After the impact
At the end of the Cretaceous, 66 million years ago, a large meteorite impact event caused the most recent of five major mass extinction events in the Earth’s history. The dinosaurs, marine species and whole groups of ammonites were wiped out. Although the ecosystems recovered fairly quickly, their appearances were changed forever. Palaeontologists from the Museum für Naturkunde in Berlin and from FAU have now carried out a detailed investigation of the ecological shifts in the oceans for the first time and documented a global regime change which was not caused by the mass extinction alone.
During the first few million years following the extinction of species the marine ecosystems were dominated by predatory molluscs. During the same time period, the number of organisms which lived on the seabed and moved freely increased. ‘These are the species which were able to flee or hide on the seabed from the rising number of predatory organisms,’ says Martin Aberhan from the Museum für Naturkunde, who is the lead author of the study.
The percentage of molluscs which did not look for living plankton but fed on dead organic particles in the sediment was also very high for a prolonged period of time. ‘When nutrition supply is interrupted, animals feeding on organic material in the seabed are less vulnerable than those which depend on plankton. This fits with the consequences of a meteorite impact event, where the darkened atmosphere caused the planktonic algae at the bottom of the food chain to decrease considerably in number because they depend on sunlight,’ says Aberhan.
The researchers established that the same ecological shifts occurred in several places at the same time, at different distances from the impact crater and in different climate zones. ‘We concluded that these shifts occurred on a global scale and that the new ecosystems did not evolve randomly but due to directed processes,’ says Aberhan. Considering the current large-scale environmental changes, this new study shows that long-term ecological consequences must be expected when ecosystems are under considerable stress and that a quick return to the initial state cannot be expected.
Wolfgang Kiessling from FAU’s Chair of Palaeoenvironmental Studies says that it is particularly remarkable that the ecological shift already becomes evident when only looking at the species that have survived because it proves that the ecological shift is not attributable to the extinction of species alone.
Published in: Aberhan, M. & Kiessling, W. 2015. Persistent ecological shifts in marine molluscan assemblages across the end-Cretaceous mass extinction. Proceedings of the National Academy of Sciences USA.