Part 1

UNITED STATES DEPARTMENT OF THE INTERIOR Fred A. Seaton, _Secretary_

NATIONAL PARK SERVICE Conrad L. Wirth, _Director_

For sale by the Superintendent of Documents, U. S. Government Printing Office Washington 25, D. C. Price 25 cents

THE DINOSAUR QUARRY DINOSAUR NATIONAL MONUMENT _Colorado_ · _Utah_

_By John M. Good, Theodore E. White and Gilbert F. Stucker_

NATIONAL PARK SERVICE · Washington, D. C., 1958

_The National Park System, of which Dinosaur National Monument is a unit, is dedicated to conserving the scenic, scientific, and historic heritage of the United States for the benefit and enjoyment of its people._

Contents

_Page_ THE QUARRY 2 THE DINOSAURS 3 First Discoveries 3 Position of Dinosaurs Among Reptiles 4 Geologic History 4 What They Looked Like 6 Temperature Tolerance 10 Gizzard Stones 11 THE CLIMATE, LIFE, AND LANDSCAPE OF JURASSIC TIME 12 How Do We Know? 14 ANIMALS FROM THE QUARRY 15 Why So Many? 19 How Were They Preserved? 21 How Were They Exposed? 24 WHY DID DINOSAURS BECOME EXTINCT? 25 HISTORY AND DEVELOPMENT OF THE QUARRY 26 Discovery and Early Years 26 Starting the Quarry 28 Extent and Development of the Find 28 Work Methods 32 Further Development 34 Protecting the Quarry 35 Present Development 37 THE SCENE TODAY 38 KEY TO PRONUNCIATION 46 SUGGESTED READINGS 47

As you approach Dinosaur National Monument from Jensen, Utah, you see the mass of Split Mountain and the deep, short canyons that scar its south slope near the Green River’s gorge. As you cross the National Monument boundary the grand view is lost and you begin to notice details. The masses of gray shale that seem to be carelessly piled against the tilted sandstone layers are bare of vegetation. The ground between the hills and the Green River is covered with sagebrush and greasewood, while along the river itself are a few large cottonwood trees and many bushes. A sharp turn brings a change of scene as your car enters a portal in the wall you have been following. The pronounced tilt of the rocks becomes more obvious.

A final steep climb and the visitor center is at hand. This building encloses a significant part of the Dinosaur Quarry, perhaps the greatest deposit of fossil dinosaur bones known today. From this quarry have come many of the dinosaur skeletons that are seen today in our great museums. After parking, a short walk to the overlook on the southeast reveals a splendid view of Split Mountain. Between that broad arch of eroded sandstone and the quarry lie steeply tilted sedimentary rocks of various compositions and hues. Buff and gray sandstones that weather into soft shapes are separated by reddish-brown shale. Directly to the east is a section of varicolored shale whose pastel pinks, reds, greens, grays, and whites justify the name of “rainbow beds” that was given them by geologists. In the upper part of this section are hard sandstone and limestone layers that resist the erosive action of wind and water. They stand higher than the softer shales and form hogbacks that rim Split Mountain.

One of these layers can be traced across the ravine immediately east of the parking area into the sandstone ledge that forms the north wall of the visitor center. This is the famous Dinosaur Ledge.

The Quarry

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.

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?

POSITION OF DINOSAURS AMONG REPTILES

It seems there are several orders of reptiles similar to and closely related to the dinosaurs. Remains of these reptiles are found in the sedimentary rocks which contain the earliest known dinosaurs. A number of them resembled the dinosaurs but do not quite meet the requirements as far as details of the skeleton are concerned. In the scheme of classification these orders of reptiles are grouped together into the subclass _Archosauria_. This subclass includes the dinosaurs, crocodiles, and the flying reptiles. The lizards, snakes, turtles, and the tuatera of New Zealand belong to other subclasses of reptiles which have been distinct from that of the dinosaurs as far back in geologic time as we can trace them. The kinship between the dinosaurs and the small lizards living in the monument today lies only in that both are reptiles. The only living relatives of the dinosaurs are the alligator and the crocodile.

The dinosaurs were so numerous, and so dominated the whole of the Mesozoic Era, that this period of earth history is frequently referred to as the Age of Reptiles.

GEOLOGIC HISTORY

The Mesozoic Era began some 200 million years ago and ended some 60 million years ago. Although many other animals lived during that era, the dinosaurs were the dominant forms of animal life on land. The 140 million years of the Mesozoic are divided into geologic periods named Triassic (the oldest), Jurassic, and Cretaceous (the most recent). Continental deposits representing each of these periods have been found in all parts of the world and on all continents. Dinosaur bones have been found in these deposits—even in such far-away places as Australia and the southern tip of South America. Only Jurassic dinosaurs have been found at Dinosaur National Monument.

The oldest known dinosaurs are found in rocks of the Triassic Period. The smaller of these were chicken-size and the largest were about as big as kangaroos. All of these Triassic dinosaurs were two-footed. They can be divided into flesh-eaters and plant-eaters, although none are believed to have been particularly specialized in their food habits. In general the flesh-eaters were small, agile, and had sharp teeth for seizing and overpowering active prey. The plant-eaters were larger with rather long front legs and small blunt teeth suited only to cropping vegetation. These plant-eaters are believed to be the Triassic ancestors of the giant marsh-dwelling dinosaurs of the Jurassic and Cretaceous Periods.

A greater variety of dinosaurs lived during the Jurassic Period than in the Triassic. Both two- and four-footed types were present. The flesh-eaters remained two-footed but increased in size. _Antrodemus_, perhaps the best known, was much bigger than a kangaroo. The larger plant-eaters weighed from 30 to 40 tons and all were four-footed. The largest land animals, they lived on dry land and in the swamps that formed an important part of the Jurassic landscape. 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.

New and interesting dinosaurs were present among the flesh-eaters. Horned forms, somewhat similar to the rhinoceros but much larger, were common. Also common were the turtle-like ankylosaurs. Perhaps the oddest and most interesting dinosaurs of the Cretaceous were the two-footed hadrosaurs. These excellent swimmers had weird head shapes with complicated skull passages and openings. They were a very successful group and at least 15 different kinds are known from the Cretaceous rocks of North America.

WHAT THEY LOOKED LIKE

Ideas about the external appearances of dinosaurs have been developed after many years of work and study. They are a combination of the ideas of several people who had studied different specimens of a single species. Let us review briefly the materials and work necessary to arrive at a reasonably accurate picture of the body form and external appearance of these strange reptiles.

The first requirement for arriving at a good idea of the build and physical attitude of an animal is a nearly entire skeleton. We cannot have too much of the animal’s skeleton missing or we may make a serious error. But if the left hind leg is missing and we have the right, we are not seriously handicapped. However, if both hind legs are missing we must restore them according to a similar animal whose hind legs are known.

After the nearly entire skeleton has been found it must be collected with great care. This is a rather involved process and, for some of the large dinosaurs, 2 or 3 months work may be required. The specimen is first uncovered and the fossil bone is treated with a preservative such as gum arabic, shellac, or one of the plastics. An accurate diagram of the specimen as it lies in the rock is made on cross-ruled paper. A trench 2 or 3 feet wide is then dug around the specimen. The depth of the trench is determined by the width of the specimen and the nature of the rock.

If the specimen is too large to take out in one piece, as most dinosaurs are, it is divided into sections which are numbered serially as they are taken out. Each section is bandaged in strips of burlap dipped in plaster of Paris. After the plaster has set, the section is turned over and the bottom is sealed with burlap and plaster. The section is labeled with the appropriate number and the section and number are shown on the diagram.

When all of the sections have been bandaged and numbered they are packed in strong wooden boxes and shipped to the laboratory.

The work in the laboratory is more involved than that in the field, and extreme care must be exercised to be sure that the bones will be undamaged. In most cases the bones have been broken by natural causes as they lay in the rock before discovery. All the pieces of each bone must be thoroughly cleaned and securely cemented together. This is a very time-consuming task and for a large dinosaur like _Apatosaurus_ it requires 3 men 4 or 5 years to complete the task.

After all of the bones are cleaned and cemented together the vertebral column is laid out in its proper sequence on a sand table. Special care is exercised to be sure that the vertebrae fit correctly with each other. In this way the correct curvature of the vertebral column is determined. 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.

Now that the framework of an animal has been set up so that it could move about if it had muscles, skin, and life, how do we know how large the muscles were and where they were placed? 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. Thus if we know what muscle we are looking for and the size and shape of its muscle scar, we can determine whether the muscle is a spindle-shaped mass or a broad sheet.

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. If they did not possess a waterproof covering of scales they would die in a few hours as a result of the loss of body moisture by evaporation through the skin. It is possible that some of the marsh dwellers like _Apatosaurus_ had naked skin which was, as in the elephant, nearly an inch thick. The elephant does not possess sweat glands but the outer half of its skin is composed entirely of dead cells which form a covering as waterproof as the scales of today’s reptiles.

There have been only a few lucky finds of mummified dinosaurs which show the impressions of the scales. 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 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.

TEMPERATURE TOLERANCE

We know the body temperatures of reptiles vary with that of the air or water in which they live, as they have no means of internal temperature control. They are very sluggish when their body temperatures are low and become more active as these temperatures rise, but only to a certain point. If the body temperatures of reptiles become too high, they die in a few minutes.

A group of physiologists from Columbia University spent nearly 2 months in southern Florida experimenting on reptiles. They determined the rate of rise of body temperatures of large lizards and alligators of all sizes during exposure to the midday sun. As was expected, the smaller the reptile the more rapid the rise in body temperature. Dinosaurs were reptiles so we can make two assumptions: That their physiology was very similar to that of living reptiles; and that the rate of rise of their body temperatures from exposure to the sun would follow the principles found for living reptiles.

By applying these principles to the dinosaurs, this group of scientists calculated that if the great bulk of an _Apatosaurus_ were exposed to the direct rays of the sun at an air temperature of 110° F. for 36 to 40 hours, its body temperature would rise only 1° F. Therefore, if these calculations are correct, it is probable that the very size of the huge dinosaurs operated to maintain a fairly constant body temperature. Consequently, daily and seasonal temperature changes probably did not affect the activities of the large dinosaurs. However, the activities of the small ones may have been affected by the daily range in temperature.

GIZZARD STONES

For many years rounded stones with a very high polish have been found in the sedimentary rocks which contain bones of extinct reptiles. The polish on these stones is very much higher than could have been applied by the action of water or wind. Some look as though they had been polished by a jeweler. Since we cannot attribute this very high polish to wind or water action, we must seek another agent.

Just as chickens swallow fine gravel for their gizzards to aid digestion, so it is thought that some large dinosaurs swallowed stones for the same purpose. There is some evidence to support this idea. Several specimens of a group of swimming reptiles, called _plesiosaurs_, which swarmed the Jurassic and Cretaceous seas, have been found with highly polished stones inside the rib basket. Also a mass of highly polished stones was found similarly associated with one dinosaur, _Protiguanodon_, in the Lower Cretaceous rocks of Mongolia.

On the other hand, no highly polished stones have been found associated with the specimens in the Dinosaur Quarry or anywhere in the quarry. A search of the many publications on dinosaurs has not turned up any mention of highly polished stones being associated with any of the many specimens found in North America. Thus the evidence which we have does not permit us to say that the dinosaurs found in the quarry did or did not possess gizzard stones.

The Climate, Life, and Landscape of Jurassic Time

The geologists who attempt to reconstruct the geography and climate of the Jurassic Period first gather all possible facts and try to fit them together to form a logical pattern. The results are then examined for weak points and an attempt is made to find field evidence throwing light on these weak points. The final result represents the sum of our knowledge at the time but is subject to change as new facts are obtained. Thus the following outline represents present thinking that may be changed somewhat by future studies.

The land for miles around the Dinosaur Quarry was a low-lying desert in early Jurassic time. The mountains you see now had not yet been formed, and the whole desert area lay close to sea level. Great restless sand dunes drifted across this level land to form a blanket 700 feet thick. As the earth’s crust sank, these dunes were covered by a long arm of an arctic sea that extended southward along the present trend of the Rocky Mountains across Canada, Montana, Wyoming, and Utah. Millions of years later, in late Jurassic time, when the Morrison formation was deposited, the area rose again and the stage was set for the dinosaurs.