Evolutionary Change

In western Nebraska the savanna environment lasted for only a very short time, in a geologic sense, before it gave way to a wave of advancing grasslands, the third phase of Tertiary environment in the area. Tallgrass prairie such as that still found 325 kilometers (200 miles) east of Agate a century ago must have been first among the grassland types. Trees, when present at all, were restricted to the borders of streams. Then as the climate became even more arid the prairie or tall grass retreated eastward, while the forest moved before it even farther to the east and south, and the modern shortgrass of the plains took its place. Today Agate lies in one of the valleys whose rivers are slowly dissecting the High Plains.

The modern plains are dominated by short, curly, sodforming buffalo grass, a plant well adapted to the area’s light rainfall, periodic droughts, low humidity, rapid evaporation, and high winds. The dominant vertebrate animals are burrowers and grazers, and dogs are the primary carnivores. Hoofed animals such as the pronghorn, the ultimate in the running and bounding adaptation; jumpers and hoppers, such as jackrabbits and jumping mice and rats; and burrowing mound builders, such as the prairie dog (a large ground squirrel), the pocket gopher, and harvester ants typify the major occupations of plains animals.

The environmental type seen on the Great Plains of North America is elsewhere best developed in the Pampas of Argentina, the Puztas of Hungary, the Veld of Africa, and the Steppes of Russia. In the climatic classification of the climatologist and geographer, the termsteppe climateis applied to all these areas, the Great Plains included.

If the savanna is the halfway station between forests and grasslands, then the fossil fauna of the Early Miocene at Agate was a fauna in the beginning of a serious transition. In the vicinity of Agate, the fauna from the Late Oligocene was dominated by mammals with low-crowned teeth. The crown is that part of the tooth which is above the roots and exposed beyond the gums. Among the herbivores, thebrowsers can live a long life with low-crowned teeth. But when any appreciable amount of grass, particularly the short, tough grass of the plains and the abrasive dirt and sand that accompanies it, becomes part of an herbivore’s diet, there is a great increase in the rate of tooth wear. Teeth which have evolved for browsing quickly wear down to the gums and the individual dies of starvation.

Accompanying the development of extensive grasslands came the evolution of the high-crowned tooth. This process begins simply with the growth of a taller crown that erupts completely from the gum right after the milk or deciduous teeth fall out. Another step is the development of a longer or higher crown most of which is held in the jaw and then slowly pushed out as the chewing surface is worn down. This is the “mechanical pencil” effect in that the “lead” may be pushed out as needed. Teeth of this type are perhaps best seen in the later horses. From their appearance in the Late Paleocene until the end of the Early Miocene, all horses had low-crowned teeth. With these they could chew the soft leaves and twigs of trees and shrubs, first in the forests and later in the groves and clumps on the developing savanna. By Early Miocene (i.e., Harrison) times, there was only a slight increase in crown height inParahippus, but it had evolved an increasingly complicated crown pattern which served to lengthen the time it took for the tooth surface to wear down flat. With the greater aridity of the changing climate, the teeth ofParahippusbecame higher and higher crowned, as the individuals with the best teeth lived longest and had greater opportunity to produce offspring than those with lower-crowned teeth. In some species, the tooth material called cement, which ordinarily covers the roots of the teeth, began also to cover the enamel of the crown and give additional wearing strength to the teeth. Soon after the beginning of the Middle Miocene, two species had developed cement-covered teeth whose crowns were high enough to warrant placing them into two new genera of horses,MerychippusandProtohippus. These forms, first recognized in the Lower Sheep Creek Beds in the Agate area, were the first horses to use the mechanical-pencil effect, having cheek teeth that continued to rise out of the jaw as the tooth was worn down.Merychippuslatergave rise to a line of three-toed horses, which lived on into the Pliocene;Protohippusgave rise to a line which ultimately led toEquus, the modern horse.

The ultimate in high-crowned teeth occurs when roots do not ever form at the base of the tooth; additional crown material is constantly added at the bottom of the tooth as it is pushed out of the gum. This type of growth resembles the foundry process of extrusion, where metal or plastic is pushed through a mold to produce a continuous strand. This extreme development is seen in the incisors or gnawing teeth of beavers, gophers, and other Late Oligocene rodents, and in the grinding teeth of only a few forms. The cheek teeth (the grinders) of modern pronghorns (artiodactyls), gophers (rodents), and rabbits (lagomorphs) are typical of this kind of development today. During the Middle Oligocene, only the strange little fox terrier-sized, flat-headed oreodonLeptauchenia, the tiny “deer”Hypisodus, and the rabbitPalaeolagushad mechanical pencil-type teeth. Some of the rhinos then had fairly tall crowns, but these don’t really qualify as high-crowned teeth. It was not until later on, when the grasslands took over completely, that high-crowned teeth really came into their own.

There was no dramatic change in the fauna at the beginning of the Miocene, and many Oligocene genera carried over into the new epoch. Most of the Eocene hold-overs, primitive animals that had survived in the extensive forests, became extinct when the forests began to retreat; but for the most part the record continued undisturbed. This is to be expected where the deposition of sediments continues without interruption. (Remember that the epochs, periods, and eras were originally based on breaks in the European sedimentary record reflecting local events which would not necessarily show up in North America’s sediments.)

By the time the Harrison Formation was deposited, the development of the halfway world of the savanna was beginning to affect the fauna. Although the Oligocene and the very earliest Miocene mammal faunas were highly varied and rich in types of animals, much of this was due to the continued presence of primitive and archaic forms, and to the explosive development of rhinos and oreodons. With the savanna becoming the dominant landscape, the shift to grazing and away from browsing became evident. Or, at least, the presence of animals that both browsed and grazed was indicative of changing times. As was mentioned earlier, grazing and burrowing are characteristics of plains herbivores. In such a transitional period we would expect to find an increase in burrowers and grazers as grasslands became more common.

Animal species respond to environmental changes in a variety of ways. Simply put, some species die off, some adapt physically, and some move to a different habitat. On the next few pages are examples showing how three species responded to long-term environmental changes in the area around Agate Fossil Beds. TheStenomylusline died off;Miohippus’evolutionary line remained a grazing animal but changed physically over the years, eventually becoming the modern horse; and thePalaeocastorline moved from land to water, gradually evolving into the beaver.Each of these three animals is portrayed here with partial skeleton, musculature, and outer skin to help you see its general composition and to emphasize certain physical features that developed in the species over time. Paleontologists, of course, work this way. From fragments and bones they reconstruct full skeletons, and from surmises about muscular structure, often based on present-day animals, they project the appearance of the animal. The artist, in this case Jay Matternes, then brings together these bits of evidence to give us a picture of life long ago.StenomylusStenomylusA small, gazelle-like camel similar to the present-day gerenuk of Africa.Stenomylusis the second most common animal found in the fossil beds at Agate.Stenomylushad hard hooves like modern antelopes and deer, unlike modern camels which have flesh-padded feet adapted to desert terrain. The three-hued coat is inferred from the coat of the modern gazelle, a similar form in adaptation.Stenomylus’evolutionary line eventually died out in North America at the end of the Pleistocene. No one knows why both camels and horses died out on this continent.The distance between grid lines represents five centimeters.1The ears moved in a parallel fashion, not independently; the parallel movement is inferred from modern llamoids, to whichStenomylusis related.2Stenomylus’musculature was adapted for high-speed running, similar to the present-day pronghorn.3The back structure suggests thatStenomyluswould have made short, choppy leaps, not the graceful, arcing leaps of a modern impala.4Limbs were long in proportion to the body, allowing the animal to run with great speed.5Stenomylushad a hard, chitinous hoof, an adaptation for greater running speed, and for sure footing on rough terrain.MiohippusMiohippusOver the last 60 million years the horses have evolved from small, terrier-sized animals to the diversity of size we know today, from the huge Clydesdales to the diminutive Shetland ponies. The three-toed early horse known asMiohippuswas about the size of a sheep. The descendants ofMiohippusapparently went in two directions in their evolution: One group continued to be forest-grazing, three-toed horses that eventually reached the size of modern horses but died out later. The other group, through such intermediate forms asParahippus, became grassland forms that led eventually to the modern one-toed horses. Horses became extinct in North America at the end of the Pleistocene, but no one knows why. They continued to evolve on other continents and were re-introduced in historic times.The distance between grid lines represents five centimeters.1The back was straighter and stiffer than in earlier horses, partly because of the increasing size of the animals and partly to allow sustained open-plains running.2Limbs were long in proportion to the body, an evolutionary trend in the horses for speed in open-plains running, rather than darting about in forests.3Most of the weight of the animal was on the middle toe, which has become a single toe in modern horses. This is an adaptation for endurance and stability in open grasslands.4The upright mane is a primitive horse characteristic; wild horses today have reverted to this trait.5The coat is shown as striped, a probable holdover from earlier horses that dwelled in forests, where a striped coat would provide camouflage.6A large, deep mandible supported teeth adapted to grazing and the grinding of grasses and other wild plants. The teeth were deep-rooted and continuously erupted as the surface was worn down by the grit and dirt that came with the large quantities of plant food consumed daily.PalaeocastorPalaeocastorPalaeocastorwas an ancient beaver whose mode of life was like that of a modern prairie dog—land-oriented instead of water-oriented.Palaeocastorwas small, about 12 centimeters (5 inches) high, and about 30 centimeters (12 inches) long. Its fossilized spiral burrows, calledDaemonelix, survive to tell us what its habitation was like, a feature unique toPalaeocastoramong all the fossil beavers. TheDaemonelixshown here dwarfs a member of Olaf A. Peterson’s field crew from the Carnegie Museum. The bones of aPalaeocastorand one of its predators were found at the bottom of one such burrow, helping to prove thatPalaeocastorwas responsible for making these corkscrew holes in the ground.The distance between grid lines represents five centimeters.1The powerful jaw and musculature allowed for grazing on grasses and other plants, as well as masticating. The teeth were deep-rooted and would continue to erupt as the surface was worn down.2The complex musculature supported the use of the forelimbs in burrowing.Palaeocastorhad a collarbone or clavicle, like us, for greater agility in using the forelimbs.3The forelimbs were adapted to burrowing in the ground.4The tail is like that of a modern burrowing rodent, such as a muskrat, whereas the modern beaver has a different, very specialized tail.Daemonelix

Each of these three animals is portrayed here with partial skeleton, musculature, and outer skin to help you see its general composition and to emphasize certain physical features that developed in the species over time. Paleontologists, of course, work this way. From fragments and bones they reconstruct full skeletons, and from surmises about muscular structure, often based on present-day animals, they project the appearance of the animal. The artist, in this case Jay Matternes, then brings together these bits of evidence to give us a picture of life long ago.

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

The distance between grid lines represents five centimeters.

1The ears moved in a parallel fashion, not independently; the parallel movement is inferred from modern llamoids, to whichStenomylusis related.2Stenomylus’musculature was adapted for high-speed running, similar to the present-day pronghorn.3The back structure suggests thatStenomyluswould have made short, choppy leaps, not the graceful, arcing leaps of a modern impala.4Limbs were long in proportion to the body, allowing the animal to run with great speed.5Stenomylushad a hard, chitinous hoof, an adaptation for greater running speed, and for sure footing on rough terrain.

1The ears moved in a parallel fashion, not independently; the parallel movement is inferred from modern llamoids, to whichStenomylusis related.

2Stenomylus’musculature was adapted for high-speed running, similar to the present-day pronghorn.

3The back structure suggests thatStenomyluswould have made short, choppy leaps, not the graceful, arcing leaps of a modern impala.

4Limbs were long in proportion to the body, allowing the animal to run with great speed.

5Stenomylushad a hard, chitinous hoof, an adaptation for greater running speed, and for sure footing on rough terrain.

Over the last 60 million years the horses have evolved from small, terrier-sized animals to the diversity of size we know today, from the huge Clydesdales to the diminutive Shetland ponies. The three-toed early horse known asMiohippuswas about the size of a sheep. The descendants ofMiohippusapparently went in two directions in their evolution: One group continued to be forest-grazing, three-toed horses that eventually reached the size of modern horses but died out later. The other group, through such intermediate forms asParahippus, became grassland forms that led eventually to the modern one-toed horses. Horses became extinct in North America at the end of the Pleistocene, but no one knows why. They continued to evolve on other continents and were re-introduced in historic times.

The distance between grid lines represents five centimeters.

1The back was straighter and stiffer than in earlier horses, partly because of the increasing size of the animals and partly to allow sustained open-plains running.2Limbs were long in proportion to the body, an evolutionary trend in the horses for speed in open-plains running, rather than darting about in forests.3Most of the weight of the animal was on the middle toe, which has become a single toe in modern horses. This is an adaptation for endurance and stability in open grasslands.4The upright mane is a primitive horse characteristic; wild horses today have reverted to this trait.5The coat is shown as striped, a probable holdover from earlier horses that dwelled in forests, where a striped coat would provide camouflage.6A large, deep mandible supported teeth adapted to grazing and the grinding of grasses and other wild plants. The teeth were deep-rooted and continuously erupted as the surface was worn down by the grit and dirt that came with the large quantities of plant food consumed daily.

1The back was straighter and stiffer than in earlier horses, partly because of the increasing size of the animals and partly to allow sustained open-plains running.

2Limbs were long in proportion to the body, an evolutionary trend in the horses for speed in open-plains running, rather than darting about in forests.

3Most of the weight of the animal was on the middle toe, which has become a single toe in modern horses. This is an adaptation for endurance and stability in open grasslands.

4The upright mane is a primitive horse characteristic; wild horses today have reverted to this trait.

5The coat is shown as striped, a probable holdover from earlier horses that dwelled in forests, where a striped coat would provide camouflage.

6A large, deep mandible supported teeth adapted to grazing and the grinding of grasses and other wild plants. The teeth were deep-rooted and continuously erupted as the surface was worn down by the grit and dirt that came with the large quantities of plant food consumed daily.

Palaeocastorwas an ancient beaver whose mode of life was like that of a modern prairie dog—land-oriented instead of water-oriented.Palaeocastorwas small, about 12 centimeters (5 inches) high, and about 30 centimeters (12 inches) long. Its fossilized spiral burrows, calledDaemonelix, survive to tell us what its habitation was like, a feature unique toPalaeocastoramong all the fossil beavers. TheDaemonelixshown here dwarfs a member of Olaf A. Peterson’s field crew from the Carnegie Museum. The bones of aPalaeocastorand one of its predators were found at the bottom of one such burrow, helping to prove thatPalaeocastorwas responsible for making these corkscrew holes in the ground.

The distance between grid lines represents five centimeters.

1The powerful jaw and musculature allowed for grazing on grasses and other plants, as well as masticating. The teeth were deep-rooted and would continue to erupt as the surface was worn down.2The complex musculature supported the use of the forelimbs in burrowing.Palaeocastorhad a collarbone or clavicle, like us, for greater agility in using the forelimbs.3The forelimbs were adapted to burrowing in the ground.4The tail is like that of a modern burrowing rodent, such as a muskrat, whereas the modern beaver has a different, very specialized tail.

1The powerful jaw and musculature allowed for grazing on grasses and other plants, as well as masticating. The teeth were deep-rooted and would continue to erupt as the surface was worn down.

2The complex musculature supported the use of the forelimbs in burrowing.Palaeocastorhad a collarbone or clavicle, like us, for greater agility in using the forelimbs.

3The forelimbs were adapted to burrowing in the ground.

4The tail is like that of a modern burrowing rodent, such as a muskrat, whereas the modern beaver has a different, very specialized tail.

Daemonelix

A grazing animal is fairly easy to recognize, but how can we recognize a burrower? Some have radically adapted limbs and claws. Obvious cases are the common garden mole and the armadillo. The mole has powerful attachments for the muscles of the upper arm on the humerus, a bone so flattened that its width has come to match its length. Moles also have long, broad digging claws. The armadillo, which is also a digger but not a burrower in the same way a mole or a gopher is, has large curved claws for digging. Moles did start to become quite common in the Late Oligocene, so we can assume that a good burrowing environment was present.

Another group which became extraordinarily common in the Late Oligocene of western North America was that of the ancestral pocket gopher. Direct proof that this group actually burrowed does not exist, but the abundance of fossil gophers suggests that they might have lived underground in colonies.

A real surprise at Agate is the number of beaver burrows. The famousDaemonelixor “devil’s corkscrew” attests to the dense population ofPalaeocastor. By that relatively advanced stage of beaver evolution, the animals might be expected to behave like the modern-day muskrat, perhaps digging dens along stream borders and spending some of their time in the water. The presence of skeletons in the spiral burrows, however, indicates thatPalaeocastorwas primarily a burrower, one which perhaps lived very much like our present-day prairie dog. Despite that, there is no apparent structural modification to indicate burrowing abilities.

Changing environmental conditions were pushingPalaeocastortoward extinction in the Early Miocene. The disappearance of that ancient beaver, while not unusual, presents a problem for the careless observer who might assume that ancient animals behaved like their modern counterparts. The burrowing beaversof Miocene Agate certainly have no modern counterparts.

While we can delineate in a general way the prehistoric life of Agate, we can’t describe the past in any detail. Plants most directly reflect the effects of climate—and plant fossils are absent at Agate. As the base of the food chain, plants carry the influences of climate on to the plant-eating animals. From the numerous animal fossils found at Agate we have learned most of what is known about the environment of that time. Sediments tell a good part of the story, and floras from other localities help, but much of Agate’s ancient ecology must be inferred from the bones.

Today, standing on the porch of the visitor center or walking along the path to University and Carnegie Hills, visitors find themselves in the midst of the shortgrass prairie. Five distinctive plant communities share this prairie, coexisting in a dynamic relationship which depends upon local climate variations.

Even to the untrained eye, it is evident that the basic short-grass pattern has been modified by the shape of the land and by the Niobrara River. In the stream valley, along the tributaries, and on shaded north-facing slopes, the shortgrass community is mixed with taller grasses. If a dry cycle began, the short grasses would take over the whole area by migrating downslope from the exposed prairies. Of interest is the fact that over-grazing by either domesticated or wild animals will have the same effect as a dry period in that taller grasses will be replaced by short ones.

Let’s examine the five communities present today so we can appreciate the complexity of relationships between living things and the earth upon which they depend.

First, we can begin in the Niobrara River itself. The river’s water-dwelling plant inhabitants include algae, which grow underwater.

Between the river and the dry ground is a second community—the marsh—which is often more wet than dry. The marsh has its own characteristic plant association. Most familiar are the cattails, mints, and willows, but just as important ecologically are arrowleaf, rush sedge, marshweed and blue verbena. These are moisture-loving plants that thrive on being thoroughly soaked during the wet part of the year.

Beyond the marsh on the valley floor is a third community. Here the water table (the top of the saturated soil and rock zone) is close enough to land surface that the plants can easily send their roots down into the saturated zone. Here, in what the plant ecologists call the “sub-irrigated floor plain” we find a mid-grass community. Eighty-five percent of the vegetation is slender wheatgrass. Its wheat-like heads may, under favorable conditions, grow to a height of one meter (three feet). At Agate it is seldom over knee high. Kentucky bluegrass takes care of another 10 percent of the plant population. Imported from Europe as a pasture grass in the 1600’s, it spread so rapidly that it often beat the settlers onto new land as they moved westward. The remaining five percent includes imported redtop and such native grasses as switchgrass, foxtail barley, little bluestem, prairie cordgrass, and inland saltgrass. Wildflowers such as Flodmon thistle, yarrow, heath aster, salsify, and blue-eyed grass complete the community.

Moving farther away from the stream, we rise up onto terraces within the valley. These terraces represent levels where the stream paused in its downcutting and cut sideways for awhile. At a drier level, on deep, well-drained sandy soils, they support the fourth or mixed-grass community.

No exotics have yet appeared in this plant community. The grasses include prairie sandreed, sand bluestem, blue grama, needle-and-thread grass, and Indian ricegrass. Wildflowers include the prominent phlox, penstemon, and lupine. Unwelcome (to man and his grazing animals) isAstragalus, the selenium-concentrating plant better known as loco weed. The brittle prickly pear and spiderwort cactus are found here too.

At higher levels in the terrace community, slightly steeper slopes and shallower soils cause some change in this mixed-grass assemblage. Here the dominant grasses are little bluestem, threadleaf sedge, needle-and-thread grass, and blue grama. Lupine disappears, and common pricklypear becomes the only cactus. In this community is found the yucca, its flowers a beautiful soft yellow in season and its spiny leaves painful at any time of the year. Avoid this plant; yucca spines break off under the skin and soon cause irritating festers. The yucca moth, often seenflying around the yucca seed pods, lays eggs in the plant’s lemon-sized fruits. Inside the fruit are long rows of flattened, wedge-shaped seeds. When the yucca moth eggs hatch into caterpillars, they eat their way through the seeds, killing them. On the other hand it is the yucca moth with its long tongue that is solely responsible for pollinating the yucca flower! If you find a yucca fruit in early summer, you can (elsewhere than in the park) slice through it and see the caterpillars at work.

On the high bluffs and overgrazed terraces is the fifth community, the short grass. This community too can be divided into two slightly different parts. The bluffs support blue grama grass, needle-and-thread grass, and Sandberg blue grass. Flowers and shrubs includeEriogonum, brittle pricklypear cactus, pepperweed, penstemon, broom snakeweed, fringed sagewort, and yucca. The other part of this community, the overgrazed terraces, have threadleaf sedge, needle-and-thread grass, and blue grama. Except for the familiar penstemon, all the flowers are restricted to this community. Gronwell, menzania, and bee plant are indicators of overgrazing.

Certain cyclical variations are characteristic of these plant communities. First, the shortgrass and mixed-grass areas ebb and flow with changing moisture conditions from year to year. Second, grass populations change with the seasons. Cool-season grasses (foxtail barley, Indian rice grass, Kentucky bluegrass, needle-and-thread grass, Sandberg blue grass, and slender wheatgrass) flourish during spring and fall. During the warm summer the blue grama, inland saltgrass, little bluestem, prairie cordgrass, prairie sandreed, and switchgrass predominate. This natural adaptation to seasonal conditions uses the greatest potential of the growing season and at the same time provides species that will flourish in both wet and dry cycles.

After reading this last section, you might look back at the section on Early Miocene ecology. Comparison reveals that a great deal of information can be obtained by examining living plants. In contrast, the lack of fossil flora from the Early Miocene at Agate has resulted in a scarcity of ecological information from that early epoch. Scientists begin their reasoning by such comparisons; you can begin your own exploration of the past in the same way.

Ask a ranger for directions to the protected example of a Devil’s Corkscrew, the fossilized burrow of a small, beaver-like animal calledPalaeocastor. See pages68-69 for more information about this interesting animal.

Northwestern Nebraska 69 kilometers (43 miles) north of Scottsbluff along the Niobrara River.

1,116 hectares (2,762 acres).

Temperatures range from winter lows of -38° C (-36° F) to summer highs of 39° C (101° F). Winter temperatures average 1° C (33° F), and winter snow averages 60 centimeters (2 feet) for the whole winter. However, snowdrifts can be much higher. Summer nights are cool, with temperatures averaging 10° C (50° F). Average annual precipitation is 41 centimeters (16 inches), with most precipitation in April and May.

Most people go to the park some time between June and August, but you can avoid the high summer temperatures by visiting in the spring, fall or—if you don’t mind the cold and snow—in the winter. Spring can be blustery, but the fall is usually dry and the days are cool. Check ahead on local weather conditions if you plan a winter visit. Museums and tourist attractions in nearby Fort Robinson are open Memorial Day to Labor Day.

A ranger is on duty to help you and answer your questions. Fossil exhibits and part of James H. Cook’s personal collection of Indian items are on display in the visitor center, and publications about the park, paleontology, and history are on sale.

A trail from the visitor center takes you on a tour to both University and Carnegie Hills, with an interpretive display at each. The roundtrip distance is three kilometers (two miles) and takes about one hour. You may fish for German brown and rainbow trout in the Niobrara River if you have a Nebraska fishing license. The park has several tables for picnickers.

The park has no camping facilities, but there are state campgrounds near Harrison and near Fort Robinson, Nebraska, and a commercial campground on Nebr. 26 between Mitchell and Scottsbluff, Nebraska.

Hotels, motels, food stores, outdoor supply stores, and restaurants are available in Scottsbluff, Nebraska. A motel, restaurant, gas station, and grocery store are in Mitchell, Nebraska, 55 kilometers (34 miles) south of the park. There are a motel, food store, drugstore, and restaurant in Harrison, Nebraska, 37 kilometers (23 miles) north of the park, and there are motels and restaurants at Fort Robinson, Nebraska, 37 kilometers (23 miles) east of Harrison, or 74 kilometers (46 miles) northeast of the park.

Buses—The nearest bus connections are in Scottsbluff, Nebraska. Airport—Scottsbluff, Nebraska, has an airport served by a scheduled commercial airline. Rentals—Cars may be rented at the airport or at car rental agencies in Scottsbluff.

June 5, 1965.

To reach the park from Scottsbluff, Nebraska, take Nebr. 26 west to Mitchell, then Nebr. 29 north to the park. From Fort Robinson, Nebraska, take Nebr. 20 west to Harrison, then Nebr. 29 south to the park.

Plains statesHigh-resolution Map

The trail from the visitor center takes you across the Niobrara River, up University Hill to the fossil layer, then to the fossil exhibit on Carnegie Hill, and back to the visitor center. The walk takes about one hour.

Two fishermen try their luck in the Niobrara.

To ensure your safety and to protect the park’s natural and historical resources, several regulations have been established by the National Park Service. Collecting of fossils, rocks, plants, or other objects is not permitted. Please be sure to leave everything as you find it along the trails and throughout the park for others to enjoy. If you have any questions about park regulations and policies, please ask the staff. The rangers are here to help you and to enforce the regulations.

Though snakes are not prevalent, be sure to watch for rattlesnakes as you walk about through the park, along the trails, and near the exhibits at Carnegie and University Hills. Avoid them if you see them, but do not harm them. As a general rule it is best to keep a good distance from any wildlife you see, not only to protect yourself and your children, but to avoid frightening or hurting the animal. It is best to observe wildlife at a safe distance with field glasses. While walking about the park, do not take chances by climbing on loose rock, or going into unauthorized areas, and do not let your children go beyond your control. Park your vehicle in authorized places and observe the normal rules of road safety and courtesy while you are in the park, and when entering and leaving it.

One of the joys of visiting the national parks, author Freeman Tilden once said, is having an unexpected, provocative experience. You go to a park to see or do one thing, and you come across something else that strikes your fancy as well. Tilden called it serendipity. At Agate Fossil Beds National Monument, one such experience might be birdwatching. In this piece, Doris B. Gates writes of her annual bird surveys in this area.

In western Nebraska the northern part of the Great Plains ends at the Pine Ridge, an escarpment circling from Wyoming across Nebraska’s north edge and winding into South Dakota. A major grass of this mixed prairie is little bluestem, Nebraska’s state grass, whose rusty-red hue in fall and winter gives much of the state its characteristic color.

These plains are rarely broken by cultivation and only a few houses with their few trees break the landscape. The land’s major change comes where the Niobrara River, here little more than a narrow creek, cuts a valley whose rock outcroppings provide homes for rock wrens, chipmunks, and bushy-tailed wood rats better known as pack or trade rats.

Swainson’s hawk

Here, since 1967, near Agate Fossil Beds National Monument, my partner and I have taken part in the annual Breeding Bird Survey for the U.S. Fish and Wildlife Service. Part of one of our survey routes, Highway 29, crosses the monument’s west end. We know the area—in June at least—quite intimately, when there is nothing quite so beautiful as a sunrise over these flower-dotted, green-grassed rolling hills along the Niobrara.

We go many kilometers and make many bird counting stops, then we drop into the little valley where the Niobrara flows and suddenly we hear and see birds in such rapid succession that we have difficulty getting them all named in the three minutes allowed us under the survey rules. Actually, three stops are influenced by the river: on the south edge we have found a common nighthawk, a lark sparrow, and a Say’s phoebe; on the north end the rock wren sings its un-wrenlike song. Near the bridge, where a narrow belt of shrubs and trees—mostly willows—hugs the river, we have logged the following: common flicker, a red-headed woodpecker, eastern and western kingbirds, western wood peewees, a blue jay, black-capped chickadees, house wrens, a brown thrasher, robins, yellow warblers, black-billed magpies, common grackles, black-headed grosbeaks, American goldfinches, and the non-native house sparrow and starling. Only once did we see or hear a black-billed cuckoo.

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Red-winged blackbird chick

Long-billed curlew chick

Long-billed marsh wren

Canada geese

Long-billed curlew male

House wren

Nighthawk

Marsh hawk chicks

Killdeer

Great horned owl

Western meadowlark

American bittern

Pocket gopher

Jackrabbit

Hognose snake

Fence lizard

Coyote

Pronghorn

If we stop and peer into a large culvert under the highway we may scare out a cloud of cliff swallows whose mud nests are stuck on culvert walls. Barn and rough-winged swallows are more rarely seen—usually near the Agate buildings.

Near scattered farmhouses we may see logger-head shrikes; by one water tank we usually find a few killdeer. These and such birds as the long-billed curlew, upland sandpipers, and sharp-tailed grouse break the near monotony of such prairie birds as western meadowlarks (Nebraska’s state bird), lark buntings, horned larks, and chestnut-collared longspurs. Lark buntings line the utility wires, taking off to sing their territorial songs, and descending with butterfly-like motions.

Hawks are here—red-tails, Swainson’s, ferruginous, marsh, and the little American kestrel—but in small numbers. We search long rows of fence posts for a burrowing owl and occasionally see one. Great-horned owls frequent tall cottonwood trees around the Agate ranch buildings. This is also the country of turkey vultures, golden eagles, and prairie falcons, but we have not been lucky enough to see them yet.

Mammals are more elusive. Cattle pasture conspicuously on land formerly claimed by the buffalo (bison). We see pronghorns each year. A lone coyote is the only other relatively large mammal we have logged. Check a good mammal book and you will appreciate what lives here largely invisible to the untrained eye: shrews, moles, bats, cottontails and two kinds of jackrabbits, pocket gophers, prairie dogs, kangaroo rats, voles, several kinds of mice, two kinds of ground squirrel, muskrats, beaver, raccoons, minks, badgers, longtailed weasels, two kinds of skunks, occasional porcupines and bobcats, white-tailed deer, and mule deer. Consider yourself lucky if you see the swift fox, mountain lion, and the rare black-footed ferret.

Life abounds here in other forms less noticeable to eyes trained on the Breeding Bird Survey: various species of amphibians, reptiles, fish, and the numerous insects associated with grasslands. We hear perhaps too much about rattlesnakes—western Nebraska has only the prairie rattler, whose numbers are now much reduced. Other snakes include western hognosed, blue racer, bullsnake, and the plains, wandering, and red-sided garter snakes.

Many museums throughout the world have displays of fossils from the Agate Fossil Beds. Very few of them actually collected their own material. Museum curators are dedicated “horse traders” and fossil-swapping is part of the business. When museums such as the Carnegie Museum of Pittsburgh or the American Museum of Natural History in New York make collections like the ones made at Agate earlier in this century, they usually have some trading stock left over after completing their study collections and exhibits. They then can trade an extraMenocerasslab, for example, for a dinosaur skeleton from some faraway corner of the Earth.

At several museums in this country you can see mounted skeletons of several animals found at Agate, along withMenocerasslabs (sections of rock with the bones still imbedded) or models and dioramas of Agate specimens. To the right are listed, in order of proximity to the park, some of the museums and their specimens from Agate.

The United States Museum of Natural History, Smithsonian Institution, has many fossils that depict the life of the most recent 65 million years and several murals by artist Jay H. Matternes showing the life of each of the epochs. The Miocene mural, reproduced on pages20-21of this handbook, is among these reconstructions. It depicts ancient life around what is today known as Agate Fossil Beds National Monument.

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