The Project Gutenberg eBook ofAgate Fossil Beds National Monument, Nebraska

The Project Gutenberg eBook ofAgate Fossil Beds National Monument, NebraskaThis ebook is for the use of anyone anywhere in the United States and most other parts of the world at no cost and with almost no restrictions whatsoever. You may copy it, give it away or re-use it under the terms of the Project Gutenberg License included with this ebook or online atwww.gutenberg.org. If you are not located in the United States, you will have to check the laws of the country where you are located before using this eBook.Title: Agate Fossil Beds National Monument, NebraskaAuthor: United States. National Park ServiceRelease date: January 4, 2018 [eBook #56303]Most recently updated: October 23, 2024Language: EnglishCredits: Produced by Stephen Hutcheson and the Online DistributedProofreading Team at http://www.pgdp.net*** START OF THE PROJECT GUTENBERG EBOOK AGATE FOSSIL BEDS NATIONAL MONUMENT, NEBRASKA ***

This ebook is for the use of anyone anywhere in the United States and most other parts of the world at no cost and with almost no restrictions whatsoever. You may copy it, give it away or re-use it under the terms of the Project Gutenberg License included with this ebook or online atwww.gutenberg.org. If you are not located in the United States, you will have to check the laws of the country where you are located before using this eBook.

Title: Agate Fossil Beds National Monument, NebraskaAuthor: United States. National Park ServiceRelease date: January 4, 2018 [eBook #56303]Most recently updated: October 23, 2024Language: EnglishCredits: Produced by Stephen Hutcheson and the Online DistributedProofreading Team at http://www.pgdp.net

Title: Agate Fossil Beds National Monument, Nebraska

Author: United States. National Park Service

Release date: January 4, 2018 [eBook #56303]Most recently updated: October 23, 2024

Language: English

Credits: Produced by Stephen Hutcheson and the Online DistributedProofreading Team at http://www.pgdp.net

*** START OF THE PROJECT GUTENBERG EBOOK AGATE FOSSIL BEDS NATIONAL MONUMENT, NEBRASKA ***

Agate Fossil BedsAgate Fossil Beds National MonumentNebraskaProduced by theDivision of PublicationsHarpers Ferry CenterNational Park ServiceU.S. Department of the InteriorWashington, D.C.

Agate Fossil Beds National MonumentNebraska

Produced by theDivision of PublicationsHarpers Ferry CenterNational Park Service

U.S. Department of the InteriorWashington, D.C.

National Park Handbooks, compact introductions to the great natural and historic places administered by the National Park Service, are designed to promote understanding and enjoyment of the parks. Each is intended to be informative reading and a useful guide before, during, and after a park visit. More than 100 titles are in print. This is Handbook 107. You may purchase the handbooks through the mail by writing to Superintendent of Documents, U.S. Government Printing Office, Washington DC 20402.

What was life like in North America 20 million years ago? Agate Fossil Beds provides a glimpse of that time, long before the arrival of man, when now-extinct creatures roamed the land which we know today as Nebraska.Part 1of this handbook introduces you to the park;Part 2brings life to the fossil specimens and examines the areaâ€™s geological and ecological evidence; andPart 3presents concise guide and reference information.

James H. Cook examines a fossil fragment at the quarries near Agate Springs Ranch about 1918.

Besides fossils, Cook also collected Indian artifacts and kept many of them on the walls of his study in the ranch house.

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, travelerâ€”to one and all, rich or poor.

A movie script? Not at allâ€”these are the essentials of the life of James H. Cook. Known as â€œCaptain,â€ James Cook became the owner, in 1887, of the Agate Springs Ranch, founded earlier by his father-in-law. Under Cookâ€™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 grassesâ€”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.

Professor Othniel C. Marsh, back row center, of Yale University and his students look as if they are equipped for a frontier hunting expedition. But instead of looking for live animals in the West, they were hunting for fossilized remains of ancient beasts. Marsh and his crews made many such trips, and it was on one early trip that Cook and Marsh met, in Sioux country.

Professor Marsh and the great Sioux chief Red Cloud greet each other in New Haven in 1880.

Professor Edward Drinker Cope competed with Marsh for the best fossils. He once made the mistake of reconstructing a skeleton hind end foremost; Marsh never let him forget it.

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 â€œdistanceâ€ 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, Wyomingâ€”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 Grahamâ€™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 â€œprove upâ€ 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 throughthe 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 Cookâ€™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 â€œa beautifully petrified piece of the shaft of some creatureâ€™s leg bone.â€ They carried it back to the house but didnâ€™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 Cooksâ€™ 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.

University Hill, left, and Carnegie Hill dominate the Niobrara River Valley. The hills received their names from the paleontological teams that worked them from the University of Nebraska and the Carnegie Museum.

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 â€œstone bonesâ€ 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.

An upland sandpiper, one of many birds that can be seen at Agate Fossil Beds, perches on a fence post.

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 menâ€™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 rhinocerosMenoceras, but the site also is known for fossils of the gazelle-like camelStenomylus, the early small horseMiohippus, 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 Cookâ€™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 Cookâ€™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.

Next to the fence stands a windmill, which once provided water for excavation teams.

The narrow Niobrara River winds through the surrounding tableland, carving out bluffs and exposing occasional fossils.

In time the Cooksâ€™ 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, inPart 2of 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.

Text: James R. and Laurie J. MacdonaldIllustrations: Jay H. Matternes

This mural depicts life in the Agate Fossil Beds area in the early Miocene Epoch, about 20 million years ago when the story on the following pages takes place. The painting is a composite of life at that time; if you had been there then, you would not have been able to see all of these forms of life together at any given moment! The original mural hangs in the fossil halls at the Smithsonian Institutionâ€™s National Museum of Natural History in Washington, D.C.

Key to mural

Come enter into our imaginations and return to a day along the Niobrara River in western Nebraska 20 million years ago. Letâ€™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 weâ€™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 isnâ€™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 treesâ€”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 â€œRunning Water,â€ 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 riverâ€™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, letâ€™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 onpage 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 hornsâ€”not one behind the other, but a pair near the end of the nose, side by side. To scientists today these rhinos are known asMenoceras. The nameDiceratherium, 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. Thereâ€™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. Manyof 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. Thereâ€™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 asPromerycochoerus(â€œbefore ruminant hogâ€) and is just about the largest of the oreodons. They are really a rare sight here at Agate. Perhaps the large herds ofMenocerasfill 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.

Promerycochoerus

Look to the northeast: thereâ€™s a herd ofMiohippus(â€œMiocene horseâ€) wading into the river to drink and browse in the willows along its banks. Letâ€™s walktoward the herd slowly and quietly. We should take an especially good look at this herdâ€”they are part of a doomed race! The genusMiohippusis 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.

Miohippusdid 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 genusMiohippusas paleontologists recognize it. Much of the environmental pressure coming to bear on the genusMiohippuswas 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.Miohippuswill 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 thatMiohippuseats. In eating grass, grazing animals pick up sand and silt enough to quickly wear away teeth designed for leaf-eating. The descendants ofMiohippuswill 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.

Miohippuswill 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 weâ€™ll see these primitive horses in large numbers here in North America.

Thereâ€™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 grassfrom the prairie. They seem to be enjoying their mixed diet and thriving on it, so they wonâ€™t be too badly hurt in the geologically near future when they have to eat mostly grass. This isParahippus(â€œnear horseâ€), a new kind of horse just recently evolved fromMiohippus.

Parahippus

Parahippusis a horse of destiny. For a long time some individuals ofMiohippuscarried a little extra wrinkle of enamel on the crowns of their upper grinding teethâ€”and now the wrinkle occurs in all individuals ofParahippus. Because of it,Parahippuscan 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. Itâ€™s only a small advantage, but such is the stuff that survival and evolution are made of.Parahippusis 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 horseâ€”the direct ancestor of our modern horses.

More herds are moving in on the river as the morning grows. Thereâ€™s a group of something very small moving through the tall grass, but itâ€™s completely hidden. Only the swaying of the 60-centimeter-tall blades shows that a number of animals are hurrying toward the river. Now theyâ€™ve moved out into an area of cropped grass, and we can see a herd of the diminutive deerlikeNanotragulus(â€œdwarf goatâ€). Not a great deal larger than a house cat, these little â€œdeerâ€ 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 â€œdeerâ€ 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 gaitâ€”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 swiftlyaway if danger threatens, but theyâ€™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 theyâ€™ve dived for some nearby willows. YoungNanotraguluseither learn to duck down at the sight of a passing shadow or they donâ€™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 â€œdeerâ€ and sometimes careless birds that live on this savanna. All manner of meat-eaters depend on the small animals for food, and the littleNanotragulusare most vulnerable as they move through the canopy of grass.

There donâ€™t seem to be any other herds moving into view just now; but while weâ€™re on the subject of birds, over there in that patch of short grass is a bird rarely seen in North America anymore. Itâ€™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.

Oxydactylus

Letâ€™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 calledOxydactylus(â€œsharp fingerâ€). They are browsing on the willows where the herd of Nanotragulus ran to hide.Oxydactylusis 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 ofOxydactylus; the one we are looking at stands about 1.2 meters (4 feet) high at the shoulder. Notice that they donâ€™t have humps on their backs; in this lush land there is no need to store fat against a time of possible starvation.

Stenomylus

Speaking of camels, here comes a herd ofStenomylus(â€œnarrow toothâ€) 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 familyâ€™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 littleStenomylusare going to share a tragic time with hundreds ofMenocerasonly a year or so from this day we are visiting. Later, weâ€™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, weâ€™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 isnâ€™t the Dragon of the Ishtar Gate, though it might pass for a mythical beast. What a wonderful animal! A head like a large horseâ€™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 donâ€™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.

Moropus

This chalicothere is namedMoropus(â€œsloth footâ€), 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. Letâ€™s watchMoropusas it ambles slowly across the plain, its strange stilted walk a little like that of the modern giraffe. Other animals move aside asMoropusstrides through the grass. Heâ€™s a browser, an occasional grass-eater, and even a digger of easily accessible roots and tubers. Like his cousins the rhinos, he isnâ€™t at all bright, and he has a veryshort temper. When heâ€™s annoyed, he kicks out with those claws and every animal with good sense leaves him alone. Heâ€™s respected by meat-eaters and plant-eaters alike. He walks by himself and everything else detours around him.

Dinohyus

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

Right now it looks as though heâ€™s on a collision course with theMoropus. Heâ€™s seen the larger animal, has stopped in his tracks, and is pawing the ground with his front feet. Up goes his headâ€”and listen to that roar! Heâ€™s getting a good temper worked up. Off he goes at a full gallop, right toward theMoropus. Itâ€™s hard to believe that an animal as big as that pig could charge so fast. And look at theMoropus! Heâ€™s finally realized in his dim way that heâ€™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 suddenlyDinohyusshifts his course just slightly, lets out another loud bellow as he avoids theMoropus, and thunders off toward the open prairie.

Dinohyushas a smaller relative around here somewhere, a little fellow just over one meter (three feet) high, calledEntelodon. His head is long and low and has flaring cheekbones and bumps along the underside of the jaw like his larger cousinâ€™s. Another pig that lives along the Niobrara isDesmathyus(â€œbond [filling a gap] pigâ€), a true North American pig or peccary. Its appearance probably wouldnâ€™t surpriseanyone; 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.

Syndyoceras

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 youâ€™ll see that they have two pairs of curving, unbranched horns on their heads, not the single pair of prongs youâ€™d expect on a pronghorn. These areSyndyoceras(â€œtogether hornâ€), members of a family of mammals found only in North America and now extinct. Even on the Early Miocene day weâ€™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 wasProtoceras, 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.Protocerashad 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 ofSyndyoceras.

IfSyndyocerasfails somehow to qualify as grotesque, letâ€™s jump a few million years into the â€œfutureâ€ and look at his Late Miocene descendant,Synthetoceras(â€œcombined hornâ€). Here was an animal on a par with unicorns and cyclopses. LikeSyndyocerashe 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 worldâ€™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 animalsâ€”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 ofOligobunis(â€œlittle cuspâ€) hunting near the waterâ€™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 ofStenomyluswe were following earlier you might be able to catch a glimpse of a stalking cat about the size of a mountain lion. Itâ€™s probably either an advancedNimravus(â€œancestral hunterâ€) or an earlyPseudaelurus(â€œfalse catâ€), but weâ€™ll have to get a closer look before we can be sure. Whichever it is, itâ€™s on the main line of cat evolution and will eventually end up in our familiarFelisand 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.

Daphoenodon

If you look very closely at the thicket just south of us on the hillside you can see several fox-like dogs hunting rodents. ThisNothocyon(â€œfalse dogâ€) seems to have filled approximately the fox niche during the Early Miocene. Some coyote and wolf-sized dogs are in the area too.Daphoenodon(â€œblood-reeking toothâ€) is about coyote size.Temnocyon(â€œcutting [tooth] dogâ€), 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.

Letâ€™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: aNothocyonhas caught something. Itâ€™s aMeniscomys(â€œcrescent mouseâ€), an early relative of the living mountain beaverAplodontia. Today, a single species ofAplodontia, the last of the line, is found only in the mountains of the West Coast. Itâ€™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.Meniscomyswas one of the most prominent members of the groupduring the Miocene. It had a round furry body, a round head with protruding incisors a bit like a true beaverâ€™s, and no visible tail.

Watch your step. There is the mound of a pocket gopher. It is neither our familiar western gopherThomomys(â€œheap mouseâ€) or the â€œeasternâ€ pocket gopher of the Great Plains,Geomys(â€œearth mouseâ€), but an ancient relative,Gregorymys(â€œGregoryâ€™s mouseâ€). It must be pretty successful as a burrowing animal, because we find it all over the western United States in the Early Miocene.

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