Journal of Biogeography (J. Biogeogr.) (2016) 43, 1479–1487 PERSPECTIVE Available data point to a 4-km-high Tibetan Plateau by 40 Ma, but 100 molecular-clock papers have linked supposed recent uplift to young node ages Susanne S. Renner* Systematic Botany and Mycology, University ABSTRACT The aims of this study were to synthesize data on the orogeny of Munich (LMU), Menzingerstr. 67, 80638 of the Tibetan Plateau (TP), with a focus on its elevation since the collision Munich, Germany of the Eurasian and Indian plates, and to review the arguments in 100 phy- logeny-cum-biogeography papers that have linked young inferred divergence times to recent TP uplift phases. I surveyed the literature on the geological history of the TP, focusing on different types of data used to infer its past height. I also tabulated the supposed TP history (and supporting references) in papers since 1998. Since the early 1990s, evidence from tectonics, isotopes, fossils and climate simulations increasingly indicates that the TP has been 4– 5 km high since the mid-Eocene. The data also indicate that the Indian sum- mer monsoon, South-east Asian summer monsoon, and Central Asian winter monsoon arose at different times and are unrelated to Tibetan uplift. A growing number of studies by biologists, however, are linking node ages between 0.5 and 15 Ma to specific (author-dependent) uplift phases of the TP citing geological papers that are outdated or miscited. Biogeography of the TP thus currently appears to be in a self-created bubble that encloses hundreds of authors and referees. Our understanding of the biogeography of Tibet requires up-to-date interpretation of its geological history and more fieldwork on local ecological habitat diversity, the plateau’s history during the Pleistocene and the distribution of possible refugia. *Correspondence: Susanne S. Renner, Systematic Botany and Mycology, University of Keywords Munich (LMU), Menzingerstr. 67, 80638 Himalayas, Indian plate, monsoon systems, Tibetan Fossils, Tibetan Plateau, Munich, Germany. uplift of Tibetan Plateau E-mail: [email protected] that the recent, rapid uplift of the TP caused increased specia- INTRODUCTION tion and radiation in plants, animals and fungi. Over the past 20 years, the fields of biogeography and phylo- The TP (Fig. 1) extends for c. 2000 km from east to west, geography have blossomed due to molecular sequence data, and for up to nearly 800 km from north to south (Shackleton molecular clocks, improved data on geographical occurrences, & Chang, 1988); its surface area is c. 2.5 million km2, with an and better climate data and models. Studies in both fields fre- average height of 4000–5000 m and many peaks at 7000 and quently relate divergence-time estimates to palaeogeographical 8000 m. The plateau is characterized by dry climates and arid or climatic events, usually to infer abiotic factors causing spe- ecosystems although there are also rivers, lakes and high alti- cies formation or clade diversification (including extinction). tude bogs offering more humid habitats. Not surprisingly, Examples of such studies come from the biota of the Andes given its unique physical nature and size, the TP has numerous (e.g. Hoorn et al., 2010), Mount Kinabalu (Merckx et al., endemic plant and animal species. It has been a great challenge 2015), and the Panamanian land bridge (Bacon et al., 2015). for Earth scientists to explain how a c. 4.5 km high and ‘flat’ Next to the Panamanian land bridge, it is the Tibetan Plateau plateau can develop and how it relates to present-day crustal (TP) that in the past 17 years has received most attention from movements, earthquake activity, and climate. biogeographers (see Appendix S1 in Supporting Information Here, I summarize current views on the geological history of lists almost 100 studies). The conclusion from these studies is the TP for biologists, focusing on the different types of data ª 2016 John Wiley & Sons Ltd http://wileyonlinelibrary.com/journal/jbi 1479 doi:10.1111/jbi.12755 S. S. Renner used to infer its past uplift or sinking and on evidence of recent and/or rapid uplift phases. The latter question was sug- 50° N gested by a large number of studies (see Appendix S1) that link Miocene, Pliocene and/or Pleistocene organismal radiations (usually specific nodes in molecular clock-dated phylogenies) to precise uplift phases of the plateau. If biogeography is to 30° N Tibetan Plateau stay relevant as a science it is important that we place species or biota in up-to-date geological contexts (Hoorn et al., 2010; Pacific Ocean Bacon et al., 2015; Merckx et al., 2015), and as the TP is the world’s largest and highest plateau, understanding its orogeny and the evolution of biota has intrinsic interest. Data on the 10° N Indian Indian Summer Mansoon Ocean uplift of the TP and the effects it may or may not have had on East Asian Summer Mansoon East Asian Winter Mansoon the origin of the Asian monsoon systems (Fig. 2) have not 0° been reviewed for non-geologists. Favre et al. (2015) made a 60° E 90° E 120° E 150° E start by bringing together some of the literature, but did not Figure 2 The modern Asian monsoon systems, modified with address (1) the strength of the evidence and (2) the historic permission from Zhang et al. (2012). origin of the contrasting views held by the majority of phyloge- neticists/biogeographers and the majority of Earth scientists. I end with suggestions for why the numerous young (post-Mio- Huang et al., 2015). Non-Chinese Earth scientists since cene) plant and animal clades endemic or partly endemic to (minimally) the early 1990s also hold that the TP had the TP might have nothing to do with any recent geological achieved an elevation of at least 3000 m between 45 and uplift. 30 Ma (Dewey et al., 1989: p. 727: ‘Tibet was thickened and elevated to about 3 km by a northward progression of short- ening between about 45 and 30 Ma in a regime of roughly THE UPLIFT HISTORY OF THE TIBETAN north–south plane strain.’), followed by an equilibrium of PLATEAU uplifting, faulting, and erosion (Shackleton & Chang, 1988; Dewey et al., 1989; Tremblay et al., 2015). Shackleton and Evidence from tectonic models, geological data, Chang include a critique of the views of Chinese Earth scien- magnetostratigraphy and isotopes in ancient soils tists who, of course, were working in relative isolation before and water 1978 (cf. Origin of Chinese hypotheses on a young Tibetan Geophysical studies since the early 1990s, principally of mar- uplift and its ‘control’ of the monsoon systems). ine magnetic anomalies, resulted in the now generally Stable isotope dating of mica from the Thakkola Graben accepted estimate for the timing of India’s northward pro- (Fig. 1 and below), the largest N–S graben in north-central gression at 55–57 million years ago (Ma), with 52 Ma the Nepal, to 14 Ma implies that east–west extension developed best estimate for the cessation of marine sedimentation at well before then (Coleman & Hodges, 1995, p. 49: ‘well the northern margin of the Indian plate (Rowley, 1996; before Late Miocene time’). Similarly, isotope dating of vol- canic ashes to 40, 30, and 20 Ma (Chung et al., 1998) sug- gests that the TP underwent two main stages, one beginning at 40 Ma in the southern regions and a younger one begin- ning 20 Ma in the western region, prompting Ruddiman (1998: p. 724, commentary on Chung et al.) to ask, ‘Now the question is whether further exploration of Tibet will find evidence of even earlier uplift, especially during the cooling between 55 and 40 Myr ago’. Volcanic ashes, however, may not be a good indicator of plateau height. Tectonic models in the early 1990s assumed an uplift of the TP beginning at 20 Ma, with the plateau reaching its greatest height by 8 Ma (Harrison et al., 1992) and collaps- ing since (Edwards & Harrison, 1997). These early models were soon doubted (Tapponnier et al., 2001; Rowley & Cur- rie, 2006) and of course, models per se do not provide infor- mation on elevation, but need to be constrained with Figure 1 Tibetan Plateau with sites discussed in the text proxies. Such proxies come from micro- or macrofossils or numbered: 1 = Lunpola, 2 = Namling, 3 = Thakkhola graben, from isotope ratios in ancient soils and water that are used 4 = Gyirong, 5 = Kunlun Pass, 6 = Nima, 7 = Zhada (Zanda) to infer the altitude in which particular microbes, plants or Basin, 8 = Xoh Xil. Image Landsat. animals may have lived (Harris, 2006 for a review). Given 1480 Journal of Biogeography 43, 1479–1487 ª 2016 John Wiley & Sons Ltd Old Tibetan Plateau ignored by 100 biogeography papers the immense size and time-depth of the plateau, the chal- 40 Ma slightly higher than at 20 and 0 Ma, in agreement lenge is obvious. with an assumed gradual collapse of the plateau (for exam- Tapponnier et al.’s (2001) tectonic model assumed strike- ple, Edwards & Harrison 1997). The Himalayan range in slip faulting beginning about ‘15 Ma after the onset of conti- Wang et al.’s scheme appears after 20 Ma, and it is thought nental impact’ (p. 1673; italics mine). Their map of the TP that most of the uplift of the Himalayas, Karakoram, Pamir, shows its southern region as of Eocene age, the centre as Kunlun, and Hindu Kush occurred 21–13 Ma (Searle, 2011). ‘Oligocene-Miocene?’, and the northern Qaidam Basin as Recent palaeomagnetic data suggest that the Lhasa terrane ‘Pliocene-Quarternary’. Constraints from the interior of the was high before the collision of India with Asia (Lippert TP were not yet available, hence the question mark.