Ornithopod dinosaur is a term used to describe a type of herbivorous dinosaur that walked on two legs. However, there are several synonyms for the word ornithopod dinosaur, such as "bird-footed dinosaur" and "duck-billed dinosaur." These creatures lived during the Cretaceous period, which lasted from 145 to 66 million years ago. They were known for their unique beak-like mouths and advanced chewing capabilities, making them efficient for consuming tough plant material. Other synonyms for ornithopod dinosaurs include "hadrosaur," "iguanodont," and "hypsilophodont." These creatures were some of the most dominant herbivores of their time and have been studied extensively by paleontologists to understand their behavior and evolution.