The stability of dinosaur communities before the K−Pg boundary: A perspective from southern Alberta using calcium isotopes as a dietary proxy

Abstract

Reconstructing dinosaur trophic structure prior to the Cretaceous−Paleogene (K−Pg) boundary may provide information about ecosystem organization and evolution. Using calcium isotopes, we investigate preserved biogenic isotope compositions in a set of dinosaur teeth from three continental formations from Alberta, Canada, to assess latest Cretaceous food web structure. Tooth enamel δ44/42Ca values are presented for tyrannosaurids (n = 34) and potential large herbivorous prey (n = 42) in the upper Campanian Dinosaur Provincial Park Formation, uppermost Campanian−Maastrichtian Horseshoe Canyon Formation, and upper Maastrichtian−lower Paleocene Scollard Formation, spanning the last ∼10 m.y. of the Cretaceous. The influence of diagenesis is assessed in a subset sample through major and trace elemental concentrations and ultraviolet (UV) Raman spectra, which provides a framework for interpreting calcium isotope values. In the Dinosaur Park Formation, hadrosaurid δ44/42Ca values are systematically heavier than ceratopsid values, a difference that is interpreted to reflect niche partitioning among megaherbivores. Tyrannosaurid δ44/42Ca values are scattered but on average, they are 44Ca-depleted relative to herbivorous dinosaurs in all three formations. As interpreted from the Dinosaur Park data set, tyrannosaurids may have preferentially fed on hadrosaurids. These analyses offer possibilities for testing whether trophic structure among non-avian dinosaur ecosystems changed several millions of years prior to the K−Pg boundary.