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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

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.

 
Fig. 29.: Restoration of the Duck-billed Dinosaur Trachodon.

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."


Fig. 30.: The Dinosaur Mummy. Skeleton of a Trachodon preserving

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.

Fig. 31.: The Dinosaur Mummy. Detail of skin of under side of body.

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.

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

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.

Fig. 34.: Skeleton of Saurolophus, from Upper Cretacic of Alberta.

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:

[16] Brown, Barnum. "The Trachodon Group." Amer. Mus. Jour. Vol. viii, pp. 51-56, plate and 3 text figs., 1908.

[17] Osborn, Henry Fairfield, "Dinosaur Mummy" Amer. Mus. Jour. Vol. xi, pp. 7-11, illustrated, Jan. 1911.

[18] There is some doubt whether this was really the condition during life. W.D.M.



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