In the reptile the teeth,
originally simple in construction but more numerous and continually
renewed as they wear down and fall out,[15] are banked up in several
close packed rows, the enamel borders and softer dentine giving a
wearing surface of alternating crests and hollows continually renewed,
and reinforced from time to time, by the addition of new rows of teeth
to one side, as the first formed rows wear down to the roots. This is
the best illustrated in the _Trachodon_ (see fig. 27); the other
groups have not so perfect a mechanism.
A. THE IGUANODONTS: IGUANODON, CAMPTOSAURUS.
_Sub-Order Ornithopoda or Iguanodontia._
In the early days of geology, about the middle of the nineteenth
century, bones and footprints of huge extinct reptiles were found in
the rocks of the Weald in south-eastern England. They were described
by Mantell and Owen and shown to pertain to an extinct group of
reptiles which Owen called the Dinosauria. So different were these
bones from those of any modern reptiles that even the anatomical
learning of the great English palaeontologist did not enable him to
place them all correctly or reconstruct the true proportions of the
animal to which they belonged. With them were found associated the
bones of the great carnivorous dinosaur _Megalosaurus_; and the weird
reconstructions of these animals, based by Waterhouse Hawkins upon the
imperfect knowledge and erroneous ideas then prevailing, must be
familiar to many of the older readers of this handbook.
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