Ichthyosauria

Ichthyosauria, commonly ichthyosaurs, is a clade of extinct marine reptiles that lived from the Early Triassic to the Late Cretaceous. They occupied oceans worldwide, from coastal shallows to open seas, and were among the most successful marine reptiles of their time.

Anatomy and locomotion: Ichthyosaurs had streamlined, fish-like bodies with paddle-like limbs adapted into flippers and a powerful tail used for propulsion. Most possessed a long snout with sharp teeth, though tooth and jaw shapes varied among species. A dorsal fin was present in many forms, and the tail fin was typically crescent-shaped, aiding efficient swimming. Some lineages evolved extremely large eyes, suggesting acute vision in deep or dim water, while others had more generalized skull and tooth patterns. The skeleton supported rapid, agile swimming and frequent surface breathing.

Life history and ecology: Most ichthyosaurs were viviparous, giving birth to live young, with fossils sometimes showing embryos still within the mother. They occupied a range of marine niches, from small to very large predators, feeding on fish, cephalopods, and other marine organisms. Their convergent, streamlined appearance has often drawn comparisons to dolphins and other fast-swimming marine vertebrates.

Evolution and extinction: The earliest ichthyosaurs appeared in the Early Triassic and diversified through the Jurassic, producing a wide array of forms, from medium-sized to giant species. They persisted into the Late Cretaceous but declined over time and became extinct by about 90 million years ago.

Fossil record: Ichthyosaurs are found on multiple continents, with particularly well-preserved assemblages in Europe and North America. Their fossils provide key insights into the evolution of marine reptiles and ichthyosaur physiology.