Ichthyopterygia

Ichthyopterygia refers to a subclass of fossil aquatic reptiles that lived from the late Carboniferous through the Jurassic periods. These reptiles are taxonomically synonymous with ichthyosaurs. Ichthyosaurs were highly specialized marine reptiles, resembling porpoises in appearance and habits, and were distant relatives of lizards and snakes.123

They had a wide geographic distribution, with fossils found throughout the Mesozoic Era, but were most prevalent during the Triassic and Jurassic periods. Ichthyosaurs were not dinosaurs. Their bodies were streamlined, with limbs modified into paddle-like appendages for steering and a fish-like tail for propulsion. They likely reproduced in water and were adapted for aquatic life, making them helpless on land.3