Dolphins of the Jurassic.

Ichthyosaurus By Safari LTD.
Ammonites By kaiyodo dinotales/chocolosaurs.

Ichthyosaurs (Greek for "fish lizard") were large marine reptiles. Ichthyosaurs thrived during much of the Mesozoic era; based on fossil evidence, they first appeared approximately 250 million years ago (mya) and at least one species survived until about ninety million years ago, into the Late Cretaceous. During the early Triassic Period, ichthyosaurs evolved from a group of, as yet, unidentified land reptiles that returned to the sea, in a development parallel to that of the ancestors of modern-day dolphins and whales, which they gradually came to resemble in a case of convergent evolution. They were particularly abundant in the later Triassic and early Jurassic Period, until they were replaced as the top aquatic predators by another marine reptilian group, the Plesiosauria, in the later Jurassic and Cretaceous Period. In the Late Cretaceous ichthyosaurs became extinct for as yet unclear reasons. Ichthyosaur species varied from one to over sixteen metres in length. Ichthyosaurs resembled both fish and dolphins. Their limbs had been fully transformed into flippers, which sometimes contained a very large number of digits and phalanges. At least some species possessed a dorsal fin. Their heads were pointed, the jaws often equipped with conical teeth to catch smaller prey. Some species had larger bladed teeth to attack large animals. The eyes were very large, probably for deep diving. The neck was short and later species had a rather stiff trunk. These also had a more vertical tail fin, used for a powerful propulsive stroke. The vertebral column, made of simplified disc-like vertebrae, continued into the lower lobe of the tail fin. Ichthyosaurs were air-breathing, bore live young and were probably warm-blooded.