Anomalous ¹³C enrichment in Mesozoic vertebrate enamel reflects environmental conditions in a “vanished world” and not a unique dietary physiology

Abstract

Biogeochemical analyses of organisms’ tissues provide direct proxies for diets, behaviors, and environmental interactions that have proven invaluable for studies of extant and extinct species. Applying these to Cretaceous ecosystems has at times produced anomalous results, however, as dinosaurs preserve unusually positive stable carbon isotope compositions relative to extant C3-feeding vertebrates. This has been hypothesized to be a unique property of dinosaur dietary physiology, with potential significance for our interpretations of their paleobiology. We test that hypothesis through multi-taxic stable carbon isotope analyses of a spatiotemporally constrained locality in the Late Cretaceous of Canada, and compare the results to a modern near-analogue environment in Louisiana. The stable carbon isotope anomaly is present in all sampled fossil vertebrates, dinosaur or not. This suggests another more widespread factor is responsible. Examinations of diagenetic effects suggest that, where present, they are insufficient to explain the isotope anomaly. The isotope anomaly is therefore not primarily the result of a unique dietary physiology of dinosaurs, but rather a mix of factors impacting all taxa, such as environmental and/or source-diet differences. Our study underscores the importance of multi-taxic samples from spatiotemporally constrained localities in testing hypotheses of extinct organisms and ecosystems, and in the use of modern data to “ground truth” when evaluating analogue versus non-analogue conditions in greenhouse paleoecosystems.

The nature of science: The fundamental role of natural history in ecology, evolution, conservation, and education

“…Most of these osteohistology studies are based, at least partially, on museum specimens that were initially collected for use in natural history and taxonomic projects and were thus available for study as these new approaches were developed. Additionally, the combination of these existing historical collections with new sampling and consumptive biogeochemical methods has permitted detailed ecological information to be obtained and hypotheses of community and macroecology to be tested, including but not limited to: the differentiation of grazing versus browsing diets and habitat partitioning in extinct mammals (Bocherens et al, 1996;Koch, 1998;Zazzo et al, 2000); niche partitioning and testing for competition among co-occurring large predators (Hassler et al, 2018); predator dietary shifts in response to environmental changes in European and Arctic settings before and after the last glacial maximum (Yeakel et al, 2013); community resource interchange and habitat use patterns among living vertebrates in coastal floodplain settings and their extinct counterparts in similar but still somewhat non-analogous greenhouse climates (Cullen et al, 2019(Cullen et al, , 2020(Cullen et al, , 2022(Cullen et al, , 2023; and testing macroecological concepts such as the resource breadth hypothesis using stable isotope data from feathers obtained from birds in museum collections (Rader et al, 2017).…”