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.
[Illustration: 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.
[Illustration: 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. _After
Osborn_]
"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."
[Illustration: Fig. 30.--THE DINOSAUR MUMMY. SKELETON OF A
TRACHODON PRESERVING THE SKIN IMPRESSIONS OVER A LARGE PART OF THE
BODY. _After Osborn_]
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.
[Illustration: Fig. 31.--The Dinosaur Mummy. Detail of skin of
under side of body. _After Osborn_]
[Illustration: 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.]
[Illustration: 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.
[Illustration: Fig. 34.--SKELETON OF SAUROLOPHUS, FROM UPPER
CRETACIC OF ALBERTA. _After Brown_]
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:
[Footnote 16: Brown, Barnum. "The Trachodon Group." Amer. Mus. Jour.
Vol. viii, pp. 51-56, plate and 3 text figs., 1908.]
[Footnote 17: Osborn, Henry Fairfield, "Dinosaur Mummy" Amer. Mus.
Jour. Vol. xi, pp. 7-11, illustrated, Jan. 1911.]
[Footnote 18: There is some doubt whether this was really the
condition during life. W.D.M.]