Ichthyosaurs (“fish lizards”) were a group of predatory marine reptiles that lived from approximately 250 million years ago, during the Triassic, until approximately 90 million years ago, during the Cretaceous. They evolved from terrestrial reptiles that returned to aquatic environments, comparable to the transition made by the terrestrial mammalian ancestors of modern dolphins and whales. Their fish-like features and adaptations provide an example of convergent evolution. Ichthyosaurs were widespread during the Triassic and Early Jurassic, before plesiosaurs occupied their ecological niche as large aquatic predators.
Species of Ichthyosaurs ranged from 1 to 26 metres in length and resembled both fishes and modern dolphins. Their limbs had become flippers, and their tail fin provided powerful propulsion. They had pointed snouts, with jaws often bearing conical teeth for capturing small prey. Some species had larger, blade-like teeth suited to capturing larger animals. Their very large eyes were adapted to diving at depth. Ichthyosaurs breathed air, were warm-blooded, and gave birth to live young. Many, if not all, species had a layer of fat for insulation.
