Progress and challenges in understanding Asian palaeogeography and monsoon evolution from the perspective of the plant fossil record

Land surface elevation, climate and vegetation are intrinsically linked at a range of spatial and temporal scales. In the case of Asia, complex relief hosts some of the richest biodiversity on our planet and is dominated by a system of monsoons, the features of which are determined in large part by topography and land surface characteristics, including vegetation. Such regions have not only acted as an incubator for evolving species but also as refugia during periods of environmental crisis. The exceptional topography of Asia includes the largest and highest elevated region on Earth, the Tibetan Plateau, along with the Himalaya and the Hengduan mountains, collectively referred to here as the THH region. In recent years there has been a revolution in thinking as to how the THH was formed, how the several monsoons systems that affect it have changed, and how it has influenced regional, even global, biodiversity evolution. Accurately dated plant fossils have played key roles in these advances. Here we review the complex evolution of the THH landscape, the modernization of the biota in the Paleogene, and the transition to the modern landscape and monsoon systems in the Neogene. We show how these changes in understanding have been brought about by recent fossil discoveries and new radiometric dating of previously known assemblages, methodological advances arising from integrating improved proxy data, and numerical palaeoclimate modelling. Significant knowledge gaps remain, however, which demand further advances in proxy and numerical methodologies, as well as new fossil discoveries in key locations for specific time intervals.