United States. National Park Service

“ 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. ”

“ 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. ”

“ When twilight comes, the herd draws together, colts and females toward the center and bulls around the edges. After a period of milling and pushing, the herd finally beds down for the night, with only the perimeter guards moving around on the edges.
The daily routines of the other herds of grass- and leaf-eating animals generally follow somewhat different patterns from that of the rhinos. Of them, only the piglike oreodons wallow in the river. The others spend nearly all their time out on the savanna, coming to the river only at dawn or dusk to drink. ”

“ As a general rule it is best to keep a good distance from any wildlife you see, not only to protect yourself and your children, but to avoid frightening or hurting the animal. It is best to observe wildlife at a safe distance with field glasses. While walking about the park, do not take chances by climbing on loose rock, or going into unauthorized areas, and do not let your children go beyond your control. ”

“ For a long time some individuals of Miohippus carried a little extra wrinkle of enamel on the crowns of their upper grinding teeth—and now the wrinkle occurs in all individuals of Parahippus. Because of it, Parahippus can eat grass without wearing out its teeth before reaching breeding age, making it possible for most individuals to reproduce before dying. The little wrinkle is passed on. It’s only a small advantage, but such is the stuff that survival and evolution are made of. ”

“ 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. ”

“ Now they’ve moved out into an area of cropped grass, and we can see a herd of the diminutive deerlike Nanotragulus (“dwarf goat”) . Not a great deal larger than a house cat, these little “deer” have tall grinding teeth well adapted for grass-eating. Their ancestry goes back for millions of years into the Late Eocene, when some of their ancestors stood less than 15 centimeters (6 inches) high at the shoulder. But their entire family is soon to become extinct. They are part of the grazing community, although they eat leaves and softer vegetation just as readily. ”

“ Closely connected with paleontology are several other sciences, among them geology, zoology, and botany. The paleontologist, for example, must depend on geology to provide important answers about the age of fossil specimens. Fossil botanical specimens, in turn, can provide answers about animal diets and climate. Though paleontology may center on the study of fossil remains, it is an interdisciplinary science. This fact will become increasingly apparent in the following chapters, which reveal the strands of evidence used in constructing the picture of Miocene Agate. ”

“ Then as the climate became even more arid the prairie or tall grass retreated eastward, while the forest moved before it even farther to the east and south, and the modern shortgrass of the plains took its place. Today Agate lies in one of the valleys whose rivers are slowly dissecting the High Plains.
The modern plains are dominated by short, curly, sodforming buffalo grass, a plant well adapted to the area’s light rainfall, periodic droughts, low humidity, rapid evaporation, and high winds. The dominant vertebrate animals are burrowers and grazers, and dogs are the primary carnivores. ”

“ Museum curators are dedicated “horse traders” and fossil-swapping is part of the business. When museums such as the Carnegie Museum of Pittsburgh or the American Museum of Natural History in New York make collections like the ones made at Agate earlier in this century, they usually have some trading stock left over after completing their study collections and exhibits. They then can trade an extra Menoceras slab, for example, for a dinosaur skeleton from some faraway corner of the Earth. ”

“ They’d much rather hide than flee their enemies.
These dwellers of the savanna, common during the Miocene Epoch, comprise the major species found at the Agate Fossil Beds. Their discovery in the late 1800’s and early 1900’s was highly important to the young science of paleontology. In those decades of major discoveries, large gaps remained in the story of evolution. Quarries like those at Agate helped provide the missing pieces of the puzzle. In their time, the discoveries at Agate were an important contribution toward understanding the world far beyond the dawn of mankind. ”

“ 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. ”

“ Even in Paradise an occasional calamity can occur. Agate’s misfortune appeared in the form of a drought. To the west of the plain built by the ancient Niobrara River, the Rocky Mountains began to rise again. This renewed uplift, after millions of years of relative quiet, eventually led to an even drier climate and a replacement of the savanna with a landscape of unbroken grasslands from the mountains to the Mississippi River and beyond. Trees then could survive only on canyon slopes along the courses of the few large remaining rivers that crossed the plains. ”

“ As the base of the food chain, plants carry the influences of climate on to the plant-eating animals. From the numerous animal fossils found at Agate we have learned most of what is known about the environment of that time. Sediments tell a good part of the story, and floras from other localities help, but much of Agate’s ancient ecology must be inferred from the bones.
Today, standing on the porch of the visitor center or walking along the path to University and Carnegie Hills, visitors find themselves in the midst of the shortgrass prairie. ”

“ They swoop down on the mice and pocket gophers, young rabbits and beavers, baby “deer” and sometimes careless birds that live on this savanna. All manner of meat-eaters depend on the small animals for food, and the little Nanotragulus are most vulnerable as they move through the canopy of grass.
There don’t seem to be any other herds moving into view just now; but while we’re on the subject of birds, over there in that patch of short grass is a bird rarely seen in North America anymore. ”

“ The herd seems to be made up of about 50 individuals moving through the tall grass like a flattened dark gray cloud. Suddenly they are startled by a large cat or dog stalking through the grass, and all the males on the side nearest the enemy bunch together to face the hungry hunter. Most of the herd continues to flow across the plain, and when the danger is past the guardian males catch up in a lumbering gallop.
Finally the herd reaches the river and spreads out through the shallows. It is hot today, and the flies are biting even through the tough rhino hides. ”

“ By the time the Harrison Formation was deposited, the development of the halfway world of the savanna was beginning to affect the fauna. Although the Oligocene and the very earliest Miocene mammal faunas were highly varied and rich in types of animals, much of this was due to the continued presence of primitive and archaic forms, and to the explosive development of rhinos and oreodons. With the savanna becoming the dominant landscape, the shift to grazing and away from browsing became evident. ”

“ Stenomylus is the second most common animal found in the fossil beds at Agate. Stenomylus had hard hooves like modern antelopes and deer, unlike modern camels which have flesh-padded feet adapted to desert terrain. The three-hued coat is inferred from the coat of the modern gazelle, a similar form in adaptation. Stenomylus’ evolutionary line eventually died out in North America at the end of the Pleistocene. No one knows why both camels and horses died out on this continent. ”

“ Five distinctive plant communities share this prairie, coexisting in a dynamic relationship which depends upon local climate variations.
Even to the untrained eye, it is evident that the basic short-grass pattern has been modified by the shape of the land and by the Niobrara River. In the stream valley, along the tributaries, and on shaded north-facing slopes, the shortgrass community is mixed with taller grasses. If a dry cycle began, the short grasses would take over the whole area by migrating downslope from the exposed prairies. ”

“ Animal species respond to environmental changes in a variety of ways. Simply put, some species die off, some adapt physically, and some move to a different habitat. On the next few pages are examples showing how three species responded to long-term environmental changes in the area around Agate Fossil Beds. The Stenomylus line died off; Miohippus’ evolutionary line remained a grazing animal but changed physically over the years, eventually becoming the modern horse; and the Palaeocastor line moved from land to water, gradually evolving into the beaver. ”

“ 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. ”

“ But when any appreciable amount of grass, particularly the short, tough grass of the plains and the abrasive dirt and sand that accompanies it, becomes part of an herbivore’s diet, there is a great increase in the rate of tooth wear. Teeth which have evolved for browsing quickly wear down to the gums and the individual dies of starvation. ”

“ Along the ancient Niobrara the rhino herds are not made up of the giant mammals we see in zoos today. The ones we see moving slowly toward the river on this early Miocene day are no larger than big domestic pigs. They are the first among the rhinos to have horns—not one behind the other, but a pair near the end of the nose, side by side. To scientists today these rhinos are known as Menoceras. The name Diceratherium, once used both for these small rhinos and a larger type of ancient rhino, now refers accurately to just the large rhino.
Menoceras
Look off to the south. ”

“ We search long rows of fence posts for a burrowing owl and occasionally see one. Great-horned owls frequent tall cottonwood trees around the Agate ranch buildings. This is also the country of turkey vultures, golden eagles, and prairie falcons, but we have not been lucky enough to see them yet.
Mammals are more elusive. Cattle pasture conspicuously on land formerly claimed by the buffalo (bison) . We see pronghorns each year. A lone coyote is the only other relatively large mammal we have logged. ”

“ Although the whole story of Agate Fossil Beds dates from the formation of the Earth four and one half billion years ago, only the last 600 million years is known in detail. It was about 600 million years ago that many plants and animals began to have hard parts—parts likely to be preserved as fossils. The few fossils contained in older rocks are often folded, twisted, squeezed, and distorted so that their original character is all but erased. ”

“ Check a good mammal book and you will appreciate what lives here largely invisible to the untrained eye: shrews, moles, bats, cottontails and two kinds of jackrabbits, pocket gophers, prairie dogs, kangaroo rats, voles, several kinds of mice, two kinds of ground squirrel, muskrats, beaver, raccoons, minks, badgers, longtailed weasels, two kinds of skunks, occasional porcupines and bobcats, white-tailed deer, and mule deer. Consider yourself lucky if you see the swift fox, mountain lion, and the rare black-footed ferret. ”

“ If the savanna is the halfway station between forests and grasslands, then the fossil fauna of the Early Miocene at Agate was a fauna in the beginning of a serious transition. In the vicinity of Agate, the fauna from the Late Oligocene was dominated by mammals with low-crowned teeth. The crown is that part of the tooth which is above the roots and exposed beyond the gums. Among the herbivores, the 62 browsers can live a long life with low-crowned teeth. ”

“ 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. ”

“ They had, during several million years of evolution, grown together into a single shaft and then spread out again to the sides and up. What a pity there were no little boys then, for here we have the world’s first and only self-propelled slingshot! ”

“ Northwestern Nebraska, northeastern Colorado, southeastern Wyoming, and southwestern South Dakota today remain a promised land for paleontologists studying mammal life in North America during the middle and later Cenozoic Era. The fossil deposits in the Agate area are surpassed in importance only by the Late Eocene and Oligocene deposits of the Big Badlands and Pine Ridge in South Dakota. ”

“ Generally the Harrison Formation and the overlying Marsland Formation are only moderately fossiliferous, but along the Niobrara River here at Agate, Nebraska, the accumulation of rhinoceros and camel skeletons is one of the wonders of the fossil world. Here, thousands of animals perished in two droughts which coincided with conditions perfect for preservation. About two kilometers (1.2 miles) east 51 of the Monument headquarters the dried-out, mummified bodies of perhaps a hundred or more little camels, Stenomylus hitchcocki, were buried under windblown sand during the first drought. ”