312 PETRIFACTIONS AND THEIR TEACHINGS. CHAP. III. 



compressed laterally, and largely developed in a vertical di- 

 rection. In my Memoir, in the "Phil. Trans" 1841 (pp. 

 137 140), it is stated that "from the shortness of the 

 caudal vertebrae, and the length of the spinous processes, 

 indicating a great vertical development of the tail, it is pro- 

 bable this organ was not long and slender, as in the Iguana, 

 but approximated more nearly to the tail of the Dory- 

 phorus" 



" The length of the united head and trunk, according to my 

 estimate, 1 is seventeen feet and a half ; by Professor Owen's it 

 is reduced to fifteen feet : a difference of no importance in 

 such merely approximative calculations, particularly when 

 the form of the cranium is unknown. The great discrepancy 

 is in the estimated length of the tail ; if the Iguanodon re- 

 sembled the Iguana in its caudal proportions, its total length 

 would be seventy feet ; but if the tail was short, the total 

 length of the animal would, of course, be proportionately 

 reduced, and the most gigantic individuals may not have 

 exceeded thirty feet in length." 



A recent discovery, however, supports the idea first sug- 

 gested by the stupendous size of the bones of the extremities. 



In a block of calciferous grit picked up on the sea-shore, 

 I have laid bare a chain of eleven caudal vertebrae, 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. 

 The length of four of these vertebras is equal to that of five 

 dorsals ; and their spinous and transverse processes are so 

 well developed, as to show that the tail must have been 

 greatly prolonged probably, 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 

 is, therefore, according to the present state of our knowledge, 

 not at all improbable, that the largest Iguanodons may have 

 attained a length of from sixty to seventy feet. 



Although some important points in the osteology of the 

 Iguanodon are still unknown, we may safely conclude that 

 this stupendous reptile equalled in bulk the large herbivo- 



1 " Geology of the South-East of England," p. 316. 



