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)ORULGD6WDWH8QLYHUVLW\/LEUDULHV 2020 Paleoecology of Pleistocene Mammals and Paleoclimatic Change in South China: Evidence from stable carbon and oxygen isotopes Fajun Sun, Yang Wang, Yuan Wang, Chang-zhu Jin, Tao Deng and Burt Wolff Follow this and additional works at DigiNole: FSU's Digital Repository. For more information, please contact [email protected] 1 Paleoecologies and paleoclimate of Pleistocene mammals from South China: Evidence from 2 stable carbon and oxygen isotopes 3 Fajun Suna*, Yang Wanga,b,c*, Yuan Wangc, Chang-zhu Jinc, Tao Dengc, Burt Wolffa 4 a Department of Earth, Ocean & Atmospheric Science, Florida State University and National High Magnetic 5 Field Laboratory, Tallahassee, FL 32306-4100, USA 6 b Institute of Groundwater and Earth Sciences, The Jinan University, Guangzhou, Guangdong Province, 7 510632, P. R. China 8 c Key Laboratory of Vertebrate Evolution and Human Origins, Institute of Vertebrate Paleontology and 9 Paleoanthropology, Chinese Academy of Sciences, Beijing, China 10 11 * Corresponding author at: Department of Earth, Ocean and Atmospheric Science, Florida State 12 University and National High Magnetic Field Laboratory, Tallahassee, FL 32306-4100, USA. 13 E-mail address: [email protected] (F. Sun); [email protected] (Y. Wang). 14 15 Abstract 16 The role of climate change in the evolution and diversification of hominoids remains a hotly 17 debated issue. Stable isotope analyses of fossil mammals that coexisted with the hominoids can 18 provide insights into the environments of the hominoids and shed lights on this debate. Here, we 19 report results of stable carbon and oxygen isotope analyses of tooth enamel samples from a 20 variety of Pleistocene mammals including pandas, deer, elephants, pigs, rhinos, and bovids from 21 two hominoid fossil localities (Yuweng Cave and Baxian Cave) in South China. The enamel 22 δ13C values indicate that most of the mammals living in the study area during the late Middle 23 Pleistocene had C3-based diets but a small number of individuals consumed some C4 grasses. 24 This indicates the presence of C4 plants in the region during the late Middle Pleistocene, most 25 likely in patches of open areas in a predominantly forested environment. However, during the 26 early Late Pleistocene, almost all of the mammals examined had C3-based diets, except one 27 bovid that may have ingested a small amount of C4 grasses. This indicates a dense forested 28 environment with little or no C4 grasses during the early Late Pleistocene. Like the Early 29 Pleistocene pygmy panda (Ailuropod microta) from Yanliang Cave, the late Middle Pleistocene 30 Ailuropod baconi from Yuweng Cave and the early Late Pleistocene Ailuropod melanoleuca 31 from Baxian Cave all had pure C3 diets and more restricted habitats compared to other mammals. 18 32 The reconstructed mean paleo-meteoric water δ Ow values are lower than the annual average 18 33 δ Ow value of modern precipitation in the region, suggesting that the climatic conditions during 34 the times when these Pleistocene mammals were alive were colder and/or wetter than today. In 35 addition, δ18O values of the obligate drinkers (pig, rhino, bovid) display an overall decreasing 36 trend, accompanied by increased range of δ18O variations, from the Early Pleistocene to the late 37 Middle Pleistocene and the early Late Pleistocene. This suggests that the regional climate 38 became colder and/or wetter, with increased seasonality, from the Early Pleistocene to the late 39 Middle Pleistocene and the early Late Pleistocene, likely related to the intensifications of 40 glaciation. The change in climate to colder conditions may be responsible for the extinction of 41 the Gigantopithecus in this region. 42 Keywords: Fossils; stable isotopes; habitats; paleoclimate; Yuweng Cave; Baxian Cave 43 1. Introduction 44 Fossils are important archives of ancient diets and environments and have been widely 45 utilized to address a variety of ecological and environmental questions (e.g., Cerling et al., 1997; 46 Koch, 1998; Kohn, 1999), and to test hypotheses regarding the role of climate change in human 47 evolution (e.g., Ungar and Sponheimer, 2011; Cerling, 2013; deMenocal, 2011). Stable carbon 48 and oxygen isotopic analyses of fossil mammalian tooth enamel is an important tool in the study 49 of paleoclimate and paleoecologies. Such analyses may allow insights into the biology and 50 ecology of ancient taxa and increase our understanding of the effects of a changing environment 51 on the evolution of these and related mammals (e.g., Cerling et al., 1993; Ciner et al., 2015; 52 Ciner et al., 2016). 53 Carbon isotopes are valuable for distinguishing diets based directly or indirectly on plants 54 using different photosynthetic pathways (Cerling et al., 1989; Koch, 1998; Kohn and Cerling, 55 2002). Plants can be divided into three groups based on their photosynthetic path ways: C3 plants 56 (trees, most shrubs, forbs, and cool season grasses), C4 plants (warm season grasses), and CAM 13 57 plants (succulents). In the modern world, C3 plants have δ C values ranging from –36 to – 58 22 , with an average of –27 (O’Leary, 1988; Farquhar et al., 1989; Cerling et al., 1997; 13 59 Kohn, 2010). C3 plants that grow under closed canopies have the most negative δ C values due 60 to the influence of soil respired CO2 and light limitation, while C3 plants in water stressed 61 conditions tend to have higher δ13C values (> –27 ) that can be as high as –22 in deserts 62 (e.g., Williams and Ehleringer, 1996; Cerling and Harris, 1999; Zhang et al., 2012). C4 plants, 63 mostly consisting of warm season grasses, are commonly found in low elevation grasslands at 13 64 low to mid latitudes. The δ C values of C4 plants vary from –17 to –9 , with an average of 65 –13 , much higher than those of C3 plants (Farquahar et al., 1989; Cerling and Harris, 1999). 66 The distinct isotopic difference between C3 and C4 plants is passed along the food chain to 67 animal tissues with further isotopic fractionation. Compared to bones and dentine or other tissues, 68 fossil tooth enamel often preserves its original isotopic signatures that reflect the isotopic 69 compositions of the diet and water ingested by an animal because of its large crystal size, low 70 organic content and low porosity, resulting in less influx of diagenetic fluids (Ayliffe et al., 1994; 71 Wang and Cerling, 1994). For medium to large mammalian herbivores, their tooth enamel 72 carbonate is enriched in the heavy carbon isotope 13C by 13 to 14 relative to the diet due to 73 biochemical isotope fractionation (Cerling and Harris, 1999). Thus, a tooth enamel δ13C value < 13 74 –10 is generally indicative of a pure C3 diet and a δ C value > –2 would reflect a pure C4 75 diet (e.g., LeeThorp et al., 1989; Cerling et al., 1997; Biasatti et al., 2012; Stacklyn et al., 2017). 13 76 In a dense forested environment, the end-member enamel δ C value for a pure C3 diet could be 77 as low as –17 (Cerling et al., 1997). In general, temporal shifts in the emamel-δ13C values of 78 mammals from a given locality would indicate shifts in diet, habitat, or regional climatic 79 conditions. In terms of habitat, enamel-δ13C values < –13 represent closed habitats, while 80 those > –10 suggest affinities for more open habitats. As a result, carbon isotope analyses 81 allow us to understand the feeding behavior and habitat preference of particular fossil taxa. 82 The oxygen isotope ratios (δ18O) of enamel reflect the δ18O of animals’ body water (Bryant 83 and Froelich, 1995; Kohn, 1996). The δ18O values of body water are controlled by different 84 variables, including the δ18O values of drinking water, water in food, physiological processes, 85 and mammals’ dietary/drinking behavior (Bryant and Froelich, 1995; Kohn, 1996). Studies have 86 shown that δ18O values of body water for obligate drinkers mainly carry information about 87 meteoric water because most of their ingested water comes from meteoric water (e.g., Kohn and 88 Cerling, 2002; Wang et al., 2008). The δ18O values of meteoric water are sensitive to climatic 89 variables such as temperature, seasonality of rain, and the amount of rain (Dansgaard, 1964). 90 Thus, the δ18O values of tooth enamel are a complex function of climate and have been used as a 91 proxy for paleoclimatic conditions during growth of the teeth (Wang and Deng, 2005). Obligate 92 drinkers tend to have lower body water δ18O values than mammals that obtain most of their 93 water from plants because leaf water is usually enriched in the heavy oxygen isotope 18O relative 94 to local meteoric water due to evaporation (Dongmann et al, 1974; Epstein et al., 1977). 95 Southeast Asia has been home for a diverse assemblage of mega-mammal species (Jablonski 96 et al., 2000; Wang et al., 2007). Over the last decades, hominoid fossils such as orangutan Pongo 97 and the giant ape Gigantopithecus, along with abundant coexisting mammalian fossils have been 98 discovered from a series of cave sites and fissure deposits in Guangxi Province in South China 99 (Jin et al., 2014; Liu et al., 2015; Wang et al., 2017). Homo sapiens fossils were also uncovered 100 from several cave sites including Yuweng Cave in Gongjishan (Dong et al., 2014) and Mulan 101 Mountain in the same region (Jin et al., 2009). Gigantopithecus was probably the largest ape that 102 had ever existed on Earth. They were initially identified by the German vertebrate paleontologist 103 von Koenigswald in 1935 based on the teeth that he purchased from drug stores in south China. 104 According to the fossil records，the Gigantopithecus had a relatively wider distribution during 105 the Early Pleistocene, but withdrew southward to a limited area in the Middle Pleistocene while 106 they disappeared during the Late Pleistocene (Zhao et al., 2013).

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