IGUANODON, a genus of extinct Dinosaurian reptiles, the remains of which have been found in greatest abundance in theWealden, a delta formation of the south-east of England. They also occur, though more sparingly, in the Lower Greensand, where lately (1879) Professor Prestwich announced the discovery in the “Kimmeridge Clay” of what are as yet the earliest known remains of these reptiles. Although no complete skeleton of the iguanodon has been found, such bones of it as have been obtained prove it to have been one of the largest terrestrial animals known. Thus its femur in one instance measured from 4 to 5 feet in length, with a circumference of 22 inches at its narrowest part. These and other measurements led Dr Manteli—the original discoverer of Iguanodon — and others to conclude that it probably attained a length of from 50 to 60 feet. Its front limbs appear to have been small, while the hind pair attained enormous development, and from the structure of the latter, which may be regarded as intermediate between those of existing reptiles and of birds, the iguanodon is supposed to have either habitually or occasionally walked on its hind legs like a bird. This supposition is rendered all the more probable by the discovery in the same strata of gigantic three-toed footsteps in pairs such as might have been formed by the iguanodon had it walked in this bipedal manner. The teeth of these animals formed one of their most marked characteristics,— bearing a striking resemblance to the teeth of existing iguanas in their blade-like form and serrated edges, but differing from these as well as from those of all other known reptiles in internal structure. Like existing iguanas they were probably herbivorous, using their teeth for cutting and tearing their tough ...