321 



IGUANODON. 



IGUANODON. 



223 



clavicle of the lyuanodon with the Iguana, of 75 feet from a similar 

 comparison of their femora, and of 80 feet from that of the claw-bone, 

 which if founded upon the largest specimen from Horsham, instead 

 of the one compared by Dr. llantell, would yield a result of upwards 

 of 200 feet for the total length of the Iguanodon, since the Horsham 

 phalanx exceeds the size of the largest of the recent Iguana's phalan- 

 ges by 40 times. But the same reasons which have been assigned for 

 calculating the bulk of the Meyalosaunix on the basis of the vertebra) 

 apply with equal force to the Iguanodon. Now the largest vertebra 

 of an Iguanodon which has yet been obtained does not, as has been before 

 stated, exceed 4 4 inches in length ; the most common size being 4 inches. 

 The intervertebral substance is shown by the naturally juxtaposed 

 series of dorsal vertebra in the Maidstone lyuanodon to be not more 

 than one-third of an inch in thickness. All the accurately deter- 

 mined vertebras of the Iguanodon manifest the same constancy of 

 their antero-posterior diameter which prevails in Saurians generally ; 

 the discovery of the true character of the supposed lacertian vertebra), 

 6 inches long, removes the only remaining doubt that could have 

 attached itself to this important element in the present calculation. 

 The cervical vertebrae of the Iguanodon, when discovered, if they 

 prove to differ in length from the known dorsal and caudal vertebrae, 

 will be in all probability somewhat shorter, as they are in the Hylaeo- 

 saur, and in all known Crocodiles and Lizards. It remains therefore 

 to discover the most probable number of the vertebrae and the ribs ; 

 and especially the variation in both structure and size which the ribs 

 of the lyuanodon already obtained demonstrate to have prevailed in 

 the costal series, renders it much more probable that the number of 

 the costal vertebne would resemble that of the Crocodiles, than that 

 of the Saurians or other Lizards with unusually numerous dorsal 

 vertebra;, and which possess ribs of a simple and uniform structure, 

 and of nearly equal size. The most probable number of vertebra; of 

 the trunk, from the atlas to the last lumbar inclusive, calculated from 

 Crocodilian analogies, would be 24 vertebra; ; which is also the 

 number possessed by the Iguana. Twenty-four vertebrae estimated 

 with their iuvertebral spaces at 5 inches each, give 10 feet ; if to this 

 we add the length of the sacrum, namely 17 inches, then that of 

 the tnmk of the lyuanodon would be 11 feet 5 inches, which exceeds 

 that of the Megatherium. If there be any part of the skeleton of the 

 lyuana which may with greater probability than the rest be supposed 

 to have the proportions of the corresponding part of the lyuanodon, 

 it is the lower jaw, by virtue of the analogy of the teeth and the 

 substances they are adapted to prepare for digestion. Now, the lower 

 jaw gives the length of the head in the lyuana, and this equals the 

 length of six dorsal vertebra;, so that as five inches rather exceeds the 

 length of the largest Iguanodon'i vertebra; yet obtained with the 

 intervertebral space superadded, on this calculation the length of the 

 head of the largest lyuanodon must have been 2 feet 6 inches. In 

 the description of the caudal vertebrae it has been shown that the 

 Iguanodon could as little have resembled the lyuana in the length of 

 its tail as in the anatomical characters of any of the constituent 

 vertebra; of that part; the changes which the series of six caudal 

 vertebrae present in the length and form of the spinous processes, and 

 in the place of origin of the transvers processes, indicate the tail to 

 have been shorter in the Iguanodon than in the Crocodile. Assuming 

 however that the number of caudal vertebra; of the lyuanodon 

 equalled that in the Crocodile, and allowing to each vertebra with 

 its invertebral space 4J inches, we obtain the length of 12 feet 6 inches 

 for the tail of the Iguanodon. 



Feet. 



Length of Head say 3 



Length of Trunk with Sacrum . . . .12 

 Length of Tail 13 



Total Length of the Iguanodon . ... 28 



" The same observations on the general form and proportions of the 

 animal, and its approximation in this respect to the Mammalia, 

 especially the great extinct Megatherioid or Pachydermal species, 

 apply as well to the lyuanodon as to the Megalotaurut." 



Since the original discovery of the teeth in Tilgato Forest, several 

 other portions of this remarkable animal have been found. The most 

 interesting of these were discovered by Mr. Bensted, of Maidstone, 

 in a green-sandstone quarry near that town. Other remains have also 

 been obtained from the Wealden of Sussex and the Isle of Wight. 

 On some of theoe remains Dr. Mantell thus remarks : 



" A recent discovery however supports the idea first suggested by 

 the stupendous size of the bones of the extremities. In a block of 

 c.ileiferous grit, picked up on the sea-shore, I have laid bare a chain of 

 eleven caudal vertebra;, belonging to the middle region of the tail, 

 and the bodies of these bones, instead of being abbreviated, as the 

 shortness of the known anterior caudals led us to infer, are elongated, 

 as in the corresponding part of the skeleton of the recent Iguana. 

 Tho kjgth of four of these vertebra; is equal to that of five dorsals, 

 and their spinous and transverse processes are so well developed as 

 ">w that the tail must have been greatly prolonged, probabably 

 in the same degree as in the existing Lizards. The length of the 

 femur of this individual is equal to six caudal or eight anterior dorsal 

 vertebrae. 



" It L) therefore, according to the present state of our knowledge, 



not at all improbable that the largest Iguanodons may have attained a 

 length of from 60 to 70 feet. Although some important points in 

 the osteology of the lyuanodon are still unknown, we may safely cour 

 elude that this stupendous reptile equalled in bulk the largest herbi- 

 vorous Mammalia, and was as massive in its proportions ; for living 

 exclusively on vegetables it must have had the abdominal region greatly 

 developed. 



" Its limbs must have been of proportionate size and strength to 

 sustain and move so enormous a carcass ; the hinder extremities 

 in all probability resembled the uuwieldly contour of the Hippopo- 

 tamus or Rhinoceros, and were supported by strong short feet, 

 protected by broad uugular phalanges ; the fore feet appear to have 

 been less bulky, and adapted for seizing and pulling down the foliage 

 and branches of trees ; the jaws and teeth demonstrate its power of 

 mastication, and the character of its food; while the remains of 

 coniferous trees, arborescent ferns, and eycadeous plants, which are 

 found imbedded with its remains, attest the nature of the flora 

 adapted for its sustenance." 



Whatever may be the differences of opinion as to the precise size of 

 this creature, all writers agree as to the great interest attaching to its 

 existence in this part of the world during the deposit of the great - 

 fresh-water beds that characterise the geology of the British Islands. 



The remains of the lyuanodon so carefully collected and treasured 

 by Dr. Mantell are now in the British Museum, where they will ever 

 remain a monument of his perseverance and skill, and a means of 

 enabling the student of natural history to come to his own conclusions 

 on the debateable points its structure has raised. To his account of 

 its structure Dr. Mantell adds some physiological inferences as to the 

 structure and economy of the lyuanodon, with which this notice may 

 be appropriately closed. 



" In instituting a comparison between the maxillary organs of the 

 lyuanodon and those of the existing herbivorous Lizards, with the view 

 of obtaining some physiological deductions from their peculiar osteolo- 

 gical characters, we are at once struck with their remarkable deviation 

 from all known types in the class Jteptilia. In the A mWyrhynchi, the most 

 exclusively vegetable feeders of the Saurian order, the alveolar process, 

 beset with teeth, is continued round the front of the mouth, the junction 

 of the two rami of the lower jaw at the symphysis presenting no edentu- 

 lous interval whatever, and the lips not being more produced than in 

 other reptiles ; for these creatures chip off and bruise .their food, and 

 caunot grind or masticate it : in the Iguanas, as previously shewn, 

 the same character exists. In the carnivorous Saurians the teeth aro 

 also continued to the symphysical suture on each side. The extinct 

 colossal Lizards offer no exception to this rule; in the acrodont 

 Moiotawus of the Chalk, and in the thecodont Meyalosaurus of the 

 Oolite and Wealden, the jaws are armed with teeth round the anterior 

 extremity. In short, the edentulous, expanded, scoop-shaped, pro- 

 cumbent, symphysis of the lower jaw of the Iguanodon, has no parallel 

 among either existing or fossil reptiles, and we seek in vain for 

 maxillary organs at all analogous, except among the herbivorous 

 Mammalia. 



" The nearest approach is to be found in certain Edentata, as for 

 example in the Cholaipus didactylus, or Two-Toed Sloth, in which the 

 anterior part of the lower jaw is edentulous and much prolonged. 



" The correspondence is still closer in the gigantic extinct Mylodon, 

 in which the symphysis resembles the blade of a spade used by turf- 

 diggers, and has no traces of incisive sockets ; and were not this part 

 of the jaw elevated vertically in front, and the two rami confluent, it 

 would present the very counterpart of that of the Iguanodon. 



" The great size and number of the vascular foramina distributed 

 along the outer side of the dentary bone, and beneath the border of 

 the symphysis, in the Iguanodon, and the magnitude of the anterior 

 outlets which gave exit to the vessels and nerves that supplied the 

 front of the mouth, indicate the great development of the integuments 

 and soft parts with which the lower jaw was invested. The sharp 

 ridge bordering the deep groove of the symphysis, in which there are 

 also several foramina, evidently gave attachment to the muscles and 

 integuments of the under lip ; while two deep pits for the insertion of 

 the protractor muscles of the tongue, manifest the mobility and power 

 of that organ. There are therefore strong reasons for supposing that 

 the lip was flexible, and, in conjunction with the long fleshy prehensile 

 tongue, constituted the instruments for seizing and cropping the 

 leaves and branches, which, from the construction of the molars, we 

 may infer constituted the chief food of the Iguanodon. The mechanism 

 of the maxillary organs, as elucidated by recent discoveries, is thus 

 in perfect harmony with the remarkable characters which rendered 

 the first known teeth so enigmatical ; and in the Wealden herbivorous 

 reptile we have a solution of the problem, how the integrity of the 

 type of organisation peculiar to the class of cold-blooded Vertclrata 

 was maintained, and yet adapted, by simple modifications, to fulfil 

 the conditions required by the economy of a gigantic terrestrial 

 reptile, destined to obtain support exclusively from vegetable 

 substances, in like manner as "the extinct colossal herbivorous 

 Edentata, which flourished in South America ages after the country 

 of the lyuanodon and its inhabitants had been swept from the face of 

 the earth. Thus in the unlimited production of successioual teeth 

 at every period of the animal's existence, in the mode of implantation 

 of the teeth, and in the composite structure of the lower jaw, each 



