DINOSAURS
Chapter 6:
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.
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.
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.
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:
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