UC Merced

Sharks and their relatives have been successful predators for over 400 million years, playing critical ecological roles in marine environments. Their recent, dramatic population decline—largely due to climate change—poses a serious threat to ecosystem stability. Their fossil record provides a valuable system to document how sharks have coped, survived, or declined in response to major climatic changes over geological time. Insights from these records are vital to inform current conservation practices. This dissertation investigates how major climatic events influenced the temperature, salinity, and dietary preferences of sharks that lived during the Eocene Epoch (54–33.9 Ma) in Antarctica, a region that underwent significant environmental shifts as the global climate cooled at the Epoch's end. The study develops a new protocol to isolate silver phosphate for geochemical analysis, enabling temperature and salinity estimations from bones and teeth, including various shark tooth sizes. Temperature and salinity preferences were inferred for both pelagic and benthic shark taxa (n = 16) across the Eocene. The study also examines geochemical and morphological metrics of Eocene sand tiger sharks and compares them with the critically endangered modern species Carcharias taurus. By addressing a longstanding analytical variability enigma affecting temperature and salinity estimates derived from shark teeth, we found that pelagic and benthic Eocene sharks generally preferred similar conditions, with only cooler-adapted species continuing in the fossil record likely surviving climate change. Additionally, our results suggest that fossil sand tiger sharks serve as valuable analogs for the extant C. taurus in terms of habitat and dietary preferences. Altogether, this study underscores the significant impact of climate on sharks and highlights how their fossil record can illuminate aspects of modern shark ecology.