The Project Gutenberg eBook ofThe Dinosaur Quarry. Dinosaur National Monument, Colorado-Utah

The Project Gutenberg eBook ofThe Dinosaur Quarry. Dinosaur National Monument, Colorado-UtahThis ebook is for the use of anyone anywhere in the United States and most other parts of the world at no cost and with almost no restrictions whatsoever. You may copy it, give it away or re-use it under the terms of the Project Gutenberg License included with this ebook or online atwww.gutenberg.org. If you are not located in the United States, you will have to check the laws of the country where you are located before using this eBook.Title: The Dinosaur Quarry. Dinosaur National Monument, Colorado-UtahAuthor: John M. GoodGilbert F. StuckerTheodore Elmer WhiteRelease date: June 26, 2015 [eBook #49288]Most recently updated: October 24, 2024Language: EnglishCredits: Produced by Stephen Hutcheson, Dave Morgan and the OnlineDistributed Proofreading Team at http://www.pgdp.net*** START OF THE PROJECT GUTENBERG EBOOK THE DINOSAUR QUARRY. DINOSAUR NATIONAL MONUMENT, COLORADO-UTAH ***

This ebook is for the use of anyone anywhere in the United States and most other parts of the world at no cost and with almost no restrictions whatsoever. You may copy it, give it away or re-use it under the terms of the Project Gutenberg License included with this ebook or online atwww.gutenberg.org. If you are not located in the United States, you will have to check the laws of the country where you are located before using this eBook.

Title: The Dinosaur Quarry. Dinosaur National Monument, Colorado-UtahAuthor: John M. GoodGilbert F. StuckerTheodore Elmer WhiteRelease date: June 26, 2015 [eBook #49288]Most recently updated: October 24, 2024Language: EnglishCredits: Produced by Stephen Hutcheson, Dave Morgan and the OnlineDistributed Proofreading Team at http://www.pgdp.net

Title: The Dinosaur Quarry. Dinosaur National Monument, Colorado-Utah

Author: John M. GoodGilbert F. StuckerTheodore Elmer White

Author: John M. Good

Gilbert F. Stucker

Theodore Elmer White

Release date: June 26, 2015 [eBook #49288]Most recently updated: October 24, 2024

Language: English

Credits: Produced by Stephen Hutcheson, Dave Morgan and the OnlineDistributed Proofreading Team at http://www.pgdp.net

*** START OF THE PROJECT GUTENBERG EBOOK THE DINOSAUR QUARRY. DINOSAUR NATIONAL MONUMENT, COLORADO-UTAH ***

Department of the Interior Â· March 3, 1849

UNITED STATES DEPARTMENT OF THE INTERIORFred A. Seaton,Secretary

NATIONAL PARK SERVICEConrad L. Wirth,Director

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

THEDINOSAURQUARRYDINOSAUR NATIONAL MONUMENTColoradoÂ·UtahBy JohnÂ M.Â Good, TheodoreÂ E.Â White andÂ GilbertÂ F.Â StuckerApatosaur in SwampNATIONAL PARK SERVICEÂ·Washington, D. C., 1958

By JohnÂ M.Â Good, TheodoreÂ E.Â White andÂ GilbertÂ F.Â Stucker

Apatosaur in Swamp

NATIONAL PARK SERVICEÂ·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.National Park Service Â· Department of the Interior

National Park Service Â· Department of the Interior

JURASSIC LANDSCAPE SHOWING ANIMALS AND PLANTS THAT LIVED HERE DURING MORRISON TIME. (FROM A PAINTING BY ERNEST UNTERMAN.)

Spade and Pick

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 Riverâ€™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 â€œrainbow bedsâ€ 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 Dinosaur Ledge is famous because here the worldâ€™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. 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. Theflesh-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 earthâ€™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.

Today, most of us would recognize a fossil bone for what it is, but in the 1790â€™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 â€œexpertsâ€ 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 theProceedings of the American Philosophical Societyin 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 groupDinosauria. The name is made up of two Greek words:deinos(terrible) plussauras(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 chickenand 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-eatingAntrodemus, the armoredStegosaurus, the turtle-likeAnkylosaurus, the hornedTriceratops, the hugeApatosaurus, the two-footed vegetarianCamptosaurus, and the great variety of head forms in the aquatic hadrosaurs. Although there were two distinct groups, we still retain the term â€œdinosaurâ€ 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?

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 subclassArchosauria. 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.

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 depositsâ€”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.

Coelophysisâ€”SMALL TRIASSIC DINOSAURS, FORERUNNERS OF THE HUGE DINOSAURS OF JURASSIC PERIOD. (DRAWN BY MARGARET M. COLBERT. COURTESY, AMERICAN MUSEUM OF NATURAL HISTORY.)

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 bethe 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-footTyrannosaurus, 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.

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 animalâ€™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 specimenis 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.

PUTTING PLASTER CAST ON A FOSSIL BEFORE REMOVING IT FROM THE QUARRY.

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 likeApatosaurusit 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 likeApatosaurushad 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 todayâ€™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 probablyfind that the dinosaurs exhibited as great a variety of scale-types as do todayâ€™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.

DINOSAUR FOSSIL WITH SKIN AND LIGAMENTS PRESERVED. (NOT FROM DINOSAUR QUARRY. COURTESY, AMERICAN MUSEUM OF NATURAL HISTORY.)

RARE FOSSIL OF DINOSAUR SKIN. (COURTESY, AMERICAN MUSEUM OF NATURAL HISTORY.)

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 anApatosauruswere exposed to the direct rays of the sun at an air temperature of 110Â° F. for 36 to 40 hours, its body temperature would rise only 1Â° 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.

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.

Protiguanodon.NOTE GIZZARD STONES INSIDE RIB BASKET. (COURTESY, AMERICAN MUSEUM OF NATURAL HISTORY.)

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. Severalspecimens of a group of swimming reptiles, calledplesiosaurs, 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 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 earthâ€™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.

Imagine if you can, the vast plains extending from Mexico to Canada and from central Utah to the Mississippi River. To the west were high mountains in the Great Basin region of Nevada and western Utah. From these highlands flowed great sluggish streams that carried large amounts of sand and silt. Since the plains were almost flat, swamps and small lakes were probably numerous. The streams may have changed their courses from time to time as they were not confined to deep valleys. When the whole region emerged from the sea the climate became more humid. Volcanoes were active far to the west; the winds carried clouds of ejected dust eastward and depositedthem on the plains. Semi-tropical conditions probably existed throughout the United States and in parts of Canada. These deposits are called the Morrison formation.

The warm humid climate provided ideal conditions for plant growth. Great forests of lush vegetation covered the land. Many of these plants have since disappeared, but some of their related species may be found today in the tropics. Most of the plants of our Temperate Zone had not yet evolved. However, there were tall stands of a type of pine, and other evergreens. There were also gingkos and curious tree ferns.

Various herb ferns formed a ground cover as thick and lush as grass on a well-watered prairie. Palmlike ferns resembling todayâ€™s cycads were common, while along the river grew horsetail rushes like those living today. Flowering plants of the Recent Epoch of geologic time (in which we are now living) had not yet made their appearance. Thus the hardwood, broadleaf forests of oak, elm, beech, maple, and similar trees were absent. So too were the flowering shrubs familiar to the Temperate Zone. Even the grasses were missing.

However, if you could picnic in this strange plant world you would soon be slapping mosquitos and cursing the ants. For even in such ancient times these insects were present; and so were a great variety of other insects as is known from the more than 1,000 species that have been discovered in Jurassic rocks. Among them were representatives of most modern orders such as grasshoppers, beetles, moths, ants, and flies. Jurassic insects probably looked much like those of today.

Among the most interesting of the strange reptiles were the pterosaurs that dominated the skies. They resembled the modern bats in some ways but their leathery wings were supported on each side by one finger instead of four, and their skins were scaly or bare instead of hairy. Some forms had long tails that were flattened at the tip and helped them balance in flight, but others were tailless. Some pterosaurs were no larger than sparrows while others had wing spans of 3 to 4 feet.

Crocodiles sunned themselves on the banks of sluggish streams and lakes. They probably looked a good deal like those that live in modern swamps and their habits were similar. Many a small dinosaur fell victim to their stealthy attack and disappeared beneath the waters of some ancient stream.

Birds have been found in Upper Jurassic rocks of Germany and may have lived here too. Their fossil remains would probably have been classed as reptiles had not feather imprints been a part of them. About the size of crows, these reptile-like birds had small conical teeth, three-clawed fingers on each wing, and a long tail instead of the fan of feathers seen on modern birds.

Small mammals were also living at the time the Morrison formationwas being deposited and their remains have been found in the dinosaur quarry at Como Bluff, Wyo. The largest ones were about the size of a house cat but the majority were much smaller, probably about the size of todayâ€™s mice.

We do not know much about the habits of these early mammals but they were probably rather shy and retiring. This would be expected in the world of giants where they lived. Some of them lived in trees and there was one group whose skull characteristics resemble those of the rodents. It is likely that these primitive mammals lived a life similar to that of the rodents millions of years later.

This, then, was the setting, the stage upon which the dinosaurs played their leading roles. Although we have restricted our discussion to Morrison time in northeastern Utah, the same or similar animals lived all over the world. Worldwide humid and mild climates produced a similarity of plant and animal life during most of the Mesozoic Era whose like has not been seen in the last 60 million years. It was a strange world and ruled by strange animals, but it must have been an interesting one.

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 todayâ€™s factsâ€”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.

The rocks that were deposited here in Morrison time tell us much of the story. The sandstones were once stream sandbars or perhaps beaches around lakes. The shale, siltstone, and clay were muddy stream or lake bottoms. The discontinuous ledges of conglomerate probably represent gravel bars formed during flood stages or at places where the stream currents were very swift.

Just rocks you may sayâ€”but look closely. A piece of sandstone contains grains of sand that differ from each other in size, shape, and composition. Frequently these characteristics point to the source of the sandstone and tell something about the conditions at the time it was deposited. Chunks of black material are examined closely and prove to be charcoalâ€”carbonized remains of plants.

Microscopic examination of clay fragments reveals shards of volcanic glass and ash that speak of active volcanoes. Sometimes these clays bear the carbonized imprints of delicate plants that long agosank to the bottom of some lake or stream where they were buried and fossilized.

The fossils themselves are most important in reconstructing conditions of the past. We find the shells of fresh-water clams in the sandstones with dinosaur bones. Crocodile bones are also common. We are reasonably sure, then, that these deposits of sand and mud were formed in rivers and lakes when the climate was mild.

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. We can only take the data available, arrange them as logically as possible, and continue the search for more. Some may scoff at such methods of reasoning yet they do provide good results. What other methods can be used when the world under investigation lies millions of years in the past?

In the rocks of the Morrison formation at the quarry, both orders of dinosaurs are foundâ€”SaurischiaandOrnithischia. Paleontologists have divided the dinosaurs into these two groups on the basis of important skeletal differences. These differences remain constant for the orders and vary within each order only in small details.

The important structural difference in dinosaurs is found in the pelvis. In all land vertebrates, the pelvis is made up of three pairs of bones called the ilium, pubis, and ischium. The paired ilium is joined to each side of the backbone and projects downward to meet the pubis and ischium at the socket for the head of the thigh bone. The pubis forms the front third and the ischium the rear third of this socket. In the orderSaurischiathe bones of the pelvis are arranged as in most reptiles and mammals. In the orderOrnithischiathe pubis extends backward along the ischium as it does in the birds.

Two types of saurischian dinosaurs are found in the quarry.Antrodemus, a flesh-eating type, was about the size of a horse, but was two-footed. It had strong sharp claws on its feet. Its teeth were about 2 inches long, flattened from side to side and with fine serrations on front and back edges. Actually it is not known whetherAntrodemusoverpowered and killed the large swamp-living dinosaurs, or merelyfed on their carcasses after they had died from other causes. However, there has been found in the quarries at Como, Wyo., a partial skeleton ofApatosauruswith grooves on the bones which suggest tooth marks. The spacing of these grooves fit the spacing of the teeth of a specimen ofAntrodemusfound in the same quarry.

A. ORNITHISCHIAN PELVIS. B. SAURISCHIAN PELVIS.KEY: ILâ€”ILLIUM; ISâ€”ISCHIUM; Pâ€”PUBIS.

The plant-eating dinosaurs of the orderSaurischiawhich are found in the quarry were all four-footed. They had bodies about the size of an elephant or larger. The principal differences between the flesh- and plant-eating dinosaurs were the length of the neck and tail, the details of their skull structure, and other parts of their skeleton.

Apatosaurusis perhaps the most familiar dinosaur to most of us. Its hind legs were much longer than its front ones and gave the animal a high-hipped, stooped appearance.Apatosauruswas about 70 feet long and probably weighed close to 40 tons.Diplodocuswas longer (one of them 75Â½ feet) but was slender and lightly built. Its neck was longer and it had a whiplash tail that looked much like the tail of the modern whiptailed lizard.Diplodocusalso had long pencil-like teeth different from those of any other known dinosaur.Barosaurushas an extremely long neck with long individual neck bones. Two members of the genusCamarasaurusare similar to each other except for size; one was small, but the other was as large asApatosaurus.Camarasaurushad longer front legs thanApatosaurusand was generally better proportioned.

Antrodemus,THE FEROCIOUS CARNIVORE OF MORRISON TIME. (FROM A DRAWING BY CHARLES R. KNIGHT. COURTESY, AMERICAN MUSEUM OF NATURAL HISTORY.)

THE GREAT SAURISCHIAN PLANT-EATERApatosaurus louisaeâ€”ABOUT 70 FEET LONG. (FROM A DRAWING BY A. AVINOFF, CARNEGIE MUSEUM.)

Fossils of the saurischian plant-eaters are found much more frequently than those of flesh-eaters and are usually in sedimentary rocks which contain beds of clam shells. For this reason it seems probable that they waded lagoons and streams, feeding on aquatic and bank-side vegetation. The suggestion has been made that the larger dinosaurs could not even walk on dry land because their weight would have crushed the bones of their feet; they needed the buoyancy of water to help support them. However, footprints of a huge dinosaur, much larger than any from the quarry, have been found near Glenrose, Tex. The large footprints were made on a sandy beach of a sea in Lower Cretaceous time. Thus we know that they could walk on dry land if they wanted to.

All of the dinosaurs of the orderOrnithischiawere plant-eaters, and were of both two- and four-footed types. The two-footed types found in the quarry areCamptosaurus,Dryosaurus, andLaosaurus. These forms had well developed front legs, though much shorter than their hind legs, which suggests that they may have dropped down on â€œall foursâ€ while feeding or resting. The teeth were small, chisel-shaped, and fitted only for cropping vegetation. The larger specimens ofCamptosaurusreached a length of 17 feet butLaosauruswas only 2Â½ feet long.

Stegosaurusis the only quadruped (four-footed) of this order found in the quarry. It had long hind legs and very short front legs. It reached a length of 18 to 20 feet and was 10 to 11 feet high over the hips. The most characteristic feature of this form was the double row of bony plates down the back and the group of spikes at the end of the tail. The teeth were similar to those ofCamptosaurus, but much more numerous.

Only two other groups of reptiles have been found in the quarry at Dinosaur National Monument and their remains are rare. These are the crocodiles and turtles. Two crocodiles are known; the larger one,Goniopholis, was about the size of existing alligators and did not differ in external appearance from present-day crocodiles. The smaller one was less than a foot long and resembled a 2 weeksâ€™ old alligator as much as anything. However, we know from the texture of the surface of the bone that it was not a young animal. The turtle,Glyptops, was about the same size and general appearance as the pond turtles of today.

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.

How and why did so many dinosaur skeletons accumulate here? How were they preserved? These are among the common questions asked of park rangers and naturalists at Dinosaur. The answer is a combination of circumstances and luck.

Many people get the impression from the mass of bones in the quarry wall that some catastrophe such as a volcanic explosion or a sudden flood killed a whole herd of dinosaurs in this area. True enough this could have happened, but it probably did not. The main reasons for thinking otherwise are the scattered bones and the thickness of the deposit. In other deposits where the animals were thought to have died together, the skeletons were usually complete and often all the bones were in their proper positions, or articulated. In a mass killing the bones would have been deposited on the stream or lake bottom together at the same level, but in this deposit the bones occur throughout a zone of sandstone about 12 feet thick. The mixture of swamp dwellers and dry-land types also seems to indicate that the deposit is a mixture derived from different sources. Rounded fragments of fossil bone have been discovered in the quarryâ€”fragments that attained their pebblelike shape by rolling along the stream bottom.

If the mass of bones was not the result of catastrophe what did happen? The quarry area is a dinosaur graveyard, not a place where they died. A majority of the remains probably floated down an eastward flowing river until they were stranded on a shallow sandbar. Some of them, such as the stegosaurs, may have come from far-away dryland areas to the west. Perhaps they drowned trying to ford a tributary stream or were washed away during floods. Some of the swamp dwellers may have mired down on the very sandbar that became their grave while others may have floated for miles before being stranded.

Even today similar events take place. When floods come in the spring, sheep, cattle, and deer are often trapped by rising waters and frequently drown. Their bloated carcasses float downstream until the flood recedes and leaves them stranded on a bar or shore where they lie, frequently half buried in the sand, until they decompose. Early travelers on the Missouri River reported that shores and bars were frequently lined with the decomposing bodies of bison that had perished during spring floods.

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 andnecks of the large plant feeders. These, like streaming water plants in a river, trail downstream to the east.

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