Sauropod
With much evidence, sauropods lived in groups, often large groups. They lived as a group, laid their eggs in the same places year after year, and were followed by bipedal theropods who preyed on them. Their breeding grounds had many thousands of eggs, and were laid at a particular time of the year. The cycle was repeated year after year. This suggests a seasonality in their behaviour, and also that their group behaviour was part of their defence against predators ("safety in numbers"). The evidence for all this is now overwhelming.