Pecopterids From The Lopingian Xuanwei Formation In Eastern Yunnan Province And Western Guizhou Province

Pecopterids is a general term for a group of ferns with pinnate,pinnules basally attached to pinnate rachises and pinnate veins in the Carboniferous-Permian period,mainly distributed in the Euramerican flora,the Cathaysian flora and the Angaran flora,and is an important part of the Late Paleozoic vegetation.In this paper,we applied the techniques of macrofossil sequential revision carving,acid macerated,SEM and TEM to depth and systematic research pecopterids fossils in the Lopingian Series Xuanwei Formation of the Eastern Yunnan Province and Western Guizhou Province,China.We identified 7 genera and 7 species with reproductive organs and 1 genus and 5 species with missing or poorly preserved reproductive organs.Four types with reproductive organs were newly discovered and studied in this paper for the first time,three new species of Pectinangium xuanweiensis,Qasimia yunnanica and Henanotheca qingyuensis and an undetermined species of Pecopteris(Asterotheca)sp.were established,which enriched the pecopterids composition of the Late Permian in South China.In addition,Danaeites rigida,Zhutheca densata and Szea sinensis were restudied according to the new specimens,some new features were found and some existing features were revised.The types that do not have detailed characters of the reproductive organs were assigned to the genus Pecopteris based on their fern characteristics and five species were identified:Pecpteris arborescens,P.(Asterotheca)crassinervies,P.fuyuanensi,P.marginata,and P.hemitelioides.The systematic taxonomic position of the above pecopterids without detailed characteristics of reproductive organs cannot be determined;while pecopterids with detailed characteristics of reproductive organs are classified in the families Marattiales and Gleicheniaceae,respectively.Synangia of the late Paleozoic marattialeans can be classified into two distinct subgroups based on synangial symmetry: radially symmetrical subgroup and bilaterally symmetrical subgroup.The radial symmetry subgroup includes 19 genera and the bilaterally symmetrical subgroup generally consists of eight genera.In geological history,marattialeans with bilaterally symmetrical synangia were dominant during the post-Paleozoic period and radial symmetry synangia were dominant during the Mesozoic-Cenozoic to present.The gradual dominance of the Marattiales order with bilaterally symmetrical synangia may be explained by its better adaptation to the environment.The distribution center of the Late Paleozoic Marattiales order gradually migration from the European and American flora to the Chinese flora.The Late Paleozoic Gleicheniaceae are represented by the Late Carboniferous Oligocapia and Chansitheca,as well as the Permian Szea and Henanotheca.Among them,the genera Chansitheca,Szea and Henanotheca are only recorded in the Cathaysian flora.They all have sporangia without an indusium,a transverse annulus bearing one row or several rows sclerenchymatous cells.There are four genera and eight species of Late Paleozoic Gleicheniaceae,and two genera(Hicriopteris and Gleichenites)and more than 20 species in the Mesozoic.From the Late Paleozoic to the Mesozoic,the diversity of Gleicheniaceae decreased at the genus level,but its abundance and diversity increased significantly at the species level.This change may be related to the end-Permian mass extinction,when the gleicheniaceous plants experienced a crisis and began to recover and diverge in the Middle Triassic.The present study also shows that pecopterids with detailed characteristics of reproductive organs should be systematically classified according to the characteristics of their reproductive organs,especially in situ spores,and should no longer be referred to as "pecopterids";for pecopterids without detailed characteristics of reproductive organs,it is difficult to systematically classify them according to the characteristics of their fern leaves,and they can still be referred to as "pecopterids",this means that the term "pecopterids" should only include fossil plants of this type with only nutritional fern leaves.