(2) CLIMATE, ECOLOGY, AND HUMAN EVOLUTION DURING THE PLIO-PLEISTOCENE. by. SCOTT ADAM BLUMENTHAL. A dissertation submitted to the Graduate Faculty in Anthropology in partial fulfillment of the requirements for the degree of Doctor of Philosophy, The City University of New York 2016.
(3) © 2016 SCOTT ADAM BLUMENTHAL All Rights Reserved. ii.
(4) This manuscript has been read and accepted for the Graduate Faculty in Anthropology to satisfy the dissertation requirement for the degree of Doctor of Philosophy.. Thomas W. Plummer. ___________ Date. ________________________________________________ Chair of Examining Committee. Gerald Creed ___________ Date. ________________________________________________ Executive Officer. Timothy G. Bromage Thure E. Cerling Jessica M. Rothman Supervisory Committee. THE CITY UNIVERSITY OF NEW YORK. iii.
(5) ABSTRACT ECOLOGY, CLIMATE, AND HUMAN EVOLUTION DURING THE PLIO-PLESITOCENE By Scott Adam Blumenthal Advisor: Professor Thomas W. Plummer A major goal of paleoanthropology is to identify the selective pressures associated with hominin biological and behavioral evolution, yet establishing cause-effect relationships between climate, ecology, and human evolution remains problematic. This dissertation seeks to investigate hominin paleoecology in eastern Africa by reconstructing aspects of climate and ecology using stable isotope analysis. The first part of this dissertation is focused on the ecology of primates and hominins. Modern tropical African ecosystems provide a useful model for understanding the ecological correlates of isotopic variation in the fossil record, and living primates provide a useful model for understanding the ecological significance of isotopic variation in fossil hominin tissues. Isotope data from modern primate excreta and plants shows that isotopic variation primarily relates to diet. The magnitude of isotopic variation in gorilla feces, which relates to intra-annual dietary variability, demonstrates that African apes have less isotopically variable diets than fossil hominins. Carbon isotope data from large mammalian tooth enamel in three areas (southern Kenya & northern Tanzania, northern Kenya, and northern Ethiopia) demonstrate a long-term increase in the prevalence of C4-grazing taxa over time, primarily at the expense of C3-C4 mixed feeding taxa. Pleistocene and Holocene ecosystems in southwestern Kenya, where there is the most complete record over the past 2 million years, are persistently dominated by C4-grazers.. iv.
(6) The second part of this dissertation is focused on climate and human evolution. The notion that aridity and seasonality have increased over the Pliocene and Pleistocene has remained central to models of environmental change (i.e. C4 grass expansion) and human evolution; however, few empirical records of terrestrial climate are available to assess this claim. An existing tooth enamel oxygen isotope aridity proxy is revised using a large compilation of new and existing oxygen isotope values in modern herbivore teeth from eastern and central Africa. The application of the aridity index to fossil teeth from eastern Africa, primarily the Turkana Basin, demonstrate that mesic and arid conditions were both prevalent during periods of fossil preservation. There is no long-term trend in aridity, which demonstrates that ecological changes associated with the expansion of C4 vegetation and C4 grazers may not have been driven by changes in water availability. A survey of extant equids from eastern Africa demonstrates that intra-tooth oxygen isotopic variability relates to intra-annual oxygen isotope variability in precipitation. This approach is applied to fossils from the Homa Peninsula, Kenya, demonstrating that Pleistocene hominins in this region would have experienced seasonal rainfall, similar to modern eastern African climates. No trend over time was detected in fossil intra-tooth δ18O range, although the number of localities and time periods included in this analysis are limited. Isotopic records presented in this dissertation demonstrate new ways to investigate relationships between climate, ecology, and human evolution. These findings provide new detail on hominin environments, and provide a critical test of long-assumed relationships between long-term changes in climate and ecology.. v.
(7) ACKNOWLEDGEMENTS This dissertation represents the cumulative effort and support of many mentors, colleagues, and fellow students. I first thank my advisor Tom Plummer, who provided the guidance and freedom to pursue my research. His depth of knowledge and broad thinking in paleoanthropology and paleoecology have inspired me, and this dissertation would not have been possible without his support. My work in Uganda would not have been possible without the support and encouragement of Jessica Rothman, whom I thank for introducing me to primatological perspectives. I am grateful to Tim Bromage for his support, particularly in histological studies. I owe great thanks to Thure Cerling for giving me free rein in the lab, and generously providing years of support and guidance to a visitor who never left. In addition to my committee, I thank Kendra Chritz, Naomi Levin, Christian Tryon, Tyler Faith, John Valley, and Reinhard Kozdon for their support and enthusiasm for collaboration. I would like to recognize other members of the Homa Peninsula Paleoanthropology Project (HPPP) and Lake Victoria Prehistory Project (LVPP), whose years of effort in the field and the museum have made this project possible. I am also grateful to the staff of the National Museums of Kenya (NMK) in Nairobi for facilitating access to fossil collections. I thank Emma Mbua, former Director of the Department of Earth Sciences for kindly facilitating my research. I am particularly thankful to Kyalo Manthi, Director of the Department of Earth Sciences and Paleontology Section for his enthusiastic support. I also thank the Kenya National Council for Science and Technology for permission to conduct research. I thank the Uganda Wildlife Authority and the Uganda National Council for Science and Technology for permission to conduct research. I thank Aggrey Rwetsiba and Fred Kisame for their support. I am particularly grateful to the park wardens who have made this research. vi.
(8) possible. I would like to acknowledge the support of field assistants, including Peter Irumba, James Magaro, Moses Musana, and Hillary Musinguzi, as well as the rangers in Queen Elizabeth National Park, Kidepo Valley National Park, Lake Mburo National Park, and Bwindi Impenetrable National Park. I thank the New York Consortium in Evolutionary Primatology (NYCEP) community, particularly Eric Delson, for providing a supportive community during my early years of graduate school. I am particularly grateful to NYCEP for providing funding to conduct pilot research and attend numerous conferences. Fellow NYCEP students Claudia Astorino, Ashley Bales, Margaret Bryer, Emma Finestone, Frances Forrest, Eva Garrett, Justin Gladman, Caley Johnson, Zach Klukkert, Jennifer Parkinson, Su-Jen Roberts, and Julia Zichello all provided invaluable friendship and intellectual stimulation in New York and beyond. I thank the Utah Biology and Geology Departments for welcoming a long-term anthropologically-inclined visitor. I thank former members of the Cerling lab, including Kendra Chritz, Kevin Uno, Dan Davis, Glynis Jehle, Yuri Kimura, and Esperanza Zagal, for fostering a productive lab environment. I also thank Jim Burdette, Suvankar Chakraborty, Dale Heisler, Roger Husted, Mike Lott, and Willow Toso for technical support during mass spectrometer repairs. I also thank members of various field teams in Kenya for providing training and assistance, including the Homa Peninsula team (Tom Plummer, Laura Bishop, Jim Oliver, Dave Braun), the Rusinga team (Kieran McNulty, Holly Dunsworth, Will Harcourt-Smith, Thomas Lehmann, Dave Fox), the Turkana Geology Field Course (Frank Brown and Thure Cerling) and the Koobi Fora Field School (Jack Harris, Dave Braun, Emma Mbua, Purity Kiera).. vii.
(9) I also would like the thank my undergraduate mentors Mark Jenike, who introduced me to the discipline and humored an eager underclassman who had many questions, and Stan Ambrose, whose mentorship in archaeology and geochemistry as well as his encouragement and enthusiastic scholarship proved invaluable in my early academic development. I also thank my parents, Annette and Lawrence Blumenthal, and siblings Seth and Melissa, for their lifelong support and love. Finally, I thank Kendra Chritz, from whom I’ve learned most about science and life. I could not have completed this thesis without you. This research was financially supported by the National Science Foundation, Leakey Foundation, Wenner-Gren Foundation, National Geographic Society, the Hard Tissue Research Program in Human Paleobiomics, and Sigma Xi.. viii.
(10) TABLE OF CONTENTS ABSTRACT. iv. ACKNOWLEDGEMENTS. vi. LIST OF TABLES. xi. LIST OF FIGURES. xii. INTRODUCTION ENVIRONMENTAL DETERMINANTS OF HUMAN EVOLUTION OBJECTIVES REFERENCES. 1 2 11 16. SECTION 1: PRIMATE AND HOMININ ECOLOGY CHAPTER 1. Stable Isotopic Variation in Tropical Forest Plants for Applications in Primatology ABSTRACT INTRODUCTION METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES SUPPLEMENTARY TABLE TO CHAPTER 1. 26 27 27 29 31 31 35 35 41. CHAPTER 2. Detecting intraannual dietary variability in wild mountain gorillas by stable isotope analysis of feces. ABSTRACT INTRODUCTION RESULTS DISCUSSION CONCLUSION MATERIALS AND METHODS REFERENCES SUPPORTING INFORMATION TO CHAPTER 2. 56 57 57 58 59 61 61 61 63. CHAPTER 3. Human evolution and the expansion of grazerdominated biomes ABSTRACT INTRODUCTION MATERIALS AND GEOLOGICAL CONTEXT METHODS. 72 72 72 79 88. ix.
(11) RESULTS AND DISCUSSION REFERENCES. 90 127. SECTION 2: CLIMATE AND HOMININ EVOLUTION CHAPTER 4. Terrestrial aridity and Plio-Pleistocene hominin environments ABSTRACT INTRODUCTIONS METHODS MATERIALS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES SUPPLEMENTAL FIGURES TO CHAPTER 4. 147 147 147 151 162 165 177 178 187. CHAPTER 5. Stable isotope time-series in mammalian teeth: In situ δ18O from the innermost enamel layer ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES. 190 191 191 194 196 199 201 201. CHAPTER 6: Oxygen isotope time-series in equid teeth: reconstructing Pleistocene paleoseasonality in southwestern Kenya ABSTRACT INTRODUCTION MATERIALS METHODS RESULTS DISCUSSION CONCLUSIONS REFERENCES SUPPLEMENTAL TABLE TO CHAPTER 6 SUPPLEMENTAL FIGURES TO CHAPTER 6. 205 205 205 210 212 215 222 226 227 240 241. CONCLUSIONS CLIMATE, ECOLOGY, AND HUMAN EVOLUTION FUTURE DIRECTIONS REFERENCES. 246 247 254 257. APPENDICES APPENDIX FOR CHAPTER 3 APPENDIX 1 FOR CHAPTER 4. 268 269 343. x.
(12) APPENDIX 2 FOR CHAPTER 4 APPENDIX 3 FOR CHAPTER 4 APPENDIX FOR CHAPTER 5 APPENDIX 1 FOR CHAPTER 6 APPENDIX 2 FOR CHAPTER 6 APPENDIX 3 FOR CHAPTER 6 APPENDIX 4 FOR CHAPTER 6 APPENDIX 5 FOR CHAPTER 6 BIBLIOGRAPHY. 348 406 423 428 429 432 438 443 445. xi.
(13) LIST OF TABLES CHAPTER 1 Table 1 Stable Isotopic Composition of Plants in Kibale National Park, Uganda. 32 41. Table S1. Identification, location, and stable isotope values for plants from Kibale. CHAPTER 2 Table 1 Summary statistics for feces stable carbon and nitrogen isotope values. 59. Table S1. Dry mass fruit intake in 2-mo bins. 65. Table S2. Stable isotope measurements of staple foods from Bwindi. 66. Table S3. Measurements of all plant food samples from Bwindi. 67. Table S4. Measurements of manually separated skin/pulp and seeds from staple fruits. 68. Table S5. Measurements of gorilla feces. 69. CHAPTER 3 Table 1 Average δ13C values for APP taxa and G:M:B in southern Kenya and northern Tanzania Table 2. Average δ13C values for APP taxa and G:M:B in Afar. CHAPTER 6 Table S1 Comparison of the magnitude of isotopic shift (δ18O range) by sampling method. 94 96 240. xi.
(14) LIST OF FIGURES CHAPTER 1 Figure 1 The carbon (δ13C) and nitrogen (δ15N) isotopic composition of plants. 31. Figure 2. Relationship between carbon and nitrogen isotopic composition of lower and upper crown layer samples. 32. Figure 3. Boxplots of the carbon and nitrogen isotopic composition of mature leaves and young leaves from the crowns of common tree species. 33. Figure 4. Histograms of carbon and nitrogen isotopic composition of Kibale plants. 34. CHAPTER 2 Figure 1 Stable isotope values of feces from Bwindi gorillas and staple foods. 58. Figure 2. Stable carbon isotope profiles from feces of four gorillas. 59. Figure 3. Comparison of carbon isotopic composition of gorilla feces, modeled fruit intake, and observed fruit intake. 60. Figure S1. Measurements of mass of seeds and pulp/skin from ripe staple fruits. 64. Figure S2. Stable isotope measurements of gorilla feces. 65. CHAPTER 3 Figure 1 δ13C values of major APP families over time in southern Kenya and northern Tanzania. 91. Figure 2. δ13C values of all APP lineages over time in southern Kenya and northern Tanzania. 92. Figure 3. Percent G:M:B of APP lineages over time in southern Kenya and northern Tanzania. 93. Figure 4. Long-term trends in the proportion of diet categories among APP taxa. 115. Figure 5. Proportions of C4 grazers, C3-C4 mixed feeders, and C3 browsers among APP taxa. 116. xii.
(15) Figure 6. Ternary diagram. 117. CHAPTER 4 Figure 1 Map of sampling localities for modern teeth. 150. Figure 2. Oxygen isotopic enrichment between enamel and meteoric water. 153. Figure 3. Body water oxygen inputs. Measured and predicted oxygen isotopic enrichment between enamel and meteoric water. 154. Figure 4. Oxygen isotopic enrichment between enamel of extant ES and EI taxa in eastern and central Africa. 169. Figure 5. Paleoaridity calculated using all evaporation insensitive taxa and only hippopotamidae. 171. Figure 6. Compilation of data indicating aspects of climate/hydrology and ecology over the past 5 million years in the Turkana Basin, Kenya. 174. Figure S1. δ18O values in fossil EI taxa from the Turkana Basin. 187. Figure S2. Oxygen isotopic enrichment between enamel of fossil ES and EI. 188. Figure S3. Water deficit and potential evapotranspiration compared to mean annual precipitation and mean annual temperature. 189. CHAPTER 5 Figure 1 Schematic diagram of enamel maturation parameters. 193. Figure 2. BSE-SEM image of woodrat incisor. 194. Figure 3. SEM image of woodrat incisor enamel with SIMS pit. 195. Figure 4. Enamel thickness measurements. 196. Figure 5. Enamel mineralization measurements. 197. xiii.
(16) Figure 6. Location of SIMS sample pits. 198. Figure 7. Laser ablation and SIMS intra-tooth δ18O. 199. CHAPTER 6 Figure 1 Enamel mineralization. 216. Figure 2. Intra-tooth δ18O of Mongolian horse teeth. 217. Figure 3. Climate data for tooth sampling locations in Kenya and Uganda. 219. Figure 4. Intra-annual range in oxygen isotopic composition of precipitation, extant zebra teeth, and fossil equid teeth. 221. Figure S1. BSE-SEM image of Mongolian horse tooth germ. 241. Figure S2. Image of horse tooth after laser ablation sampling. 242. Figure S3. Enamel sampling procedure in a fossil equid tooth. 243. Figure S4. Mean monthly oxygen isotopic composition of precipitation and intra-tooth oxygen isotope profiles of horse teeth from northern Mongolia. 244. Figure S5. Fossil equid intra-tooth carbon and oxygen isotope profiles. 245. CONCLUSIONS Figure 1 Compilation of data characterizing PliocenePleistocene climate and ecology in the Turkana Basin, Kenya. 251. xiv.
(17) INTRODUCTION A major goal of paleoanthropology is to identify the selective pressures associated with survival and reproduction that led to hominin biological and behavioral change. Early human evolutionary studies tended to focus on intrinsic explanations, such that adaptive feedbacks led directly from early to later innovations (i.e. bipedality, tool use, hunting, brain expansion, food sharing, language) (Darwin, 1871; Dart, 1925; Bartholomew and Birdsell, 1953; Washburn, 1960; Isaac, 1978). A similar view has been more recently articulated as the autocatalytic model, which suggests that evolutionary forces independent of natural selection were largely responsible for human evolutionary history (McKee, 1999). Since the 1980s, however, focus shifted to extrinsic explanations for human evolution including more ecologically sophisticated ideas about interactions between hominins and dynamic biotic and abiotic environments (Brain, 1981; Hill, 1981; Laporte and Zihlman, 1983; Vrba, 1985; Hill, 1987; Vrba, 1988; 1989; Stanley, 1992). Establishing cause-effect relationships between climate, ecology, and human evolution remains problematic due to a mismatch between the space-time scales of environments as experienced by hominins and empirical paleoenvironmental data, as well as insufficient consideration of mechanisms relating environmental drivers to evolutionary change (Behrensmeyer, 2006; Behrensmeyer et al., 2007; Kingston, 2007). For example, early attempts to link climate and human evolution relied on correlations between global climate records and the appearance of particular hominin species, anatomy, and behavior (Butzer, 1977; Brain, 1981; Vrba, 1985; 1988; 1989; deMenocal, 1995; Potts, 1998a). However, while global-and continental-scale climate records are important for understanding potential mechanisms driving regional- and local-scale environmental change, global climate is not directly informative on the environmental conditions experienced by hominins. Despite the often ambiguous results of. 1.
(18) conventional site-based paleoenvironmental analyses using lithofacies and taxon-based faunal analyses (Hill, 1981; Kingston, 2007), a number of more recent developments have transformed hominin paleoecology: (1) development of geochemical and morphological tools for quantitatively reconstructing specific terrestrial environmental parameters, including paleovegetation (Cerling et al., 2011; Magill et al., 2013b; Barr, 2015; Plummer et al., 2015), paleoaridity (Levin et al., 2006), and paleotemperature (Passey et al., 2010); (2) the availability of increasingly large, long-term, intra- and inter-basinal fossil and isotopic datasets (Bobe et al., 2007; Cerling et al., 2011; Levin et al., 2011; Bibi and Kiessling, 2015; Cerling et al., 2015a; Lüdecke et al., 2016); (3) greater focus on multi-proxy perspectives on paleoenvironmental change (deMenocal, 2004; Behrensmeyer, 2006; Kingston, 2007; Trauth et al., 2007; Bibi et al., 2013; Feakins et al., 2013; Levin, 2015; Plummer et al., 2015).. ENVIRONMENTAL DETERMINANTS OF HUMAN EVOLUTION There are a number of useful reviews on environments and human evolution (Potts, 1998b; deMenocal, 2004; Behrensmeyer, 2006; Kingston, 2007; Potts, 2007; deMenocal, 2011; Potts, 2012a; 2013; Levin, 2015; Maslin et al., 2015), all of which have contributed to the following discussion. Environmental determinants of human evolution can be classified by mode and tempo of inferred climatic or ecological change: (1) long-term environmental persistence, (2) long-term environmental change, (3) punctuated environmental change, and (4) continuous environmental change. In the following discussion, I differentiate between climatic (moisture, temperature) and ecological (vegetation, fauna) determinants.. 2.
(19) Long-term environmental persistence Ecology The model of long-term ecological persistence is a form of the “savanna hypothesis” (that I would term the “savanna persistence hypothesis”), which focuses on a long-term association of hominins with savannas since the last common ancestor with chimpanzees (Dart, 1925; Bartholomew and Birdsell, 1953; Jolly, 1970; Brain, 1981; Laporte and Zihlman, 1983; Bender et al., 2012; Domínguez-Rodrigo, 2014). This model is supported by woody cover reconstructions using the carbon isotopic composition of paleosol carbonates, which demonstrates the dominance of relatively open habitats (woody cover <50%) in the OmoTurkana and Awash Basins throughout the past 6 million years (Cerling et al., 2011). However, it remains uncertain if woody cover variation within savanna biomes is important for hominin adaptation (Cerling et al., 2011). The savanna biome is inherently heterogeneous and may be associated with a coherent set of selection pressures related to resources availability and predation risk regardless of variation in vegetation structure within the biome (DomínguezRodrigo, 2014). Colloquial misuse of the term savanna is common, but the following ecological definition is widely accepted: a mixed C4 grass-tree landscape with a continuous grass/herbaceous ground layer and a discontinuous woody layer maintained by rainfall, fire, herbivory, and soil fertility (Scholes and Archer, 1997; Sankaran et al., 2005; Good and Caylor, 2011; Lehmann et al., 2011; Ratnam et al., 2011; Guan et al., 2014; Parr et al., 2014). This definition corresponds to ca. 1080% woody cover, which includes vegetation structure categories grassland, wooded grassland, and woodland/bushland/thicket/shrubland, as defined by the United Nations Educational, Scientific, and Cultural Organization (UNESCO) (F. White, 1983). Grasslands are defined as. 3.
(20) <10% woody cover, and should not be equated with savannas, although both savannas and open grasslands can be identified as tropical grassy biomes that are associated with a unique set of ecological processes and interactions that contrast with tropical forest, steppe, and desert biomes (Parr et al., 2014). The savanna hypothesis has received attention in recent debates on the environmental context of the putative early hominin Ardipithecus ramidus at Aramis ca. 4.4 Ma (T. D. White et al., 2009; Cerling et al., 2010; 2014; Domínguez-Rodrigo, 2014; T. D. White, 2014; Cerling et al., 2015b; T. D. White et al., 2015). Ar. ramidus was originally described as inhabiting a primarily wooded habitat (T. D. White et al., 2009; WoldeGabriel et al., 2009), which in combination with relatively closed, wooded environmental reconstructions of other late Miocene-early Pliocene putative hominins (Sahelanthropus, Orrorin, Ardipithecus) (WoldeGabriel et al., 1994; Pickford and Senut, 2001; WoldeGabriel et al., 2001; T. D. White et al., 2009; WoldeGabriel et al., 2009) was used to falsify the savanna hypothesis. However, geological and isotopic evidence demonstrates that the environments of all three putative early hominin genera included open areas with C4 grass (Zazzo et al., 2000; Vignaud et al., 2002; Levin et al., 2008; T. D. White et al., 2009; WoldeGabriel et al., 2009; Cerling et al., 2010; 2011; Bamford et al., 2013; Roche et al., 2013), and mixed C3-C4 plant communities including a mosaic of grassy and wooded habitats are entirely consistent with the ecological definition of the savanna (Domínguez-Rodrigo, 2014; Cerling et al., 2015a).. Climate The model of long-term climatic persistence focuses on a long-term association of hominins with high temperatures (Passey et al., 2010). This model is supported by clumped-. 4.
(21) isotope paleothermometry, which demonstrates that hominins would have had to accommodate consistently or repeatedly high thermal stress throughout the Plio-Pleistocene (Passey et al., 2010). Fossil soil temperatures from ca. 4 to 1 million years ago were greater than modern soils in the Turkana Basin, which is one of the hottest areas on Earth today. This technique has not yet been widely applied in paleoanthropological studies outside of the Turkana Basin.. Long-term environmental change Ecology The model of long-term ecological change is a different version of the savanna hypothesis (that I would term the “C4 grass expansion hypothesis”), which focuses on a longterm trend from ca. 4-1 million years ago towards increasing prevalence of open C4 grass- and grazer-dominated landscapes, based on faunal, isotopic, pollen, and phytolith records (Cerling, 1992; Stanley, 1992; Behrensmeyer et al., 1997; Reed, 1997; Bobe and Behrensmeyer, 2004; Wynn, 2004; Feakins et al., 2005; Bobe et al., 2007; Bonnefille, 2010; Cerling et al., 2011; Levin et al., 2011; Barboni, 2014; Plummer et al., 2015; Cerling et al., 2015a). This differs from the savanna persistence hypothesis in that it focuses on the culmination of a long-term trend towards generally more open environments in the early Pleistocene, and is not associated with the earliest stages of human evolution. Faunal and isotopic analyses demonstrate that the timing and magnitude of long-term ecological changes vary within and across basins (Bobe et al., 2007; Cerling et al., 2011; Levin et al., 2011), suggesting that additional long-term records are needed to understand regional variability in the expansion of grass-dominated biomes. The expansion of savannas is often linked with an increase in environmental heterogeneity and a broadening of hominin habitat use in the early Pleistocene (Bobe and Behrensmeyer, 2004; Plummer, 2004;. 5.
(22) Wynn, 2004; Kingston, 2007; Plummer et al., 2009; Barr, 2015; Plummer et al., 2015; Reynolds et al., 2015), although directly assessing the spatial heterogeneity of hominin paleoenvironments remains a challenge.. Climate The first model of long-term climatic change is the cooling model, which suggests that global cooling associated with the development of high-latitude ice sheets (Shackleton et al., 1984; Zachos et al., 2001) was an important driver of speciation and extinction across mammalian lineages that in turn determined the ecological context of human evolution (Brain, 1981; Vrba, 1988; 1992; 1995a; 1996). However, the effects of global cooling varied regionally, and the tropics may have been buffered against high-latitude climate change (i.e. glaciation) (Marlow et al., 2000; Ravelo et al., 2004; Denison et al., 2005; Feakins and deMenocal, 2010). Additionally, more recent geological and paleoclimatic work demonstrates that long-term trends in Neogene African climate change are more likely driven by Milankovitch periodicities in insolation (deMenocal, 2004; Trauth et al., 2009; Maslin et al., 2014) and geological processes such as tectonic uplift (Slingo et al., 2005; Trauth et al., 2005; Sepulchre, 2006; Spiegel et al., 2007; Trauth et al., 2007; Kaspar et al., 2010; Prömmel et al., 2013; Lepre, 2014) rather than long-term cooling. The second model of long-term climatic change is the aridity model, which suggests that regional African aridification since the late Miocene represents an important driver of hominin origins and evolution, particularly by driving grass expansion and changing the distribution of habitats and food resources (Vrba, 1989; Stanley, 1992; Bromage and Schrenk, 1995; deMenocal, 1995; Reed, 1997; deMenocal, 2004; Zhang et al., 2014). Regional aridification has. 6.
(23) been inferred from marine records of dust (deMenocal, 1995; 2004) and pollen (Bonnefille, 2010), terrestrial faunal (Reed, 1997; Bobe and Eck, 2001; Bobe and Behrensmeyer, 2004; Bobe, 2006; Fernández and Vrba, 2006; Bobe et al., 2007; Bobe and Leakey, 2009; Bibi and Kiessling, 2015), and paleosol carbon (deMenocal, 2004; Wynn, 2004; Sepulchre, 2006; Spiegel et al., 2007; Maslin et al., 2014) and oxygen (Cerling et al., 1977; Cerling and Hay, 1986; Cerling et al., 1988; Levin et al., 2011) isotope records, as well as climate models (Sepulchre, 2006; Prömmel et al., 2013; Sommerfeld et al., 2014). However, the most commonly used terrestrial aridity indicators (the abundance of C4 vegetation and alcelaphini and antilopini bovid tribes) are likely biased by ecology (diet, habitat), and an independent terrestrial paleoaridity proxy is needed evaluate local- and basin-scale changes in water availability (Levin, 2015).. Punctuated environmental change Ecology The model of punctuated ecological change is the turnover-pulse hypothesis, which suggests that periodic pulses of synchronized speciation and extinction among mammalian herbivore lineages during intervals of cold, arid, variable climate represent periods of habitat restructuring relevant to hominin evolution (Vrba, 1985; 1988; 1992; 1995b; 1995a; 1999). It was suggested that climate (warm, cold) and dietary (specialist, generalist) adaptations determined patterns of turnover. However, subsequent faunal studies suggest that the relationship between climate and faunal change is less straightforward than previously believed (Behrensmeyer et al., 1997; Bobe and Eck, 2001; Bobe and Behrensmeyer, 2004; Bibi and Kiessling, 2015), and the relevance of less punctuated faunal turnover to hominin environments is unclear.. 7.
(24) Climate The model of punctuated climatic change is the pulsed climate variability hypothesis, which suggests that long-term aridification in eastern Africa was punctuated by periodic humid intervals, and that wet-dry cycling was associated with extreme environmental variability that caused speciation and extinction among hominin taxa (Trauth et al., 2007; Maslin and Trauth, 2009; Trauth et al., 2010; Shultz and Maslin, 2013; Maslin et al., 2014; 2015; Trauth et al., 2015). The presence of large lakes is suggested to have caused vicariance and allopatric speciation among hominin populations, assuming lakes represent sufficient barriers to gene flow (Trauth et al., 2010). Regional humid periods are inferred from compilations of sedimentological data indicating the appearance of large lakes, which seem to appear at 400-kyr and 800-kyr periodicities associated with orbital forcing (Trauth et al., 2007). However, identifying the timing and stability of lake formation can be ambiguous (Owen et al., 2008; 2009; Trauth and Maslin, 2009; Lepre, 2014), and the relative importance of climate versus tectonic forcing is not always straightforward (Bergner et al., 2009). It may be that some but not all lakes represent sensitive indicators to climate change (Olaka et al., 2010; Trauth et al., 2010; Borchardt and Trauth, 2012).. Continuous environmental change Ecology The model of continuous ecological change is the shifting heterogeneity model, which suggests that hominin environments since the late Miocene were characterized by constantly changing patterns of spatial environmental heterogeneity (Kingston, 2007). The model assumes that variation in solar insolation on Milankovitch (precession) periodicities drives patterns of. 8.
(25) rainfall seasonality in tropical Africa that, mediated by tectonic activity and global climate events, results in shifting patterns of plant and animal distribution and community structure. These processes would ultimately determine the abundance and distribution of resources and drive hominin dispersal patterns. Consistent with predictions of this model, Milankovitch periodicities are evident in Plio-Pleistocene records of climate (Deino et al., 2006; Ashley, 2007; Kingston et al., 2007; Lepre et al., 2007; Joordens et al., 2011; Magill et al., 2013a) and vegetation (Magill et al., 2013b). However, hydroclimate does not always respond to orbital forcing in a synchronous manner across eastern and central African lake basins (Joordens et al., 2011; Deino, 2012; Berke et al., 2014; Lepre, 2014), suggesting that additional work is needed to investigate the uniformity of environmental feedbacks to Milankovitch cyclicity.. Climate The model of continuous climatic change is the variability selection hypothesis, which suggests that a long-term increase in, or sustained periods of, environmental variability (in time and/or space) enhances instability in selective pressures, leading to the evolution of increased adaptive versatility or adaptability (Potts, 1996; 1998a; 1998b; 2007; 2012b). The model suggests that adaptations that increase fitness in novel environments given variable selective conditions will ultimately be more evolutionarily successful than adaptations for specific habitats and/or consistent selective conditions. Regular or predictable patterns of environmental variability, such as seasonal- or Milankovitch-scale cycles, is not considered to meet these criteria. The notion that environmental variation increased over the Plio-Pleistocene is based primarily on global climate records from marine cores, and assumes that regional climate in eastern Africa also became more variable over time, and that climate variability is associated. 9.
(26) with ecological variability. Periods of high variability (wet-dry cycling), predicted on the basis of eccentricity-modulated precession of solar insolation and recognized in marine dust and sapropel records, are linked to sedimentary records of environmental variability and key events in human evolution (appearance or disappearance of species and stone tool industries) (deMenocal, 2004; 2011; Potts, 2013; Potts and Faith, 2015). Mathematical modeling (Kussell and Leibler, 2005; Grove, 2011a; 2011b; Carja et al., 2014) and observational studies on other organisms (Woods et al., 2011; Brown et al., 2013) support the feasibility of variability selection as a fitnessenhancing mechanism. There is increasingly abundant terrestrial evidence for climate variability at various time intervals in the geological record in eastern Africa, on Milankovitch- to millennial-scales (Deino et al., 2006; Ashley, 2007; Kingston et al., 2007; Lepre et al., 2007; Scholz et al., 2007; Trauth et al., 2007; Larrasoaña et al., 2013; Magill et al., 2013a; Berke et al., 2014; Wilson et al., 2014; Trauth et al., 2015), and high resolution pollen (Bonnefille et al., 2004) and leaf wax biomarker records (Magill et al., 2013b) demonstrate substantial ecological remodeling associated with climatic variability. More work is needed to evaluate the relationship between climate (wet versus dry) and variability in local ecological conditions (plant-animal communities) relevant to hominin survival. Additionally, it remains unclear if long-term increases in large-scale climate variability are associated with increasingly variable local, terrestrial environmental conditions.. Summary These perspectives are not necessarily mutually exclusive, and largely reflect time-space scale differences of available paleoclimate and paleoecology proxies (Behrensmeyer et al., 2007; Kingston, 2007). For example, marine records are typically continuous and characterized by high. 10.
(27) time resolution and low spatial resolution, while terrestrial records are typically discontinuous and characterized by relatively low time resolution and high spatial resolution. Ultimately, perspectives of environmental variation likely need to be integrated with perspectives of longterm environmental persistence or change. For example, the long-term persistence of the savanna biome need not imply that climatic and environmental conditions were static, but instead that within a given range of variation certain ecological processes might have occurred throughout a certain period of time. A cohesive theory that integrates these disparate climatic and ecological processes into a single framework that identifies adaptively significant environmental variation is ultimately needed to test cause-effect relationships between environmental change and human evolution (Kingston, 2007).. OBJECTIVES In this dissertation I investigate hominin environments during the Plio-Pleistocene in eastern Africa. To evaluate the relationships between changes in climate and ecology I focus on isotopic records in mammal tissues. I follow two general approaches: (1) analysis of tissues/excreta and foods of modern animals (mammalian herbivores, primates) as ecological analogs for paleo-ecosystems, and (2) analysis of fossils to directly evaluate aspects of hominin environments (climate, vegetation, fauna). The study of modern materials includes carbon and nitrogen isotope analysis of plants and primate excreta as well as carbon and oxygen isotope analysis of mammalian herbivore tooth enamel. The study of fossil materials includes carbon and oxygen isotope analysis of mammalian herbivore tooth enamel. Mammalian tooth enamel isotopes records reflect ecological information at the time scale of fossil preservation (101-5 years) and the spatial scale of fossil collection and herbivore ecology. 11.
(28) (100-4 km), and are well-suited to investigate local, terrestrial conditions experienced by hominins (Kingston, 2007; Bedaso et al., 2013; Cerling et al., 2015a). Other available paleoenvironmental proxies include herbivore taxonomic abundance (Vrba, 1980; Bobe et al., 2002; Bobe and Behrensmeyer, 2004; Bobe et al., 2007; Bibi and Kiessling, 2015), community structure (Andrews et al., 1979; Reed, 1997; Reed and Russak, 2009; Louys et al., 2014), locomotor ecomorphology (Plummer and Bishop, 1994; Kappelman et al., 1997; Kovarovic and Andrews, 2007; Barr, 2015; Plummer et al., 2015), craniodental morphology (Spencer, 1997), and dental wear patterns (Fortelius and Solounias, 2000; Ungar et al., 2007; Louys et al., 2012; Scott, 2012), as well as pollen (Bonnefille et al., 2004; Bonnefille, 2010), phytoliths (Barboni et al., 1999; 2010), and the carbon isotopic composition of leaf wax biomarkers (Magill et al., 2013b) and paleosol carbonates and organic matter (Cerling, 1992; Cerling et al., 2011). Compared to conventional morphological approaches, enamel isotopic analyses are less biased by taxonomic uniformitarianism, observer or classification error, and decoupled changes in environments, behavior, and morphology (Domínguez-Rodrigo and Musiba, 2010; Bibi et al., 2013; DeSantis et al., 2013; Lister, 2013; Louys et al., 2015). Additionally, enamel isotope records provide an ecological perspective that includes the diets and habitats of other animals on the landscape, unlike non-faunal proxies, such as paleosols or pollen. However, while enamel isotopic records are useful for evaluating long-term trends, short-term variation is often masked due to the discontinuous and time-averaged nature of the terrestrial macrofossil record. Therefore, I focus on evaluating evidence for long-term environmental persistence and change. I focus on southwestern and northern Kenya, where sediments preserve abundant fossil and archaeological material spanning the Pliocene and Pleistocene. I use carbon and oxygen isotopic records in fossil herbivore tooth enamel to reconstruct adaptively significant. 12.
(29) environmental parameters, including aspects of vegetation and faunal ecology, aridity, and seasonality during the Pliocene and Pleistocene. The development of long-term paleoclimatic and paleoecological records in southwestern Kenya provides a new perspective on regional variability in environmental change. The first part of this dissertation is focused on the ecology of primates and hominins. Modern tropical African ecosystems provide a useful model for understanding the ecological correlates of isotopic variation in the fossil record, and living primates provide a useful model for understanding the ecological significance of isotopic variation in fossil hominin tissues. In Chapters 1 and 2, I report on isotopic studies on the ecology of plants and primates in southwestern Uganda. These studies contribute to a growing body of literature on the isotopic composition in modern primate tissues/excreta and tropical plants by evaluating how isotopic variation is sensitive to aspects of diet and habitat. I show that isotopic variation in plants (Chapters 1 and 2) and great ape tissues (Chapters 2) primarily relate to differences in diet. The magnitude of isotopic variation in gorilla feces, which relates to intra-annual dietary variability, demonstrates that African apes have less isotopically variable diets than fossil hominins (Chapter 2). In Chapter 3, I use the carbon isotopic composition of fossil teeth of large mammalian herbivore Artiodactyla-Perisodactyla-Proboscidea (APP) taxa in southern Kenya (& northern Tanzania), northern Kenya (Turkana), and northern Ethiopia (Afar) to investigate the long-term changes in herbivore diet and ecosystem structure. I find that there is a long-term increase in the proportional representation of C4-grazing taxa over time, primarily at the expense of C3-C4 mixed feeding taxa. Pleistocene and Holocene ecosystems in southwestern Kenya, where there is the most complete record over the past 2 million years, are dominated by C4-grazers. The. 13.
(30) prevalence of C4-grazer dominated ecosystems since the early Pleistocene contrasts with the abundance of C3 browsers and woody vegetation among most modern savanna/mosaic biomes in the Lake Victoria region and across eastern Africa. Therefore, modern ecosystems may have developed recently, and may not provide useful analogs for reconstructing ancient environments as recently as the last few millennia. These findings suggest that ecological processes and interactions, rather than simply climatic forcing, are important for understanding human evolution among expanding C4 grass-dominated environments. The second part of this dissertation is focused on climate and human evolution. The notion that aridity and seasonality have increased over the Pliocene and Pleistocene has remained central to models of environmental change (i.e. C4 grass expansion) and human evolution; however, few empirical records of terrestrial climate are available to assess this claim. In Chapter 4, I revise an existing aridity index for estimating water deficit in the fossil record using the oxygen isotopic composition of mammalian herbivore tooth enamel. I present a large compilation of new and existing oxygen isotope values in modern herbivore teeth from eastern and central Africa to identify taxa that are sensitive (ES) and insensitive (EI) to evaporation, primarily due to differences in drinking behavior, and show that the oxygen isotopic enrichment between ES and EI taxa can be used to calculate water deficit. I use oxygen isotope values in fossil teeth from eastern Africa, primarily the Turkana Basin, to reconstruct paleoaridity over the Plio-Pleistocene. I show that mesic and arid conditions were both prevalent during periods of fossil preservation, demonstrating that hominins experienced variable climatic conditions and were able to accommodate highly arid conditions as early as >4 Ma. There is no long-term trend in aridity, which demonstrates that ecological changes associated with the expansion of C4 vegetation and C4 grazers may not have been driven by changes in water availability.. 14.
(31) In Chapters 5 and 6, I focus on reconstructing seasonality in the fossil record. Tooth enamel microsampling has long been suggested to provide a means to reconstruct climate (i.e. rainfall) seasonality in the hominin fossil and archaeological record; however, this approach has not been widely applied due to problems associated with signal time-averaging due to enamel maturation and sampling, and a lack of understanding of how seasonality is recorded in enamel isotopic profiles in eastern African herbivores. In Chapter 5, I evaluate the relationship between enamel mineralization and intra-tooth isotope profiles, focusing on an incisor from a woodrat subjected to an experimentally induced, isotopically controlled water-switch. I show that in situ sampling techniques, including laser ablation and secondary ion mass spectrometry (SIMS), can be used to sample discrete enamel maturation layers, and demonstrate that reducing sample spot size is not effective for reducing signal time-averaging. I also show that backscattered electron imaging in the scanning electron microscope (BSE-SEM) can be used to estimate changes in enamel mineral content along the growth axis with high spatial resolution. The innermost enamel layer (<20 µm from the enamel-dentine junction) is more highly mineralized than other enamel layers early in the maturation process, and sampling within this zone using SIMS provides the least time-averaged isotope profile. Lastly, in Chapter 6 I focus on enamel mineralization and microsampling in wild large mammals (equids). I demonstrate that in situ sampling with laser ablation is useful for investigating the relationships between enamel maturation and isotopic variability in large mammal teeth, but is not ideal for widespread application because it requires destructive sectioning and does not effectively remove signal time-averaging compared to conventional (hand drill) sampling. Using conventionally sampled wild eastern African equid teeth, I show that there is a linear relationship between intra-tooth oxygen isotopic variability and intra-annual. 15.
(32) oxygen isotopic variability in precipitation. Using this approach, I estimate the magnitude or intensity of intra-annual variation in precipitation in the fossil record. Pleistocene hominins in southwestern Kenya would have experienced seasonal rainfall, similar to modern eastern African climates. No trend over time was detected in fossil intra-tooth δ18O range, although the number of localities and time periods included in this analysis are limited. In summary, isotopic records from mammal tissues in this dissertation demonstrate new ways to investigate relationships between climate and ecology in Pliocene-Pleistocene hominin environments. Carbon isotopes in modern primate excreta provide insight into the ecology of fossil hominins, and carbon isotopes in fossil mammalian herbivore tooth enamel provide insight into the plant-animal communities that determine selective conditions experienced by hominins. Oxygen isotopes in mammalian herbivore tooth enamel provide the records of terrestrial climate, including aridity and seasonality, in eastern Africa. These findings provide new detail on hominin environments, and provide a critical test of long-assumed relationships between climate and ecology.. REFERENCES Andrews, P., Lord, J.M., Nesbit Evans, E.M., 1979. Patterns of ecological diversity in fossil and modern mammalian faunas. Biological Journal of the Linnean Society. 11, 177–205. Ashley, G., 2007. Orbital rhythms, monsoons, and playa lake response, Olduvai Basin, equatorial East Africa (ca. 1.85–1.74 Ma). Geology. 35, 1091–1094. Bamford, M.K., Senut, B., Pickford, M., 2013. Fossil leaves from Lukeino, a 6-million-year-old Formation in the Baringo Basin, Kenya. Geobios. 46, 253–272. Barboni, D., 2014. Vegetation of Northern Tanzania during the Plio-Pleistocene: A synthesis of the paleobotanical evidences from Laetoli, Olduvai, and Peninj hominin sites. Quaternary International. 322-323, 264–276. Barboni, D., Ashley, G.M., Domínguez-Rodrigo, M., 2010. Phytoliths infer locally dense and heterogeneous paleovegetation at FLK North and surrounding localities during upper Bed I time, Olduvai Gorge, Tanzania. Quaternary Research. 74, 344–354. Barboni, D., Bonnefille, R., Alexandre, A., Meunier, J., 1999. Phytoliths as paleoenvironmental indicators, west side Middle Awash Valley, Ethiopia. Palaeogeography Palaeoclimatology. 16.
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