Polycotylus, whose name means "many-ridged", was a small, short-necked plesiosaur that swam the warm Late Cretaceous seas around 85 million years ago. Unlike its long-necked cousins, Polycotylus had a compact, muscular body, a short neck, and a long, narrow jaws filled with sharp interlocking teeth perfect for snatching fish and squid. Its four powerful paddle-like flippers drove it through the water in a flying motion much like a modern sea turtle, making it a swift and agile hunter of the open sea. Reaching around three meters in length, it lived in the Western Interior Seaway of what is now North America, where it shared the water with giant mosasaurs and enormous fish. Fossils of Polycotylus have preserved mothers with single, unusually large unborn young inside them, suggesting these marine reptiles gave live birth at sea and invested heavily in a small number of offspring.