Dinosaurs, with Special Reference to the American Museum Collections

by William Diller Matthew

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.