- The Hadrosaurs have been given the nickname "duck bills" because of their mysteriously shaped mouths. They looked like flat, toothless beaks. Their grining dental batteries composed of hundreds of tightly compacted teeth, evidence of high food-volume intake, related perhaps to high metabolism. Even more interesting was the rest of the head. It had a crest, which was a long nose-bone, sticking out on top of the head. Several different shapes and sizes of these crests existed. Samples of Hadrosaurs have even come with intact skin, so we know almost exactly how they looked like. Some hadrosaurs were 9 feet (2.7 meters) tall at the hips and more than 30 feet (9 meters) long.
- Iguanodons weighed as much as 4.5 metric tons, was 7.5 m (25 ft) long, and stood up to 4.5 m (15 ft) tall on its hind legs. The long, flat head ended in a horny beak, and its jaws contained teeth somewhat like those of an iguana. They had a bony spike on the thumb of each forelimb.
- Protoceratops ("first horned face") was a small, plant-eating dinosaur living in the Mongolia area about 97 million years ago to about 65 million years ago. The forerunner of the ceratopsians, Protoceratops grew to a length of about 1.8 m (about 6 ft), weighed about 347 pounds (180 kg) and walked on four legs. It would have been hip-high to a human adult. It had a short tail and a small bony neck frill at the back of its skull where its strong jaw muscles attached. Its facial horns were only just beginning to evolve, perhaps just as a bump on the nose and ridges over the eyes. Holes in the frill made the skull light so that the animal could make fast, defensive movements. Protoceratops held its head low for grazing, using its parrotlike beak to snip off low leaves, which were swallowed whole, since the teeth were of no use for chewing. Its front feet had five toes.
- Triceratops was a four-legged, plant-eating dinosaurs, weighing several tons, that lived during the Cretaceous period. Triceratops had three horns: one centrally located just above the nostrils and a pair that projected from the forehead. The skull was quite large in proportion to the rest of the body. A bony frill at the back of the skull protected the neck and anchored powerful jaw and neck muscles. With head lowered and horns pointing forward, all backed up by its enormous bulk, Triceratops must have been a tough challenge to predators such as Tyrannosaurus rex.
- Pachycephalosaurus was a plant-eating, birdlike, beaked dinosaur that lived about 97 million to about 65 million years ago. This two-legged dinosaur was about 8 m (about 27 ft) long; its head was 25 cm (10 in) thick with a crown of spikes and bumps and little space for its small brain. Its body was designed like a battering ram, with a spine that locked rigidly to withstand impacts. Pachycephalosaurus's thick skull may have allowed it to butt heads with others of its kind without injuring its brain. It may have fought by ramming the soft bellies of other dinosaurs.