The mystery of the extinction of the ichthyosaurs
An extremely dense study (1) published in Nature Communications and of which Valentin Fischer, a lecturer at the University of Liege, is the first author, removes some of the mystery surrounding the extinction of the ichthyosaurs at the end of the Cretaceous. The interest of this study, however, lies in the methods used to reach its conclusions: rather than considering averages based on variable factors over long periods (several million years), the researchers were able to avail of access to data on this occasion (sea levels and global temperatures), which enabled them to make a more in-depth analysis by taking account of the dynamics of environmental phenomena during the Cretaceous. They were able to deduce that the ichthyosaurs disappeared quickly (though not suddenly), in two phases that coincided with overwhelming changes in the marine environment. These changes were due, in particular, to the rapid separation of the continents 95 million years ago. Sea levels were up to 150 metres higher than today and all the ice had disappeared from our planet!
The results of this research published in Nature Communications corroborates and completes the thesis of the researcher from Liege. It appears that there was indeed both a lot of diversity (the number of different species) and a lot of disparity (the number of different morphologies) during the Cretaceous. “In addition to this fact”, explains Valentin Fischer, “they had never been so disparate since the end of the Triassic (210, 220 million years ago). Moreover, this disparity seems to have lasted up to the middle of the Early Cretaceous: we observed a peak in the level of disparity around 120 to 130 million years ago. This tied in with the fact that there also seemed to be a lot of different species”.
(1) Extinction of fish-shaped marine reptiles associated with reduced evolutionary rates and global environmental volatility, Valentin Fischer et al. Nature Communications 2016.