217 



IGUANODON. 



IGUANODON. 



218 



of tail large, spiiiose. T. marmoratus, the Trachycyclus; Brazil and 

 Rio Grande. 



"H" Interparietal plate large ; back or tail crested. 



38. Taraguira. Back not crested; scales of back small, of the 

 throat granular ; tail round, with a slight crest, and moderate scales ; 

 car toothed in front. T. torquala, the Taraguira ; Kio Janeiro and 

 Brazil. T. Darwinii, Darwin's Taraguira; Brazil and Abrolhos 

 Inlet. T. Smithii, Smith's Taraguira ; Brazil. 



39. Microlophus. Back and tail lowly crested ; scales of tho back 

 unequal, small ; tail with moderate scales ; the ear toothed in front. 

 M. Pervianu3, the Microlophe ; Peru, Copiapo, and Iquique. 



40. Ojtlurut. Nape with a small crest ; scales of back large, of the 

 sides small; tail round, with rings of large spiuose scales. 0. 

 Srazilicntii, the Brazilian Oplurus ; Brazil. 



41. Strobilunu. Nape, back, and tail, slightly crested; scales of 

 back moderate ; tail with rings of large spinose scales. torqvatus, 

 the Strobilurua; Brazil. 



4'2. Uraniicodon. Nape and back lowly crested; scales of the 

 back large, rhombic ; sides of body and throat simple ; tail round, 

 lender, with moderate scales, slightly keeled above. U. pictum, the 

 1 Uraniscodon ; Brazil. 



43. Plica. Nape and back lowly crested; scales of the back small; 

 sides with two folds ; the throat with groups of spin s ; tail round, 

 f lender, keeled above with moderate scales. P. umbra, the Plica ; 

 Nortli America (?) and Georgia (?). P. punctala, the Dotted Plica ; 

 Tropical America. 



. Body depressed, with small scales; back rarely crested; tail 



conical 



a. Sides rounded ; femoral and preanal pores none ; eyebrow 

 scales small. 



44. Leiosaurus. Tail with granular scales ; scales under the eye 

 all small. L. Bdlii, Bell'a Leiosaurus i; South America. L. foiciatus, 

 the Banded Leiosaurus ; South America. 



45. KploUemui. Tail with granular scales, with an elongated 

 scale under the eye. D. Darwinii, Darwin's Diplolsemus; Pata- 

 gonia. D. Hibronii, Bibron's Diplokemus ; South America and 

 Chili. 



46. Tropidurui. Tail round, with rings of large scales; nape lowly 

 crested, interparietal (?). T. cydurus, the False Quetz Palea; 

 Brazil. 



47. L'ranocenlron. Tail depressed with rings of large scales ; nape 

 not crested ; interparietal smalt U. azureum, the Doryphore ; Brazil. 



i. Sides rounded ; femoral and preanal pores distinct, near vent. 



48. Phrymatui-us. Tail round, with rings of large scales; the nape 

 not crested. P. Palluma, the Palluma ; Chili 



c. Sides with a slight fold ; scales uniform ; body roundish. 



49. Callitaurtu. Ventral scales smooth; femoral pores distinct. 

 C. draconoidet, the Callisaurus ; California. 



50. Tropidoyatter. Ventral scales 3-keeled; femoral pores none. 

 T. Blaim-Mii, the Tropidogaster. 



d. Sides serrated ; body very depressed ; femoral pores distinct. 



51. P/trtjnosoma. Head spinose; back and tail with scattered 

 tubercular scales. P. Douglasii, Douglas's Phrynosoma ; California. 

 P. orbiculare, the Tapayaxin ; Mexico. P. Utainvillii, the Crowned 

 Tapayaxin ; California. P. cornotum, the Texian Tapayaxiu ; Ar- 

 kansas, North America, and Texas. 



IGUANODON (Iguana and oSovs (oMvros), a tooth), a genus of 

 extinct Reptiles of large size, discovered by Dr. Mantell, and named by 

 him from the resemblance of its teeth to those of the recent Iguana. 

 As the discovery of this animal is one of great interest in the records 

 of British Paleontology, and illustrates the success attendant upon 

 accurate investigation in this department of human inquiry, we give 

 the history of it in Dr. Mantell's own words : 



" Soon after my first discovery of bones of colossal reptiles in the 

 strata of Tilgate Forest, some teeth of a very remarkable character 

 particularly excited my curiosity, for they were wholly unlike any 

 that had previously come under my observation; even the quarry- 

 men, accustomed to collect the remains of fishes, shells, and other 

 objects imbedded in the rocks, had not observed fossils of this kind ; 

 and, until shown some specimens which I had extracted from a block 

 of stone, were not aware of the presence of such teeth in the stone 

 they were constantly breaking up for the roads. The first specimen 

 that arrested my attention was a large tooth, which, from the worn, 

 smooth, and oblique surface of the crown, had evidently belonged to 

 an herbivorous animal ; and so entirely resembled in form the corre- 

 sponding part of an incUor of a large pachyderm ground down by 

 use that I was much embarrassed to account for its presence in such 

 ancient strata, in which, according to all geological experience, no 

 fo.-wil remains of Mammalia would ever be discovered; and as no 

 known existing reptiles are capable of masticating their food, I could 

 Dot venture to assign the tooth in question to a saurian. 



"As my friend Mr. (now Sir Charles) Lyell was about to visit 

 Paris, I availed myself of the opportunity of submitting it to the 

 examination of Baron Cuvier, with whom I had the high privilege of 

 correspond iug ; and, to my astonishment, learned from iny friend, 



that M. Cuvier, without hesitation, pronounced it to be an upper 

 incisor of a Rhinoceros. 



" I had previously taken this tooth, and some other specimens, to a 

 meeting of the Geological Society in London, and showed them to 

 Dr. Bucklaud, Mr. Conybeare, Mr. Clift, and other eminent men who 

 were present, but without any satisfactory result; in fact, I was 

 discouraged by the remarks that the teeth were of no particular 

 interest, as there could be but little doubt they belonged either to 

 some large fish allied to the Anarhicas Lupus, or Wolf-Fish, the crowns 

 of whose incisors are of a prismatic form, or were mammalian teeth 

 obtained from a diluvial deposit. Dr. Wollaston alone supported my 

 opinion, that I had discovered the teeth of an unknown herbivorous 

 reptile, and encouraged me to continue my researches. And, as if to 

 add to the difficulty of solving the enigma, some metacarpal bones 

 which I soon after discovered in the same quarry, and forwarded to 

 Paris, were declared to belong to a species of Hippopotamus. Subse- 

 quently a dermal horn, or tubercle, from the same stratum, was 

 declared by competent authorities to be the lesser horn of a Rhino- 

 ceros ; and Dr. Buckland, with the generous kindness which marked 

 his character, wrote to guard me against venturing to publish that 

 these teeth, bones, and horn were found in the ' iron-sand formation,' 

 with which the Tilgate beds were then classed, as there could be no 

 doubt they belonged to the superficial diluvium ; and as the upper 

 beds of the conglomerate in which these first specimens were found 

 was only covered by loam and vegetable earth, there was no clear 

 stratigraphical evidence to support a contrary opinion. Other speci- 

 mens however were soon procured by stimulating the diligent search 

 of the workmen by suitable rewards, and at length teeth were 

 obtained which displayed the serrated edges, the longitudinal ridges, 

 and the entire form of the unused crown. I then forwarded specimens 

 and drawings to Baron Cuvier, and repaired to London, and with the 

 aid of that excellent man the late Mr. Clift, ransacked all the drawers 

 in the Hunterian Museum that contained jaws and teeth of reptiles, 

 but without finding any that threw light on the subject. Fortunately, 

 M. Samuel Stuchbury, then a young man, was present, and proposed 

 to show me the skeleton of an Iguana, which he had prepared from a 

 specimen that had long been immersed in spirits ; and, to my great 

 delight, I found that the minute teeth of that reptile bore a closer 

 resemblance in their general form to the fossils from Tilgate Forest 

 than any others with which I was able to institute a comparison. It 

 was not however until I had collected a series of specimens exhibiting 

 teeth in various stages of maturity and detrition that the correctness 

 of my opinion was admitted, either as to the character of these 

 dental organs, or the geological position of the rocks in which they 

 were imbedded." (' Petrifactions and their Teachings.') 



From their first discovery the teeth of this animal have excited 

 the greatest amount of interest on account of their peculiar structure. 

 In his report to the British Association, on the ' British Fossil 

 Reptiles,' Professor Owen gives an elaborate account of their structure 

 and functions : 



" The teeth of the Iguanodon," says the Professor, " though 

 resembling most closely those of the Iguana, do not present an exact 

 magnified image of them, but differ in the greater relative thickness 

 of the crown, its more complicated external surface, and still more 

 essentially in a modification of the internal structure by which tho 

 Iguanodon equally deviates from every other known reptile. As in 

 the Iguana, the base of the tooth is elongated and contracted, while 

 the crowo is expanded and smoothly convex on the inner side. When 

 first formed it is acuminated, compressed, its sloping sides serrated, 

 and its external surface traversed by a median longitudinal ridge, and 

 coated by a layer of enamel ; but beyond this point the description of 

 the tooth of the Iguanodon indicates characters peculiar to that genus. 

 In most of the teeth that have hitherto been found three longitudinal 

 ridges traverse the outer surface of the crown, one on each side of 

 the median primitive ridge ; these are separated from each other, and 

 from the serrated margins of the crown, by four wide and smooth 

 longitudinal grooves. The relative width of these grooves varies in 

 different teeth; sometimes a. fourth small longitudinal ridge is 

 developed on the outer side of the crown. The marginal serrations 

 wnich at first sight appear to be simple notches, ns in the Iguana, 

 present under a low magnifying power the form of transverse ridges, 

 themselves notched so as to resemble the mainmillated margins of the 

 unworn plates of the elephant's grinder. Slight grooves lead from 

 the interspaces of these notches upon the sides of the marginal 

 ridges. These ridges or dentations do not extend beyond the 

 expanded part of the crown ; the longitudinal ridges are continued 

 farther down, especially the median ones, which do not subside till 

 the fang of the tooth begins to assume its subcylindrical form. The 

 tooth at first increases both in breadth and thickness ; it then 

 diminishes in breadth, but its thickness goes on increasing ; in the 

 large and fully-formed teeth the fang decreases in every diameter, and 

 sometimes tapers almost to a point. The smooth unbroken surface 

 of such fangs indicates that they did not adhere to the inner side of 

 the maxilla;, as in the Iguana, but were placed in separate alveoli, as 

 in the Crocodile and Megalosaur ; such support would appear indeed 

 to bj indispensable to teeth so worn by mastication as those of the 

 lyuanodon. The apex of the tooth soon begins to be worn away, and 

 it would appear by many specimens that the teeth were retained 



