The Duck-Billed Dinosaurs and their close relatives form the dinosaur group known as Ornithopoda (Or-nith-oh-pod-a). "Ornithopod" means "bird foot" and alludes to the three-toed hind feet found in the more advanced members of the group. Ornithopods were generally bipeds (walked on two feet), although the relatively long forearms suggest that they could also have gotten down on all fours to walk. At the front of the mouth, there was a horny beak used to nip vegetation. Ornithopods first appeared in the Jurassic Period as relatively small forms and then evolved into very large dinosaurs in the Cretaceous, often bearing spectacular crests on their heads.
One of the earliest Ornithopods was Camptosaurus (Camp-toe-soar-us), which lived during the Late Jurassic Period of North America, approximately 150 million years ago. Camptosaurus grew to 20 feet in length and stood about 4 feet high at the hip. Unlike the more advanced ornithopods, Camptosaurus had four toes on the hind feet, a primitive feature. The hand bore five fingers, the first finger (thumb) modified to form a small spike.
Somewhat more advanced than Camptosaurus was Iguanodon (Ee-gwano-don) from the Early Cretaceous of Europe, with close relatives living elsewhere in the world. "Iguanodon" means "Iguana Tooth," referring to the teeth which are strikingly similar to those of the modern-day Iguana lizard (although considerably larger in size).
Iguanodon was one of the first dinosaurs to be named by science. Initially, only fragments of this dinosaur were known (leading to a very fanciful reconstruction), but in 1878 many nearly complete and articulated skeletons were found in a Belgian coal mine. This marks the first time in history that complete dinosaur skeletons were available for scientists to study.
Iguanodon was about 33 feet in length and had a spiked thumb like that of Camptosaurus, but much larger in size. The hind foot was of the classic ornithopod type, with three prominent, hoof-like toes.
A fanciful and greatly outdated reconstruction of Iguanodon based on fragmentary material. The thumb spike was placed on the nose!
Another primitive ornithopod was Hypsilophodon (Hip-si-loaf-oh-don). Interestingly, it was more primitive than Camptosaurus, but lived later in time, during the Early Cretaceous Period. It lived in Europe and is another example of dinosaur that was known to science early on.
Hypsilophodon was relatively small (about 8 feet long), agile, and lightly built. Like Camptosaurus, it had four toes on the hind feet (a primitive feature). Although there was a horny beak at the front of the mouth, the upper jaw bore five teeth just behind this beak. In other Ornithopods this area is devoid of teeth and, thus, there is a toothless gap between the beak and the cheek teeth.
Owing to its agility and the long fingers and toes, Hypsilophodon was originally believed to be a climber and there are reconstructions of Hypsilophodon standing on tree branches. Modern interpretations place Hypsilophodon firmly on the ground as a terrestrial biped.
The apex of Ornithopod evolution took the form of the duck-billed dinosaurs or Hadrosaurs (Had-row-soars). As the name "duck-bill" suggests, the beak in these forms was broad and flat, much like the bill of a duck. Hadrosaurs also had greatly enlarged nostrils (the nasal bones are more than half the length of the skull) and, in some forms, the nasal structures were significantly expanded to form bizarre, bony crests. The navigation bar to your left will take you to pages that describe some of the hadrosaur dinosaurs in detail.