The Medals of Creation, Volumes 1 and 2 / First Lessons in Geology and the Study of Organic Remains

by Gideon Algernon Mantell

Fig.	1.—	Outer aspect of an upper tooth (in a reversed position), worn flat, and with the fang absorbed; fig. 3, inner aspect of the same tooth. a, a. Flat grinding surface, produced by mastication when all the thickly enamelled portion of the crown is worn away. c. Cavity produced by the pressure of a new tooth.
	2.—	Lower tooth of a young animal, slightly worn: inner aspect.
	4.—	Outer Surface of a lower tooth of an adult; and fig. 5, innersurface of the same. a, a. The hard cutting edge of the oblique surface worn by mastication. c. Indentation produced by the pressure of a successional tooth.
	6.—	Edge view of the serration on fig. 5; magnified.

The dentine is less vascular, and therefore hardest, on that side of the crown which has the thicker coat of enamel; hence the tooth wears away faster on one side than on the other, and an oblique grinding surface, with a sharp edge of enamel, is maintained until the crown is worn away. The internal structure of the teeth of the Iguanodon is thus in perfect accordance with their external configuration, and must have been admirably adapted, in every stage, for the laceration and comminution of the tough vegetable substances which, there is every reason to conclude, constituted the food of this colossal oviparous quadruped.

Vertebra of the Iguanodon,[644] [Lign. 206], p. 653; Lign. 224.—The remains of the vertebral column of the Iguanodon, consisting generally of broken and water-worn dorsal and caudal vertebræ, deprived of their processes and reduced to the state of the specimens represented [Lign. 206], figs. 6 and 8, are so abundant in some of the Wealden strata, that a short account of their characters may be useful. A reference to [Lign. 206], and its description, will render the following remarks intelligible to the general reader. The vertebræ of the Iguanodon are distinguishable from those of other reptiles which occur in the same strata by the following peculiarities, which the figure of a perfect specimen of a caudal vertebra ([Lign. 206], fig. 3) will serve to illustrate. The body, or centrum, is either flat or somewhat depressed on both articular faces; its sides are nearly flat, or somewhat convex, vertically (as in fig 3), and slightly concave lengthwise, or from front to back: in some examples, the body is more contracted towards the inferior surface, as in fig. 6; and in the vertebræ, near the middle of the tail, the sides are compressed, so as to give an angular contour and somewhat vertical elongation to the face, as in fig. 4; but in the dorsal vertebræ, the articular faces are nearly circular, but somewhat higher than wide. In the caudal vertebræ, the inferior angles of the body are truncated (w, figs. 3, 4), and present an oblique, smooth face, to articulate with the chevron bone (fig. 3, f). The annular part is united to the body by suture (fig. 3, o), and anchylosed in the dorsal vertebræ; and in these bones the neural arch is very high, and greatly expanded, and its bases extend transversely inwards, and join each other below the spinal canal, forming a ring, or bony channel, to contain the spinal chord.[645] "The transverse processes are straight, and very long in the vertebræ from the middle of the trunk, indicating a considerable expanse of the abdominal cavity, adapted for the lodgment of the capacious viscera of a herbivorous quadruped." (Owen.) The spinous processes ([Lign. 206], fig. 3, d) are large and of great height in the anterior caudal vertebræ, [Lign. 224]; and here the chevrons, or hæmapophyses ([Lign. 224], b, and [Lign. 206], fig. 2, and fig. 3, f), are also of considerable length; the bases of the latter are always united ([Lign. 206], fig. 2, g), and often blended, so as to form but one face for articulation with the truncated inferior angles of the body of the vertebra:, leaving a vertically elongated channel for the passage of the large blood-vessels of the tail. The external surface of the vertebræ of the Iguanodon is more or less marked with fine longitudinal striæ; those of the Megalosaurus have a smoother and more polished surface.[646]

[644] A detailed account of the elements of the spinal column of the Iguanodon, and remarks on various fossil vertebræ, the relations of which with the Iguanodon have been considered doubtful, will be found in Petrif. pp. 256-279.

[645] See also lithographs of dorsal and caudal vertebræ from the Kentish Rag; Owen’s Monog. Cret. Rept. (Pal. Soc.) 1851.

[646] See Rep. Brit Assoc. 1841, pp. 125-133, where an elaborate investigation of the vertebra: of the Iguanodon is given by Professor Owen.

Lign. 224. Six Caudal Vertebra of the Iguanodon. ¹/₁₄ nat. size.
Wealden. Tilgate Forest.

a, a. Spinous processes (neurapophyses), from 13 to 151/2 inches in height. b, b. Three displaced chevron bones (hæmapophyses), imbedded in the stone near their original position at the junction of the bodies of the vertebræ. c. Anterior articular face of a vertebra.