NEOSELACHIAN (CHONDRICHTHYES, ELASMOBRANCHII) DIVERSITY ACROSS THE CRETACEOUS-TERTIARY BOUNDARY

Abstract

Fishes are often thought to have passed through mass extinctions, including the Cretaceous–Tertiary (KT) event, relatively unscathed. We show that neoselachian sharks suffered a major extinction at the K/T boundary. Out of 41 families, 7 became extinct (17±12%). The proportional measure increases at lower taxic levels: 56±10% loss of genera (loss of 60 out of 107) and 84±5% loss of species (loss of 182 out of 216). However, the Maastrichtian and Danian are characterized by a high number of singleton taxa. Excluding singletons we have calculated a 34±11% loss of genera and a 45±9% loss of species. The simple completeness metric (SCM) for genera displays a decrease from the Maastrichtian (94%) to the Danian (85%) indicating a rather complete fossil record of neoselachian genera. The extinctions were heavy among both sharks and batoids (skates and rays), but most severe among batoids, which lost almost all identifiable species. There were equal losses among open marine apex predators (loss of Anacoracidae, Cretoxyrhinidae, and Scapanorhynchidae) and durophagous demersal forms from the continental shelf and shallow seas (Hypsobatidae, Parapaleobatidae, Sclerorhynchidae, Rhombodontidae). Benthopelagic and deep-sea forms were apparently little affected. New families with similar ecological roles (Carcharhinidae, Isuridae, Torpedinidae) replaced these families in the Danian, and full diversity of the different shark and batoid groups had been recovered by the end of the Paleocene or early Eocene. Sharks and rays suffered levels of extinction entirely in line with other groups of organisms at the K/T extinction event.