Leaf megafossils of Betula yunnanensis sp. nov. (Betulaceae) from the Mangbang Formation, SW China and its taphonomic implications

Well preserved late Pliocene–early Pleistocene megafossil leaves of Betula yunnanensis Zhi-Cheng Lin et Bai-Nian Sun sp. nov. were collected from the Mangbang Formation in southeastern Tengchong County, West Yunnan Province, China. Species determination was achieved by comparing the leaf architecture, cuticle and fine venation of the newly discovered specimens with thirty-four extant Betula species occurring in China and Japan, and four selected extinct species from China and Poland. Leaf architecture shows that the fossil species are most similar to the species of section Betulaster. Cuticular analysis of all the six species found in China and Japan belonging to section Betulaster (including Betula alnoides, B. rhombibracteata, B. cylindrostachya, B. luminifera, B. maximowicziana, B. fujianensis) was subsequently performed. Comparisons made between the extant and the extinct species confirm that based on leaf size, numbers of lateral vein and trichome types, B. yunnanensis is a new species. An explanation of why and how the peltate scales are only preserved as shield remains in the fossil materials is given.