Travelling as a herd provides safety in numbers because it is difficult for a hungry predator to pick out just one animal for slaughter. Group members can also warn each other if there are flesh-eaters on the prowl. It is possible that, for these reasons, some plant-eating dinosaurs formed herds. We know that certain dinosaurs travelled in groups because large clusters of their fossil bones and footprints have been found together. These dinosaurs may also have trudged vast distances together to find good grazing land and breeding sites. These journeys are called migrations. Today, many animals follow a herding life for much the same reasons as their ancient ancestors.
In Late Cretaceous times, herds of Pachyrhinosaurus migrated north from what is now Alberta, Canada, to the Arctic. Feeding on large-leafed plants, they remained there until driven south again by the bitterly cold winter. We know they made these epic treks because fossils of this lumbering herbivore have been discovered in Alberta and 3,500 km (2,200 miles) away in northern Alaska, USA.
Long journeys can prove hazardous for migrating animals because predators lurk at every turn. Travelling in search of fresh grass, wildebeest migrate distances of up to 2,900 km (1,800 miles) through Tanzania and Kenya. They often risk attack by crocodiles as they cross rivers. It is likely migrating dinosaurs would have faced similar dangers, perhaps also falling victim to crocodilians.