Upper Cretaceous
The event brought about the extinction of the pliosaurs, and most ichthyosaurs, and most lines of pterosaurs. Although the cause is uncertain, the result starved the Earth's oceans of oxygen for nearly half a million years. This caused the extinction of about 27 percent of marine invertebrates, including certain planktonic and benthic foraminifera, mollusks, bivalves, dinoflagellates and calcareous nannofossils. This global environmental disturbance increased atmospheric and oceanic temperatures. Boundary sediments show an enrichment of trace elements, and contain elevated δ13C values. δ13C varies in time as a function of biological productivity. This means the seas were no longer so favourable for life at that time, and many species went extinct.