John M. Good

“ Perhaps the most handsome year-round resident is the magpie with its long, iridescent tail, black and white body, and white patches on its wings. One other resident makes his presence known by his eerie cry on frosty, moonlit nights—the western horned owl. He hunts every night, summer and winter, but is seldom seen. Occasionally he is disturbed upon his daylight roost and as he skillfully dodges through the junipers, he makes a joke of the story that owls don’t see well in daylight.
The mammals that live in the vicinity of the Dinosaur Quarry are almost never seen. ”

“ In the present as in the past, the kinds and abundance of plants set definite limits as to the species and numbers of animals an area may support. Thus, if man changes the plants of an area he will surely change the animals too, whether he realizes it or not.
If you drive to the quarry in the heat of the day you will see only a few of the birds that live here. They don’t like to hunt their food during those hot hours. Frequently a turkey vulture sails majestically above the plains along the Green River. ”

“ We reason by analogy. For example, fossil plants and animals have counterparts or descendants in the world of today. We assume, in the absence of contrary evidence, that the fossil animals lived like their present-day counterparts. Although no birds, mammals, or pterosaurs have been found in this quarry, they were probably living here with the dinosaurs. It is possible, in fact probable, that some modern animals and plants live in different environments than did their Morrison ancestors and relatives but we have no way of knowing which ones they were. ”

“ But the sagebrush flats and brushy ravines are not left vacant by this wholesale migration, for as the summer residents move out the winter residents move in. The Oregon and gray-headed juncos spend the entire winter here. Great flocks of mountain bluebirds descend from the mountains and piñon jays make the hills resound with their screams. Canada geese and golden-eye ducks live on the Green River and remain until it freezes. The harsh croak of the raven is seldom heard in summer but often in winter. ”

“ Any small, striped mammal seen near the quarry is probably a ground squirrel, as chipmunks are rare here.
The water problem is an ever-present one for the mammals as well as the plants. At first this may seem strange with the Green River so close and several springs in the hills, but most of the smaller animals have very restricted ranges. A deer mouse, for example, seldom travels more than 100 feet from his home burrow in his entire lifetime. The kangaroo rat and the desert woodrat also have limited ranges although theirs are somewhat larger than those of deer mice. ”

“ Some of them like the ground squirrels hibernate and sleep the winter away, but the majority must rustle their “daily bread.” Winter storms drive the mule deer down from the high country. Mice tunnel through the snow in search of food. The white-tailed jackrabbit and the snowshoe hare change their coats from brown to white. In particularly hard winters the animals die in great numbers, first the weak and old, then the young, and sometimes even animals in prime condition fail to survive.
The reptiles that make their homes in the Quarry Area of Dinosaur National Monument are few in number. ”

“ The concentration and burial of dinosaur bones is only the beginning of the fossil story. The combination of circumstances which operated here was a common one and yet fossil quarries are rare. Why? The bones have to be preserved and this seldom happens. The bones that are buried in one flood are frequently unearthed and scattered by the next. Those that are exposed to the weather usually disintegrate completely in a few years. The bones in the Dinosaur Quarry did not. ”

“ At Dinosaur National Monument only Morrison rocks of the upper Jurassic Period contain the fossil bones of dinosaurs. After Morrison time, the Cretaceous seas invaded this area. More than 5,000 feet of sandstone, shale, and mudstone were formed from sediments deposited in these seas.
Elsewhere in North America and the rest of the world, the diversity and numbers of dinosaurs actually increased. Entirely new groups evolved and achieved success in the battle for survival. The climax of reptile development seems to have come near the end of Cretaceous time in the Mesozoic Era. ”

“ Each has adjusted its needs to those limiting factors—winter cold, summer heat, and aridity. A great number of plants grow on the monument that have not been mentioned here, but they are like the typical plants and have similar ways of meeting the problems of survival.
Many people who profess an interest in nature admit they cannot get very excited about plants. Such disinterest may result in minimizing the importance of plants in the general scheme of nature. That would be a major error. The plants of the world are the foundation upon which other forms of life are dependent. ”

“ As exhibit material it was without rival. It was mounted as found, lying on its side, the bones fixed in death in the matrix in which they had been preserved—a fitting climax to the 13 consecutive years that had seen an unknown sandstone ridge in Utah become Dinosaur National Monument.
In those 13 years the Carnegie Museum had taken from the quarry parts of 300 dinosaur specimens, 2 dozen of which were mountable skeletons. Ten different species were represented. It was the best collection of Middle Mesozoic monsters in the world. ”

“ This is a good time to stop and try to explain that this story, of plants and animals of the past, has a firm foundation in today’s facts—it is not a fantasy.
The methods by which geologists and paleontologists have established the age, climate, and life of Morrison time cannot be described for you here in detail. To attempt such a description would require too much space and would probably seem dull to most readers. Perhaps the best approach is to describe some features and explain how they contribute to our knowledge. ”

“ In Dinosaur National Monument, the positions in which partial skeletons of the dinosaurs lie suggest that they decomposed on a sandbar. The bones on the underside of a skeleton are often arranged as they were when the animal was alive, while those on the upper or exposed side may be scattered. Such scattering would be expected as the ligaments and muscles holding the bones together decomposed; stream currents and scavengers could then disperse them. Stream currents are suggested by the position of the long, flexible tails and 21 necks of the large plant feeders. ”

“ 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 4 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. ”

“ The Dinosaur Ledge is famous because here the world’s greatest store of fossil bones of these long extinct reptiles has been uncovered. Two groups, or orders, of dinosaurs have been discovered, with a number of different types or kinds somewhat related to each other within these orders. From the fossil bones, scientists can tell that these creatures varied greatly in size and habits of living.
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. ”

“ Along the river bank, gnawed tree stumps, a few fresh chips, and perhaps a webbed footprint tell us beaver have been active during the night. The paired hind footprints of the kangaroo rat are common on the hillside. ”

“ Surely one of the most useful and interesting of their abilities is that of utilizing metabolic water. Such water is obtained through oxidation of hydrogen contained in food and is a by-product of metabolism. Putting it another way, during the digestive process these animals are able to manufacture water from the chemical constituents of their food and the oxygen in their blood. ”

“ The first of the armored plant-eating dinosaurs, Stegosaurus, inhabited the dry plains. There were also some smaller, kangaroo-size plant-eaters that were two-footed.
A wide variety of dinosaur fossils has been found in the rocks of the Cretaceous Period, the last of the Mesozoic Era. The huge swamp dwellers still thrived. The flesh-eaters had evolved much larger types and included 40-foot Tyrannosaurus, the largest that ever lived. All the flesh-eaters walked on their hind legs as did their predecessors of the Jurassic and Triassic Periods. ”

“ It is necessary to have a thorough knowledge of the muscles of a recent animal similar to the one we are restoring so that we will know what we are looking for in the fossil. The areas at which muscles are attached to bones are called muscle scars and are identified by their rough surfaces. Often the necessary information can be obtained from publications which usually represent the work done by graduate students for advanced degrees. At other times we must make our own investigation. ”

“ The dinosaur hordes were wiped out and the reptiles reduced to the position of relative insignificance they occupy today. Such a profound and sudden change in the evolutionary trend of life must have had a cause, and scientists have sought it. Several theories have been proposed to explain extinction of dinosaurs, and they are most interesting. ”

“ The proper relationships of the hip bones and ribs to the vertebrae, the shoulder blade to the ribs, and elements of the limb bones to each other are determined in the same manner. All of this work is necessary to correctly fashion the steel framework which will support the skeleton when it is placed on exhibition. The results of this careful work must be the framework of an animal which could, if living, easily go through the normal activities of life such as securing food and escaping enemies. ”

“ The partial skeletons of more than 20 individual dinosaurs and the scattered bones of about 300 more have been discovered in the Dinosaur Quarry. Many of the best specimens may be seen today at museums of natural history in the larger cities of the United States and Canada. The quarry is easily the largest and best preserved deposit of Jurassic dinosaurs known today. ”

“ Often lizards are seen whose tails are missing. When the tail is pulled or injured it can be shed by its owner. The shed tail may wriggle for several minutes and attract the predator’s attention while the lizard escapes. The tailless lizard soon grows another one that is usually recognizable by its subdued or otherwise different color pattern. Sometimes the broken tail does not fall off so it and the new tail form a fork. ”

“ We know that all lizards do not possess the same type of scales, and therefore, by analogy, we cannot assume that the dinosaurs did. Eventually, we will probably 9 find that the dinosaurs exhibited as great a variety of scale-types as do today’s lizards. As yet we have found nothing in the fossil record which indicates the color of the dinosaurs. Again, we can only assume that they exhibited as great a variety of colors as do our lizards. So also, we assume their body functions were somewhat similar to the reptiles and other related animals we know today. ”

“ These conditions could explain local extinction, but there were places where these changes did not occur and yet all dinosaurs in all places died.
A one-time favorite theory suggested that increasing numbers of small mammals ate dinosaur eggs, but there were many mammals eating dinosaur eggs during all of Cretaceous time and the dinosaur hordes increased. Many more mammals during succeeding ages have not killed off the turtles, snakes, lizards, and crocodiles that lay eggs and exist in great numbers today. ”

“ In spite of their retiring habits, they reveal their presence in a number of ways. Patches of bare earth under sagebrush and nearby sandy slopes are crisscrossed with tiny paths beaten into the dust by deer mice. ”

“ After we have determined the size and position of the muscles which operate the limbs, head, and neck, we have a reasonably accurate idea of the external form of the animal, but we still know nothing of the nature of the skin which covered the body. Since dinosaurs were reptiles, we are obliged to assume that they were covered with a scaly skin in order to preserve the body moisture. None of the modern reptiles possess sweat glands in the skin. ”

“ After the sediments became rock and the bones had probably been replaced by stone (fossilized) , this part of the world, which lay near or below sea level for millions of years, began to rise. Great forces acted upon the earth’s crust. These forces created faults, or fractures, in the rock crust along which movement occurred. And what had once been sea bottom was moved upward and became lofty mountains. This titanic change has been called the Laramide Revolution; it closed the Mesozoic Era with the formation of the Rocky Mountains. ”