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.
[Illustration: Fig. 35.--Skull and lower jaw of Armored Dinosaur
_Ankylosaurus_, from Upper Cretacic (Edmonton formation) of
Alberta. Left side view. _After Brown_]
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.
[Illustration: Fig. 36.--_Ankylosaurus_, top view of skull in fig.
35. _After Brown_]
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_.