THE BEAKED DINOSAURS.
ORDER ORTHOPODA (ORNITHISCHIA OR PREDENTATA.)
The peculiar feature of this group of Dinosaurs is the horny beak or
bill. The bony core sutured to the front of the upper and lower jaws
was covered in life by a horny sheath, as in birds or turtles. But
this is not the only feature in which they came nearer to birds than
do the other Dinosaurs. The pelvic or hip bones are much more
bird-like in many respects, especially the backward direction of the
pubic bone, the presence of a prepubis, in the number of vertebrae
coössified into a solid sacrum, in the proportions of the ilium and so
on. Various features in the anatomy of the head, shoulder-blades and
hind limbs are equally suggestive of birds, and it seems probable that
the earliest ancestors of the birds were very closely related to the
ancestors of this group of Dinosaurs. But the ancestral birds became
adapted to flying, the ancestral Predentates to terrestrial life, and
in their later development became as widely diversified in form and
habits as the warm-blooded quadrupeds which succeeded them in the Age
of Mammals.
[Illustration: Fig. 25.--Skulls of Iguanodont and Trachodont
Dinosaurs. _Iguanodon_ and _Camptosaurus_ of the Jurassic and
Comanchic; _Kritosaurus_ and _Corythosaurus_ of the Middle
Cretacic (Belly River); _Saurolophus_ of the late Cretacic
(Edmonton); _Trachodon_ of the latest Cretacic (Lance). The
Iguanodon is European, the others North American. All 1/25 natural
size.]
These Beaked Dinosaurs were, so far as we can tell, all vegetarians.
Unlike the birds, they retained their teeth and in some cases
converted them into a grinding apparatus which served the same purpose
as the grinders of herbivorous quadrupeds. It is interesting to
observe the different way in which this result is attained. In the
mammals the teeth, originally more complex in construction and fewer
in number, are converted into efficient grinders by infolding and
elongation of the crown of each tooth so as to produce on the wearing
surface a complex pattern of enamel ridges with softer dentine or
cement intervening, making a series of crests and hollows continually
renewed during the wear of the tooth. 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. Life size
restorations of these and other extinct animals were erected in the
grounds of the Crystal Palace at Sydenham, London, and in Central
Park, New York. Those in London still exist, so far as the writer is
aware, but the stern mandate of a former mayor of New York ordered the
destruction of the Central Park models, not indeed as incorrect
scientifically, but as inconsistent with the doctrines of revealed
religion, and they were accordingly broken up and thrown into the
waters of the Park lake. Small replicas of these early attempts at
restoring dinosaurs may still be seen in some of the older museums in
this country and abroad.
[Illustration: Fig. 26.--SKELETON OF CAMPTOSAURUS, AN AMERICAN
RELATIVE OF THE IGUANODON.]
The real construction of the Iguanodon was gradually built up by later
discoveries, and in 1877 an extraordinary find in a coal mine at
Bernissart in Belgium brought to light no less than seventeen
skeletons more or less complete. These were found in an ancient
fissure filled with rocks of Comanchic age, traversing the
Carboniferous strata in which the coal seam lay, and with them were
skeletons of other extinct reptiles of smaller size. The open fissure
had evidently served as a trap into which these ancient giants had
fallen, and either killed by the fall or unable to escape from the
pit, their remains had been subsequently covered up by sediments and
the pit filled in to remain sealed up until the present day. These
skeletons, unique in their occurrence and manner of discovery, are the
pride of the Brussels Museum of Natural History, and, together with
the earlier discoveries, have made the _Iguanodon_ the most familiar
type of dinosaur to the people of England and Western Europe.
[Illustration: Fig. 27.--Teeth of the duck-billed dinosaur
_Trachodon_. The dental magazine has been removed from the lower
jaw and is seen to consist of several close-set rows of numerous
small pencil-like teeth which are pushed up from beneath as they
wear off at the grinding surface.]
_Camptosaurus._ The American counterpart of the Iguanodons of Europe
was the _Camptosaurus_, nearly related and generally similar in
proportions but including mostly smaller species, and lacking some of
the peculiar features of the Old World genus. In the National Museum
at Washington, are mounted two skeletons of _Camptosaurus_, a large
and a small species, and in the American Museum a skeleton of a small
species. It suggests a large kangaroo in size and proportions, but the
three-toed feet, with hoof-like claws, the reptilian skull, loosely
put together, with lizard-like cheek teeth and turtle beak indicate a
near relative of the great _Iguanodon_.
_Thescelosaurus._ The Iguanodont family survived until the close of
the Age of Reptiles, with no great change in proportions or
characters. Its latest member is _Thescelosaurus_, a contemporary of
_Triceratops_. Partial skeletons of this animal are shown in the
Dinosaur Hall; a more complete one is in the National Museum.
FOOTNOTES:
[Footnote 15: Trachodont teeth never drop out, they are completely
consumed. Only in the Iguanodonts and Ceratopsia are they shed.--B.
Brown.]