Research On Four Fossil Plants From The Pliocene In Baoshan Of Yunnan And Analysis Of Palaeoenvironment

The cuticular microstructures of four angiosperm fossil plants from the Pliocene Mangbang Formation and the Yangyi Formation in Baoshan, Yunnan Province were studied in this paper. The four fossil plants are Quercus presenescens Z. K. Zhou, Quercus cf. wulongensis Li et Guo, Mallotus cf. hookerianus (Seem.) Muell. Arg. and Osmanthus cf. marginatus (Champ. ex Benth.) Hemsl. The use of scanning electron microscope (SEM), transmission electron microscope (TEM) and light microscope (LM) helps the classification of fossil plants.The fossils of Quercus presenescens and Quercus cf. wulongensis from the Yangyi Formation are different from their nearest living species in having no or less trichomes, which implies that the common existence of trichomes in living species of Quercus sect. Heterobalanus is perhaps the result of an adaptation to the climatic change, or may be due to the evolution of trichome in Quercus Subgenus. By comparing the fossils of Mallotus cf. hookerianus and Osmanthus cf. marginatus from the Mangbang Formation with their nearest living species, it can be find that the distribution range of Mallotus hookerianus and Osmanthus marginatus distinctly moved towards low latitudes, which implies that the climate in the Pliocene was warmer than that of today in Tengchong, Yunnan.The palaeoclimate in the Pliocene of Yangyi, Yunnan was reconstructed quantitatively by "Climate analysis of endemic species" method making use of the climatic parameter of the distribution area of Q. senescens and Q. pannosa. The mean annual temperature that Q. pannosa and Q. presenescens could live together was -3～16.9℃, and the mean annual rainfall was 407.6～1211.7mm. These climatic indices showed that the two fossil plants had distributed in a cool and sub-humid environment just like the cool-temperature zone or mountain vegetation zone in the Pliocene. By contrast with previous research, the region of Yangyi in the Pliocene had presented the climatic pattern of three-dimensional mountain climate.Based on the Nearest Living Relative Method (NLR), the paleoaltitude are estimated by the found fossils of Quercus sect. Heterobalanus from the Yangyi Formation, Yunnan Province. The result indicates that the Yangyi fossil set has a palaeoaltitude range of 2500～3500m.