Marine reptiles were a diverse group of reptiles that lived in the oceans during the Mesozoic Era, which lasted from about 252 to 66 million years ago. They included well-known species like ichthyosaurs, plesiosaurs, and mosasaurs. Unlike modern reptiles, these creatures adapted to life in the water, developing streamlined bodies and specialized limbs for swimming. These reptiles were not dinosaurs, but they coexisted with them. Marine reptiles varied in size, from small, agile hunters to massive predators. They played important roles in their ecosystems, feeding on fish, squid, and other marine life, showcasing the diversity of life in ancient oceans.