The meat-eaters were active creatures provided with powerful jaws and teeth. They were unarmored, moved about on their hind feet, and during their time were the most highly advanced of all animals. Tyrannosaurus with a length of forty-five feet or more, and Deinodon, nearly as large, were among the greatest of these. Both lived in the Cretaceous period. Their teeth were simple but strong, knife-like, curved, and finely serrated. Skulls were large and the forelimbs were reduced almost to a state of uselessness. Large carnivores lived also during Jurassic time and even as far back as late Triassic. Early Triassic forms were of smaller size.
More primitive flesh-eating dinosaurs of the Triassic and Jurassic periods were delicately proportioned and lightly built bipeds bearing some resemblance to birds. Struthiomimus, which means ostrich-resembling, was about the size of the bird which provides the name. It was slender in the limbs, three-toed, long necked, long tailed. The skull was small, forelegs long for a biped. Unlike most dinosaurs it was toothless. All these bird-like carnivores were small as compared with other contemporary forms. Compsognathus, of Germany, and one of the smallest of all dinosaurs, had a length of less than three feet, including the long tail.
One of the Large Jurassic Dinosaurs (Diplodocus longus)
This magnificent specimen, exhibited by the Denver Museum of Natural History, has a length of seventy-five feet six inches. Two years were required to complete the task of removing the bones from the matrix rock and preparing them for mounting. Diplodocus was one of many large reptiles which inhabited western North America a hundred and fifty million years ago. The skeleton was obtained from the Morrison beds of eastern Utah. The same formation is exposed in many Colorado localities, including the foothills west of Denver, where it acquired its name from the town of Morrison.
In Jurassic time there became prominent a group of large dinosaurs which were more equally developed as to fore and hind limbs. They were sluggish creatures, quadrupedal in their manner of locomotion, vegetarians in regard to their diet. Some of them reached enormous proportions and it is believed that they resorted to life in the water in order to get part of the weight off their feet. Diplodocus and Brontosaurus are the names of well-known giants in this group. They had long necks and tails, very small skulls, were the largest of all land animals and are known to have reached a length of eighty feet or more. Some estimates, based on measurements of incomplete skeletons, have exceeded one hundred feet, but these extremes are somewhat questionable. Diplodocus was the more elongated of the two, with much of its length in the whip-like tail. Our mounted skeleton has a length of seventy-five feet six inches, measured along the vertebrae. Its height at the pelvis is twelve feet six inches.
The teeth of these large quadrupeds are of a slightly broadened and blunted form which has caused some speculation as to their possible use. It has even been suggested that the animals were fish-eaters but this seems impossible in view of the great size and general characteristics of the group. Although they differ extremely in some respects, they are regarded as being more closely related to the carnivores than to the herbivores of the second great branch of the tribe.
The unquestioned herbivores, constituting this second branch of the dinosaurian race, also include both bipeds and quadrupeds. The better known plant-eaters were large animals but not such monsters as Tyrannosaurus or Brontosaurus. Of the bipeds, Trachodon is perhaps best known. It is one of the duck-billed dinosaurs which had an average length of about thirty feet. The duckbills were unarmored, active animals, good swimmers as well as runners. They were prominent and widely distributed during late Cretaceous time. Many skeletons have been found in western North America. Natural casts and impressions of mummified remains indicate that the hides were scaly and the feet provided with webs between the toes. The bill was broad, flat, and toothless, but the sides of the mouth were provided with a large number of simple teeth closely arranged in parallel rows. The fine skeleton exhibited in our hall is thirty feet six inches in length. Near relatives of Trachodon, such as Corythosaurus had hollow, bony crests, combs, or tubular structures on top of the head. These may have been of some service in connection with breathing while feeding under water.
A Duck-billed Dinosaur of the Cretaceous Period (Trachodon mirabilis)