Chapter II: Part 3: Guide and Adviser 74 (1)

Contents for this section 77

1 Welcome to Agate Fossil Beds

Worlds of Past and Present

Imagine that you are a healthy young man, raised conservatively in Michigan several years after the end of the Civil War. You are a skilled all-around hunter and trapper. The railroad has just spanned the continent, and stories of the West, its dangers, its people, and its opportunities come to you frequently. You and a friend decide you must see this land for yourself, and you save your money carefully against the day when you will be ready to go west. Around 1869, at age 12, that day comes.

At Fort Leavenworth, Kansas, you meet several cattlemen who tell you and your friend where to get work as cattle herders. Before many years have passed you have been a cowpuncher in Texas, you have fought Comanches, and you have bossed a ranch crew for a wealthy Englishman. You go on to fight the famous Apache Chieftain Geronimo as a scout with the U.S. Cavalry, and you befriend a famous Sioux chief, Red Cloud. You marry, buy a ranch in western Nebraska, and raise a family. And you become something of a legend in your own time, your ranch known for its hospitality to Indian, scientist, traveler—to one and all, rich or poor.

A movie script? Not at all—these are the essentials of the life of James H. Cook. Known as “Captain,” James Cook became the owner, in 1887, of the Agate Springs Ranch, founded earlier by his father-in-law. Under Cook’s watchful eye, the ranch prospered and became a second home both for the Oglala Sioux and for paleontologists bent on excavating the fossilized remains of the life of 20 million years ago, found here along the Niobrara River in western Nebraska.

This land, now encompassing Agate Fossil Beds National Monument, is punctuated with low bluffs ascending westward toward the Rockies. It is a land of sharp contrasts, of cool, inviting riverbanks and parched ridges, the most famous of which are the fossil-bearing Carnegie and University Hills. The surrounding grassy plains are a tapestry of wild grasses—prairie sandreed, blue grama, little bluestem, and needle-and-thread. The wildflowers lupine, spiderwort, western wallflower, sunflower, and penstemon add touches of blue, purple, orange, yellow, and red to the tapestry. In summer the dark green spears of the small soapweed, a yucca, dot the brown grasses of the hillsides. And just as they did more than 20 million years ago, cottonwoods and willows provide shade and shelter for birds and other animals along the river.

Looking out over the rippling grasses, you grasp the fact that Nebraska is larger than all of New England and feel the awesome spaciousness of the Great Plains. The word “distance” has a different meaning here than it does in the East. When James Cook came to the upper Niobrara River, the closest town was Cheyenne, Wyoming—more than 160 kilometers (100 miles) to the southwest.

It was there, in Cheyenne, that Cook met Dr. Elisha B. Graham in 1879, the year Graham selected this land for a cattle ranch as an investment and as a summer retreat for his family. Graham named the place the 04 Ranch, apparently because it is near the 104th meridian. Cook visited the ranch often in the early 1880s and courted Elisha and Mary Graham’s daughter Kate. They were married in 1886 and lived near Socorro, New Mexico, for a year before returning to Nebraska with their newborn child, Harold, and buying the ranch from Dr. Graham, who moved to California.

Cook began at once to make improvements to the ranch. He planted trees by the hundreds and carried water to them faithfully to get them started. As settlers failed to “prove up” their land claims over the years, he added new lands to the ranch and changed the name to Agate Springs Ranch in recognition of the native moss agates and the many springs in the valley. He and Kate raised fine race horses as well as cattle.

The period in which the Cooks took over the ranch was one of transition from the frontier days of migrations and Indian wars to more settled, orderly lives. Ranching and farming became the dominant mode of life in the eastern approaches to the Rockies. Even oil exploration played a part in the development of the land. The transition was a difficult one for many, Indian and settler alike.

In some ways Kate Cook represented both the old and the new in Nebraska. She was a fine horsewoman; one day she rode a bucking horse through the streets of Cheyenne sidesaddle to win a bet for her husband. She was refined, too, having taught herself French so she could read French literature. Her mother, Mary Graham, became the first postmistress for the small community around Agate.

And James Cook was more than an adventuresome frontiersman. He was actively interested in community and national affairs and in current scientific questions. He became a patient, knowledgeable mediator between the Indians and the settlers, and he was looked upon by the Oglala Sioux as a friend and host, and sometimes employer.

The Cooks became involved in a great scientific enterprise quite accidentally around 1885, the year before their marriage. On a ride up the conical buttes not far from the ranch house, a glitter under a rock shelf caught Cook’s eye. They found fragments of bones scattered on the ground. At first they assumed the bones were those of an Indian. But Cook found instead “a beautifully petrified piece of the shaft of some creature’s leg bone.” They carried it back to the house but didn’t report the find until after they bought the ranch. Erwin Barbour of the University of Nebraska was the first to respond to their reports and in 1892 became the first professional geologist to visit the area and do some prospecting.

The Cooks’ discovery thrust them and their ranch into a subtle battle in the American West, a continuing struggle to find the best fossils with which to reconstruct the ancient past. For centuries it had been thought that life on our planet was only a few thousand years old, but by the late 19th century science had evolved beyond that point of view. Now paleontologists and their excavation teams were scouring the West in search of fossils that might provide clues to the beginnings of life.

The two most noted antagonists in this feverish search were Professors Edward D. Cope of Philadelphia and Othniel C. Marsh of Yale University. Cook knew them both, but the discoveries at Agate would wait for the next generation of scientists.

Cook had first met Marsh in 1874. Marsh had just arrived in Oglala Sioux country to hunt fossils, but the Sioux Chief Red Cloud was suspicious. Red Cloud was convinced Marsh and his men were just another party of gold seekers. Cook, an able linguist, was then trailing cattle from Texas to the northern railroads and reservations. He persuaded Red Cloud that Marsh wanted only “stone bones” and averted a potentially disastrous clash. This incident led to a lifelong friendship between Cook and Red Cloud. And for Marsh this proved to be the last of many expeditions as he relied on others to send him specimens from likely fossil sites throughout the West.

Professor Cope and his crews often worked the same localities as Marsh. Like Marsh, Cope tried to get the best specimens, and each occasionally outbid the other for them, leaving bewildered farmers and ranchers to puzzle over these men’s obsession with the past. Conflict also arose over the naming of animals previously unknown to science.

The hills of Agate Springs Ranch proved to be a rich archive of ancient life. Dr. Barbour and his students confined their efforts to what soon became known as University Hill. Thus began a quiet rivalry with Olaf Peterson and his crew from the Carnegie Museum in Pittsburgh, Pennsylvania, who worked what became known as Carnegie Hill. The most numerous fossils these teams found at Agate are the remains of the pony-sized rhinoceros _Menoceras_, but the site also is known for fossils of the gazelle-like camel _Stenomylus_, the early small horse _Miohippus_, and the corkscrew burrows of an ancient beaver, _Palaeocastor_.

Other distinguished scientists visited Agate over several decades. Among them were Henry Fairfield Osborn and Albert Thompson of the American Museum of Natural History in New York. The collections these men made at Agate are still being studied and exhibited.

James and Kate Cook’s older son Harold caught the fever, too. He became a trained geologist and in 1910 married another geologist, Eleanor Barbour, daughter of the distinguished Nebraska geologist. The new generation of Cooks continued the tradition of hospitality and scientific interest, encouraging further excavations of the fossil treasures of Agate. Perhaps Harold Cook’s greatest moment of scientific glory came in 1926, when he and other scientists participated in the finds at Folsom, New Mexico, which proved to be a turning point in the study of the human prehistory of North America. George McJunkin, a black cowboy, had spotted the ribs of an animal protruding from the banks of an arroyo. The Folsom spearpoint and the bones of an extinct form of bison found there indicated that humans had lived on this continent for more than 10,000 years, a startling revelation at that time though today scientists put the figure at more than 40,000 years.

In time the Cooks’ house became a repository for a substantial number of Indian artifacts and natural history specimens. On summer weekends and holidays tourists ventured out to the ranch to see the Cook Museum of Natural History. James Cook personally guided many through the collection, but usually the whole family participated, leading the curious through three rooms and a small hallway.

Harold Cook wanted Agate Springs Ranch to provide an enduring memorial to the ancient past. Soon after his death in 1962 his second wife, Margaret Crozier Cook, and friends began a campaign to add the fossil beds to the National Park System. Their efforts succeeded in 1965, when Congress authorized the establishment of Agate Fossil Beds National Monument.

Today you can walk about Carnegie and University Hills where the great digs took place. You can see a few exposed fossil specimens, and you can try to recreate in your mind the life and landscape of this part of Nebraska 20 million years ago. To help you do that, we have asked paleontologists James R. and Laurie J. Macdonald, in Part 2 of this handbook, to take you on a journey to the past and then examine the evidence.

Welcome to the worlds of past and present at Agate Fossil Beds National Monument.

2 A Landscape Rich With Life

_Text: James R. and Laurie J. Macdonald_
_Illustrations: Jay H. Matternes_

1/Moropus
2/Promerycochoerus
3/Menoceras
4/Oxydactylus
5/Daphoenodon
6/Stenomylus
7/Dinohyus
8/Merychyus
9/Palaeocastor
10/Parahippus
11/Syndyoceras

A Visit to the Past

Come enter into our imaginations and return to a day along the Niobrara River in western Nebraska 20 million years ago. Let’s go back and have an imaginary look. To set the mood, think about the wild animal movies made in modern Africa during the last 40 years. Think of a land swarming with life, of extensive grasslands dotted with trees through which great herds of grass- and leaf-eating animals are wandering. Look sharply into the shadows under the trees and amid the high grass where the meat-eaters are resting or stalking their prey. When you have this picture of wildlife in mind we’re ready for our journey into the past.

Projecting ourselves back those 20 millions of years, we find ourselves in a landscape filled with animals. Some of the animals are not much different from those living today, but others are so bizarre that you may have a hard time believing they really existed.

Dawn is building a new day, and those animals which hunt and feed at night are disappearing into their lairs. There are so many kinds of livings to be made that the day isn’t long enough for all animal varieties to be about and active only in daylight. As the light spreads over the land we see that it is an open, sunny place of mixed grasses and trees—mostly grassland, but here and there single trees or small clumps not big enough to be called groves. We would call it a savanna.

A broad river runs through the land, and for lack of a better name we can call it the Niobrara or “Running Water,” the name given by Indians to the much smaller modern stream. This ancient Niobrara was a bold, wide stream with deep pools and sandbars. It was not cutting a valley as its modern counterpart is doing, but was carrying sand and silt down from the then-young Rocky Mountains. It sometimes flooded, and as it spread out over the wide, flat plain it deposited layers of sand and silt that geologists today call the Harrison Formation. The ancient Niobrara and other similar rivers spread the same sediments over nearby areas in eastern Wyoming and southwestern South Dakota. In the sediments, paleontologists would one day find millions of bones.

Our ancient river was the center of life for untold numbers of animals. They lived in it, along its banks, in the willow thickets that grew on its more permanent sandbars, and on the broad, tree-dotted plains that stretched to the horizon beyond the river’s normal course. Great herds of small horses, rhinoceroses, camels, and other dwellers on the savanna came to water holes to drink and perhaps to wallow in the cool and refreshing pools. Although all else might be anticlimactic, let’s look at the rhinoceroses first.

We know that in the modern world rhinos belong in Africa and southeastern Asia, not North America, yet this continent was the major home of these strange beasts for millions of years. Rhinos did not become extinct in North America until about 5 million years ago, during the Pliocene (see geologic time chart on page 46). 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.

Look off to the south. There’s a herd moving slowly but purposefully down to its favorite watering hole. You can see that the males have the paired nose horns, and that the females, which are about the same size, do not. Trotting amid the herd are fat little colts whose seriousness of purpose belies their youth. 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. Many of the adults go into deeper pools to roll and soak while the young drop their serious attitudes and frolic in the shallows.

As the day wears on, the herd leaves the river and feeds on the leaves and stems of scattered trees and willow thickets along the river. 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.

Oreodons were among the most abundant medium-sized animals of the Middle Tertiary. A strictly North American group, they have been described as looking like a cross between a sheep and a pig. As small as a house cat or as big as a domestic pig, these mammals reached a peak in abundance and variety between the Middle and Late Oligocene (though they are known from the Late Eocene through the Late Miocene). This peak probably has never been equalled by any other group of mammals in such a size range.

As we look out among the herds of animals dotting the plain, we can see only a few small bands of oreodons. There’s a group coming toward us now. These are some big, ugly ones with large triangular-shaped heads. The backs of their cheek bones flare out far to the sides, so that with their narrow snouts they are most peculiar looking. Their bodies are long and rather nondescript, and their legs are short but slender. This particular kind is known as _Promerycochoerus_ (“before ruminant hog”) and is just about the largest of the oreodons. They are really a rare sight here at Agate. Perhaps the large herds of _Menoceras_ fill their ecologic niche locally, and the oreodons have found they cannot successfully compete with the rhinos for food, water, and living space. After all, not everything can fit into Paradise.

Look to the northeast: there’s a herd of _Miohippus_ (“Miocene horse”) wading into the river to drink and browse in the willows along its banks. Let’s walk toward the herd slowly and quietly. We should take an especially good look at this herd—they are part of a doomed race! The genus _Miohippus_ is making its last stand at this time. When conditions change, well adapted species may restrict their ranges to what is left of the old environment; they may adapt, if they are able, to the new conditions; or they may not survive if they cannot adapt.

_Miohippus_ did all these things. Some species of the genus became extinct. Some evolved into something else. But the end result was the complete termination of the genus _Miohippus_ as paleontologists recognize it. Much of the environmental pressure coming to bear on the genus _Miohippus_ was a result of mountain building to the west. As the young Rockies rose, rain-bearing winds from the oceans far to the west were wrung of their moisture. This same circumstance makes the high plains a land of little rain today.

The scattered trees and groves we see from our vantage point of long ago will disappear and be replaced with a sea of drought-tolerant grasses. In effect, the savannas will give way to prairies. _Miohippus_ will soon be yielding its place to descendants which can eat grass as a steady diet. Grass is much harsher on the teeth than the foliage that _Miohippus_ eats. In eating grass, grazing animals pick up sand and silt enough to quickly wear away teeth designed for leaf-eating. The descendants of _Miohippus_ will become better runners, too, with longer and more powerful legs. As the trees disappear there will no longer be friendly clumps of greenery to hide behind when hungry meat-eaters are on the prowl. From now on, fleetness of foot will be a most important factor in horse survival.

_Miohippus_ will also give rise to somewhat larger forest horses that will survive on into the Pliocene in patches of woodland. They will be little changed except in size (some came to be nearly as large as the modern horse), and some of them will even cross the Bering Land Bridge into Eurasia. This is the last time, however, that we’ll see these primitive horses in large numbers here in North America.

There’s another herd of small horses moving across the plain toward the river from the south. These are feeding as they move across the savanna, eating both leaves from the scattered trees and grass from the prairie. They seem to be enjoying their mixed diet and thriving on it, so they won’t be too badly hurt in the geologically near future when they have to eat mostly grass. This is _Parahippus_ (“near horse”), a new kind of horse just recently evolved from _Miohippus_.

_Parahippus_ is a horse of destiny. 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. _Parahippus_ is the forerunner of a vast array of different three-toed, long-limbed prairie horses that will be the most numerous members of their family until nearly the end of the Pliocene. From one of their descendants will come the first one-toed horse—the direct ancestor of our modern horses.

More herds are moving in on the river as the morning grows. There’s a group of something very small moving through the tall grass, but it’s completely hidden. Only the swaying of the 60-centimeter-tall blades shows that a number of animals are hurrying toward the river. 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. We call them “deer” because they look just like miniature deer, but the two families are really only distantly related.

As this group scampers toward the river, we can see that they have a peculiar crouching gait—their forelegs are so much shorter than their hind legs that they seem to be running continuously downhill. They are dainty little animals with small, delicate heads and short, slender limbs. They can bound swiftly away if danger threatens, but they’d rather hide in the thick brush. A few of the females have fawns with them, tiny things less than 10 centimeters (4 inches) tall. Look at them all scatter! The shadow of a hawk has passed over the group, and in their fright they’ve dived for some nearby willows. Young _Nanotragulus_ either learn to duck down at the sight of a passing shadow or they don’t get a chance to learn at all. This time they all got away, and the hawk will have to look elsewhere for a meal.

Buteos or buzzard hawks are common along the Niobrara in the Early Miocene, sailing on the warm updrafts on broad, short wings that let them ride the lightest airs. 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. It’s a guan, a ground-living bird related to the grouse and sagehens. It must be far from home this morning; most of its time is spent in the thick brush farther back from the river. A heavy body and long neck and tail make this animal easy to identify.

Let’s look at some of the individuals and small groups that are moving or resting within view. The camels with the very slender legs and long necks are called _Oxydactylus_ (“sharp finger”). They are browsing on the willows where the herd of Nanotragulus ran to hide. _Oxydactylus_ is an important camel, standing about at the midpoint in the evolution of this North American family of mammals. The camels will remain stay-at-homes in the continent of their origin until they spread into Eurasia and South America at the beginning of the Pleistocene Epoch, some 17.5 million years after the rhinos died out at Agate. There are many species of _Oxydactylus_; the one we are looking at stands about 1.2 meters (4 feet) high at the shoulder. Notice that they don’t have humps on their backs; in this lush land there is no need to store fat against a time of possible starvation.

Speaking of camels, here comes a herd of _Stenomylus_ (“narrow tooth”) bounding through the tall grass on the south bank of the river. This is a strange little long-neck camel that strayed off the main line of the family’s evolution. Less than 60 centimeters (24 inches) high at the shoulder, it looks very much like the living African antelope called the gerenuk. _Stenomylus_, with its long and delicate legs and tall cheek-teeth, is perfectly adapted for living in and eating the abundant grass which billows on this tree-dotted plain. Yet many of the little _Stenomylus_ are going to share a tragic time with hundreds of _Menoceras_ only a year or so from this day we are visiting. Later, we’ll move ahead to that time so you can see that natural disaster, now preserved in rock, as it happened.

When you travel back 20 million years in time you would expect to find unbelievably bizarre animals. So far, we’ve seen some offbeat specimens, but there has been nothing really out of this world. Now, if you look to the north by the lone oak tree, you will see a real prize. Do you see that hulk stepping out of the shade? No, it isn’t the Dragon of the Ishtar Gate, though it might pass for a mythical beast. What a wonderful animal! A head like a large horse’s, a neck somewhat slimmer, long front legs, sloping back, short hind legs, and a little switch tail. Watch with your field glasses when it moves out onto the bare ground. See the feet? They don’t have hooves; each toe ends in a great curved claw! This is one of the fabulous chalicotheres, a relative of the horses and the rhinos. There were never very many of them living at one time, but the family lived in Eurasia from the Eocene, some 55 million years ago, through the Pleistocene; and here in North America from the Late Eocene to the Middle Miocene.

This chalicothere is named _Moropus_ (“sloth foot”), and it is little wonder that when paleontologists first discovered his foot bones (without an associated skull) they thought they had found the feet of a ground sloth. Let’s watch _Moropus_ as it ambles slowly across the plain, its strange stilted walk a little like that of the modern giraffe. Other animals move aside as _Moropus_ strides through the grass. He’s a browser, an occasional grass-eater, and even a digger of easily accessible roots and tubers. Like his cousins the rhinos, he isn’t at all bright, and he has a very short temper. When he’s annoyed, he kicks out with those claws and every animal with good sense leaves him alone. He’s respected by meat-eaters and plant-eaters alike. He walks by himself and everything else detours around him.

Look down toward the river, and we may see an exception. That two-meter (six-foot) high “pig” walking away from the river, covered with mud, is heading right toward the _Moropus_. His name is _Dinohyus_ (“terrible pig”), and he’s just as short-tempered and stupid as _Moropus_. He looks like a giant peccary, but his size and over-large head give him away as an entelodont (“complete tooth”). These are pig-like animals, usually of large size, that aren’t related to the domestic pigs at all. _Dinohyus’_ skull is nearly one meter (three feet) long, and those tusks are as thick as a man’s wrist. Though we missed seeing him earlier, he must have been wallowing in the mud under the overhanging willows. Now he’s heading away from the river in search of lunch. He’s not very choosy about what he eats; it might be succulent leaves or fruits, or even the carcass of a dead animal. _Dinohyus_ is an omnivore, eating almost anything that has nourishment.

Right now it looks as though he’s on a collision course with the _Moropus_. He’s seen the larger animal, has stopped in his tracks, and is pawing the ground with his front feet. Up goes his head—and listen to that roar! He’s getting a good temper worked up. Off he goes at a full gallop, right toward the _Moropus_. It’s hard to believe that an animal as big as that pig could charge so fast. And look at the _Moropus_! He’s finally realized in his dim way that he’s about to be attacked. Up he goes on his hind legs, holding his front legs out ready for a downward blow with all eight claws. But suddenly _Dinohyus_ shifts his course just slightly, lets out another loud bellow as he avoids the _Moropus_, and thunders off toward the open prairie.

_Dinohyus_ has a smaller relative around here somewhere, a little fellow just over one meter (three feet) high, called _Entelodon_. His head is long and low and has flaring cheekbones and bumps along the underside of the jaw like his larger cousin’s. Another pig that lives along the Niobrara is _Desmathyus_ (“bond [filling a gap] pig”), a true North American pig or peccary. Its appearance probably wouldn’t surprise anyone; it looks very much like the peccaries that live in the American Southwest today. Its distant cousin, the domestic pig, was domesticated in the Old World from a European species of wild hog, and it was spread throughout the world by European colonists. In America, peccary evolution has run a long and conservative path. This group has changed relatively little in the 35 million years since it first appeared in the Late Eocene.

Now for another weird and wonderful beast! Trotting daintily out of a thicket on our left is a herd of something you might think were deer or pronghorn. But if you look closely you’ll see that they have two pairs of curving, unbranched horns on their heads, not the single pair of prongs you’d expect on a pronghorn. These are _Syndyoceras_ (“together horn”), members of a family of mammals found only in North America and now extinct. Even on the Early Miocene day we’re visiting, they are scarce, moving only in small herds. The rear pair of horns is not remarkable, but the front ones, which rise from a large bump near the nose, curl up and away from each other, ending in blunt tips.

The first member of this family was _Protoceras_, which lived in the hills and mountains of western South Dakota during the Late Oligocene, just a few million years before the day we are visiting at Agate. Paleontologists have found battered scraps of its skeletons in the White River Badlands where perhaps they were washed by heavy spring rains running off the hills to the west. _Protoceras_ had six bony bumps on its head that presumably bore short horns; one pair was over the nose, another was over the eyes, and a third was near the back of the skull. Probably it was the direct ancestor of _Syndyoceras_.

If _Syndyoceras_ fails somehow to qualify as grotesque, let’s jump a few million years into the “future” and look at his Late Miocene descendant, _Synthetoceras_ (“combined horn”). Here was an animal on a par with unicorns and cyclopses. Like _Syndyoceras_ he had two tall horns at the back of his head; but something had happened to the curved ones on his nose. 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! Tie a rubber band to the tips of his nose horns, fill your pocket with pebbles, and saddle up.

You may be wondering by now about the smaller animals—the rodents and small carnivores. We have not seen any of them so far. Most carnivores work at night, but there should be a few about. Down by the river is a pair of _Oligobunis_ (“little cusp”) hunting near the water’s edge. They look something like modern badgers but are really more closely related to the weasels. If you look just to the right of the herd of _Stenomylus_ we were following earlier you might be able to catch a glimpse of a stalking cat about the size of a mountain lion. It’s probably either an advanced _Nimravus_ (“ancestral hunter”) or an early _Pseudaelurus_ (“false cat”), but we’ll have to get a closer look before we can be sure. Whichever it is, it’s on the main line of cat evolution and will eventually end up in our familiar _Felis_ and the other living cats. There should also be some sabretooth cats lurking about; they are found in nearby deposits of the same age, though not at Agate itself.

If you look very closely at the thicket just south of us on the hillside you can see several fox-like dogs hunting rodents. This _Nothocyon_ (“false dog”) seems to have filled approximately the fox niche during the Early Miocene. Some coyote and wolf-sized dogs are in the area too. _Daphoenodon_ (“blood-reeking tooth”) is about coyote size. _Temnocyon_ (“cutting [tooth] dog”), is a little larger, probably substituted for the wolf in the local fauna, and is characterized by its heavy head and long, strong jaws. If we could get a close look at its teeth, we would see that they are like those of the Cape Hunting Dog living today in South Africa.

Let’s move away from the river a half-kilometer (0.3 mile) or so and see if we can find something different. That thicket ahead might produce a couple of rabbits. Look, there at the edge of the thicket: a _Nothocyon_ has caught something. It’s a _Meniscomys_ (“crescent mouse”), an early relative of the living mountain beaver _Aplodontia_. Today, a single species of _Aplodontia_, the last of the line, is found only in the mountains of the West Coast. It’s the most primitive living rodent, not related to the Canadian beaver, and sole survivor of a suborder which was the earliest rodent group to evolve. _Meniscomys_ was one of the most prominent members of the group during the Miocene. It had a round furry body, a round head with protruding incisors a bit like a true beaver’s, and no visible tail.

Watch your step. There is the mound of a pocket gopher. It is neither our familiar western gopher _Thomomys_ (“heap mouse”) or the “eastern” pocket gopher of the Great Plains, _Geomys_ (“earth mouse”), but an ancient relative, _Gregorymys_ (“Gregory’s mouse”). It must be pretty successful as a burrowing animal, because we find it all over the western United States in the Early Miocene.

A hundred meters (300 feet) more and we’ll show you the surprise of the day. Here we are in what looks like a prairie dog town. But those aren’t prairie dogs. They’re a little larger, and quite unfamiliar by modern standards. Can’t guess what they are? These are beavers—_Palaeocastor_ (“ancient beaver”) to be exact. Here in the Early Miocene of North America, beavers don’t build dams. In fact they live neither at the water’s edge nor, like muskrats, in the water. They dig deep, spiral burrows in well drained ground. Some of their burrows are 2.5 meters (8 feet) deep, but 2 meters (6.5 feet) is about average. Down and around and around the burrows go, like giant corkscrews, always ending in straight shafts slanting slightly upward so that living chambers will not be flooded by rainwater running down the burrows.

Paleontologists have called the preserved burrows “devil’s corkscrews”—_Daemonelix_—since the time they were first found. At first, scientists thought they might be holes left by the giant tap roots of some unknown plant. But when _Palaeocastor_ skeletons were found in the bottoms of the spirals, almost everyone had to concede that they were truly beaver burrows. Admittedly, the skeleton of a _Nothocyon_ was found in one burrow; but this predator probably followed a beaver home for supper and just stayed. Three other kinds of beavers lived around Agate in the Early Miocene, but their bones have never been found in the burrows. No one knows what they did for homes: perhaps their burrows were much shallower or were in the river banks where running water soon destroyed them.

Near the river bank in some soft sand is a nest of tortoise eggs. The hot sun has brought the babies out of their shells and they’re stumbling off in all directions. Right now the biggest is only about twice the size of a silver dollar; but when they’re grown they’ll be about 60 centimeters (24 inches) across the shell, or perhaps even larger. They’re strict vegetarians, grazing and browsing on soft plants and leaves. There are probably some pond turtles around too, but we’ve never seen any.

A little farther up the bank, under the roots of that big walnut tree, is a rabbit’s burrow. Several _Palaeolagus_ (“ancient rabbit”) live there with their many offspring. Although they look very much like cottontails, their ears are smaller and they haven’t the same leaping and running ability. 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.

Today, advances in paleontology still depend primarily upon major field discoveries, but paleontologists also make use of highly refined analytical and measurement techniques. 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.

The Mark of Death Upon the Land

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. Those rivers flowed toward the central lowlands of North America, once an embayment of the Gulf of Mexico. This Mississippi Embayment, as it is called by geologists, extended as far north as the present location of Cairo, Illinois.

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)

Cenozoic Quaternary Pleistocene 10,000 to 2 million
Tertiary Pliocene 2 to 5 million
Miocene 5 to 23 million
Oligocene 23 to 34 million
Eocene 34 to 55 million
Paleocene 55 to 65 million
Mesozoic Cretaceous 65 to 138 million
Jurassic 138 to 205 million
Triassic 205 to 240 million
Paleozoic Permian 240 to 290 million
Carboniferous 290 to 365 million
Devonian 365 to 410 million
Silurian 410 to 435 million
Ordovician 435 to 500 million
Cambrian 500 to 570 million
Precambrian 570 to 4,500+ million

The Geologic History of Agate