Effects of the Cretaceous-Tertiary Boundary Event on Bony Fishes

Abstract

The effects of the Cretaceous-Tertiary boundary (KTB) event on the bony fishes are explored. The data are compiled by the analysis of the literature concerning bony fihes occurrences ranging from the Late Jurassic to the Paleocene, and resting on more than 750 references. The quality of the fossil record of bony fishes during the Campanian-Danian span is checked by calculation of the simple completeness metric (SCM). The analysis shows that (1) ten families (19% of the total) became extinct during or at the end of the Maastrichtian; (2) most of the victims (80%) were families exclusively restricted to marine environments; (3) most of the families (94%) with freshwater and/or brackish representatives during the Late Cretaceous crossed the KTB; (4) most of the victims (90%) were fast swimming and piscivorous predators. Extinction of this type of fishes is more easily explainable by a collapse of their food chain based on plankton. No extinction of planktivorous families, the intermediate level between plankton and piscivores, is observed. This fact is explain by ecological reasons (representatives of these families were living in brackish or freshwater) and by taxonomical reasons (phylogenetic relationships are unresolved and the families are not included in the analyses). These results are discussed in the light of some possible bias inherent to the fossil record and its study. The general trophic dependent pattern of extinctions agrees better with the expected consequences of a short-term catastrophic event than with a long term environmental change. It fits well the expected consqeuences of an impact: a break in the primary production by darkening of the atmosphere due to the dust generated by the impact, and followed by a chain of effects on the higher levels of the food chain, while detritus feeders and most of the following organisms survived, because there never was a lack of food at the base of the trophic chain.