Quercus (subg. Cyclobalanopsis) leaf and cupule species in the late Miocene of eastern China and their paleoclimatic significance

The fossil record of Quercus subgenus Cyclobalanopsis can be traced back to the Late Eocene of eastern Asia based on fossil foliage and acorns. We refer new occurrences of leaf and acorn fossils from the upper Miocene of Tiantai, eastern Zhejiang, China, to two new species, Quercus paraglauca sp. nov. and Quercus heterobracteolata sp. nov.. Q. heterobracteolata represents the earliest confirmed fossil acorn of the subgenus Cyclobalanopsis in China. A review of other occurrences reported in the literature reveals that the divergence of subgenus Cyclobalanopsis occurred not later than the Eocene, and in the Miocene Cyclobalanopsis was already widely distributed. Comparisons of cuticular structure between Q. paraglauca and its nearest living relative species (NLR) Q. glauca suggest that: 1) atmospheric CO2 concentration in the late Miocene was ca. 400 ppmv, i.e. higher than the present natural CO2 concentration, eliminating the industrial influence; 2) the Q. glauca trichome base density is sensitive to the environmental changes; and 3) the late Miocene climate of Zhejiang (eastern China) was warmer and more humid than today.