Jeremy E. Martin, Peggy Vincent, Théo Tacail, Fatima Khaldoune, Essaid Jourani, Nathalie Bardet & Vincent Balter (2017)
Calcium Isotopic Evidence for Vulnerable Marine Ecosystem Structure Prior to the K/Pg Extinction.
Current Biology (advance online publication)
Calcium isotopes retain biogenic values in a Cretaceous marine vertebrate assemblage
Isotopic variability in primary consumers parallels that of modern analogs
A single calcium source for apex predators points to a Cretaceous wasp-waist food web
Marine ecosystems were vulnerable prior to the K/Pg mass extinction
The collapse of marine ecosystems during the end-Cretaceous mass extinction involved the base of the food chain up to ubiquitous vertebrate apex predators. Large marine reptiles became suddenly extinct at the Cretaceous-Paleogene (K/Pg) boundary, whereas other contemporaneous groups such as bothremydid turtles or dyrosaurid crocodylomorphs, although affected at the familial, genus, or species level, survived into post-crisis environments of the Paleocene and could have found refuge in freshwater habitats. A recent hypothesis proposes that the extinction of plesiosaurians and mosasaurids could have been caused by an important drop in sea level. Mosasaurids are unusually diverse and locally abundant in the Maastrichtian phosphatic deposits of Morocco, and with large sharks and one species of elasmosaurid plesiosaurian recognized so far, contribute to an overabundance of apex predators. For this reason, high local diversity of marine reptiles exhibiting different body masses and a wealth of tooth morphologies hints at complex trophic interactions within this latest Cretaceous marine ecosystem. Using calcium isotopes, we investigated the trophic structure of this extinct assemblage. Our results are consistent with a calcium isotope pattern observed in modern marine ecosystems and show that plesiosaurians and mosasaurids indiscriminately fall in the tertiary piscivore group. This suggests that marine reptile apex predators relied onto a single dietary calcium source, compatible with the vulnerable wasp-waist food webs of the modern world. This inferred peculiar ecosystem structure may help explain plesiosaurian and mosasaurid extinction following the end-Cretaceous biological crisis.