Part 2

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.