DINOSAURS
Chapter 7:
THE BEAKED DINOSAURS
(Continued).
B.
The Duck Billed Dinosaurs,—Trachodon, Saurolophus, etc.
Sub-Order Ornithopoda; Family
Trachodontidæ.
These
animals of the Upper Cretaceous are probably descended from the Iguanodonts of
an older period. But the long ages that intervened, some millions of years, have
brought about various changes in the race, not so much in general proportions as
in altering the form and relations of various bones of skull and skeleton and
perfecting their adaptation to a somewhat different habit of life, so that they
must be regarded as descendants perhaps, but certainly rather distant relatives,
of the older group.We know more about the Trachodonts than any other
dinosaurs. For not only are the skeletons more frequently found articulated, but
parts of the skin are not uncommonly preserved with them, and in one specimen at
least, so much of the skin is preserved that it may fairly be called a "dinosaur
mummy." This specimen of Trachodon is in the American Museum, and beside
it are two fine mounted skeletons of the largest size. There is also on
exhibition a panel mount of a nearly related genus,
Saurolophus the skeleton lying as it was found in
the rock, and a fine skeleton of a third genus
Corythosaurus with the skin partly preserved on both
sides of the crushed and flattened body stands beside it. In the
Tyrannosaurus group when completed will appear a fourth skeleton of the
Trachodon. Several skulls and incomplete skeletons on exhibition and other
skeletons not yet prepared add to the Museum collection of this group. Trachodon
skeletons may also be found in the Museums of New Haven, Washington,
Frankfurt-on-the-Main, London and Paris, but nowhere a series comparable to that
displayed at the American Museum.
THE TRACHODON GROUP.
The following description of the Trachodon group is
by Mr. Barnum Brown and first appeared in the American
Museum Journal for April 1908:[16]
"This group takes us back in imagination to the
Cretaceous period, more than three millions of years
ago, when Trachodonts were among the most numerous of
the dinosaurs. Two members of the family are represented
here as feeding in the marshes that characterized the
period, when one is startled by the approach of a
carnivorous dinosaur, Tyrannosaurus, their enemy, and
rises on tiptoe to look over the surrounding plants and
determine the direction from which it is coming. The
other Trachodon, unaware of danger, continues peacefully
to crop the foliage. Perhaps the erect member of the
group had already had unpleasant experiences with
hostile beasts, for a bone of its left foot bears three
sharp gashes which were made by the teeth of some
carnivorous dinosaur.
Fig.
28.—Mounted Skeletons of
Trachodon in the American Museum. Height of
standing skeleton 16 feet, 10 inches.
"By thus grouping the skeletons in lifelike
attitudes, the relation of the different bones can best
be shown, but these of course are only two of the
attitudes commonly taken by the creatures during life.
Mechanical and anatomical considerations, especially the
long straight shafts of the leg bones, indicate that
dinosaurs walked with their limbs straight under the
body, rather than in a crawling attitude with the belly
close to the ground, as is common among living reptiles.
"Trachodonts lived near the close of the Age of
Reptiles in the Upper Cretaceous and had a wide
geographical distribution, their remains having been
found in New Jersey, Mississippi and Alabama, but more
commonly in Wyoming, Montana, and the Dakotas. A
suggestion of the great antiquity of these specimens is
given by the fact that since the animals died layers of
rock aggregating many thousand feet in vertical
thickness have been deposited along the Atlantic coast.
"The bones of the erect specimen are but little
crushed and a clear conception of the proportions of the
animal can best be obtained from this specimen. It will
be seen that the Trachodon was shaped somewhat like a
kangaroo, with short fore legs, long hind legs, and a
long tail. The fore limbs are reduced indeed to about
one-sixth the size of the hind limbs and judging from
the size and shape of the foot bones the front legs
could not have borne much weight. They were probably
used in supporting the anterior portion of the body when
the creature was feeding, and in aiding it to recover an
upright position. The specimen represented as feeding is
posed so that the fore legs carry very little of the
weight of the body. There are four toes on the front
foot but the thumb is greatly reduced and the fifth
digit or little finger, is absent." (Subsequent
discoveries have shown that the arrangement of the
digits made by Marsh and followed in this skeleton is
incorrect. It is the first digit that is absent, and the
fifth is reduced.)
"The hind legs are massive and have three well
developed toes ending in broad hoofs. The pelvis is
lightly constructed with bones elongated like those of
birds. The long deep compressed tail was particularly
adapted for locomotion in the water. It may also have
served to balance the creature when standing erect on
shore. The broad expanded lip of bone known as the
fourth trochanter, on the inner posterior face of the
femur or thigh bone was for the attachment of powerful
tail muscles similar to those which enable the crocodile
to move its tail from side to side with such dexterity.
This trochanter is absent from the thigh bones of
land-inhabiting dinosaurs with short tails, such as
Stegosaurus and Triceratops. The tail muscles
were attached to the vertebrae by numerous rod-like
tendons which are preserved in position as fossils on
the erect skeleton. Trachodonts are thought to have been
expert swimmers. Unlike other dinosaurs their remains
are frequently found in rocks that were formed under sea
water probably bordering the shores but nevertheless
containing typical sea shells.
"The elaborate dental apparatus is such as to show
clearly that Trachodonts were strictly herbivorous
creatures. The mouth was expanded to form a broad
duck-like bill which during life was covered with a
horny sheath, as in birds and turtles. Each jaw is
provided with from 45 to 60 vertical and from 10 to 14
horizontal rows of teeth, so that there were more than
2000 teeth altogether in both jaws.
"Among living saurians, or reptiles, the small South
American iguana Amblyrhynchus may be compared in
some respects with the Trachodons notwithstanding the
difference in size. These modern saurians live in great
numbers on the shores of the Galapagos Islands off the
coast of Chile. They swim out to sea in shoals and feed
exclusively on seaweed which grows on the bottom at some
distance from shore. The animal swims with perfect ease
and quickness by a serpentine movement of its body and
flattened tail, its legs meanwhile being closely pressed
to its side and motionless. This is also the method of
propulsion of crocodiles when swimming.
"The carnivorous or flesh-eating dinosaurs that lived
on land, such as Allosaurus and Tyrannosaurus,
were protected from foes by their sharp biting teeth,
while the land-living herbivorous forms were provided
with defensive horns, as in Triceratops, sharp
spines as in Stegosaurus or were completely
armored as in Ankylosaurus. Trachodon was not
provided with horns, spines or plated armor, but it was
sufficiently protected from carnivorous land forms by
being able to enter and remain in the water. Its skin
was covered with small raised scales, pentagonal in form
on the body and tail, where they were largest, with
smaller reticulations over the joints but never
overlapping as in snakes or fishes. A Trachodon skeleton
was recently found with an impression of the skin
surrounding the vertebrae which is so well preserved
that it gives even the contour of the tail as is shown
in the illustration (fig. 32).
"During the existence of the Trachodonts the climate
of the northern part of North America was much warmer
than it is at present, the plant remains indicating a
climate for Wyoming and Montana similar to what now
prevails in Southern California. Palm leaves resembling
the palmetto of Florida are frequently found in the same
rocks with these skeletons. Here occur also such, at
present, widely separated trees as the gingko now native
of China, and the Sequoia now native of the Pacific
Coast. Fruits and leaves of the fig tree are also
common, but most abundant among the plant remains are
the Equisetae or horsetail rushes, some species of which
possibly supplied the Trachodons with food.
After Osborn
Fig. 29.—Restoration of the Duck-billed Dinosaur
Trachodon. This restoration, made by Mr. Knight
under supervision of Professor Osborn, embodies the
latest evidence as to the structure and
characteristic poses of these animals, the character
of the skin and their probable habits and
environment.
"Impressions of the more common plants found in the
rocks of this period with sections of the tree trunks
showing the woody structure will be [have been]
introduced into the group as the ground on which the
skeletons stand. In the rivers and bayous of that remote
period there also lived many kinds of Unios or
fresh-water clams, and other shells, the casts of which
are frequently found with Trachodon bones. The fossil
trunk of a coniferous tree was found in Wyoming, which
was filled with groups of wood-living shells similar to
the living Teredo. These also will be introduced in the
ground-work.
"The skeleton mounted in a feeding posture was one of
the principal specimens in the Cope Collection, which,
through the generosity of the late President Jesup, was
purchased and given to the American Museum. It was found
near the Moreau River, north of the Black Hills, South
Dakota, in 1882, by Dr. J.L. Wortman and Mr. R.S. Hill,
collectors for Professor Cope. The erect skeleton came
from Crooked Creek, central Montana, and was found by a
ranchman, Mr. Oscar Hunter, while riding through the bad
lands with a companion in 1904. The specimen was partly
exposed, with backbone and ribs united in position. The
parts that were weathered out are much lighter in color
than the other bones. Their large size caused some
discussion between the ranchmen and to settle the
question, Mr. Hunter dismounted and kicked off all the
tops of the vertebrae and rib-heads above ground,
thereby proving by their brittle nature that they were
stone and not buffalo bones as the other man contended.
The proof was certainly conclusive, but it was extremely
exasperating to the subsequent collectors. Another
ranchman, Mr. Alfred Sensiba, heard of the find and
knowing that it was valuable 'traded' Mr. Hunter a
six-shooter for his interest in it. The specimen was
purchased from Messrs. Sensiba Brothers and excavated by
the American Museum in 1906."
After Osborn
Fig. 30.—The Dinosaur Mummy.
Skeleton of a Trachodon preserving the skin
impressions over a large part of the body.
THE DINOSAUR "MUMMY."
We all believe that the Dinosaurs existed. But
to realize it is not so easy. Even with the help of the
mounted skeletons and restorations, they are somewhat
unreal and shadowy beings in the minds of most of us.
But this "dinosaur mummy" sprawling on his back and
covered with shrunken skin—a real specimen, not restored
in any part—brings home the reality of this ancient
world even as the mummy of an ancient Egyptian brings
home to us the reality of the world of the Pharaohs. The
description of this unique skeleton by Professor Henry
Fairfield Osborn first appeared in the Museum Journal
for January 1911.[17]
"Two years ago (1908) through the Jesup Fund, the
Museum came into possession of a most unique specimen
discovered in August 1908, by the veteran fossil hunter
Charles H. Sternberg of Kansas. It is a large
herbivorous dinosaur of the closing period of the Age of
Reptiles and is known to palaeontologists as
Trachodon or more popularly as the 'duck-billed
dinosaur.'
"The skeleton or hard parts of these very remarkable
animals had been known for over forty years, and a few
specimens of the epidermal covering, but it was not
until the discovery of the Sternberg specimen that a
complete knowledge of the outer covering of these
dinosaurs was gained. It appears probable that in a
number of cases these priceless skin impressions were
mostly destroyed in removing the fossil specimens from
their surroundings because the explorers were not
expecting to find anything of the kind. Altogether seven
specimens have been discovered in which these delicate
skin impressions were partly preserved, but the
'Trachodon mummy' far surpasses all the others, as it
yields a nearly complete picture of the outer covering.
"The reason the Sternberg specimen (Trachodon
annectens) may be known as a dinosaur 'mummy' is
that in all the parts of the animal which are preserved
(i.e. all except the hind limbs and the tail),
the epidermis is shrunken around the limbs, tightly
drawn along the bony surfaces, and contracted like a
great curtain below the chest area. This condition of
the epidermis suggests the following theory of the
deposition and preservation of this wonderful specimen,
namely: that after dying a natural death the animal was
not attacked or preyed upon by its enemies, and the body
lay exposed to the sun entirely undisturbed for a long
time, perhaps upon a broad sand flat of a stream in the
low-water stage; the muscles and viscera thus became
completely dehydrated, or desiccated by the action of
the sun, the epidermis shrank around the limbs, was
tightly drawn down along all the bony surfaces, and
became hardened and leathery, on the abdominal surfaces
the epidermis was certainly drawn within the body
cavity, while it was thrown into creases and folds along
the sides of the body owing to the shrinkage of the
tissues within. At the termination of a possible
low-water season during which these processes of
desiccation took place, the 'mummy' may have been caught
in a sudden flood, carried down the stream and rapidly
buried in a bed of fine river sand intermingled with
sufficient elements of clay to take a perfect cast or
mold of all the epidermal markings before any of the
epidermal tissues had time to soften under the solvent
action of the water. In this way the markings were
indicated with absolute distinctness, ... the visitor
will be able by the use of the hand glass to study even
the finer details of the pattern, although of course
there is no trace either of the epidermis itself, which
has entirely disappeared, or of the pigmentation or
coloring, if such existed.
"Although attaining a height of fifteen to sixteen
feet the trachodons were not covered with scales or a
bony protecting armature, but with dermal tubercles of
relatively small size, which varied in shape and
arrangement in different species, and not improbably
associated with this varied epidermal pattern there was
a varied color pattern. The theory of a color pattern is
based chiefly upon the fact that the larger tubercles
concentrate and become more numerous on all those
portions of the body exposed to the sun, that is, on the
outer surfaces of the fore and hind limbs, and appear to
increase also along the sides of the body and to be more
concentrated on the back. On the less exposed areas, the
under side of the body and the inner sides of the limbs,
the smaller tubercles are more numerous, the larger
tubercles being reduced to small irregularly arranged
patches. From analogy with existing lizards and snakes
we may suppose, therefore, that the trachodons presented
a darker appearance when seen from the back and a
lighter appearance when seen from the front.
After Osborn
Fig. 31.—The
Dinosaur Mummy. Detail of skin of under side of
body.
Fig. 32.—Skin impression from the tail of a
Trachodon. The impressions appear to have been
left by horny scutes or scales, not overlapping like
the scales on the body of most modern reptiles, but
more like the scutes on the head of a lizard.
Fig.
33.—Skull of Gila Monster (Heloderma), for
comparison of surface with skin impressions of
Trachodon. Enlarged to
4/3.
"The thin character of the epidermis as revealed by
this specimen favors also the theory that these animals
spent a large part of their time in the water, which
theory is strengthened by the fact that the diminutive
fore limb terminates not in claws or hoofs, but in a
broad extension of the skin, reaching beyond the fingers
and forming a kind of paddle.[18] The marginal web which
connects all the fingers with each other, together with
the fact that the lower side of the fore limb is as
delicate in its epidermal structure as the upper,
certainly tends to support the theory of the swimming
rather than the walking or terrestrial function of this
fore paddle as indicated in the accompanying preliminary
restoration that was made by Charles R. Knight working
under the writer's direction. One is drawn in the
conventional bipedal or standing posture while the other
is in a quadrupedal pose or walking position, sustaining
or balancing the fore part of the body on a muddy
surface with its fore feet. In the distant water a large
number of animals are disporting themselves.
"The designation of these animals as the
'duck-billed' dinosaurs in reference to the broadening
of the beak, has long been considered in connection with
the theory of aquatic habitat. The conversion of the
fore limb into a sort of paddle, as evidenced by the
Sternberg specimen, strengthens this theory.
"This truly wonderful specimen, therefore, nearly
doubles our previous insight into the habits and life of
a very remarkable group of reptiles."
Saurolophus, Corythosaurus. In the latest
Cretaceous formation, the Lance or Triceratops beds, all
the duck-billed dinosaurs are much alike, and are
referred to the single genus Trachodon. In
somewhat older formations of the Cretacic period there
were several different kinds. Saurolophus has a
high bony spine rising from the top of the skull; in
Corythosaurus there is a thin high crest like the
crown of a cassowary on top of the skull, and the muzzle
is short and small giving a very peculiar aspect to the
head. Complete skeletons of these two genera are
exhibited in the Dinosaur Hall; the Corythosaurus
is worthy of careful study, as the skin of the body,
hind limbs and tail, the ossified tendons, and even the
impressions of the muscular tissues in parts of the body
and tail, are more or less clearly indicated.
After Brown
Fig. 34.—Skeleton
of Saurolophus, from Upper Cretacic of Alberta.
These Duck-billed Dinosaurs probably ranged all over
North America and the northerly portions of the Old
World during the later Cretacic. Fragmentary remains
have been found in New Jersey and southward along the
Atlantic coast. A partial skeleton was described many
years ago by Leidy under the name of Hadrosaurus
and restored and mounted in the museum of the
Philadelphia Academy of Sciences. Telmatosaurus
of the Gosau formation in Austria also belongs to this
group, and fragmentary remains have been found in the
upper Cretacic of Belgium, England and France.
FOOTNOTES:
|
