Shuang-Xing Guo

Constant elevation of southern Tibet over the past 15 million years.

The uplift of the Tibetan plateau, an area that is 2,000 km wide, to an altitude of about 5,000 m has been shown to modify global climate and to influence monsoon intensity. Mechanical and thermal models for homogeneous thickening of the lithosphere make specific predictions about uplift rates of the Tibetan plateau, but the precise history of the uplift of the plateau has yet to be confirmed by observations. Here we present well-preserved fossil leaf assemblages from the Namling basin, southern Tibet, dated to ∼15 Myr ago, which allow us to reconstruct the temperatures within the basin at that time. Using a numerical general circulation model to estimate moist static energy at the location of the fossil leaves, we reconstruct the elevation of the Namling basin 15 Myr ago to be 4,689 ± 895 m or 4,638 ± 847 m, depending on the reference data used. This is comparable to the present-day altitude of 4,600 m. We conclude that the elevation of the southern Tibetan plateau probably has remained unchanged for the past 15 Myr.

TRIFOLIOLATE LEAVES OF PLATANUS BELLA (HEER) COMB. N. FROM THE PALEOCENE OF NORTH AMERICA, GREENLAND, AND ASIA AND THEIR RELATIONSHIPS AMONG EXTINCT AND EXTANT PLATANACEAE

Trifoliolate leaves of Platanus bella (Heer) comb. n., a species previously known only from the Paleocene of western Greenland, are newly recognized from the Paleocene of northern Wyoming, U.S.A., and Altai of Xinjiang Province, northwestern China, indicating that the species was circumboreal in the early Tertiary. Epidermal anatomy preserved in specimens from all three areas confirms that these compound leaves belong to the Platanaceae. Platanus bella (Heer) comb. n. differs from modern species of Platanus but resembles the European Tertiary species Platanus fraxinifolia (Johnson & Gilmore) Walther and Platanus neptuni (Ettingshausen) Bůžek, Holý & Z. Kvaček, in the presence of large peltate glandular trichomes. We erect a new subgenus, Glandulosa, to accommodate P. bella, P. fraxinifolia, and P. neptuni. Each of these species possesses similar leaf epidermal structure, with the characteristic platanaceous stomatal apparatus and compound hair bases. In addition, the fossils bear peltate glandular trichomes on the epidermal surfaces that are not known among extant Platanus species. Reproductive structures linked to P. neptuni indicate that subgenus Glandulosa is properly placed in the Platanaceae but that it is a distinct clade from those of the extant subgenera Platanus and Castaneophyllum Leroy. We also review the status of the fossil genera Debeya and Dewalquea, to which some Cretaceous and Tertiary leaves of similar morphology have been placed, and reject the use of either of these names to accommodate leaves of subgenus Glandulosa.

Late Miocene palaeoflora and palaeoclimate of Lincang (China)

The Miocene Lincang leaf assemblage is used in this paper as proxy data to reconstruct the palaeoclimate of southwestern Yunnan (SW China) and the evolution of monsoon intensity. Three quantitative methods were chosen for this reconstruction, i.e. Leaf Margin Analysis (LMA), Climate Leaf Analysis Multivariate Program (CLAMP), and the Coexistence Approach (CA). These methods, however, yield inconsistent results, particularly for the precipitation, as also shown in European and other East Asian Cenozoic floras. The wide range of the reconstructed climatic parameters includes the Mean Annual Temperature (MAT) of 18.5-24.7 °C and the Mean Annual Precipitation (MAP) of 1213-3711 mm. Compared with the modern Lincang climate (MAT, 17.3 °C; MAP, 1178.7 mm), the Miocene climate is slightly warmer, wetter and has a higher temperature seasonality. A detailed comparison on the palaeoclimatic variables with the coeval Late Miocene Xiaolongtan flora from the eastern part of Yunnan allows us to investigate the development and interactions of both South Asian and East Asian monsoons during the Late Miocene in southwest China, now under strong influence of these monsoon systems. Our results suggest that the monsoon climate has already been established in southwest Yunnan during the Late Miocene. Furthermore, our results support that both Southeast Asian and East Asian monsoons co-occurred in Yunnan during the Late Miocene.