The groups that did not survive the massive extinction include the dinosaurs, pterosaurs, and some families of birds and marsupial mammals on land. In the oceans, mosasaurs, plesiosaurs, some families of teleost fishes, ammonites, belemnites, rudist, trigoniid, and inoceramid bivalves became extinct, as well as over half the oceans’ various plankton groups. Some groups appear to have vanished completely at the end of the Cretaceous period, whereas others were already gradually diminishing in diversity in the last 10 million years of the Cretaceous period.