DINOSAURS
Chapter 8:
THE BEAKED DINOSAURS
(Continued.)
C. The
Armored Dinosaurs—Stegosaurus, Ankylosaurus.
Sub-Order Stegosauria.
This group of dinosaurs is most remarkable for the massive bony armor plates,
crests or spines covering the body and tail. They were more or less completely
quadrupedal instead of bipedal, with straight post-like limbs and short rounded
hoofed feet adapted to support the weight of the massive body and heavy
armature. Although so different superficially from the bird-footed biped
Iguanodonts they are evidently related to them, for the teeth are similar, and
the horny beak, the construction of the pelvis, the three-toed hind foot and
four-toed front foot all betray relationship. From what we know of them it seems
probable that they evolved from Iguanodont ancestors, developing the bony armor
as a protection against the attacks of carnivorous dinosaurs, and modifying the
proportions of limbs and feet to enable them to support its weight. They were
evidently herbivorous and some of them of gigantic size. Smaller kinds with less
massive armor have been found in Europe but the largest and most extraordinary
members of this strange race are from North America.
STEGOSAURUS.
This extraordinary reptile equalled the Allosaurus in
size, and bore along the crest of the back a double row
of enormous bony plates projecting upward and somewhat
outward alternately to one side and the other. The
largest of these plates situated just back of the pelvis
were over two feet high, two and a half long, thinning
out from a base four inches thick. The tail was armed
with four or more stout spines two feet long and five or
six inches thick at the base. In the neck region and
probably elsewhere the skin had numerous small bony
nodules and some larger ones imbedded in its substance
or protecting its surface. The head was absurdly small
for so huge an animal, and the stiff thick tail
projected backward but was not long enough to reach the
ground. The hind limbs are very long and straight, the
fore limbs relatively short, and the short high arched
back and extremely deep and compressed body served to
exaggerate the height and prominence of the great
plates. The surface of these plates, covered with a
network of blood-vessels, shows that they bore a
covering of thick horny skin during life, which probably
projected as a ridge beyond their edges and still
further increased their size. The spines of the tail,
also, were probably cased in horn.
This extraordinary animal was a contemporary of the
Brontosaurus and Allosaurus, and its discovery was one
of the great achievements of the late Professor Marsh.
The skeletons which he described are mounted in the Yale
and National Museums. Another skeleton was found in the
famous Bone-Cabin Quarry, near Medicine Bow, Wyoming, by
the American Museum Expedition of 1901. This skeleton,
at present withdrawn from lack of space, will be mounted
in the Jurassic Dinosaur Hall in the new wing now under
construction.
After Brown
Fig.
35.—Skull and lower jaw of Armored Dinosaur
Ankylosaurus, from Upper Cretacic (Edmonton
formation) of Alberta. Left side view.
ANKYLOSAURUS.
Related to Stegosaurus, equally huge, but very
different in proportions and character of its armor was
the Ankylosaurus of the late Cretacic. This animal, a
contemporary of the Tyrannosaurus and duck-billed
dinosaurs was more effectively though less grotesquely
armored than its more ancient relative. The body is
covered with massive bony plates set close together and
lying flat over the surface from head to tip of tail.
While the stegosaur's body was narrow and compressed, in
this animal it is exceptionally broad and the wide
spreading ribs are coössified with the vertebrae, making
a very solid support for the transverse rows of armor
plates. The head is broad triangular, flat topped and
solidly armored, the plates consolidated with the
surface of the skull and overhanging sides and front,
the nostrils and eyes overhung by plates and bosses of
bone; and the tail ended in a blunt heavy club of
massive plates consolidated to each other and to the tip
of the tail vertebrae. The legs were short, massive and
straight, ending probably in elephant-like feet. The
animal has well been called "the most ponderous animated
citadel the world has ever seen" and we may suppose that
when it tucked in its legs and settled down on the
surface it would be proof even against the attacks of
the terrible Tyrannosaur.
After Brown
Fig. 36.—Ankylosaurus,
top view of skull in fig. 35.
This marvellous animal was made known to science by
the discoveries of the Museum parties in Montana and
Alberta under Barnum Brown. Fragmentary remains of
smaller relatives had been discovered by earlier
explorers but nothing that gave any adequate notion of
its character or gigantic size. From a partial skeleton
discovered in the Hell Creek beds of Montana, and others
in the Edmonton and Belly River formations of the Red
Deer River, Alberta, it has been possible to reconstruct
the entire skeleton of the animal, save for the feet,
and to locate and arrange most of the armor plates
exactly. A skeleton mount from these specimens will
shortly be constructed for the Cretaceous Dinosaur Hall.
Scelidosaurus, Polacanthus, etc. Various
armored dinosaurs, of smaller size and less heavily
plated, have been described from the Jurassic, Comanchic
and Cretacic formations of Europe. The best known are
Scelidosaurus of the Lower Jurassic of England, and
Polacanthus of the Comanchic (Wealden).
Stegopelta of the Cretaceous of Wyoming is more
nearly related to Ankylosaurus. |
