During the Triassic and the Jurassic began a change in the oceans’ animal life which culminated during the Cretaceous.
Some animal groups, including lampshells and sea lilies, became increasingly rare. Meanwhile, other animal groups that had been less predominant – such as sea urchins, snails and mussels – experienced a great increase in species diversity.
It is also during this time that a number of new, efficient predators evolved – crustaceans with powerful claws, mosasaurs and bony fish.
Another important event was the mass extinction that ended the Cretaceous. It is estimated to have wiped out three fourths of all plant and animal species on Earth, including all the pterosaurs, plesiosaurs and dinosaurs (except birds).
Plesiosaur, one of the many species that became extinct at the end of the Cretaceous.
Image: Simon Stålenhag