In Hand Museum - Iguanodon atherfieldensis

Nobody knows who first discovered dinosaur bones, or even when that happened, but we do know when the earliest scientific descriptions of dinosaur bones were written. Englishman Gideon Mantell found large reptile bones and teeth in Sussex in the early 1820s. He published his scientific description in 1825, one year after William Buckland's description of Megalosaurus. Because the teeth of Mantell's fossil creature resembled those of a modern iguana, he called his discovery Iguanodon. In 1853, paleontologist Richard Owen supervised the construction of life-sized models of Mantell's Iguanodon. While totally inaccurate by modern standards, these reconstructions were one of the first attempts to popularize dinosaurs. The body was postured similar to lizards with which Owen was familiar, so with its spike-like thumb placed on the nose, Iguanodon looked a lot like a reptilian rhino. To further enhance its novelty, the back was originally left open so the empty interior could be used as a dining area.

Discovery
One of the richest dinosaur finds ever discovered was in the mining town of Bernissart, Belgium. From 1878 to 1881, 39 different Iguanodon skeletons were dug from a layer of clay that cut across a coal seam 322 meters (over 1000 ft.) under the earth. Many of the skeletons were complete and they provide us with an outstanding record of this dinosaur. No further excavations were made before the mines were abandoned in 1921. Flooding has since closed the mines to paleontologists.

Taxonomy
Almost all dinosaurs are grouped into either the Saurischia or Ornithischia. Iguanodon is an ornithopod dinosaur which is a group within the ornithischian side. Ornithopods are one of the three large and diverse groups that comprise this half of the dinosaur family tree: Thyreophora, and Marginocephalia fill out the three. Ornithopods are distinguished from the other Ornithischians by several evolutionary novelties: the premaxillary teeth (teeth at the front of the mouth) are set lower than the maxillary teeth (teeth at the back of the mouth); the hinge point for the lower jaw is set well below the level of the lower tooth rows; and they have a distinctive arrangement of the bones of the face ( the way the premaxillary, maxillary and nasals are connected). The ornithopods are further divided into five families. The two best know are the Iguanodontidae (the name for all the types of Iguanodon when taken together) and Hadrosauridae (all hadrosaurs). Iguanodontids include Iguanodon, Camptosaurus and Ouranosaurus.

Iguanodontids first appeared in the Late Jurassic and prospered through the Early Cretaceous (a 50 million year span). They were largely replaced in the second half of the Cretaceous by the more advanced and very successful hadrosaurs.

Anatomy
Iguanodon was a large animal reaching up to 10 meters in length. From its skeletal structure we know it walked on all fours and extended its tail straight out behind, but could stand on its hind legs for browsing or defending itself. The "thumb" on each of its front legs was armed with a large spike, presumably to deter predators. Its toes had hoof-like tips on the ends.

You'll notice the skull is very horse-like with its long snout. Iguanodon used its toothless beak to crop plants and then chewed them with many leaf-shaped cheek teeth before swallowing. The development of cheeks and a grinding movement with the teeth may have provided these Ornithopods with an evolutionary advantage over other plant eaters (like the giant sauropods) that swallowed vegetation without chewing and used a bird-like gizzard to grind their food. Mammals move their lower jaws from side to side and up and down to grind foods between top and bottom teeth. Most reptiles, including dinosaurs, cannot move their jaws that way. Iguanodon skulls are jointed so closing the jaws forces the top teeth outward across the chewing surfaces of the lower teeth, creating a grinding action. The cheeks keep food in the mouth until swallowed.