IGUANODON (iguana, and Gr. odous. tooth), a genus of remarkable gigantic dino saurian reptiles, more abundant in the Wealden beds of Kent, Sussex. and the isle of Wight than any other genus of associated saurians. Their singular structure, differing in many important particulars from any known reptile, long caused great diversity of opinion as to their true position. Dr. Mantell, their original discoverer and their learned expounder, first knew of their existence from some enormous bones, which. notwithstanding their colossal size, he considered reptilian. A large tooth next turned up, whose smooth-worn crown attested its having belonged to a herbivorous animal. Numerous other specimens of teeth were in progress of time discovered, and Dr. Man tell found that they corresponded in a remarkable manlier with the teeth of the small American lizard, the iguana, although they exhibited very striking and important dif ferences. Since the original discovery of the teeth, several other portions of this remarkable reptile have been found. 'the fragmentary and imperfect materials which have yet turned up make any estimate of the size of this animal purely hypothetical. Dr. :Haute11's estimate is as much as 70 ft. in extreme length, while prof. Owen con siders it to have been not over 28 feet.
The structure of the skeleton is very remarkable. The fragments of the upper and lower jaw show that the head was produced into a short snout, which supported a nasal horn. The vertebral column was somewhat fish-like, the joints being slightly concave
on both surfaces: yet it had lofty neural arches, and tile sacrum was composed of five anchylosed joints, a structure found in no other reptile. The limbs were long and strong, raising the body some distance from the ground. The largest femur yet found measures 4 ft. 8 in. in length, and the shaft has a circumference of 25 inches. The leg terminated in a three-toed foot, which produced the enormous tridactyle impressions on the argillaceous Wealden beds that were for some time considered to be the foot-prints of huge birds. The discovery by prof. Owen of all the bones of a perfect foot, how ever, conclusively connects these impressions with the iguanodon. His figure, in a recent volume of the paleontographical society's publications, exhibits a foot 21 in. long by tJ in. broad.
The teeth of the iguanodon, while bearing a general resemblance to those of the iguana, were much more complicated both in external form and internal structure than in any other known reptile. In all other known reptiles IIM.ifqrtically.ftht teeth are always sharp-edged, and fitted only to cut off the plants' on Which they feed, but the worn crowns in this animal show that the iguanodon thoroughly triturated its food before swallowing it.