Artwork showing the relative scale of humans and Edmontosaurus. This animal belonged to the very successful group of hervivorous dinosaurs, flourishing during the Late Cretaceous period, called hadrosaurs ('duck-billed' dinosaurs). It lived alongside Tyrannosaurus rex and Triceratops in North America, during the waning millennia of the Cretaceous period, and grew to lengths of 12 m (39 ft).