tter on which
it fed. There can therefore be no doubt but that the _Iguanodon_,
in spite of its immense bulk, was an herbivorous Reptile, and lived
principally on the foliage of the Cretaceous forests amongst which
it dwelt. Its size has been variously estimated at from thirty to
fifty feet, the thigh-bone in large examples measuring nearly
five feet in length, with a circumference of twenty-two inches
in its smallest part. With the strong and massive hind-limbs are
associated comparatively weak and small fore-limbs; and there
seems little reason to doubt that the _Iguanodon_ must have walked
temporarily or permanently upon its hind-limbs, after the manner of
a Bird. This conjecture is further supported by the occurrence in
the strata which contain the bones of the _Iguanodon_ of gigantic
three-toed foot-prints, disposed _singly_ in a double track. These
prints have undoubtedly been produced by some animal walking on
two legs; and they can hardly, with any probability, be ascribed
to any other than this enormous Reptile. Closely allied to the
_Iguanodon_ is the _Hadrosaurus_ of the American Cretaceous, the
length of which is estimated at twenty-eight feet. _Iguanodon_
does not appear to have possessed any integumentary skeleton; but
the great _Hyloeosaurus_ of the Wealden seems to have been furnished
with a longitudinal crest of large spines running down the back,
similar to that which is found in the comparatively small Iguanas
of the present day. The _Megalosaurus_ of the Oolites continued
to exist in the Cretaceous period; and, as we have previously
seen, it was carnivorous in its habits. The American _Loelaps_
was also carnivorous, and, like the Megalosaur, which it very
closely resembles, appears to have walked upon its hind-legs,
the fore-limbs being disproportionately small.

[Illustration: Fig. 209.--Teeth of Iguanodon Mantellii. Wealden,
Britain.]

Another remarkable group of Reptiles, exclusively confined to
the Cretaceous series, is that of the _Mosasauroids_, so called
from the type-genus _Mosasaurus_. The first species of _Mosasaurus_
known to science was the _M. Camperi_ (fig. 210), the skull of
which--six feet in length--was discovered in 1780 in the Maestricht
Chalk at Maestricht. As this town stands on the river Meuse,
the name of _Mosasaurus_ ("Lizard of the Meuse") was applied
to this immense Reptile. Of late years the remains of a large
number of Reptiles more or less closely related to _Mosasaur