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The mystery of the extinction of the ichthyosaurs
3/8/16

This raises a final question: what happened during this latter phase with the last existing niche, the one which includes the ichthyosaurs with large teeth? “Their final extinction is associated with slower evolution and stong environmental instability, but we do not know which factors were precisely at play ”, says Valentin Fischer. “We return to the food theory. At that time, the ichthyosaurs only occupied one niche. They were more vulnerable. And at the end of the Cenomanian, there were extinctions of cephalopods and that could have had an impact on the ichthyosaurs but it is not an optimal answer as these last ichthyosaurs occupied a niche with many possible sources of prey. More importantly, there were a lot of changes in the entire marine biosphere”.
squelette ichtyosaure
The end of the Cenomanian saw a large peak in temperatures. There was no longer any ice on Earth; water no longer cooled and ocean circulation slowed down. Almost all the marine groups experienced great upheavals. It was not a massive extinction because some groups disappeared but others adapted to these new conditions and evolutionary radiations occurred. New lineages of bony fish and sharks appeared, especially those that currently populate the present-day oceans. What could be a possible cause of this shake-up? The separation of the continents which had never been happening so quickly. This separation altered ocean currents, global ocean circulation and sea levels. Volcanic eruptions were frequent, which released a series of greenhouse gases into the atmosphere causing ice to melt and increasing sea levels again. All these factors were interconnected. Sulphur compounds were dissolved in the water and directly or indirectly increased its acidity. The sea beds seemed to be deprived of oxygen. “We therefore do not know exactly what happened to the last ichthyosaurs. There is undoubtedly no single cause that alone brought about their extinction”, says Valentin Fischer. “We will probably never know the full truth”.

Unless… In continued collaboration with the Matt Friedman of the University of Oxford, Valentin Fischer is going to abandon the ichthyosaurs to extend his research to other sea groups in order to have a more precise idea as to what happened at other levels of the food chain. In this context, the laboratory in Liege, renamed EDDy lab (Evolution and Diversity Dynamics lab) in tribute to the work of Professor Edouard Poty, who was succeeded by Valentin Fischer, is going to focus on the evolution of fish and reefs made up of bivalves (rudists and hippuritoids), which became dominant during the Cretaceous replacing coral reefs before these recovered and the bivalves disappeared…at the same time as the dinosaurs! Yet another story to be told.

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