The correct option is A Ichthyosaurs
Ichthyosaurs are large extinct marine reptiles. They thrived during much of the Mesozoic era; based on fossil evidence, they first appeared around 250 million years ago, and at least one species survived until about 90 million years ago, into the late Cretaceous. During the early Triassic period, Ichthyosaurs evolved from a group of unidentified land reptiles that returned to the sea. They were particularly abundant in the later Triassic and early Jurassic periods. In the late Cretaceous, their last lineage became extinct for unknown reasons.