Part 4

During the first rumbles of this upheaval there were occasional instabilities in the weather of the Great Plains. From the fossil evidence of Carnegie Hill, University Hill, and the Stenomylus quarry, we can see that drought touched the land.

What happens when disaster stalks the land? That question, so pertinent to an understanding of fossil deposition at Agate, can be answered best by looking at the normal scheme of life. Animal populations are cyclic, increasing rapidly to near the highest numbers which can be supported on available food supplies. If times are good, animal populations can be quite high. If the food supply decreases, massive dieoffs result. Successive cycles of plenty and poverty then produce high populations followed by dieoffs.

The fossil evidence suggests that a prolonged drought occurred during the Golden Age at Agate, resulting in death everywhere. The vast numbers of rhino skeletons preserved at Carnegie Hill and University Hill provide paleontological evidence that the drought must have lasted for several years.

Climates change slowly, and there are wet and dry cycles. Every rancher and farmer discovers this when he plows new land during a wet cycle, for sooner or later drier years catch up with him. He expects the optimum to be the standard; but he is badly hurt during average times, and really suffers when the dry years come. It is the same with populations of wild animals. When the times are good and the grass and trees are lush, fat, and green, more of the young survive and the whole population flourishes. The plant-eaters expand their herds and the meat-eaters increase to keep up with the better food supply the plant-eaters provide. In each case the standards for survival are lowered, and the less than perfect can survive and in turn produce young of their own. But when the water fails and plants refuse to grow, the herbivores starve and the carnivore population in turn declines. Nature is indifferent—neither cruel nor kind. When times are bad every species is improved, for the strongest and most tenacious survive to reproduce themselves. There are benefits to hardship.

So it was at Agate only a year or so after the day of our visit. The river died for a while. As with many rivers much of its water flowed beneath the surface, through the sand and gravel of the bed. When the ancient Niobrara died there was still water moving through the sands and filling the low spots in its bed. Some animals could dig down to it and survive, others could stake claims to the diminishing water holes. So the thirsty, suffering herds of Menoceras went to the river and found no water. The strong held the water holes. The smart dug into the sand and made their own water holes. The rest died. They died by the hundreds, and thousands. Mixed with the carcasses of Menoceras were other victims: occasional chalicotheres, giant pigs, oreodons, cats, dogs, and a variety of equally thirsty smaller animals. Perhaps most of the animals went farther up or down stream, or perhaps they chose not to die at the river. Whatever the pattern of dying might have been, we know that Menoceras left untold numbers of skeletons on the broad, flat, and dry bottom of the ancient Niobrara.

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.

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.

Geologic Time Chart Period Epoch Time span (years before present)