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Mostly about Unearthing the Fossils of Dinosaurs


by C. L. Stong
February, 1959


AMONG THE MOST POPULAR exhibits at any museum of natural history are the skeletons of dinosaurs. Of the millions of Americans who enjoy such exhibits, few realize that they can hunt and find such bones with no more equipment than the family automobile and some inexpensive tools which one can carry on one's back. According to Cresson H. Kearny, a petroleum geologist of Montrose, Col., the surface of many western states abounds with fragments of dinosaur bones, and on public lands U. S. citizens can gather as many as they want.

"Here is one national resource," writes Kearny, "in no danger of short supply. The best hunting grounds for dinosaur bones are the areas of soft sediments where erosion constantly brings specimens to the surface. Millions more are doubtless hidden within the rocks. If one is in fairly good physical condition and likes to hike, here is an undeveloped avocation which for me is more satisfying than catching stocked trout in a stream teeming with tourists. In dinosaur-bone country you can sometimes walk for days without seeing another human being, and you can enjoy not only the hunt for bones but also the grandeur of wilderness. Furthermore, if the amateur bone-hunter studies a bit, and then uses common sense in evaluating and handling his finds, he can render substantial help to paleontologists.

Figure 1: Cresson H. Kearny provides a scale for a huge Brachiosaurus bone found by Mrs. Eddie Jones of Delta, Col.

"Recently two amateur uranium prospectors found the largest leg bone-the left humerus of a Brachiosaurus-ever reported. Mrs. Eddie Jones of Delta, Col., and her husband were examining the Morrison formation, a deposit which has become famous for its fossils of large dinosaurs. Suddenly her Geiger counter began to click rapidly, although all she could see underfoot was the bluish shale of the Morrison. When the Joneses dug down a few inches they found a slightly fractured but complete fossil bone seven feet one inch long and 26 inches across at the broadest end [see Figure 1]. As is often the case, the organic material of the fossilizing bone had concentrated-uranium minerals that had moved in dilute solutions through the almost impervious shale. A number of uranium minerals readily replace carbonaceous material, such as old driftwood or bone. It is remarkable how much 'hotter' a fossil bone can be than the surrounding rock.

"Unfortunately the Joneses did not realize that their bone was destined to set a new record for size and would ultimately attract proportionate scientific interest. Furthermore, they were afraid that rival prospectors, then busy staking claims in the area, might find and take it. So they drove their jeep up to the find and carted away, like so much ore, over five hundred pounds of the biggest pieces, almost breaking their springs in the process Back home in Delta, some 14 miles away, they roughly aligned the various chunks on the front porch for their neighbors to see.

"One night several weeks later I chanced to be passing through Delta on a geological trip and heard about the find. When I visited the Jones home in the evening, I actually tripped over the pieces of a specimen such as I had dreamed about since my first visit as a boy to the great dinosaur halls of the American Museum of Natural History.

"So it came about that one Sunday I put the Joneses' Brachiosaurus humerus together for them. Later, while on a trip to the East, I told paleontologists at both the American Museum of Natural History and the Smithsonian Institution about this bone, one far larger than any they possessed. When I described its size by gesturing toward the ceiling, however, I received only skeptical smiles. Finally I submitted a photograph of the bone, myself and a yardstick. That did the trick.

"Both the Smithsonian and the American Museum soon asked the Joneses for their bone, but the Smithsonian asked first. This spring we had the satisfaction of watching Peter Vaughn of the Smithsonian and two assistants skillfully cover each fragment with wet paper and then wrap it with a layer of burlap soaked in plaster of Paris. The next day the paleontologists packed the hardened packages in wooden crates filled with shavings and shipped them off to Washington. Before long the Joneses' Brachiosaurus humerus will be displayed against a column in the Smithsonian to help visitors picture one of the largest animals ever to walk the earth.

"What is the scientific significance of this huge bone? According to Edwin H. Colbert of the American Museum, the largest dinosaur bone previously found is the Brachiosaurus humerus excavated in Colorado by the Chicago Natural History Museum some 50 years ago. It is a little over six feet, eight inches long. This humerus once supported a Brachiosaurus which weighed about 100,000 pounds. The Joneses' seven-foot one inch humerus must have belonged to an animal that weighed some 120,000 pounds! The head of the animal, judging by the height of a reconstructed Brachiosaurus skeleton in the Berlin Museum, must have towered 44 feet above the ground. This must surely approach the engineering limits for a land animal.

Figure 2: Leg bone of a Brontosaurus is compared to the femur of an American Indian

"Although the relatively common Brontosaurus is often cited to represent immensity among land animals, the rarer Brachiosaurus was a much larger animal. Both monsters were saurischians, one of the two orders of dinosaurs. Like dinosaurs of the other order (the ornithischians), the saurischian dinosaurs were descended from the small, agile, carnivorous Thecodonts of the Triassic Period of some 200 million years ago. The Thecodonts ran on powerful hind legs; their-front limbs were adapted for grasping. Yet Brachiosaurus, which evolved and became extinct during the Jurassic Period of about 150 million years ago, was a ponderous herbivorous reptile that not only walked: on all four feet but also carried most of its weight on front legs decidedly longer and larger than its hind legs. Above its shoulders rose a towering neck which supported a small head with jaws and teeth so insignificant that it is hard to understand how the animal could have eaten enough to grow a body of so many tons. No doubt it spent most of its time in fresh-water lakes filled with plant life. Obviously Brachiosaurus was highly specialized for an aquatic existence; its nostrils pointed upward out of a sort of turret on the top of its head. Probably when Brachiosaurus was hiding from the worst predator of the period, the Allosaurus, its head looked like a small log floating in a muddy lake.

"The mighty leg bones of Brachiosaurus were barely adequate to support its weight. As the animals evolved their size increased, and more individuals in each generation died because their leg bones had broken under the strain. Their weight went up as the cube of their linear dimension, whereas the strength of their bones could increase only with the square of this dimension. Eventually Brachiosaurus became too specialized to cope with the changes in its environment, and it died out millions of years earlier than other dinosaurs did.

"All animal skeletons are made of material with essentially the same strength, whether the animal be a dinosaur or a mouse. This strength increases with the cross-sectional area of bone. Those dinosaur bones which did not have to bear heavy loads took advantage of engineering opportunities for light construction. When it came to supporting dead weight, however, the huge land dinosaurs found no solution other than solid columns of bone, as straight as possible to minimize bending stresses. The photograph above dramatizes this point; it compares the five-foot two-inch femur of a Brontosaurus and the corresponding leg bone of a six-foot American Indian. If the two structures were cut at right angles to their long axes, the leg bone of the Indian would of course have a hole in the center, but the dinosaur femur would be solid. The marrow of such solid bones is represented by large cells distributed throughout the bone.

"The problems of biological engineering suggested by the skeletons of large dinosaurs have given rise to some ingenious speculations. For example, the paleontologist W. D. Matthew believed that these animals could not walk unless they were partly supported by water. He wrote: 'The imperfect joints of the limb and foot bones were covered during life with thick cartilage, like the joints of whales, sea lizards and other aquatic animals. If the full weight of the animal came on these imperfect joints, the cartilage would yield and the ends of the bones would grind against each other, thus preventing the limb from moving without tearing the joint to pieces. The massive, solid limb and foot bones weighted the limbs while immersed in water, and served the same purpose as the lead in divers' shoes, enabling the Brontosaurus to walk about firmly and securely underwater.'

"It was with considerable interest that I measured the joint areas and cross sections of both the Joneses 'Brachiosaurus humerus and the femur of the six-foot Indian. I counted as effective only those areas of the joint which were loaded when the leg was in a straight position. The lower, smaller joint of the Brachiosaurus humerus has a corrected bearing area of 1SS.S square inches, as contrasted to a similarly corrected bearing area of 1.84 square inches for the ball of the Indian's femur. If the Brachiosaurus had weighed 120,000 pounds, and if this one humerus joint took the whole weight, then the stress per square inch on the effective surface of the leg joint was 783 pounds.

"Now let us assume that the Indian weighed 200 pounds, and, for purposes of argument, that he was carrying a burden weighing 800 pounds. (Of course this is a mighty heavy load, but I have seen professional porters carry such loads in China.) If the entire weight were supported by one leg, the stress on the joint would be 548 pounds per square inch. The British biologist J. B. S. Haldane stated that the human leg would fail (with a fracture of the femur) under a load 10 times body weight; I have loaded my Indian with only four times his body weight. So if we grant that the cartilage of a Brachiosaurus was as strong as that of a man, and it may well have been stronger, then this largest of land animals could even have stood on one leg without wrecking its joints!

"Our dinosaur was in even better shape with respect to the strength of its leg bone: when it stood on one leg, its humerus, with a minimum cross section of 76.7 square inches, withstood a stress of 1,565 pounds per square inch. The solid bone of our Indian's femur had a cross section of .55 square inch; when he stood on one leg and carried a burden of 800 pounds, the stress on the bone was 1,820 pounds per square inch. Thus it seems probable that the Brachiosaurus could walk easily and safely from lake to lake without injuring its legs.

"Any student of the earth will find pleasure in reconstructing the world of the great dinosaurs of the Morrison formation in western Colorado and eastern Utah. On the Uncompahgre Plateau the evidence is especially clear. The first, horizon with abundant dinosaur remains is the lower part of the Brushy Basin formation, which constitutes the uppermost member of the Morrison. The Brushy Basin member is mostly a series of variegated bluish and purplish bentonitic shales and clays, deposited largely in quiet fresh-water lakes in a flat Jurassic world. But near the bottom of the Brushy Basin are numerous sandstone beds, often cross-bedded and showing other indications of having been laid down by swift streams that transported poorly sorted gravels along with driftwood (now petrified in interesting green and brown colors) and dinosaur bones (especially those of Brontosaurus). Then the earth sank over a large area embracing what is now most of the Uncompahgre Plateau, and the region became a quiet, muddy freshwater lake that was the home of the Joneses' huge Brachiosaurus. Some 200 feet of fine clay was deposited in this lake, so it must have existed for a long time.

"This quiet refuge for overspecialized giants was ruined when, at the beginning of the Cretaceous Period some 125 million years ago, the gravels and sands of the widespread Dakota sandstone blanketed the whole series of lake-deposited clays and shales of the Brushy Basin, bringing in deciduous leaves, now fossilized, that tell of new uplands and a changing world in which Brachiosaurus failed to survive.

"It is easy to see how a swift river, bearing coarse gravels as well as the bones of dinosaurs that had died farther upstream, often broke up the skeletons of even the largest animals. It is difficult to understand, however, how the giant humerus of the Joneses' Brachiosaurus came to be buried all by itself, for it certainly came to rest on the bottom, and far from the shore, of the lake. Perhaps the carcass floated into the lake and decomposed. The heavy humerus could then have broken away and sunk, to be petrified, collect uranium minerals and ultimately be found by an energetic lady with a Geiger counter.

"What would seem to be the best hunting ground for the amateur collector of dinosaur bones extends in a wide belt from Colorado to Alberta. State geological maps make it easy to find areas where Jurassic and Cretaceous sediments outcrop. A little local inquiry should lead one to areas where fossil bones have actually been discovered. The amateur should steer clear of areas such as Dinosaur National Monument, where dinosaur bones are found in hard conglomerate or sandstone. In these areas bones can be got out only by means of difficult mining operations, including the use of rock drills and dynamite.

"The prospector who seeks big fossils should get away from roads and farms. He must learn to use his eyes and to form a mental image of what a dinosaur bone looks like. He should remember that the early explorers of the West, including a number of good geologists, must have walked over numerous specimens without recognizing them as fossils. As a pioneer geologist once wrote in regard to the discovery of dinosaur fossils in the West, 'Most great discoveries are due to a state of mind rather than to accident.'

"The beginner should read extensively about dinosaurs and the art of finding and collecting them. An excellent reference is The Dinosaur Book, by Edwin H. Colbert. Visits to museums and talks with paleontologists are also helpful. The differences in form and color which distinguish a fossil from the rock in which it is found are subtle and easily escape the eye. One acquires the knack of spotting fossils quickest by exploring with a worker experienced in the field.

"How to get the specimen out of the ground also presents a problem. A light shovel, a sharp miner's pick and a prospector's hammer are the basic tools. A chisel, a supply of quick-drying plastic cement and a small brush are often very useful. The professional paleontologist always shellacs bones before he moves them, and then applies a protective cocoon of plaster of Paris and fabric. This technique may be impractical for the amateur who merely wants to take a bone home. In the case of larger bones, cocooning results in heavy packages that must be transported by a truck.

"Rare specimens deserve to be got out in the best professional manner. If they prove too much to handle, leave them in place and inform a paleontologist of their whereabouts. Always submit photographs and scaled sketches. Fossil bones that have petrified into hard rock can be got out and restored at home by another technique, even when broken into many pieces.

"This method is illustrated by the manner in which my son and I collected the first dinosaur bones he had found, when he was only 11. While hunting for petrified wood in the old river channel of the lower Brushy Basin member of the Morrison, he saw what he first thought was a strangely white petrified tree limb. To his delight, it proved to be the end of a dinosaur leg bone. He soon had the pieces all numbered, wrapped in paper and ready to go into our car, a half mile away.

"One bone often leads to another, and in this instance the next proved to be a hard but badly fractured Brontosaurus femur weighing about 250 pounds. Had we covered it with plaster of Paris, our package would have been so heavy that we would have been compelled to build a road up to our excavation.

"On our next trip to the area we first removed the overburden and placed atop the bone a measuring rod somewhat longer than the specimen. A mark was made on each major fragment of the bone and a sketch was drawn of the undisturbed fragments, along with the scale, including the distance between the marks. The fragments were next labeled, numbered serially and carefully removed for carting away. After we had got the pieces home, the indexed sketch enabled us to reassemble them quickly.

"An added complication was introduced by the fact that many of the fragments were shattered into dozens of smaller pieces. We solved this problem by cementing the smaller pieces together with quick-drying plastic cement before removal. These cemented chunks, which weighed a pound or so, were also labeled, and after being wrapped in newspaper were placed in our dog's pack. (The dog was a Saint Bernard.) My son did most of this work, and in the process learned something of the less pleasurable side of science, especially when a windstorm blew sand in his eyes. Then he and our Saint Bernard carried the big femur across terrain that would stop a tank. In the process the dog doubtless established a record for the largest bone brought home by his kind.

"The lighter you travel when prospecting, whether for uranium or dinosaurs, the more ground you can cover and the more likely you are to hit pay dirt. A plywood pack-board of the Army type, a waterproof bag, a light sleeping bag, a nylon poncho, a couple of canteens, about 12 pounds of ready-to-eat dry food and a few light tools will enable you to hunt for five days in areas far from roads. Until you start collecting fossils you will have complete freedom of movement, thus making it easy for you to get into virgin dinosaur country.

"My son and another boy are shortly leaving for just such a five-day hunt for dinosaurs. They are going into the area of the upper Morrison outcroppings in a remote part of the Uncompahgre Plateau, where they will be up to 10 miles from the nearest jeep road. During the hunt they will probably not see another human being. We recently received a letter from a paleontologist informing us that the small dinosaurs of the Morrison are now the only known species that have not been extensively collected and studied. The boys, assisted by a Geiger counter, will accordingly concentrate on small dinosaurs and try to bring back skulls and pelvises-bones prized even by our foremost museums.

Figure 3: A hatchet-type planimeter to measure irregular areas

"In contrast with British amateurs, thousands of whom diligently collect well-known though insignificant fossils, relatively few Americans take an active interest in hunting our fossil treasures. This strikes me as most unfortunate. But after all, as my old professor of geology at Oxford once remarked, 'Americans are a young people living in a young country and still have time.'"

Walter Hobson, a mechanical engineer of Philadelphia, submits the design for a planimeter to measure the area of an irregular shape. His planimeter, of the hatchet type, was constructed in the 1900s, and has been used extensively for map work as well as for measuring the irregular areas encountered in problems of mechanical design. Details of construction are given in the drawing at left. The only critical dimension is the distance between the tracing point and the point at which the rounded knife-blade makes contact with the paper, which should be 10 inches. The tracing point is first set on the estimated center of the figure to be measured. The blade is pressed into the paper at any convenient point, and a straight line is drawn from. the tracing point to the point where the blade touches the paper. The tracing point is moved along the straight line to its intersection with the figure, then around the figure and finally along the straight line to the point of origin. The knife is kept upright and m light but firm contact with the paper during the tracing operation. The motion of tracing causes the knife to make a zigzag excursion away from the line, as shown at upper left in the illustration. Measure the distance between the final position of the knife and the line and multiply it by 10. The product is the area in square inches of the figure.

Rene A. Wurgel, who described a novel method of mounting a diagonal mirror in a small telescope in this department last November, calls attention to an error in the associated drawing. The brass rings which support the mirror should be attached to the main tube of the telescope by two bolts instead of four, as illustrated. This permits the rings to be turned for collimation. Wurgel also suggests that the rings be made of relatively thin material, i.e., on the order of .025 inch thick.


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