Illustration of a herd of triceratops dinosaurs. These animals were common in the late Cretaceous period, from around 70 million years ago until the extinction of the dinosaurs some 65 million years ago. Triceratops was a herbivorous dinosaur that could reach a length of up to nine metres. It used its horns and its neck shield to defend itself against attack. Like modern plains animals, they may have lived in herds, in what is now North America.