The timing and mechanisms responsible for the expansion of C4 grasses have been a topic of considerable debate over the last two decades. Although abundant evidence indicates that there was a worldwide, rapid increase in C4 ecosystems (RICE) in the late Miocene, recent studies from the Great Plains and the Barstow Formation suggest that there may have been a significant amount of C4 biomass prior to the RICE event. This study examines stable carbon isotopic ratios of herbivore tooth enamel of 89 individuals from the Dove Spring Formation of southern California, which is geographically close to and geologically younger than the Barstow Formation. Taxa analyzed in this study include the Antilocapridae, Castoridae, Camelidae, Equidae, Gomphotheriidae, Merycoidodontidae, and Rhinocerotidae families. The enamel δ13C values of all taxa sampled are -10.1 ± 1.1 ‰ (n=89), ranging from -13.3 to -6.7 ‰. Most studies have used -8 ‰ as the cutoff for a pure C3 diet. However, a cutoff value of -8 ‰ for a pure C3 diet is reliant on the modern atmospheric δ13C value. Proxy data indicate that the δ13C value of atmospheric CO2, the carbon source of terrestrial plants, has varied significantly in the geologic past, leading to corresponding changes in the δ13C of plants and ultimately tooth enamel. The estimated δ13C value of atmospheric CO2 in the middle to late Miocene was -5.8 ± 0.2 ‰, making the pure C3 diet cutoff value higher than the modern value by ~2 ‰. With a higher end member δ13C value for a pure C3 diet, much of the reported evidence of an early spread of C4 grasses in areas such as the Great Plains and southern California may be a false signal from water-stressed C3 plants and the amount of C4 biomass in the geologic past may have been greatly over-estimated. After accounting for the changes in the δ13C of atmospheric CO2, enamel-δ13C values from the Dove Spring Formation indicate that late Miocene herbivores in the area had primarily C3 diets and lived in an environment dominated by C3 plants. Re-evaluation of previously published enamel-δ13C data from the nearby Barstow Formation to account for the carbon isotopic difference between the middle Miocene and modern atmospheric CO2 also shows that herbivores living in the area in the middle Miocene had C3-based diets. Serial isotope data from the teeth from the Dove Spring Formation revealed little or no intra-tooth δ13C variations, confirming that these ancient herbivores consumed C3 plants year round. The lack of seasonal signal in the carbon isotope data of the serial samples provides further evidence that there were little or no C4 plants in local habitats of southern California in the middle and late Miocene. If the C4 photosynthetic pathway did spread to southern California prior to the rapid increase in C4 ecosystems in the late Miocene the herbivore taxa sampled did not incorporate C4 biomass into their diets, possibly as a result of selective feeding. The results of the stable carbon isotopic analysis, along with the evidence from the rock record, the life habits of the fossil taxa present—both grazers and browsers—indicate that the area had a very different environment in the late Miocene. The carbon isotope data suggest that the environment in the El Paso Basin in the middle to late Miocene was likely consisted of diverse habitats including C3 grasslands, wooded C3 grasslands, and riparian forests. / A Thesis submitted to the Department of Earth, Ocean, and Atmospheric Science in partial fulfillment of the requirements for the degree of Master of Science. / Summer Semester 2015. / July 14, 2015. / C3/C4, enamel, Miocene, Mojave Desert, Paleodiet / Includes bibliographical references. / Yang Wang, Professor Directing Thesis; A. Leroy Odom, Committee Member; William C. Parker, Committee Member.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_253200 |
| Contributors | Bowman, Chelsie N. (Chelsie Nicole) (authoraut), Wang, Yang (professor directing thesis), Odom, A. L. (A. Leroy) (committee member), Parker, William C., 1952- (committee member), Florida State University (degree granting institution), College of Arts and Sciences (degree granting college), Department of Earth, Ocean, and Atmospheric Science (degree granting department) |
| Publisher | Florida State University, Florida State University |
| Source Sets | Florida State University |
| Language | English, English |
| Detected Language | English |
| Type | Text, text |
| Format | 1 online resource (56 pages), computer, application/pdf |
| Rights | This Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s). The copyright in theses and dissertations completed at Florida State University is held by the students who author them. |
Page generated in 0.0017 seconds