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Title: Agate Fossil Beds National Monument, Nebraska
Author: Service, United States National Park
Language: English
As this book started as an ASCII text book there are no pictures available.

*** Start of this LibraryBlog Digital Book "Agate Fossil Beds National Monument, Nebraska" ***

                           Agate Fossil Beds

                  Agate Fossil Beds National Monument

                        Division of Publications
                          Harpers Ferry Center
                         National Park Service

                    U.S. Department of the Interior
                            Washington, D.C.

                   The National Park Handbook Series

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.

                            About This Book

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 1 of this handbook introduces you to the park; Part 2
brings life to the fossil specimens and examines the area’s geological
and ecological evidence; and Part 3 presents concise guide and reference

           Library of Congress Cataloging in Publication Data

  United States. National Park Service.
  Agate Fossil Beds National Monument, Nebraska.
  (National park handbook; 107) Bibliography: p.
  Includes index.
  Supt. of Docs. no. I29.9/5:107
  1. Vertebrates, Fossil.
  2. Paleontology—Miocene.
  3. Paleontology—Nebraska—Agate Fossil Beds National Monument.
  4. Natural history—Nebraska—Agate Fossil Beds National Monument.
  5. Agate Fossil Beds National Monument, Neb.
  I. Title.
  II. Series: United States. National Park Service. Handbook—National
          Park Service; 107.
  QE841.U59    1980    566′.09782′99    80-607119


  Part 1 Welcome to Agate Fossil Beds                                   4
      Worlds of Past and Present                                        7
  Part 2 A Landscape Rich With Life                                    18
      _Text: James R. and Laurie J. Macdonald_
      _Illustrations: Jay H. Matternes_
      A Visit to the Past                                              23
      The Mark of Death Upon the Land                                  35
      The Geologic History of Agate                                    47
      Ecology: Change and Adaptation                                   53
  Part 3 Guide and Adviser                                             74
      Contents for this section                                        77

                   1    Welcome to Agate Fossil Beds

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

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

                       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

    [Illustration: 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.]

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

    [Illustration: 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 “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

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

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.

    [Illustration: 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 “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.

    [Illustration: 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 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,

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.

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

    [Illustration: The narrow Niobrara River winds through the
    surrounding tableland, carving out bluffs and exposing occasional

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

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

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

                    2    A Landscape Rich With Life

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

    [Illustration: 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 Institution’s National Museum of Natural History in
    Washington, D.C.]

    [Illustration: Key to mural]


                          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.

    [Illustration: _Menoceras_]

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.

    [Illustration: _Promerycochoerus_]

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_.

    [Illustration: _Parahippus_]

_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.

    [Illustration: _Oxydactylus_]

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.

    [Illustration: _Stenomylus_]

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.

    [Illustration: _Moropus_]

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.

    [Illustration: _Dinohyus_]

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.

    [Illustration: _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 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

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.

    [Illustration: _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. 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.

    [Illustration: _Palaeocastor_]

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

  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.

    [Illustration: Extracting a slab]

    [Illustration: Members of Peterson’s crew built a box around a slab
    in the _Stenomylus_ quarry around 1908 in preparation for shipping
    to the Carnegie Museum.]

    [Illustration: With a team of horses, O. A. Peterson’s field crew
    moves dirt out of the _Stenomylus_ quarry around 1908. The boxes in
    the foreground are resting on the quarry’s lower bone layer. Several
    specimens to the left have been strengthened with plaster for
    shipment to Pittsburgh.]

    [Illustration: Crates of prepared specimens had to be taken to
    Harrison, 37 kilometers (23 miles) north of Agate for the rail trip
    to the East. Note that the wagon is just a flat platform and that
    the driver is using the largest crate as a seat.]

    [Illustration: Paleological laboratory.]

                     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.

    [Illustration: Karl Von Linné, 1707-1778, is known as Linnaeus after
    the Latin form of his name. A Swedish botanist, he established a
    hierarchical system for classifying plants and animals that is still
    in use in a modified form. His organizing principle was the degree
    of complexity of the organisms he studied. This resulted in a system
    with seven levels: Kingdom, Phylum, Class, Order, Family, Genus, and
    Species, in descending order from the broadest category to the most
    specific. Students remember the system by the sentence “King Philip
    Crossed the Ocean For Good Soup.” Without realizing it, Linnaeus
    prepared the ground for the evolutionists, who later were able to
    demonstrate the gradual ascent of life forms from simple to complex
    by using his scheme of classification.]

    [Illustration: Jean-Baptiste de Lamarck, 1744-1829, a French
    physician and ex-military man, founded the modern study of animals
    without backbones and coined the term invertebrates to describe them
    as a group. When his battle wounds forced him to take up a new
    career, he studied botany and published a study of French plants. He
    later turned to invertebrates, and between 1815 and 1822 published
    the classic _Histoire naturelle des animaux sans vertèbres_. He
    applied his vast knowledge of living invertebrates to
    paleontological work, greatly enhancing the knowledge of fossil
    invertebrates. Lamarck was also an evolutionary theorist, and he
    believed that a single characteristic acquired by an animal during
    its lifetime could be passed on to its descendants by heredity
    (modern genetic theory was unknown at that time). He saw that
    evolution must have taken a long time to occur, and he supported the
    principle which has since become known as uniformitarianism.]

    [Illustration: Georges Cuvier, 1769-1832, was a French anatomist and
    paleontologist who specialized in the study of animals with
    backbones, the vertebrates. He had a long and brilliant career as a
    professor, eventually becoming France’s minister of the interior in
    1832. His skill as a comparative anatomist enabled him to understand
    how vertebrate fossils should be reconstructed to form a complete
    skeleton, and he was one of the first to use the small muscle scars
    on fossil bones to reconstruct the extinct animal’s musculature. His
    classic work _Récherches sur les Ossemens Fossiles de Quadrupèds_
    was published in 1812. He is known for his theory of a series of
    natural catastrophes, each supposedly obliterating all extant life,
    to account for the great variety of ancient fossils. This theory was
    later supplanted by the theory of continuous evolution supported by
    Darwin, Lyell, and others.]

    [Illustration: Charles Darwin, 1809-1882, is today a household name
    that is still invoked in controversy as it was more than a hundred
    years ago. An extraordinarily patient and insightful biologist,
    Darwin contributed the idea of natural selection, the “weeding out”
    of unfit individuals and species, and described it as the guiding
    principle of the evolution of life on this planet. His book _On the
    Origin of Species by Means of Natural Selection_, published in 1859,
    is the most important landmark in evolutionary studies. This was the
    culmination of decades of work, leading to conclusions startlingly
    similar to those of his fellow Englishman, Alfred Wallace. Darwin
    knew nothing of the genetic principle of biological heredity and
    variation, which has now assumed equal importance with natural
    selection in the study of the evolution of life. For
    paleontologists, Darwin’s work meant they must look for transitional
    forms of life and not content themselves with Cuvier’s assumptions
    that past life forms had been static and unchanging. During his
    travels in South America, Darwin contracted a disease, now known as
    Chagas’ disease, and suffered intense pain and discomfort the rest
    of his life. He died of a heart attack on April 19, 1882, and was
    buried in Westminster Abbey in London a few days later.]

    [Illustration: Charles Lyell, 1797-1875, revolutionized the study of
    geology partly by publicizing the earlier work of James Hutton, who
    died the year Lyell was born in Scotland, and partly by infusing the
    science with his own highly disciplined point of view. His greatest
    contribution was the firm establishment of Hutton’s principle of
    uniformitarianism, or uniformism, which became the foundation for
    all modern geological work. Put simply, this is the principle that
    the processes we see operating to form and shape the Earth today
    have always operated in the past. Once this is admitted, it becomes
    clear that past geological time is vast, not short, a truly stunning
    notion for Lyell’s time but a commonplace fact today. The first
    volume of his _Principles of Geology_ was published in 1830; in his
    later works he championed Darwin’s own revolutionary point of view,
    adding his own powerful arguments in support of the idea of natural

    [Illustration: Alfred Wallace, 1823-1913, was the co-originator,
    with Darwin, of the principle of natural selection, or “survival of
    the fittest.” The main difference between the two was that Wallace
    did not believe that natural selection explained things as well as
    Darwin thought it did, which has been borne out to a large extent by
    modern studies of genetic variation. Wallace worked in South
    America, along the Amazon and Rio Negro rivers, and in East Asia. He
    showed that the animals on either side of a line between Borneo and
    the Celebes Islands are radically different in their makeup and
    origin. Now known as “Wallace’s Line,” his work has been vindicated
    by additional modern studies. Although Wallace did not become as
    well known as Darwin, his brilliant, independent studies lent a
    great deal of weight to the Darwinian view of evolution.]

    [Illustration: _The largest divisions of geologic time are eras,
    shown above in chronological order from the oldest on the bottom to
    the most recent on top. The scale at left shows the relative
    duration of each era. As the chart shows, geologists further divide
    time into periods and, in the Cenozoic Era, into epochs. The
    fossilization of animals in the Agate Springs area of Nebraska took
    place in the Miocene Epoch. Adjustments to this time chart are made
    as new data becomes available, so it should not be thought of as an
    unchanging reference. This diagram is adapted from one in The
    Emergence of Man series published by Time-Life Books._]

                           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

Although the whole story of Agate Fossil Beds dates from the formation
of the Earth four and one half billion years ago, only the last 600
million years is known in detail. It was about 600 million years ago
that many plants and animals began to have hard parts—parts likely to be
preserved as fossils. The few fossils contained in older rocks are often
folded, twisted, squeezed, and distorted so that their original
character is all but erased. That isn’t always the case, of course. Some
of these old rocks, the Belt Series in Montana, look as though they were
deposited only a few million years ago; they contain traces of algal
colonies indicative of the generally simple life forms on the primitive
Earth. The old rocks, deposited during the first four billion years of
Earth’s history, record the Precambrian Eons, spanning eight-ninths of
geologic time.

The evolutionary development of skeletal remains has aided in the study
of geologic history. The last 600 million years have been divided into
units for ease of discussion and comparison. The three largest divisions
are the eras—Paleozoic (ancient life), Mesozoic (middle life), and
Cenozoic (recent life). We are viewing all this from our vantage point
at (what is now) the most recent episode of the Cenozoic.

To begin at the known beginning, we only need go back to the start of
the Paleozoic Era some 600 million years ago. No Precambrian, Paleozoic,
or Mesozoic rocks can be seen around Agate, but we know from rocks found
in comparable areas about what to expect under the surface at Agate:
thousands of meters of sedimentary rocks, most of them laid down in an
ocean. During the Paleozoic and most of the Mesozoic eras, up until
about 70 million years ago, the west-central United States was covered
by seas. The area now occupied by the Rocky Mountains was then a long
north-south trough in which thick sediments collected. To the east, the
present Great Plains area was the floor of a shallower sea. Sediments
collected in the trough and on the sea bottom. Gradually, over a period
of 530 million years, the sediments accumulated to a thickness of over
2,100 meters (6,900 feet). A dynamic “give-and-take” process, this
sedimentation was the result of periods when the sea rose and fell
several times.

If the Paleozoic sounds a little dull, it’s because we haven’t told the
whole story. During the Paleozoic Era, all the major groups of organisms
evolved. The seas swarmed with trilobites and shellfish of all kinds,
some weird and fantastic and some very like those alive today. With them
coexisted fish and sea-lilies, seaweeds and giant swimming “scorpions.”
For the first time, plants and then animals came out of the sea to live
on the land. These events and creatures are preserved in Paleozoic
rocks. The Mesozoic Era saw the development of mammals from reptiles,
the rule of giant dinosaurs, and the beginnings of flight. Strange
reptiles evolved and returned to the sea, or glided through the air on
motionless wings. The Sundance Formation, deposited in the northern
Rocky Mountains about the middle of the Mesozoic Era, is noted for the
masses of bullet-shaped squid shells found in it. Water, land, and air
were full of life.

In the Middle Mesozoic, the trough drained and much of it became an area
of swamp and tropical forest extending from Montana to southern Utah.
This was the domain of our largest dinosaurs, giant reptiles whose bones
were preserved in impressive numbers. Como Bluff and Bone Cabin,
Wyoming; Morrison, Colorado; and Dinosaur National Monument and
Cleveland, Utah, are the sites of quarries where many fine specimens of
_Apatosaurus_, _Diplodocus_, _Stegosaurus_, and _Allosaurus_ have been
collected. These caches of bones have made our large museums showplaces
known throughout the world.

During the last 65 million years of the Mesozoic, the trough fluctuated
up and down. During much of that time a broad, shallow sea covered
central North America from the Gulf of Mexico to the Arctic Ocean. The
sea was filled with fish like the giant _Portheus_ (3.5 meters/11.5 feet
long), with squid-like animals floating about in elaborate chambered
shells, and with reptiles which had gone back to the water. Where there
was a broad coastal plain, it swarmed with dinosaurs, the ones that make
Lance Creek, Wyoming and Hell Creek, Montana famous collecting grounds
for museum field parties. Yet at the end of the era the trough was a
seaway again, and in the Agate area a final blanket of black mud, the
Pierre Shale, was deposited in the sea.

At the end of the Mesozoic Era a profound change came over the land. The
trough, with hundreds of meters of sediments accumulated on its bottom,
was drained and folded by pressures built up in the Earth’s crust. To
the south, the Colorado Plateau rose slowly and smoothly; to the north
folding and faulting built complex mountain ranges. This uplift is
called the Laramide Revolution because of the magnitude of the change it
made on the face of the continent.

At the beginning of the Cenozoic Era, about 65 million years ago, the
Rockies and the Great Plains were slowly rising. Rains fell and rivers
carried the water, wearing away the old sediments. Some sediments were
carried west into the Pacific Ocean, or deposited on the land and
covered over by new sediments. Some sediments remained within the
Rockies, settling into basins during the early Cenozoic. Other sediments
were carried east by the rivers, beyond the Great Plains and into the
Mississippi Embayment. Mountain building and erosion tended to cancel
out one another in the Rockies, preventing the mountains from reaching
great heights. The mountain bases were perhaps no more than 300 meters
(1,000 feet) above sea level, and the crests perhaps 600 meters (2,000
feet) above that.

Before long, the basins within the Rockies filled with sediments. The
basins overflowed, and at last sediments began to cover the Great
Plains. This was near the end of the Eocene Epoch, about 35 million
years ago. Subtropical rivers, flowing sluggishly, rolled out over their
banks and left their loads of silt and clay on the featureless plain.

The oldest part of the blanket of sediments, the White River Beds,
extended from Saskatchewan to Texas. Nearly 200 meters (650 feet) of
muds, clays, silts, and river gravels were laid down during the 11
million years of the Late Eocene and Oligocene Epochs. Magnificent
exposures of these beds can be seen at Scotts Bluff National Monument in
the valley of the North Platte, in Toadstool Park north of Crawford,
Nebraska, and particularly in the Big Badlands of southwestern South

The kind of floodplain deposition characteristic of the Oligocene on the
Great Plains ended about the beginning of the next epoch, the Miocene.
In Nebraska the process continued, but eventually erosion began wearing
away the accumulated sediments. The land to the west was uplifted a
little, and the streams flowed off the high ground fast enough to cut
down into what they had just deposited. On this eroded surface, the
layers of tan silts, fine sands, and clays known as the Gering Formation
were deposited.

On top of the Gering Formation, in the Late Oligocene, is the Monroe
Creek Formation, the oldest formation actually exposed in the Agate
area. This formation is named for exposures in Monroe Creek Canyon north
of Harrison, Nebraska, and may be up to 75 meters (245 feet) thick. You
can see a little of the Monroe Creek Formation’s pinkish silts and
volcanic glass shards exposed in the valley of the Niobrara River. Where
it is more exposed by erosion than at Agate, the Monroe Creek Formation
forms magnificent cliffs along the Pine Ridge and similar areas of high
ground. The best local examples are at Fort Robinson State Park between
Harrison and Crawford, Nebraska. A close look can be obtained in Smiley
Canyon just west of the fort, where old U.S. Highway 20 is maintained as
a scenic drive.

After the Monroe Creek interval, near the end of the Oligocene,
deposition of the famous Agate Fossil Beds began. Geologists have named
this sequence of grayish silts and sands the Harrison Formation for its
occurrence near Harrison, Nebraska. A short interval of erosion
separates it in some areas from the Monroe Creek Formation below, and
its coarser sands indicate increasing uplift of lands to the west. Wind
played a smaller role in deposition than in Monroe Creek times, though
that is certainly not true at the _Stenomylus_ quarry. The Harrison
Formation was the last of the truly widespread deposits seen in the
Miocene of the Great Plains. Many rivers flowing eastward from the
Rockies contributed sands to Wyoming, South Dakota, and Nebraska.

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

Shortly after the camels were buried there was a brief period of erosion
and then the Marsland Formation began to be deposited. Named for a
little village east of Agate, the Marsland Formation consists of basal
river channel deposits followed by about 45 meters (150 feet) of
wind-blown tan-and-gray sands. It is in one of these river channel
deposits that the Agate rhinoceros quarries are located.

The second drought occurred early in Marsland times and literally
hundreds of the little rhino, _Menoceras_, were preserved when their
carcasses were broken up by a reborn river and buried like a mat of
jackstraws in a river lake.

After Marsland times there was more erosion, in some places by rushing
streams that cut down 91 meters (300 feet) through soft sediments, to
the top of the Monroe Creek Formation. In these channels the
Runningwater Formation was deposited because it filled in the stream
valleys and wound around the high spots. This channel deposit is not
found everywhere, but it does have an equivalent in southwestern South
Dakota. Other deposits of similar age are found in many parts of the
Great Plains, and they contain fossil animals like those found in the
Runningwater Formation.

The turbulent streams which deposited the Runningwater Formation were
flowing off newly uplifted land to the west. This was the beginning of
the most recent major uplift of the Rocky Mountains, and it signalled a
great change in the pattern of deposition on the Great Plains. No longer
would broad blankets of sediments be deposited by sluggish streams
originating in the low, broad warp of the Rockies.

This latest uplift is called the Rocky Mountain Revolution. It brought
on a period of alternating cycles of deep channel cutting and stream
deposition. Floodplain deposits were restricted to narrow ribbons in
river-cut valleys. Even more important than the changes in deposition
was the effect of this uplift on the climate. As the Rockies began to
rise to their present height, the climate became increasingly arid and
the tree-dotted savanna of the old Great Plains gave way to grasslands.

Several kilometers south of Agate, the Sheep Creek Formation was laid
down during the Middle and Late Miocene. The appearance of the grazing
horse _Merychippus_ in these channel and floodplain deposits marked the
establishment of the grasslands as the newly dominant ecosystem of the
Great Plains. At that time the “modern” fauna began to replace the old,
and new patterns of life were established.

Again rejuvenation of the stream system, probably reflecting further
uplift in the west, started another erosional interval that began to
wash away the beds just deposited. When deposition followed in the Late
Miocene, a new series of channel and floodplain deposits, the Lower
Snake Creek Beds, was laid down. On them was deposited the Upper Snake
Creek Beds, and together they span most of the Late Miocene and the
Early and Middle Pliocene epochs. Harold Cook collaborated with W. D.
Matthew of the American Museum of Natural History, publishing important
papers on the numerous finds from these fossiliferous deposits. Animals
new to science are still being discovered in the Snake Creek Beds.

After Snake Creek times, the area immediately around Agate was left out
of the mainstream of events on the Great Plains. The continuing uplifts
of the Rocky Mountains were no longer recorded here in cycles of
downcutting and channel deposition. If the cycles continued here, all
traces have now been washed away—an unlikely possibility. The view from
the high plains above the valley of the Niobrara River reveals only the
rolling surface of the pre-Runningwater deposits.

A more complete record is found in the river terraces of major streams,
the North Platte to the south and the White and Cheyenne Rivers to the
north. These terraces tell the story of continuing uplifts. To the
south, east, and northeast of the Platte the record is also written in
fossil bones, but these are outside the scope of our story.

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

                     Ecology: Change and Adaptation

During the Age of Mammals (the Tertiary Period), three major
environments dominated western Nebraska. The first of these occurred
during the Paleocene, Eocene, and Oligocene epochs. This was a forest
system where trees were the major component of the flora. Meadows were
found only in scattered areas and can be considered a minor element.
There is no geologic or paleontologic record of the Paleocene and Eocene
in the Agate area, but when our present knowledge of the early Tertiary
Rocky Mountain floras is projected eastward a bit, a predominantly
forested landscape is indicated.

It is in some ways ironic that while the Oligocene land-laid sediments
of southwestern South Dakota, western Nebraska, southeastern Wyoming,
and northeastern Colorado contain one of the best vertebrate fossil
records in the world, the plant record is almost non-existent.
Unfortunately the groundwater chemistry that was so right for the
preservation of bones was hostile to the preservation of plants.
Hackberries (_Celtis_) and walnuts (_Juglans_) are the only recorded
plant species from the Oligocene in this very large area. Because these
are such widespread and climatically tolerant types, they tell us almost
nothing about the environment. Indications of the flora at Agate may be
obtained, however, from the extraordinary Late Eocene flora found at
Florissant, Colorado, south of Denver. Although this deposit does
contain some upland species, it generally indicates a warm temperate
forest including such things as horsetail rushes, ferns, cattails,
grasses and sedges, poplar, willow, birch, oak, elm, serviceberry,
sycamore, maple, sumac, and—of course—hackberries and walnuts.

During the Early Miocene, slightly changed climatic conditions brought
about by minor uplifts in the Rocky Mountain area transformed the
immediate area of western Nebraska into a savanna of mixed trees and
grasslands. This second system probably reached its climax just about
the time the Harrison Formation was being laid down during the Early
Miocene. This was a savanna with scattered clumps of trees, gallery
forests, and grasslands. The modern world’s richest and most diverse
fauna of hoofed mammals can be found on the savannas of east Africa. On
the savannas, grazing and browsing (grass eating and leaf eating)
adaptations of the larger plant eaters are represented.

    [Illustration: 35 million years ago]

    [Illustration: 25 million years ago]

    [Illustration: 15 million years ago]

    [Illustration: 35 million years ago, life along the Niobrara River
    near Agate would have appeared something like this. Two oreodons (1)
    have startled an alligator (2) and two hippopotamus-like
    _Aepinacodons_ (3) along the river bank. Climbing a tree is an
    opossum (4), one of the oldest forms of life in the world today.
    Note the many familiar trees and plants, particularly the
    cottonwood, willow, beech, dogwood, and cattail.]

    [Illustration: 25 million years ago, a savanna dominates the Agate
    landscape. Copses of oak and pine are interspersed with open
    grassland. In the foreground are several _Parahippus_ (1), an
    ancestor of today’s horse, while _Oxydactylus_ camelids (2) move
    away into the distance and, overhead, a hawk (3) searches for

    [Illustration: 15 million years ago, the Agate landscape has changed
    to an open prairie. A small herd of _Merychippus_ horses (1) races
    toward the arroyo in the distance, narrowly escaping ambush by a
    large, leopard-like cat known as _Pseudaelurus_ (2). A few
    cottonwoods, elms, sycamores, and willows grow along the river, but
    cedars predominate in the arroyo in the middle ground, where they
    are protected from winds that sweep across the plains. Though the
    animals have changed, the landscape is essentially like this today.]

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 term _steppe
climate_ is 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, the browsers 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

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 in _Parahippus_,
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 of
_Parahippus_ became 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,
_Merychippus_ and _Protohippus_. 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. _Merychippus_ later gave rise
to a line of three-toed horses, which lived on into the Pliocene;
_Protohippus_ gave rise to a line which ultimately led to _Equus_, 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 oreodon _Leptauchenia_,
the tiny “deer” _Hypisodus_, and the rabbit _Palaeolagus_ had 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

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.

                          Evolutionary Change

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

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

            The distance between grid lines represents five centimeters.

    [Illustration: 1 The ears moved in a parallel fashion, not
    independently; the parallel movement is inferred from modern
    llamoids, to which _Stenomylus_ is related.

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

    3 The back structure suggests that _Stenomylus_ would have made
    short, choppy leaps, not the graceful, arcing leaps of a modern

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

    5 _Stenomylus_ had 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 as _Miohippus_ was about the size of a sheep. The
descendants of _Miohippus_ apparently 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 as _Parahippus_, 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.

    [Illustration: 1 The 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.

    2 Limbs 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.

    3 Most 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.

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

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

    6 A 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.]


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

            The distance between grid lines represents five centimeters.

    [Illustration: 1 The 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.

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

    3 The forelimbs were adapted to burrowing in the ground.

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

    [Illustration: 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

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 famous
_Daemonelix_ or “devil’s corkscrew” attests to the dense population of
_Palaeocastor_. 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 that _Palaeocastor_ was 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

Changing environmental conditions were pushing _Palaeocastor_ toward
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 beavers of 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

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) is
_Astragalus_, 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 seen flying 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 include _Eriogonum_,
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.

                         3    Guide and Adviser

    [Illustration: Ask a ranger for directions to the protected example
    of a Devil’s Corkscrew, the fossilized burrow of a small,
    beaver-like animal called _Palaeocastor_. See pages 68-69 for more
    information about this interesting animal.]

                           Visiting the Park

                        Contents of This Section

  Visiting the Park                                                    77
      When to Visit
      Visitor Center
      Nearby Accommodations
      Establishment Date
  Protection                                                           80
      Park Regulations
      Safety Tips
  Birding Along the Niobrara                                           81
      Taking the Annual Count
  Collections of Agate Springs Fossils                                 86
  NPS Areas With Fossil Exhibits                                       88
      Fossil Butte
      Petrified Forest
      John Day
  Nearby National Parks                                                90
      Devils Tower
      Fort Laramie
      Jewel Cave
      Mount Rushmore
      Scotts Bluff
      Wind Cave
  Not So Nearby National Parks                                         92
      Bighorn Canyon
      Little Bighorn
      Rocky Mountain
      Theodore Roosevelt
  Armchair Explorations                                                93


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.

                             When to Visit

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.

                             Visitor Center

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


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.

                         Nearby Accommodations

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.

                       Establishment of the park

June 5, 1965.

                            Mailing Address

  Agate Fossil Beds
  National Monument, 301 River Road,
  Harrison, NE 69346.


    [Illustration: 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.]

                     [Illustration: Plains states]


    [Illustration: 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.]

    [Illustration: Two fishermen try their luck in the Niobrara.]

                            Park Regulations

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.

                              Safety Tips

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

                       Birding Along the Niobrara

                        Taking the Annual Count

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.

    [Illustration: 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.

                                                   _continues on page 85_

    [Illustration: Red-winged blackbird chick]

    [Illustration: Long-billed curlew chick]

    [Illustration: Long-billed marsh wren]

    [Illustration: Canada geese]

    [Illustration: Long-billed curlew male]

    [Illustration: House wren]

    [Illustration: Nighthawk]

    [Illustration: Marsh hawk chicks]

    [Illustration: Killdeer]

    [Illustration: Great horned owl]

    [Illustration: Western meadowlark]

    [Illustration: American bittern]

    [Illustration: Pocket gopher]

    [Illustration: Jackrabbit]

    [Illustration: Hognose snake]

    [Illustration: Fence lizard]

    [Illustration: Coyote]

    [Illustration: 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.

                  Collections of Agate Springs Fossils

                         Museums You Can Visit

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 extra
_Menoceras_ slab, 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 with _Menoceras_ slabs (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 pages 20-21 of this
handbook, is among these reconstructions. It depicts ancient life around
what is today known as Agate Fossil Beds National Monument.

  The Trailside Museum
  Fort Robinson, Nebraska 69339.
      _Menoceras_ slab, skeleton, and restoration
      _Stenomylus_ skeleton on a slab, and a prepared limb
      _Palaeocastor_ in a _Daemonelix_
      _Palaeocastor_ in a plaster cast
  Museum of Geology, South Dakota School of Mines and Technology
  Rapid City, South Dakota 57701.
      _Menoceras_ slab, beautifully prepared
  The Geological Museum
  University of Wyoming, Laramie, Wyoming 82070.
      _Menoceras_, mounted skeleton
      _Stenomylus_ slab containing most of a skeleton
  University of Nebraska State Museum
  101 Morrill Hall, 14th and U Streets, Lincoln, Nebraska 68508.
      _Moropus_, mounted skeleton
      _Palaeocastor_ skeleton in a _Daemonelix_; also, two other
      _Menoceras_ slab
      _Dinohyus_ skeleton
      _Stenomylus_, a group of skeletons
  Field Museum of Natural History
  Roosevelt Road at Lake Shore Drive, Chicago, Illinois 60605.
      _Menoceras_ slab
      _Moropus_ skeleton
  The University of Michigan Exhibit Museum
  1109 Geddes Rd., Ann Arbor, Michigan 48104.
      _Menoceras_ slab and mounted skeleton
      _Dinohyus_ eating dead Menoceras, a diorama
      _Stenomylus_ skeleton and model
  Carnegie Museum
  4400 Forbes Ave., Pittsburgh, Pennsylvania 15213.
      _Promerycochoerus_ slab
      _Menoceras_ slab and mounted skeleton
      _Moropus_, mounted skeleton
      _Dinohyus_, mounted skeleton
      _Stenomylus_, three skeletons mounted in a group
  The American Museum of Natural History
  Central Park West and 79th St., New York, New York 10024.
      _Moropus_ skeleton
      _Menoceras_ slab and skulls, one used in a sequence showing
      collecting and preparation techniques
      _Dinohyus_ skull
      _Stenomylus_, nine skeletons and a reconstruction of the group
      in life
  Museum of Comparative Zoology
  Harvard University, Oxford Street, Cambridge, Massachusetts 02138.
      _Menoceras_ slab
      _Dinohyus_ skeleton
      _Stenomylus_ skeleton

                     NPS Areas With Fossil Exhibits

Several fossil sites in the United States are under the protection of
the National Park Service. Besides Agate, the major ones are:

                  Badlands National Park, South Dakota

    [Illustration: Badlands]

Prominent deposits from the Oligocene Epoch, predecessor to the Miocene,
combine with a rugged, eroded landscape and abundant wildlife to make
Badlands a park where the natural processes of the past combine with
those of today. The National Park Service maintains a Fossil Exhibit
Trail at Badlands and presents fossil cleaning demonstrations. Prominent
fossils are those of ancient camels, giant pigs, sabertooth cats,
_Protoceras_, and _Brontotheres_. Mailing address: P.O. Box 6, Interior,
SD 57750.

             Dinosaur National Monument, Colorado and Utah

    [Illustration: Dinosaur]

The late Jurassic muds and sands of the Morrison Formation have been a
major source of dinosaur bones for more than a century. Steeply tilted
strata near Vernal, Utah, were the source of tons of bones for the
Carnegie Museum of Pittsburgh. This quarry site became the nucleus of
Dinosaur National Monument. The bone-bearing stratum has been exposed by
careful excavation, so that bones and partial skeletons of numerous
dinosaurs are exposed in high relief. The entire quarry face is covered
by a glass-walled structure that forms a large gallery. Mailing address:
4545 E. Hwy. 40, Dinosaur, CO 81610.

           Florissant Fossil Beds National Monument, Colorado

This site has long been famous for its fossils of insects and plants
preserved in fine-grained sediments. Specimens of _Brontothere_ indicate
an Eocene age for the deposits. Mailing address: P.O. Box 185,
Florissant, CO 80816.

    [Illustration: Florissant]

                Fossil Butte National Monument, Wyoming

Within the strata of this rock remnant of an ancient lake is one of the
most extensive concentrations of fossilized freshwater fish known to
science. The site is about 18 kilometers (11 miles) west of Kemmerer,
Wyoming. Mailing address: P.O. Box 592, Kemmerer, WY 83101.

                Petrified Forest National Park, Arizona

    [Illustration: Petrified Forest]

Here in the Late Triassic Chinle Formation are widespread deposits of
petrified logs. Some are nearly 2 meters in diameter and 60 meters long
(6.5 by 197 feet). Preserved in bright colors of opal and other
minerals, the most common trees are relatives of the living monkey
puzzle or Hawaiian star pine. Paleontologists believe many of the logs
floated to the area in Triassic rivers and became stranded. In the
museum are displays of various fossil plant species and animal fossils
from the same deposits. Mailing address: P.O. Box 2217, Petrified Forest
National Park, AZ 86028.

             John Day Fossil Beds National Monument, Oregon

With a total of about 5,700 hectares (14,100 acres) in several
noncontiguous units in north-central Oregon, this park provides an
extensive record of Earth history dating back at least 37 million years.
Plant and animal fossils are present in great variety. Mailing address:
HCR 82, Box 126, Kimberly, OR 97848.

             Hagerman Fossil Beds National Monument, Idaho

Within the banks of the Snake River are preserved the last vestiges of
late Pliocene life before the Ice Age and modern flora and fauna
appeared. Mailing address: P.O. Box 570, Hagerman, ID 83332.

                         Nearby National Parks

While you’re in the Agate Fossil Beds area, why not see some other sites
in the National Park System? These parks offer a variety of experiences
from frontier history presentations to caving.

Badlands National Park is 97 kilometers (60 miles) southeast of Rapid
City, South Dakota. This wonderland of bizarre, colorful spires and
pinnacles, massive buttes, and deep gorges is open all year, though
blizzards may temporarily block roads in the winter. Campfire programs
and guided nature walks are presented. Backpackers will enjoy the park’s
wilderness area. The park has a herd of about 300 bison and some prairie
dog towns. Mailing address: P.O. Box 6, Interior, SD 57750.

    [Illustration: Devils Tower]

Devils Tower National Monument is 47 kilometers (29 miles) northwest of
Sundance, Wyoming. Known as Mato Tipila (Bear Lodge) to the Lakota, this
towering landmark looms over the Belle Fourche River in the northeast
corner of Wyoming. Here the Black Hills meet the plains grasslands, and
you will likely see prairie dogs, as well as other mammals and a variety
of birds. The park is open all year. Mailing address: P.O. Box 10,
Devils Tower, WY 82714.

    [Illustration: Fort Laramie]

Fort Laramie National Historic Site is 5 kilometers (3 miles) southwest
of Fort Laramie, Wyoming. The first fort on the site was built in 1834
and soon became a lucrative center of the fur trade. The U.S. Army took
over in 1849, using the fort to protect the Oregon Trail. The fort was
abandoned by the Army in 1890. Several buildings are furnished as they
would have been during the Army years of the 1870s and 1880s. The park
is open all year. Mailing address: HC 72, Box 389, WY 82212.

Jewel Cave National Monument is located on U.S. 16, 24 kilometers (15
miles) west of Custer, South Dakota. The cave’s name comes from the
myriads of jewel-like calcite crystals that adorn its walls. Tours are
conducted daily from mid-May through September. Tours, if any, the rest
of the year are irregular. Mailing address: RR 1, Box 60 AA, Custer, SD

    [Illustration: Mount Rushmore]

Mount Rushmore National Memorial is 40 kilometers (25 miles) southwest
of Rapid City, South Dakota. The mountain sculpture of Washington,
Jefferson, Theodore Roosevelt, and Lincoln is best viewed under morning
light. From June 1 to Labor Day the faces are illuminated at night. The
park is open all year. Mailing address: P.O. Box 268, Keystone, SD

    [Illustration: Scotts Bluff]

Scotts Bluff National Monument is 8 kilometers (5 miles) southwest of
Scottsbluff, Nebraska. This massive rock promontory rises 245 meters
(800 feet) above the valley floor, and it served as a landmark to
Indians, fur traders, and settlers traveling the Oregon Trail. It was
named for a fur trapper, Hiram Scott, and has remained a symbol of the
great overland migrations. The park is open all year. Mailing address:
P.O. Box 27, Gering, NE 69341.

Wind Cave National Park is 16 kilometers (10 miles) north of Hot Springs
in southwest South Dakota. Two worlds meet here: the underground world
of the cave and the life of the surface prairie. The cave gets its name
from the wind blowing into or out of the cave. Mailing address: RR 1,
Box 190, Hot Springs, SD 57747.

                      Not So Nearby National Parks

By expanding your travel perimeter even farther beyond Agate Fossil
Beds, you can take in these other National Park System sites.

Bighorn Canyon National Recreation Area straddles the Montana-Wyoming
border, 67 kilometers (42 miles) from Hardin, Montana, and at Lovell,
Wyoming. Access to boat ramps and campgrounds is from both ends of the
long reservoir. Yellowtail Dam tours are given from Memorial Day to
Labor Day. The visitor centers are open all year. Mailing address: P.O.
Box 458, Fort Smith, Montana 59035.

Little Bighorn Battlefield National Monument is 24 kilometers (15 miles)
south of Hardin, Montana. Here on June 25, 1876, Lt. Col. George
Armstrong Custer and five 7th Cavalry companies attacked and were
surrounded and killed by Indians. Mailing address: P.O. Box 39, Crow
Agency, MT 59022.

    [Illustration: Rocky Mountain]

Rocky Mountain National Park is northwest of Denver and about 3
kilometers (2 miles) west of the community of Estes Park, Colorado. The
park is one of America’s most accessible mountainous areas. Trail Ridge,
which crosses the Continental Divide, offers breathtaking views. Elk,
mule deer, bear, cougar, and bighorn sheep roam mountain crags, meadows,
and valleys. Mailing address: Estes Park, CO 80517.

    [Illustration: Theodore Roosevelt]

Theodore Roosevelt National Park is on Interstate 94 at Medora, North
Dakota. A separate unit is 90 kilometers (56 miles) north on U.S. 85. In
these magnificantly colored badlands along the Little Missouri River
Roosevelt had an open-range ranch and developed his practical
conservation philosophy. Both units have campgrounds. Mailing address:
P.O. Box 7, Medora, ND 58645.

                         Armchair Explorations

                    Some Books You May Want to Read

  Bartlett, Richard A., _Great Surveys of the American West_, University
  of Oklahoma Press, 1962.

  Camp, Charles L., _Earth Song: A Prologue to History_, American West
  Publishing Co., 1970.

  Colbert, Edwin H., _Evolution of the Vertebrates_, John Wiley and
  Sons, Inc., 1969.

  Cook, Harold J., _Tales of the 04 Ranch_, University of Nebraska
  Press, 1968.

  Cook, James H., _Fifty Years on the Old Frontier_, University of
  Oklahoma Press, 1980.

  Gould, Stephen Jay, _Ever Since Darwin: Reflections in Natural
  History_, W. W. Norton and Co., 1977.

  Howard, Robert West, _The Dawn-seekers_, Harcourt Brace Jovanovich,

  Johnson, Kirk R. and Richard K. Stucky, _Prehistoric Journey: A
  History of Life on Earth_, Roberts Rinehart, 1995.

  Lanham, Url, _The Bone Hunters_, Columbia University Press, 1973.

  Laporte, Léo F., _Evolution and the Fossil Record_, W. H. Freeman Co.,

  Larson, Robert W., _Red Cloud: Warrior-Statesman of the Lakota Sioux_,
  University of Oklahoma Press, 1997.

  Mason, Stephen F., _A History of the Sciences_, Collier Books, 1970.

  Meade, Dorothy Cook, _Heart Bags & Handshakes: The Story of the Cook
  Collection_, National Woodlands Pub. Co., 1994.

  Osborn, Henry F., _Cope: Master Naturalist_, Princeton University
  Press, 1931.

  Paul, R. Eli, _Autobiography of Red Cloud: War Leader of the Oglalas_,
  Montana Historical Society Press, 1997.

  Plate, Robert, _The Dinosaur Hunters: Othniel C. Marsh and Edward D.
  Cope_, McKay Co., 1964.

  Raup, David M. and Steven M. Stanley, _Principles of Paleontology_, W.
  H. Freeman Co., 1978.

  Romer, Alfred Sherwood, _Vertebrate Paleontology_, University of
  Chicago Press, 1966.

  Schuchert, Charles and Clara Mae LeVene, _O.C. Marsh: Pioneer in
  Paleontology_, Yale University Press, 1940.


  _Numbers in italics refer to photographs, illustrations, charts, or

  _Aepinacodon_ _54-55_, 60
  Agate Fossil Beds National Monument 11, 14, 50;
      animals at, _20-22_, 24-34, _84_;
      birding at, 81, _82-83_, 85;
      established, 17, 78;
      geology of 23, 47-52;
      museum specimen of, 38, _86-87_;
      topography of, 7;
      visitor information 77-80
  Agate Springs Ranch 7, 10, 17;
      excavations at, 38, _39_; fossils from, _40-41_, 86-87
  Alligator _54-55_, 60
  American Museum of Natural History 14, 38, 52, 87
  _Aplodontia_ 32

  Badlands National Park, South Dakota _88_, 90
  Barbour, Erwin H. 11, 14, 38
  Big Badlands, South Dakota 49, 52
  Bighorn Canyon National Recreation Area, Montana-Wyoming 92
  Bittern, American _83_
  Blackbird, red-winged _82_
  Bone Cabin, Wyoming 48
  Breeding Bird Survey, U.S. Fish and Wildlife 81, _82-83_, 85
  Buteos (buzzard hawks) 28

  Cambrian period _46_
  Camels. _See_ _Oxydactylus_, _Stenomylus_
  Camping 78
  Carboniferous period _46_
  Carnegie Hill _12-13_, 14, 37, 77
  Carnegie Museum 14, 38, 39, _40-41_, 69, 87, 88
  Carnivores, small 32-34
  Cenozoic Era _46_, 47, 49, 52
  Chalicotheres. _See_ _Moropus_
  Cheyenne River 52
  Cleveland, Utah 48
  Colorado Plateau 49
  Como Bluff, Wyoming 48
  Cook, Eleanor Barbour 14
  Cook, Harold 10, 14, 17, 52
  Cook, James H. _6_, 8, 10-11, 14, 77;
      buys Agate Springs Ranch, 7, 10;
      discovers fossils, 11, 24, 38
  Cook, Kate Graham 10-11, 14
  Cook, Margaret Crozier 17
  Cook Museum of Natural History 17
  Cope, Edward Drinker _9_, 11, 14
  Coyote _84_
  Cretaceous period _46_
  Curlew, long-billed _82_
  Cuvier, Georges 42, _43_, 45
  Custer Battlefield National Monument. _See_ _Little Bighorn
          Battlefield National Monument_

  _Daemonelix_ 33, _69_, 70, 86
  _Daphoenodon_ _20-21_, 22, 32, 38
  Darwin, Charles 43, _44_, 45
  Devil’s Corkscrew _76_
  Devils Tower National Monument, Wyoming _90_
  Devonian period _46_
  _Diceratherium_ 24. _See also_ _Menoceras_
  _Dinohyus_ _20-21_, 22, 30, 87
  Dinosaur National Monument, Colorado and Utah 42, 48, _88_
  Drought 35, 36, 50-51

  Ecology 53, 61-73
  _Entelodon_ 30
  Entelodont 30
  Eocene epoch 25, 27, 29, 31, _46_, 49, 53, 63, 88
  _Equus_ 63
  Excavations 38, _39_

  Field Museum of Natural History 87
  Flora 7, 10, 53, _54-59_, 60, 71-73
  Florissant Fossil Beds National Monument, Colorado 53, 88, _89_
  Folsom, New Mexico 14;
      spearpoint, 17
  Fort Laramie National Historic Site, Wyoming _90_
  Fort Robinson State Park, Nebraska 50, 77
  Fossil Butte National Monument, Wyoming 89
  Fossils _38-41_, 47, 86-89

  Geological Museum, University of Wyoming 86
  Geology 35, _46_, 47-52
  Geese, Canada _82_
  Gerenuk 29
  Gering Formation 50
  Gopher, pocket _84_
  Graham, Elisha B. 10
  Graham, Mary 10-11
  Grasslands 26, 35, 51, 61, 71-72
  _Gregorymys_ 33
  Guan 28

  Hagerman Fossil Beds National Monument, Idaho 89
  Harrison Formation 23, 50, 63
  Hawk _56-57_, 60;
      marsh _83_;
      nighthawk _83_;
      Swainson’s _81_
  Horses 62-63, _66-67_. _See also_ _Merychippus_, _Miohippus_,
          _Parahippus_, _Protohippus_
  Hutton, James 45

  Jackrabbit _84_
  Jefferson, Thomas 42
  Jewel Cave National Monument, South Dakota 91
  John Day Fossil Beds National Monument, Oregon 89
  Jurassic period _46_

  Killdeer _83_

  Laboratory _40-41_
  Lamarck, Jean-Baptiste de _43_
  Laramide Revolution 49
  Linnaeus, Carolus _43_
  Little Bighorn Battlefield National Monument 92
  Lucretius (Titus Lucretius Carus) 42
  Lyell, Charles 42, 43, _45_

  Map _78_, _79_
  Marsh, Othniel C. _8_, _9_, 11
  Marsland Formation 50, 51
  Matthew, W. D. 52
  McJunkin, George 14
  Meadowlark, western _83_
  _Meniscomys_ 32-33
  _Menoceras_ 14, _20-21_, _22_, _24_, 25, 36, 38, 51, 86, 87
  _Merychippus_ 52, _58-59_, 60, 62-63
  _Merychyus_ _20-21_, 22
  Mesozoic era _46_, 47-49
  Miocene epoch _46_, 49-52, 71-73;
      animals of 20-37, 62, 63, _64-69_, 70;
      birds of 28
  _Miohippus_ 25-26, 27, 64, _66-67_
  Mississippi Embayment 35, 49
  Monroe Creek Formation 50
  Morrison, Colorado 48
  _Moropus_ _20-21_, 22, _29-30_, 86-87
  Mount Rushmore National Memorial, South Dakota _91_
  Museum of Comparative Zoology, Harvard University 87
  Museum of Geology, South Dakota School of Mines and Technology 86
  Museums, fossils at _86-87_. _See also_ _American Museum of
          Natural History_, _Carnegie Museum_

  _Nanotragulus_ 27-28
  National Park Service 17, 88-92
  Nighthawk _83_
  _Nimravus_ 32
  Niobrara River 7, _16_, 23-24, 36, 37, 50, _54-55_, _60_
  North Platte River 52
  _Nothocyon_ 32, 33

  Oglala Sioux Indians 7, 11. _See also_ _Red Cloud_
  _Oligobunis_ 32
  Oligocene epoch 25, 31, _46_, 49, 50, 52, 53, 70, 88;
      animals of 61, 63
  Opossum _54-55_, 60
  Ordovician period _46_
  _Oreodon_ 25, _54-55_, 60, 63
  Osborn, Henry F. 14, 38
  Owl, great horned _83_
  _Oxydactylus_ _20-21_, 22, 28, _56-57_, 60

  _Palaeocastor_ 14, _20-21_, 22, _33_, 64, _68-69_, 70-71, 77, 86
  _Palaeolagus_ 34
  Paleocene epoch _46_, 53
  Paleozoic era _46_, 47-48
  _Parahippus_ _20-21_, 22, _27_, _56-57_, 60, 62, 67
  Permian period _46_
  Peterson, O. A. 14, 38, 39
  Petrified Forest National Park, Arizona _89_
  Pigs 30-31
  Pine Ridge, South Dakota 52
  Pleistocene epoch 28-29, _46_, _64_, 67
  Pliocene epoch 24-25, 27, _46_, 52, 63
  _Portheus_ 48
  Precambrian era _46_
  _Promerycochoerus_ _20-21_, 22, 25, 87
  Pronghorn (artiodactyls) 63, _84_. _See also_ _Syndyoceras_
  _Protoceras_ 31
  _Protohippus_ 62, 63
  _Pseudaelurus_ 32, _58-59_, 60

  Quaternary period _46_

  Red Cloud 9, 11
  Rhinoceros 24-25, 50, 51, 63
  Rocky Mountain National Park, Colorado 92
  Rocky Mountain Revolution 51, 52
  Runningwater Formation 51
  Rodents 32-34

  Sandpiper, upland _14_
  Scotts Bluff National Monument, Nebraska 49, _91_
  Sheep Creek Formation 52
  Silurian period _46_
  Smiley Canyon, Nebraska 50
  Snake, hognose _84_
  _Stenomylus_ 14, _20-21_, 22, _29_, 37, _39_, 50, _64-65_, 86, 87;
      _hitchcocki_, 51
  Sundance Formation 48
  _Syndyoceras_ _20-21_, 22, _31_
  _Synthetoceras_ 31-32

  Teeth, high-crowned 62-63
  _Temnocyon_ 32
  Tertiary period _46_, 53
  Theodore Roosevelt National Park, North Dakota 92
  Thompson, Albert 14, 38
  Toadstool Park, Nebraska 49
  Tortoise 33-34
  Trailside Museum, Nebraska 86
  Triassic period _46_

  Uniformitarianism 42, 43, 45
  University Hill 7, _12-13_, 35;
      digging at, 14;
      formation of 37;
      tourist facilities at, 77
  University of Nebraska State Museum 86

  Visitor information 77-80, 86-92
  Von Linne, Karl _43_

  Wallace, Alfred _45_
  White River 52;
      Badlands 31;
      Beds 49
  Wildflowers 7, 10
  Wind Cave National Park, South Dakota 91
  Wren, house _82_;
      long-billed marsh _82_

  ★GPO: 1999—454-765/00504
  Reprint 1999

                         National Park Service

The National Park Service expresses its appreciation to all those
persons who made the preparation and production of this handbook
possible. The Service also gratefully acknowledges the financial support
given this handbook project by the Oregon Trail Museum Association, a
nonprofit group that assists interpretive efforts at Agate Fossil Beds
National Monument.


James R. and Laurie J. Macdonald, authors of “A Landscape Rich With
Life” in Part 2, are paleontologists who live in Sunnyvale, California,
and teach nearby.

Doris B. Gates, writer of “Birding Along the Niobrara” in Part 3, is a
retired biology professor who lives in Chadron, Nebraska.


R.R. Donnelly & Sons Co. 79.


  Jay H. Matternes, who painted the wildlife panoramas and animal
          features on the cover and in Part 2, is a paleontological
          reconstruction artist who lives in Fairfax, Virginia. In Part
          2 his illustrations appear on pages 20-21, 24, 25, 27-33,
          54-59, 64-69.
  American Museum of Natural History 9 Cope.
  Greg Beaumont 14, 81-84.
  Carnegie Museum 38-41.
  Library of Congress 43-45.
  James O. Milmoe 12-13, 15, 16, 76.
  Peabody Museum of Natural History, Yale University 8.
  All other illustrations are from the files of Agate Fossil Beds
          National Monument and the National Park Service.

                    U.S. Department of the Interior

The mission of the Department of the Interior is to protect and provide
access to our Nation’s natural and cultural heritage and honor our trust
responsibilities to tribes. The National Park Service preserves
unimpaired the natural and cultural resources and values of the National
Park System for the enjoyment, education, and inspiration of this and
future generations. The National Park Service cooperates with partners
to extend the benefits of natural and cultural resource conservation and
outdoor recreation throughout this country and the world.

                           Agate Fossil Beds

     _Through the remains of animals long extinct, excavated here at
    this site, Agate Fossil Beds National Monument tells the story of
    the Miocene Epoch—the Age of Mammals—that occurred 5 to 23 million
    years ago. The scene on the front cover is from a mural by artist
    Jay H. Matternes that depicts animals of the Early Miocene._

    [Illustration: _In addition to fossils, the park has an extensive
    collection of Plains Indian art and artifacts, such as this shirt
    that belonged to Red Cloud._]

                          Transcriber’s Notes

—Retained publication information from the printed edition: this eBook
  is public-domain in the country of publication.

—Relocated all image captions to be immediately under the corresponding
  images, removing redundant references like “preceding page”.

—Silently corrected a few palpable typos.

—In the text versions only, text in italics is delimited by

—Conjecturally restored one subsection of the index entry for “Agate
  Springs Ranch”

*** End of this LibraryBlog Digital Book "Agate Fossil Beds National Monument, Nebraska" ***

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