Finally the rains fell in the mountains to the west. The river filled with water again and ran in sheets across the plain. At Agate the millions of Menoceras bones and lesser numbers of the bones of other animals were swept for a few hundred meters downstream and into some sort of backwater or river lake—possibly a great meander, or an oxbow lake. There, like a gigantic mass of jackstraws, they were piled in a tangled mat 30 centimeters (12 inches) thick, covering an unknown number of hectares. All we really know is that they were moved far enough to get thoroughly jumbled, but not far enough to be badly broken or much eroded by the action of the water.
The mass of bones was soon buried by the sands and silts dropped by the reborn river, and by wind-carried debris swept off the parched land. Once buried, the bones were partially petrified by mineral water flowing beneath the surface. The land was built up a few hundred meters by sediments continually brought down from the mountains to the west. Eventually, continued uplifts of the Rockies and the Great Plains combined with erosional cycles to leave the modern Niobrara River. The two erosional remnants known today as Carnegie and University Hills were produced by the cutting of the modern river system. On the sides of these hills were exposed the tangle of bones which marked the site of ancient tragedy.
But this wasn’t the only scene of mass death to be preserved here in the fossil record. A few kilometers away an earlier drought took a toll of many other animals. The little gazelle-like camel Stenomylus tells the same story in scores of skeletons east of the Menoceras burial ground.
These graceful little camels may have died at the edges of their vanished water hole. The skeletons are mostly undisturbed except for a few pulled apart by meat-eaters. Scores of their dried out, mummified carcasses were buried about the same time as the rhinos on the river’s dry bottom. Like the Menoceras, the camels lay there for millions of years, intact in their death poses, the muscles in the backs of their necks pulling their heads back sharply into an unnatural position. There they lay until men discovered them.
Our imaginary journey into the past has reached its end. We have seen a day at Agate as it might have been 20 million years ago. We have watched the animals going about their daily lives during times of plenty and have seen it as it was later, when death’s heavy hand left a magnificent fossil heritage. This unique place is a window into the past, a window through which we can look back at any time and observe life at Agate millions of years ago.
Excavations at Agate Springs
The first fossils were collected in volume in 1904 by Olaf Peterson of the Carnegie Museum in Pittsburgh. Excavations have continued, off and on, to the present. As early as 1892, Erwin Barbour’s student F. C. Kenyon had retrieved a few bones from the site but their significance was overlooked. Rancher James Cook first picked some up in the 1880s and may have first noticed such deposits, without particularly recognizing them, in the 1870s.
Other institutions soon joined Carnegie in extracting slabs of the great Menoceras bone-bed, and occasional Moropus and Dinohyus specimens. The University of Nebraska opened a new quarry in 1905. Henry Fairfield Osborn, president of the American Museum of Natural History and one of the greatest popularizers and exponents of evolutionary science, and his chief preparator Albert Thomson began work in 1907. F. B. Loomis of Amherst College discovered the nearby Stenomylus quarry the same year. Yale University’s R. S. Lull soon followed.
From 1911 to 1923 the American Museum became the main excavator at Agate, but increasingly their attention was drawn elsewhere, including the later Miocene Snake Creek Beds 20 miles to the south. There, for awhile, great excitement centered around a worn tooth thought to be from an early human ancestor until the tooth was proven to be from an ancient peccary.
Until 1981, only occasional excavations for bonebed slabs and Stenomylus marked the next 50 years. Then, Robert M. Hunt Jr. of the University of Nebraska reopened the main quarries and a little-known side area, and found evidence of an extensive carnivore den of the beardog Daphoenodon.
In some cases, individual fossil bones were removed one by one, a very slow and painstaking process but when possible large blocks of fossil-bearing sediments were removed and shipped to laboratories for cleaning and analysis. The tools, chemicals, and special conditions necessary to extract the best specimens and most complete information are available only in a laboratory such as the one which is shown on pages [40] and 41 at the Carnegie Museum in Pittsburgh, Pennsylvania, in 1905. Slabs from Agate Fossil Beds were taken there so paleontologists could examine the evidence and figure out the past.
See pages [86]-87 for a listing of museums with specimens from Agate Fossil Beds.
Members of Peterson’s crew built a box around a slab in the Stenomylus quarry around 1908 in preparation for shipping to the Carnegie Museum.
With a team of horses, O. A. Peterson’s field crew moves dirt out of the Stenomylus quarry around 1908. The boxes in the foreground are resting on the quarry’s lower bone layer. Several specimens to the left have been strengthened with plaster for shipment to Pittsburgh.
Crates of prepared specimens had to be taken to Harrison, 37 kilometers (23 miles) north of Agate for the rail trip to the East. Note that the wagon is just a flat platform and that the driver is using the largest crate as a seat.
The Beginnings of Paleontology
Paleontology is the study of ancient life through the fossil remains of that life. Today, there are thousands of museums, societies, professional groups, and academic institutions around the world devoted to this study. Fossil remains are still being dug out of the ground in a number of localities, such as Dinosaur National Monument in Utah, but by far the great bulk of fossils now being studied were excavated during the last 100 years.
There are now about 250,000 known separate species of fossil plants and animals. Biologists are still working to explore, find, and classify all living species; they estimate that 4,500,000 species of plants and animals are now living at our own brief moment in the nearly five billion years of our planet’s history. As you can see, the fossils now known represent only a tiny fraction of all the plants and animals that have ever lived. Yet a great deal is now known about even the simple forms of life more than three billion years ago.
How has this come about? What has happened since the days of our great-grandfathers to cause this vast increase in knowledge? Men must have picked up and discussed fossils for tens or perhaps hundreds of thousands of years. We have no way of knowing what the earliest men thought about them. Their significance has been revealed slowly in the way we tend to look at time, but perhaps not so slowly when we consider how short a period man himself has been on Earth.
Lucretius, a Roman writer of the first century B.C., thought that the Earth was very young. He interpreted the fossils known to him as the remains of monsters that had grown out of the Earth just after it came into existence. Evidently he had seen partial fossils and believed them to be whole, because he postulated that the Earth had brought forth creatures that lacked one or more limbs or other body parts. Lucretius assumed, as have many others, that the varieties of animals he knew of were fixed for all time and did not change. But he did recognize the principle of evolution, that things change as time goes on, in his description of human history.
Lucretius described four ages of human life, progressing from early hunters up to the highly civilized life he knew under the Roman Republic. His work was rediscovered during the European Renaissance, when scholars once again began to inquire into the nature of seemingly inexplicable things like fossils.
Toward the end of the 18th century the confusion over the importance of fossils and their relative antiquity forced a scientific showdown. For hundreds of years, fossil bones of extinct animals unlike any ever seen had been turning up, often with tools nearby that appeared to have been shaped by human hands. A growing feeling that the Earth and therefore the fossils were very old indeed was a topic of frequent discussion in Europe and in the New World, despite the assertion by Archbishop Ussher a century earlier that the Earth was not quite 6,000 years old.
Explorers and scientists had found fossils in deep layers of rock widely separated by other layers of rock, leading many of them to conclude that now-extinct forms of life had existed before the Biblical flood. A pioneer French paleontologist, Georges Cuvier, tried to solve this dilemma in the late 1700s by postulating that there must have been several worldwide floods before the one described in the Christian Bible. Finally, this solution collapsed under the weight of new evidence as more and more studies proceeded.
In the 1830s an English geologist, Sir Charles Lyell, popularized the principle of uniformitarianism—the idea that processes we observe now, such as the steady erosion of mountains, the gradual buildup of silt as sediments in rivers, lakes, and oceans, have always occurred since the origin of the Earth. This, he then reasoned, meant that the Earth must be many millions of years old at least, instead of merely a few thousand years old.
A wave of interest in fossils and their antiquity swept communities around the world in the 1840s and 1850s. Americans interested in science from Thomas Jefferson on had advocated the collection and study of fossils, and a feverish race to build up study collections got underway that lasted into the 20th century. Today, scientists believe the Earth is more than 4.5 billion years old, its life more than 3 billion years old.
Karl Von Linné, 1707-1778, is known as Linnaeus after the Latin form of his name. A Swedish botanist, he established a hierarchical system for classifying plants and animals that is still in use in a modified form. His organizing principle was the degree of complexity of the organisms he studied. This resulted in a system with seven levels: Kingdom, Phylum, Class, Order, Family, Genus, and Species, in descending order from the broadest category to the most specific. Students remember the system by the sentence “King Philip Crossed the Ocean For Good Soup.” Without realizing it, Linnaeus prepared the ground for the evolutionists, who later were able to demonstrate the gradual ascent of life forms from simple to complex by using his scheme of classification.
Jean-Baptiste de Lamarck, 1744-1829, a French physician and ex-military man, founded the modern study of animals without backbones and coined the term invertebrates to describe them as a group. When his battle wounds forced him to take up a new career, he studied botany and published a study of French plants. He later turned to invertebrates, and between 1815 and 1822 published the classic Histoire naturelle des animaux sans vertèbres. He applied his vast knowledge of living invertebrates to paleontological work, greatly enhancing the knowledge of fossil invertebrates. Lamarck was also an evolutionary theorist, and he believed that a single characteristic acquired by an animal during its lifetime could be passed on to its descendants by heredity (modern genetic theory was unknown at that time). He saw that evolution must have taken a long time to occur, and he supported the principle which has since become known as uniformitarianism.
Georges Cuvier, 1769-1832, was a French anatomist and paleontologist who specialized in the study of animals with backbones, the vertebrates. He had a long and brilliant career as a professor, eventually becoming France’s minister of the interior in 1832. His skill as a comparative anatomist enabled him to understand how vertebrate fossils should be reconstructed to form a complete skeleton, and he was one of the first to use the small muscle scars on fossil bones to reconstruct the extinct animal’s musculature. His classic work Récherches sur les Ossemens Fossiles de Quadrupèds was published in 1812. He is known for his theory of a series of natural catastrophes, each supposedly obliterating all extant life, to account for the great variety of ancient fossils. This theory was later supplanted by the theory of continuous evolution supported by Darwin, Lyell, and others.
Charles Darwin, 1809-1882, is today a household name that is still invoked in controversy as it was more than a hundred years ago. An extraordinarily patient and insightful biologist, Darwin contributed the idea of natural selection, the “weeding out” of unfit individuals and species, and described it as the guiding principle of the evolution of life on this planet. His book On the Origin of Species by Means of Natural Selection, published in 1859, is the most important landmark in evolutionary studies. This was the culmination of decades of work, leading to conclusions startlingly similar to those of his fellow Englishman, Alfred Wallace. Darwin knew nothing of the genetic principle of biological heredity and variation, which has now assumed equal importance with natural selection in the study of the evolution of life. For paleontologists, Darwin’s work meant they must look for transitional forms of life and not content themselves with Cuvier’s assumptions that past life forms had been static and unchanging. During his travels in South America, Darwin contracted a disease, now known as Chagas’ disease, and suffered intense pain and discomfort the rest of his life. He died of a heart attack on April 19, 1882, and was buried in Westminster Abbey in London a few days later.
Charles Lyell, 1797-1875, revolutionized the study of geology partly by publicizing the earlier work of James Hutton, who died the year Lyell was born in Scotland, and partly by infusing the science with his own highly disciplined point of view. His greatest contribution was the firm establishment of Hutton’s principle of uniformitarianism, or uniformism, which became the foundation for all modern geological work. Put simply, this is the principle that the processes we see operating to form and shape the Earth today have always operated in the past. Once this is admitted, it becomes clear that past geological time is vast, not short, a truly stunning notion for Lyell’s time but a commonplace fact today. The first volume of his Principles of Geology was published in 1830; in his later works he championed Darwin’s own revolutionary point of view, adding his own powerful arguments in support of the idea of natural selection.
Alfred Wallace, 1823-1913, was the co-originator, with Darwin, of the principle of natural selection, or “survival of the fittest.” The main difference between the two was that Wallace did not believe that natural selection explained things as well as Darwin thought it did, which has been borne out to a large extent by modern studies of genetic variation. Wallace worked in South America, along the Amazon and Rio Negro rivers, and in East Asia. He showed that the animals on either side of a line between Borneo and the Celebes Islands are radically different in their makeup and origin. Now known as “Wallace’s Line,” his work has been vindicated by additional modern studies. Although Wallace did not become as well known as Darwin, his brilliant, independent studies lent a great deal of weight to the Darwinian view of evolution.