A Middle Eocene lowland humid subtropical “Shangri-La” ecosystem in central Tibet

Abstract

Tibet’s ancient topography and its role in climatic and biotic evolution remain speculative due to a paucity of quantitative surface-height measurements through time and space, and sparse fossil records. However, newly discovered fossils from a present elevation of ∼4,850 m in central Tibet improve substantially our knowledge of the ancient Tibetan environment. The 70 plant fossil taxa so far recovered include the first occurrences of several modern Asian lineages and represent a Middle Eocene (∼47 Mya) humid subtropical ecosystem. The fossils not only record the diverse composition of the ancient Tibetan biota, but also allow us to constrain the Middle Eocene land surface height in central Tibet to ∼1,500 ± 900 m, and quantify the prevailing thermal and hydrological regime. This “Shangri-La”–like ecosystem experienced monsoon seasonality with a mean annual temperature of ∼19 °C, and frosts were rare. It contained few Gondwanan taxa, yet was compositionally similar to contemporaneous floras in both North America and Europe. Our discovery quantifies a key part of Tibetan Paleogene topography and climate, and highlights the importance of Tibet in regard to the origin of modern Asian plant species and the evolution of global biodiversity.

Spatiotemporal maintenance of flora in the Himalaya biodiversity hotspot: Current knowledge and future perspectives

“…The advantage of the fossil record is that it documents the location in time and space of extinct organisms but it is, by its very nature, incomplete as only a small fraction of organisms alive at any one time become fossilized. Previous studies have generally been based on these rare occurrences (Deng et al, 2019;Ding et al, 2017;Spicer et al, 2017;Srivastava & Mehrotra, 2010;Su et al, 2020). Other than finding more fossils, there are several ways by which the record of past biome assemblies can be improved.…”

“…( 2020 ) cast doubt upon this simplistic model of plateau formation and instead argues for a more complex process that involved earlier collisions of Gondwanan terranes with Asia, forming a high relief landscape before the arrival of the Indian subcontinent. A recent study constrained the middle Eocene height of a valley in Central Tibet to ~1,500 m (Su et al., 2020 ), while the proto‐Himalaya started building against the pre‐existing Gangdese highland along the southern margin of what would later become the Tibetan Plateau. Radiochemical and fossil evidence indicates that the proto‐Himalaya began to grow against the then ~4,000 m‐high Gangdese Mountains from ~1,000 m in the late Paleocene to ~2,000 m in the early Miocene, with some parts attaining about 5,000 m by around 15 Ma (Ding et al., 2017 ), and that Mount Everest area had already attained ≥5,000 m by the early Miocene (Gébelin et al, 2013 ).…”

Diachronous Growth of the Northern Tibetan Plateau Derived From Flexural Modeling

“…The growth and uplift of the Tibetan plateau (Figures 1a and 1b) has implications for our knowledge of continental tectonics and intracontinental deformation (Cheng et al., 2014; Clark & Royden, 2000; DeCelles et al., 2002; Law & Allen, 2020; Murphy et al., 1997; Rowley, 1996; Tapponnier et al., 2001; Wang et al., 2008; Yin & Harrison, 2000) and the evolution of the East Asian monsoon (An et al., 2001; Clift et al., 2008; Harris, 2006; Licht et al., 2014; Molnar et al., 1993; Porter, 2001). Despite ongoing debate, numerous paleoaltimetry studies based on stable isotope hydrology, clumped isotope thermometry, and physiognomy of plant fossils have provided constraints on the early Cenozoic paleoelevation for the southern Tibetan plateau (Botsyun et al., 2019; Ding et al., 2014; Garzione et al., 2000; Hoke et al., 2014; Quade et al., 2011; Su et al., 2020). However, the early Cenozoic paleoelevation of the northern Tibetan plateau remains unclear, partly due to the inapplicability of these paleoaltimetry approaches to northern Tibet (Quade et al., 2011; Rowley & Garzione, 2007; Song et al., 2020).…”

Effects of Tibetan Plateau Growth, Paratethys Sea Retreat and Global Cooling on the East Asian Climate by the Early Miocene

“…(2021). Recent geological studies have demonstrated that the central TP was uplifted after the southern and northern parts of the TP (e.g., Fang et al., 2020; Spicer et al., 2020; Su et al., 2020). These features may markedly affect the local climate but do not change the large‐scale effects of TP growth shown here and in previous studies (e.g., S. F. Li et al., 2021).…”

“…Except for the topographic changes that occurred around the TP, our topographic scenarios have relatively low elevations in other Asian topographic regions; this may also have affected East Asian climate (Sha et al., 2018; Zhang, Jiang, & Zhang, 2018). Although considering more topographic scenarios would improve our understanding of the climatic effects of these topographies on the East Asian monsoon, the precise reconstruction of paleoelevations in these regions is key to identifying the most accurate scenario (e.g., Fang et al., 2020; Spicer et al., 2020; Su et al., 2020).…”