sauropterygians

Sauropterygia is a clade of extinct marine reptiles that lived from the Early Triassic to the end of the Cretaceous. The group comprises several lineages, including the armored placodonts (Placodontia), the semi-aquatic nothosaurs, and the more derived plesiosaurs (Plesiosauria), from which the long-necked elasmosaurs and the short-necked pliosaurs evolved.

Morphology and ecology: Early sauropterygians such as placodonts were often broad-bodied with flattened bodies and specialized teeth for crushing molluscs. Later forms developed paddle-like limbs and more streamlined bodies for efficient swimming. Plesiosaurs typically had broad, turtle-like bodies; elasmosaurs possessed extremely long necks with relatively small heads, while pliosaurs were characterized by large heads and powerful jaws. They were carnivorous, feeding on fish, cephalopods, and other marine animals, occupying a range of marine niches.

Evolutionary history and distribution: Sauropterygians first appear in the Early Triassic after the Permian–Triassic extinction, with placodonts and nothosaurs among early forms. In the Jurassic and Cretaceous, plesiosaurs (both elasmosaurs and pliosaurs) dominated many marine ecosystems. The lineage gradually declined and became extinct by the end of the Cretaceous.

Fossil record and legacy: Fossils of sauropterygians are found on nearly every continent, with famous examples including Placodus and Nothosaurus from the Triassic, Plesiosaurus from the Jurassic, and Kronosaurus and Liopleurodon from the Cretaceous. Their diverse adaptations provide key insights into Mesozoic marine life and the evolution of marine tetrapods.