42-14 Modern Amniotes as Analogs for Paleozoic Habitat Reconstructions Using Triple Oxygen Isotope Values of Bioapatite

Session: Paleozoic Events and Processes: Sedimentary Geology, Paleontology, and Geochemistry (Posters)

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Reconstructing the primary habitat of extinct organisms is critical for understanding their ecological context. Such reconstructions inform how environmental constraints shaped the diversification of organismal lineages over geologic time. However, interpretations of Paleozoic diversification of organisms have relied on morphological proxies that often lack the ability to distinguish closely related aquatic and terrestrial environments. This study evaluates triple oxygen isotope compositions of phosphate [δ¹⁸Oₚ and Δ^′17Oₚ, where Δ^′17O=δ^′17O-0.528*δ^′18O and δ^′xO=1000*ln((δ^xO+1000)/1000)] in bioapatite as a proxy for primary habitat. δ¹⁸Oₚ and Δ^′17Oₚ reflect an organism’s body water, which is comprised of surface water sources and atmospheric O₂ contributions, enabling discrimination among aquatic and terrestrial habitats. 

We measured the triple oxygen isotope value of bioapatite from extant birds (bone), turtles (bone and scute), and crocodilians (tooth) to develop a framework for interpreting fossil habitats where morphological evidence is ambiguous. Different species known to occupy marine, freshwater, brackish, semi-aquatic, or terrestrial habitats were used for each amniote. Phosphorus concentrations ranged from 6.2-10.8 wt% P, with crocodilian tooth samples consistently having higher concentrations than turtle bone, scute and bird bone, reflecting the more highly mineralized structure of teeth. Preliminary results of Δ^′17O and δ¹⁸O values of the carbonate portion of turtle bones and scute demonstrated isotopic differences among habitat types. Here, we expand on these results to the phosphate portion of bioapatite, a more recalcitrant molecule that resists diagenesis and expand the framework to different amniotes. Together, these results establish the feasibility of applying δ¹⁸Oₚ and Δ^′17Oₚ analyses to fossil bioapatite preserved in Paleozoic sedimentary rocks as a proxy for primary habitat. 

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