Sauropod dinosaurs were plant-eaters (herbivores) that included the largest land animals that have ever lived. First appearing in the Late Triassic Period (about 210 million years ago), sauropods diversified into many forms during the Jurassic. Still, they maintained a basic body form of with a long neck, a long tail, and a small head. Some sauropods may have browsed like giraffes, using teeth adapted for cutting and stripping plants of their leaves; others may have grazed for low-growing plants which they took whole and chewed. Early studies of sauropods proposed they were aquatic, using the logic that their huge bodies could not be supported on land. Later work revealed that they were probably fully terrestrial, living in a wide variety of land ecosystems. Fossil trackways show that some sauropods traveled in herds composed of animals of different ages. Sauropods often nested together as well, evidenced by clusters of nests with fossil eggs and embryos.