Melanie A. D. During: On the verge of extinction: A multi-proxy approach to understanding life up to the KPg-extinction in North Dakota

Abstract

This thesis presents novel contributions to palaeontology, focusing on five key research areas. First, the integration of osteohistological and geochemical analyses offers a unique method for reconstructing mass-death events, confirming growth stages, and pinpointing the seasonal timing of the KPg impact to the boreal spring. This precise timing provides crucial insights into the extinction event's selectivity.

Second, the Tanis deposit from the Late Cretaceous reveals an exceptional diversity of acipenseriform fish (sturgeons and paddlefishes). This thesis explores the diversity of paddlefishes, which surpasses that observed at any other time in their evolutionary history. The presence of paddlefishes in both the Hell Creek Formation and the Early Cretaceous China indicates a higher paddlefish diversity during the Cretaceous than previously known. Furthermore, the biogeographic distribution of these species suggests a historical relationship between East Asia and North America that predates the Cretaceous, supporting a trans-Pacific connection rather than a trans-Atlantic one.

The third chapter critically examines the paper by DePalma et al. (2021) on the seasonality of the End-Cretaceous extinction. Although their findings seem to align with those in the first chapter, serious methodological concerns arise. Specifically, the lack of transparency in their stable isotope data, combined with inconsistencies in the isotopic graphs, raises doubts about the existence of the underlying data. Additionally, the apparent use of an image from one specimen—cropped and flipped 180 degrees—then reassigned to a different specimen number, further undermines confidence in the integrity of their work. These issues suggest that the results may not be based on authentic data, calling into question the validity of their conclusions. This chapter underscores the need for rigorous standards and transparency in research to ensure replicability and reliability, emphasizing the role of peer review in advancing scientific knowledge.

The fourth chapter explores the discovery of a mosasaur tooth in the Hell Creek Formation, North Dakota, using a multi-proxy approach that includes stable isotope analyses on both carbonate and phosphate fractions of the tooth enamel, as well as strontium isotope ratios. These analyses suggest a freshwater origin, challenging the traditional view of mosasaurs as strictly marine predators. This study highlights their ecological flexibility during the Late Cretaceous and offers new insights into their adaptation to the changing environments of the Western Interior Seaway.

Finally, the thesis addresses the challenge of automated segmentation in Xray tomography, particularly in palaeontology, where contrast variations and high absorption from metallic inclusions are common. The ml4paleo software suite is introduced as a solution, offering a user-friendly interface for 2D slice-based image segmentation. Its open-source nature ensures accessibility and potential benefits across multiple scientific disciplines.