yan sp.nov.,Hepaticites baojishanensis Han et Yan sp.nov.,Hepaticites sp.,and Thallites sp.The fossil liverworts have preserved many micro characteristics.Marchantites baojishanensis,Ricciopsis sp.were preserved with asexual reproductive organs and Metzgerites baojishanensis was preserved with sexual reproductive organs.The studied mentions supplement and complete the fossil record of the Late Triassic.The richer genera and species represent liverworts were an important part of the Late Triassic flora.According to the growing environment and distribution of the related living species of the fossil liverworts,the paleoclimate of the Late Triassic of Baojishan Basin is humid and warm,and rivers,lakes have existed.It is consistent with the previous conclusions by vascular plant fossils and trace fossils.So the fossil liverworts can be used to reconstruct paleoenvironment.By analyzing the relationship between the paleogeographic distribution of the fossil liverworts and the paleogeographic environment in Mesozoic and Cenozoic,it was found that the liverworts were mainly distributed in the Laurasia.The environmental adaptability of liverworts is gradually strengthening,and gradually forming a situation that is now widely distributing all the world;Combined with the extant liverworts,the evolutionary significance of the genus Marchantites was discussed preliminarily,and it can be inferred that the Marchantiopsida appeared at least in the Late Triassic.