TILTED ROCK STRATA NEAR THE DINOSAUR QUARRY.
Some were the size of chickens, others as big as horses, and others of such gigantic size that no land animal alive today can compare with them. Some were flesh-eaters as indicated by the size and shape of their teeth and their long sharp claws. Others were plant-eaters and again it is the structure of their teeth and feet that tell us this. The flesh-eaters were two-footed and walked on their hind legs, balancing themselves with heavy long tails. Their short front legs were used as clawed-arms for tearing at the flesh of other dinosaurs. Many plant-eaters, on the contrary, were large, heavy, four-footed beasts, often with long necks and tails. Many of the dinosaurs were land dwellers, and many others lived in the great marshes and swamps of the long Mesozoic (middle life) Era of the earth’s history.
Though the subclass of reptiles we call dinosaurs lived all through the Mesozoic Era, those whose fossil bones have been uncovered in this Dinosaur Quarry are embedded in a stratum of rock called the Morrison formation. This rock stratum dates from the Jurassic Period in the middle of the Mesozoic Era.
The Dinosaurs
FIRST DISCOVERIES
Today, most of us would recognize a fossil bone for what it is, but in the 1790’s things were different. Isolated legbones, vertebrae, and teeth of huge reptiles had been dug out of certain sedimentary rocks of Europe and North America but their scientific importance was little understood.
These specimens were found by people in all walks of life and it was natural that their curiosity was greatly aroused. The finders took the specimens to someone nearby whom they considered more competent to tell them something about these strange bones and teeth. In nearly all cases these “experts” were doctors of medicine. They studied the fossil specimens and reported on them at regular meetings of the learned societies of which they were members. It was customary to put the fossils in the collections of these societies where they could be studied by other members. In North America most reports of these early discoveries are found in the Proceedings of the American Philosophical Society in Philadelphia, Pa.
By 1842 accumulated knowledge of these large reptiles was sufficient to show that they were distinct from any group then known. This was first recognized by Sir Richard Owen of the British Museum. It was he who named the group Dinosauria. The name is made up of two Greek words: deinos (terrible) plus sauras (lizard).
As knowledge of these unusual reptiles increased through the discovery of additional types and more complete and better preserved specimens, it became evident that dinosaurs were neither a single group of reptiles nor were all of them large. Actually the dinosaurs show as much diversity in size, body form, and habits as any group of reptiles. The smallest dinosaur walked on its 2 hind legs like a chicken and was about the same size. The largest walked on all 4 legs, was about 80 feet long, and weighed 30 to 40 tons. As examples of variety in body form there are the two-footed, flesh-eating Antrodemus, the armored Stegosaurus, the turtle-like Ankylosaurus, the horned Triceratops, the huge Apatosaurus, the two-footed vegetarian Camptosaurus, and the great variety of head forms in the aquatic hadrosaurs. Although there were two distinct groups, we still retain the term “dinosaur” as a convenient name for all of them but qualify it by saying, flesh-eating dinosaur, plant-eating dinosaur, armored dinosaur, etc., to indicate the particular type we are talking about. Perhaps you are wondering how all these ancient creatures are related to reptiles in general. Where do they fit in the classification system devised to bring order to this mass of knowledge?