similar, if not a still warmer climate, prevailed at the time when so huge a Lizard as the Iguanodon inhabited what are now the temperate regions of the southern coasts of England. We know from the fragment of a femur, in the collection of Mr. Mantell, that the thigh-bone of this reptile much exceeded in bulk that of the largest Elephant: this fragment presents a circumference of twenty-two inches in its smallest part, and the entire length must have been between four and five feet. Comparing the proportions of this monstrous bone with those of the fossil teeth with which it is associated, it appears that they bear to one another nearly the same ratio that the femur of the Iguana bears to the similarly constructed and peculiar teeth of that animals.[1]
It has been stated, in the preceding section, that the large medullary cavities in the femur of the Iguanodon, and the form of the bones of the feet, show that this animal, like the Megalosaurus, was constructed to move on land. A further analogy between the extinct fossil and the recent Iguana is offered by the presence in both of a from of
- ↑ From a careful comparison of the bones of the Iguanodon with those of the Iguana, made by taking an average from the proportions of different bones from eight separate parts of the respective skeletons, Mr. Mantell has arrived at these dimensions as being the proportionate measure of the following parts of this extraordinary reptile:
Feet. Length from snout to the extremity of the tail 70 Length of tail 52½ Circumference of body 14½ Mr. Mantell calculates the femur of the Iguanodon to be twenty times the size of that of a modern Iguana; but as animals do not increase in length in the same ratio as in bulk, it does not follow that the Iguanodon attained the enormous length of one hundred feet, although it approached perhaps nearly to seventy feet.
As the Iguanodon, from its enormous bulk, must have been unable to mount on trees, it could not have applied its tail to the same purpose as the Iguana, to assist in climbing; and the longitudinal diameter of its caudal vertebra: is much less in proportion than in the Iguana, and shows the entire tail to have been comparatively shorter.
