Type of Document Dissertation Author Biasatti, Dana Michelle Author's Email Address firstname.lastname@example.org URN etd-04112009-113712 Title Paleoenvironments and Paleoecologies of Cenozoic Mammals from Western China based on Stable Carbon and Oxygen Isotopes Degree Doctor of Philosophy Department Geological Sciences, Department Advisory Committee
Advisor Name Title Yang Wang Committee Chair Leroy Odom Committee Member Vincent Salters Committee Member Gregory Erickson Outside Committee Member Keywords
- Carbon Isotopes
- Cenozoic Mammals
- Oxygen Isotopes
Date of Defense 2009-02-16 Availability unrestricted AbstractThree main objectives in this study were: 1) to examine climate variability throughout the Late Cenozoic and test hypotheses regarding the development of C4 ecosystems and the dynamics of the Asian monsoons in NW China; 2) to reconstruct the diets, habitats, and paleoclimates of fossil rhinocerotoids from the Linxia Basin, Gansu, China; and 3) to examine paleodiets, paleoecologies, and paleoclimates of extinct taxa and test previous hypotheses regarding expansion of C4 grasses in SW China.
To examine climate variability in NW China throughout the Late Cenozoic and to test hypotheses regarding the development of C4 ecosystems and the dynamics of the Asian monsoons, the carbon and oxygen isotopic compositions of bulk tooth enamel samples from 158 fossil mammals from the Linxia Basin, ranging in age from 25 Ma to the present, were determined and serial carbon and oxygen isotopic analyses of 368 samples from 23 fossil and modern herbivore teeth were performed. The results indicated significant changes in the climates and diets of mammalian taxa from the Linxia basin, as well as in the seasonal patterns of diet and climate, over the last 25 million years. The bulk oxygen isotope data indicated an unstable climate in the Linxia Basin from 25 to 0.05 Ma and fluctuations in the oxygen isotope data throughout the entire sedimentary sequence were consistent with previous studies that indicated a general global warming trend from ~26 Ma to 15 Ma and two major cooling phases during the Neogene. In addition, a positive delta 18-O shift in the data was similar in timing to a positive delta 18-O shift observed in fossils and paleosols from Pakistan and Nepal, suggesting a shift toward a drier and/or warmer climate on both the north and south sides of the Tibetan Plateau during the Late Miocene. Bulk delta 18-O values of fossil tooth enamel from bovids, deer, giraffes, pigs, and elephants were consistent with the positive and negative trends in horse and rhino mean delta 18-O values. The bulk carbon isotope results indicated that horses and rhinos from the Linxia Basin had pure C3 diets throughout most of the Late Cenozoic. The horse bulk delta 13-C values indicated a change to a mixed C3/C4 diet after 2.5 Ma, suggesting that C4 grasses may have not spread into the basin until after 2.5 Ma. This is much later than the proposed global C4 expansion during the Late Miocene and indicates a strengthening of the Asian summer monsoon after ~2.5 Ma, as C4 plants require sufficient summer precipitation. The data also indicated an open environment, such as a savannah or mixed woodland/steppe biome in the Linxia Basin from ~25 to 0.05 Ma. The carbon isotope compositions of enamel from bovids, deer, giraffes, pigs, and elephants were similar to those of horses and rhinos at any given age. Serial oxygen isotopic analyses showed that positive shifts to either drier and/or warmer conditions after 14, 9.5, 7.5, and 2.5 Ma were accompanied by increased seasonality and negative shifts in the bulk data at 11.5, 6.0, 4.0, and 1.2 Ma were associated with decreased seasonality. A marked increase in the serial delta 18-O ranges of both horses and bovids after 2.5 Ma is consistent with a strengthening of the summer monsoon in the region after ~2-3 Ma. The serial carbon isotope results showed that prior to 1.2 Ma, all sampled mammalian taxa had pure C3 diets. The delta 13-C ranges of all horses from or prior to the age of 2.5 Ma were smaller than those of horses from 1.2 and 0.05 Ma, which further supports changes in the composition of plant biomass in the Linxia Basin after ~2.5 Ma, as taxa with mixed C3/C4 diets would have increased delta 13-C ranges in their enamel compared to those with pure C3 diets. A negative correlation between the delta 18-O and delta 13-C values of horses from ~1.2 and ~0.05 Ma is consistent with that expected in summer monsoon regions within China and strongly supports a strengthening of the summer monsoon after 2-3 Ma. Serial analyses of five bovid individuals from ~2.5 Ma and later also showed an anti-correlation between delta 13-C and delta 18-O values for all individuals, providing further support for an enhanced monsoon climate since about 2-3 Ma.
The diets, habitats, and paleoclimates of fossil rhinocerotoids from the Linxia Basin, Gansu, China, ranging in age from 25 to 2.5 Ma, were reconstructed based on bulk and serial carbon and oxygen isotope analyses of tooth enamel. Bulk isotope analyses of 47 rhino individuals representing 11 genera and serial analyses of 15 of those individuals were performed. In addition, the bulk C and O isotopic compositions of teeth from 5 9-Ma Chilotherium individuals from the nearby Tianshui Basin were determined. The results support many previous hypotheses inferred from taxonomy and cranial and limb morphology and offer new insight on the paleoecologies of some genera. The isotopic results support the following previous hypotheses: the Late Oligocene rhino Paraceratherium inhabited a forested environment, and the coexisting rhino Allacerops lived in a relatively open habitat and had a less specialized diet; the Early Miocene Hispanotherium grazed in open steppe territory, whereas the contemporaneous Alicornops had a more generalized diet in a forested environment; and the Late Miocene rhino Parelasmotherium grazed in an open steppe habitat. The data are inconsistent with previous inferences that the rhinos Acerorhinus and Dicerorhinus dwelled in forested environments. Instead, the results indicate that these two rhinos inhabited open steppe environments. The isotopic results are not conclusive concerning the habitat of Iranotherium, but support previous hypotheses that this rhino was a specialized C3 grazer. The results also suggest that Chilotherium was a forest-dweller throughout much of the Late Miocene, but occupied a more open environment by the end of the Late Miocene. Additionally, the results are consistent with previous hypotheses that the Pliocene rhinos Shansirhinus and Coelodonta were grazers in open habitats. In general, the oxygen isotope data suggest a warming and/or drying trend in the Linxia Basin from the Late Oligocene to Late Miocene with cooling phase throughout much of the Pliocene and indicate that the regional climate was not strongly influenced by the Asian monsoon prior to 6 Ma. Finally, the carbon isotope data support that all rhinos in this study were pure C3 feeders, which suggests that C4 grasses were not an important component of the plant biomass in the Linxia Basin prior to 2.5 Ma.
To examine paleodiets, paleoecologies, and paleoclimates of extinct taxa and to test previous hypotheses regarding a global expansion of C4 grasses, the carbon and oxygen isotopic compositions of 164 fossil herbivore teeth and 10 soil samples from six localities in Yunnan Province, China, ranging in age from ~10 Ma to the present, were determined. The results reveal significant changes in the environments and diets of mammalian taxa from various regions of Yunnan Province over the last 10 million years. Prior to 2-3 Ma, while most mammals had pure or nearly pure C3 diets, some individuals may have consumed a small amount of C4 grasses (<30% C4). Since then, C4 grasses became a significant dietary component of most herbivores as indicated by higher enamel-delta 13-C values at Yuanmou and Shangri La, most likely reflecting an increased C4 biomass in local ecosystems. The carbon isotope results showed that the diets of mammals aged ~2.5 to 1.75 Ma from Shangri La ranged from pure C3 to pure C4, while 1.7 Ma horses from Yuanmou had 0-50% C4 in their diets. The paleoenvironment of Zhaotong was more open and/or water-stressed than that of Kaiyuan at ~4 Ma. Mammals living at both ~8 and 7.5 Ma in the Lufeng region had very similar diets, habitats, and experienced similar climatic conditions. Increased C4 biomass after ~2-3 Ma suggests a significant change in certain aspects of the regional climate, such as increased seasonality of rainfall or an increase in seasonal drought and fires, as these factors are important to modern grasslands. The data also indicated a change from a largely forested environment at ~8 Ma to an increasingly drier and more open environment with a mosaic of forests and grasslands after ~2-3 Ma in the Yuanmou region. Niche partitioning of various taxa from the Yuanmou Basin was also evident from the carbon isotope results. The data suggested that horses and rhinos fed in more closed or forested environments than did pigs, tragulids, and chalicotheres and that elephants may have fed in both closed and open environments. The oxygen isotope compositions of ~7.5 and 8 Ma mammals from Lufeng suggest very similar climatic conditions at both ages in that region. The oxygen isotope results show a positive shift after ~8-8.5 Ma in the Yuanmou region, which is similar in timing to shifts observed in horses, rhinos, and deer from the Linxia Basin and in fossils and paleosols from Pakistan and Nepal, suggesting a shift toward a drier and/or warmer climate at the northeast, southeast, and southern borders of the Tibetan Plateau during the Late Miocene. A negative shift in the delta 18-O values of rhinos from the Yuanmou Basin after ~5 Ma likely indicates a change to a wetter environment at that time interval, which is similar in timing to a negative shift observed in the Linxia Basin and Gyirong Basin. Overall, the oxygen isotope compositions of mammals from the Yuanmou Basin indicate a general drying of the local climate over time, which is consistent with carbon isotope results from that region.
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