The ichthyosaurs, or 'fish-reptiles', were the reptiles most highly adapted to aquatic life. They appeared
abruptly in the Early Triassic Period and by the Late Triassic to Late Jurassic they were among the
dominant large predators in many seas. Hou/euet, they declined during the Cretaceous and had all but
disappeared by the end-of-Cretaceous (K - T) mass extinction that marked the end of the Mesozoic Era.