Collaborators from four institutions will address the ecological and evolutionary responses of mammals from the Miocene fossil record of Pakistan to changes in global climate, sea level, tectonic barriers, and immigrant species. The Siwalik record consists of highly fossiliferous Neogene sediments deposited in the Himalayan foreland basin from Pakistan to Myanmar. In the Potwar Plateau of Pakistan, this record provides an unparalleled history of faunal and environmental change in a continuous sequence of strata spanning the last 18 million years. During this time period, mammalian paleocommunities exhibited a changing mixture of cosmopolitan groups, endemic lineages, and relict taxa. Environmental processes that may have driven these faunal changes are known from deep-sea cores and other geological evidence. These processes occurred at different biogeographic scales, ranging from those of the global climate system and sea level to regional (South Asian) tectonism to the local floodbasin and its vegetation and local climate. The proposed analyses will test the relationship between environmental processes and biological responses by (1) evaluating mammalian faunal change under different geodynamic and climatic conditions over the interval between 18.0 and 5.5 million years ago, and (2) integrating multiple indicators of changing paleoclimate from the Siwalik record, including a new geochemical method for estimating soil moisture using iron oxides, information from snail opercula about seasonality of precipitation, stable isotopes from tooth enamel and soil carbonate, and measures of diet and body size for extinct mammals using functional morphology.
The primary goal of this collaborative research project was to evaluate the influences of geological and climatic processes on changes in terrestrial ecosystems of northern Pakistan between 18 and 5 million years ago. Our research group, consisting of paleontologists, paleoanthropologists, geologists, and geochemists, has studied a thick sequence of fossiliferous sediments in northern Pakistan. This sequence represents a huge floodplain ecosystem that was the precursor to the Indus and Ganges river systems of today. Our research group studied fossils that were collected over many field seasons in Pakistan, refining the taxonomy of specific mammal groups, analyzing wear features on mammal teeth indicative of dietary behavior, sampling several hundred teeth and gastropod opercula for stable isotopes of carbon and oxygen, and developing new indicators of climatic conditions. This research is a collaboration among investigators from our four institutions with colleagues at the Geological Survey of Pakistan and the Pakistan Museum of Natural History. Intellectual merit: We developed a conceptual framework for analyzing the influence of geological and climatic processes on ecosystem changes. For the Indian subcontinent, mountain ranges at the contact zone between the Indian tectonic plate and the Asian tectonic plate have been actively rising for many millions of years. The height and ruggedness of these mountains make them an effective barrier against many organisms moving back and forth between the Indian subcontinent and surrounding regions. We reasoned that the effectiveness of these mountains as barriers would have waxed and waned depending on the height of the mountains, whether coastal regions at low elevation were present as a corridor for dispersal, and whether regional climates were stable or changing. These factors in different combinations give rise to four alternative geohistorical states (see Figure 1) as environmental context for ecosystem responses. First principles of ecology and evolutionary processes indicate that each state should lead to a different set of ecological and evolutionary outcomes (see Figure 2). In the context of this framework, we analyzed the record of fossil mammals from Pakistan, based on data that assembled over many years of fieldwork and study. We analyzed the appearances and disappearances of species, changes in taxonomic composition, and changes in ecological properties of mammals over four time intervals that correspond to different geohistorical states. We compared the observed changes to the changes expected under our conceptual framework. Figure 3 depicts this comparison for the large mammals of this record (large refers to mammals with estimated body weights of 1 kilogram (size of a rabbit) or more (the largest species weighed more than 1000 kg)). Figure 4 depicts this comparison for small mammals (rodents and insectivores, with estimated body weights less than 1 kilogram). For both large mammals and small mammals, the observed rates of appearance and disappearance of species, net change in diversity, and changes in faunal proportions (taxonomic and ecological) match quite well the predicted changes in Figure 2. The greatest observed rates of faunal change occurred during periods of climatic change, but more subtle changes occurred even during periods of climatic stability. The responses of large mammals and small mammals were generally similar, but small mammals showed more changes during intervals of climatic stability. These results largely support our conceptual framework and suggest that mountain barriers, sea level, and climate change have been important influences on the history of terrestrial ecosystems in this sequence. Regarding paleoclimatic indicators, research on iron oxide ratios utilized samples from ancient soils and previous information on oxygen isotopes. Higher amounts of goethite vs. hematite are associated with increased seasonal moisture in the original soils. A pilot investigation of growth banding in the opercula (entrance lids) of the semi-aquatic snail, Pila, demonstrated that growth bands in modern SE Asian species track seasonal rainfall fluctuations. Fossil opercula are thicker, suggesting adaptation to more extreme dry periods in the ancient floodplain ecosystems. Outcomes from this research include five book chapters, six papers in scientific journals, 12 conference presentations, and an informational website. This research has also stimulated plans for a monograph about the history of environmental and faunal change in this sequence. Broader impacts: This research supported undergraduate theses and research projects, graduate-student training and dissertation research, and postdoctoral training and research. In addition, we designed an informational website for public use and are contributing content to the design of the new fossil hall at the National Museum of Natural History, Smithsonian Institution. We continued collaborating with colleagues at the Geological Survey of Pakistan and the Pakistan Museum of Natural History, and initiated collaborations with paleontologists in Spain to compare the long records of environmental and faunal change from Pakistan and Spain. We are curating fossils on loan from the Geological Survey of Pakistan and maintain an electronic database with information about fossil specimens and localities. Information from this database has contributed to online databases about fossil mammals.
