Fourier analysis and the extinction of unionoid bivalves near the Cretaceous–Tertiary boundary of the Western Interior, USA: Pattern, causes, and ecological significance

The Williston Basin in the Western Interior of the USA is known for its highly diverse and well-preserved fauna of unionoid bivalves. This fauna undergoes a significant turnover near the Cretaceous–Tertiary (K/T) boundary. A quantitative study based on multivariate morphometrics has been carried out to better understand the pattern and causes of the extinction of unionoid bivalves in the K/T transition. The decrease in taxonomic diversity in the interval spanning the K/T boundary is associated with a significant shift in morphospace occupation. This shift indicates a major decrease in habitat stability. Four events and processes are discussed as possible causes of this change in habitat stability: 1) the Chicxulub impact on the Yucatán Peninsula, 2) global climate changes to some extent due to Deccan volcanism, 3) tectonic changes in the emerging Rocky Mountains, and 4) eustatic changes in the Western Interior Seaway. We conclude that the bolide impact was not the major killing agent for unionoid bivalves. The tectonic and eustatic processes are much more important to explain the unionoid faunal turnover at the end of the Cretaceous. The results and conclusions of the study are considered to be helpful to better understand the present-day distribution of unionoid bivalves.