[Illustration: Fig. 140.--Ammonites rostratus.
(Upper Greensand.)]
The _Iguanodon_, signifying _Iguana-toothed_ (from the Greek word,
οδους, _tooth_), was more gigantic still than the Megalosaurus; one of
the most colossal, indeed, of all the Saurians of the ancient world
which research has yet exposed to the light of day. Professor Owen and
Dr. Mantell were not agreed as to the form of the tail; the former
gentleman assigning it a short tail, which would affect Dr. Mantell’s
estimate of its probable length of fifty or sixty feet; the largest
thigh-bone yet found measures four feet eight inches in length. The form
and disposition of the feet, added to the existence of a bony horn (Fig.
139), on the upper part of the muzzle or snout, almost identifies it as
a species with the existing Iguanas, the only Reptile which is known to
be provided with such a horn upon the nose; there is, therefore, no
doubt as to the resemblance between these two animals; but while the
largest of living Iguanas scarcely exceeds a yard in length, its fossil
congener was probably fifteen or sixteen times that length. It is
difficult to resist the feeling of astonishment, not to say incredulity,
which creeps over one while contemplating so striking a disproportion as
that which subsists between this being of the ancient world and its ally
of the new.
[Illustration: Fig. 141.--Teeth of Iguanodon.
_a_, young tooth; _b_, _c_, teeth further advanced, and worn.
(Wealden.)]
The Iguanodon carried, as we have said, a horn on its muzzle; the bone
of its thigh, as we have seen, surpassed that of the Elephant in size;
the form of the bone and feet demonstrates that it was formed for
terrestrial locomotion; and its dental system shows that it was
herbivorous.
[Illustration: Fig. 142.--Fishes of the Cretaceous period.