UCLA

The first chapter of this thesis evaluates the preservation and geochemical fidelity of eight Late Cretaceous fossil eggshell samples from Mongolia and Alberta using polarized-light petrography, electron backscatter diffraction (EBSD), cathodoluminescence, Raman spectroscopy, conventional stable isotopes, carbonate clumped isotopes (Δ47), and triple oxygen isotopes (Δ′¹⁷O). Most specimens retain recognizable microstructure, yet petrographic preservation is not consistently coupled to isotopic fidelity. The two Alberta samples yield elevated apparent Δ47 temperatures (48.5–61.5 °C), consistent with burial-related resetting. Several Mongolian samples yield lower apparent temperatures (21.2–31.5 °C) and the strongest convergence among preservation screens; these values are treated as candidate biomineralization temperatures. Carbon-isotope values are comparatively reproducible within specimens, whereas oxygen-isotope and Δ¹⁷O results indicate variable fluid interaction. These results show that eggshell geochemistry can retain primary information, but only when interpreted within a multi-proxy preservation framework. δ13C values (−13.7‰ to −3.7‰ VPDB) prove highly robust and consistent with a C3 vegetation-dominated diet. In the best-preserved material, primarily from Mongolia, primary signatures remain intact: δ13C ranges from −6.16‰ to −4.18‰VPDB, δ18O ranges from −12.4‰ to −8.2‰ VPDB, and Δ47 temperatures yield reliable physiological estimates of 21.2 °C to 27.8 °C for oviraptorids and 31.5 °C for a hadrosaur.The second chapter applies Δ47 thermometry and bond-reordering models to fourteen paleosol-carbonate samples from the Permian Bernal Formation and Triassic Anton Chico Member at Bernal Mesa, New Mexico. Apparent temperatures range from 10.9 ± 3.2 to approximately 93 °C. Two Permian samples yield low apparent temperatures consistent with late, cool recrystallization; the remaining samples yield 52.4–93.1 °C and are interpreted as variably reset during burial. Forward models using the disordered calcite-reordering framework of Hemingway and Henkes (2021), conditioned on a prescribed Late Cretaceous peak-burial time and subsequent cooling, yield maximum burial temperatures of approximately 164–178 °C for most of the burial-reset population. These temperatures imply roughly 4.1–6.5 km of overburden for geothermal gradients of 25–30 °C km⁻¹, consistent with regional Laramide exhumation histories. The final chapter compares thermophysiological signals in marine vertebrates from two temporally distinct assemblages: a late Campanian–early Maastrichtian succession in New Jersey and the Turonian Codell Sandstone of Kansas. Phosphate oxygen isotopes (δ¹⁸Otructural-carbonate Δ47 thermometry, Fourier-transform infrared spectroscopy, and carbonate–phosphate isotope offsets were applied to tooth enamel/enameloid and co-occurring carbonate shells. New Jersey oysters and belemnites yield an ambient-water temperature near 20 °C. Mosasaur δ¹⁸Oₚ estimates average 32.6 ± 0.7 °C in New Jersey and 33.8 ± 0.8 °C in Kansas; New Jersey mosasaur Δ47 data yield 39.5 ± 6.6 °C. In Kansas, Cretoxyrhina mantelli yields 36.0 ± 0.6 °C from δ¹⁸Oₚ and 37.7 ± 5.6 °C from Δ47. These patterns are compatible with elevated heat retention in mosasaurs and C. mantelli, whereas several other taxa track local ectothermic or environmental baselines more closely. Taken together, these chapters underscore how diagenesis and taphonomic alteration do not act uniformly across different fossil substrates or isotope systems. Across the dissertation, the central methodological result is that visible microstructural preservation does not guarantee geochemical fidelity, and no single screening proxy is sufficient. Integrating multiple methods, including petrography, crystallography, spectroscopy, conventional isotopes, clumped isotopes, and explicit kinetic or thermodynamic models can identify plausible primary signals while revealing where burial, fluid exchange, mineralogy, or analytical limitations preclude strong biological, tectonic, or climatic inference. Ultimately, while this approach recovers paleobiological insights, such as variable regional endothermy in apex sharks, and the high metabolic demands that preceded the selective extinction of Cretaceous marine giants, its primary value lies in demonstrating how advanced taphonomic evaluation can unlock paleoclimates, paleobiological change, and post-depositional tectonic histories.