Fossil Exhibit Trail

Accessible to people in wheelchairs.


. . . that we are looking down from a satellite 400 miles above South Dakota and that we see the Earth in the Cretaceous Period, about 70 million years ago.

The oldest Badlands rocks are forming - dinosaurs are still alive. More than 98% of the Earth's 4.6 billion year history has passed by as we study the landscape below.

A shallow sea reaching from the Gulf of Mexico to the Arctic Ocean divides North America into two parts. South Dakota is underwater!

Several flying reptiles called Pteranodons sail like hang-gliders ablove wind-whipped water. One tilts its wings, made of soft skin stretched over a strong frame of bones, and swoops low, snatching a fish from a school chased by another reptile called Plesiosaurus. Powerful flippers propel the plesiosaur's sleek body through the water. With quick strikes of its long snake-like neck it snaps up many fish.

We can see beneath the surface where a sea turtle called Archelon paddles sedately. Ammonitids with coiled shells, and Baculites, their close relatives with straight shells, swim by jetting water from their bodies.

Large pearly clams called Inoceramus live partly buried in the mud bottom. A dead body of the huge fish-eating bird, Hesperornis, lies half covered by the dark silt, and a few dinosaur bones from a carcass that floated from a nearby shore are scattered about. Beneath the mud is a deposit of black shale made of sediment laid down earlier.

Suddenly an earthquake stirs the bottom and muddies the water.

We back off for a wider view. Volcanos erupt on the land to the west. As the years flash by, the dinosauers die out, leaving the earth to the small mammals which survive them. The sea drains away to the north exposing a muddy plain: the Rocky Mountains rise. Plants grow on the plain that was once the bottom of the sea, and develop into a forest. The chemistry of the plants, the air, and the rain gradually turns the top of the black shale into rich red soil.

Now we watch the beginning of the most recent 46 million years, 1% of Earth history. About 37 million years ago, toward the end of the Eocene Epoch, mammals come into full flower, and we take a close look.

A pair of the big rhinocerous-like titanotheres sway at the shoulders as they plod along a stream-side jungle trail. A herd of small three-toed ancestors of the modern horse look up from drinking, unware that a saber-toothed cat watches from behind some fern.

To the west, in the direction of the young, vigorous Rockies, a great storm builds. It unleashes a torrent of water and mud which rushes down to flood this area. Many animals are trapped, die, and are buried. Their flesh decays, but over the years that follow, their bones absorb minerals and turn into fossils.

For 15 million years, through the late Eocene and all of the Oligocene, the floods and deposition of mud recur many, many times. Periodically, explosive volcanos throw megatons of ash into the air; some of the ash settles in layers over the area. The climate becomes drier and cooler. The jungle gives way to grassy prairie. The mammals change from heavy, many-toed creatures that amble through jungle swamps eating soft vegetation, to swift herds of oreodonts, horses, and other mammals that browse the grassland. We see rhinos almost as fleet as race horses.

Thousands of tiny deer-like animals mince along while browsing, then bounce across the grassland like so many rubber balls when pursued by predatory dogs, hyeana, or cats. Many mannals are too small for us to see, the mmice, the bats and others. They are food for the large hawks that glide over the land.

Almost all of these animals have fewer toes than their predecessors (an adaptation for fast running)m and tough teeth which resist wear from abrasive grass, a kind of plant just coing into its own.

Big land turtles crawl everywhere, munching plants. On the ground, numberless beetles roll balls of dung made from droppings of the grazers. Singly they bury the dung in underground seclusion - or in pairs they mate and lay eggs which hatch out into maggots which feed on the dung.

A few vigorous streams snake through the area providing habitat for numerous beavers. Some small species look and live like prairie dogs, digging burrows in the soil. On the wooded banks descendants of the jungle animals make their homes.

The Oligocene Epoch ends 23 million years before the present. And so we end our imaginary ride on the satellite and find ourselves in the present again.

Except for a few places in the park where pockets of sediment about ten thousand years old survive (a time when mammoths still roamed the prairie), the conclusion of the Oligocene marks the end of the fossil record in the Badlands.

Today, with our feet planted firmly on the ground, we should consider the ages of the rock layers that surround us. We stand with our backs to the parking lot.

Buried about 300 feet beneath us is the layer called the Pierre Shale which formed on the bottom of a shallow sea in the time of the dinosaurs. Also buried beneath our feet is the Chadron Formation of the late Eocene, the address in time of titanotheres and the steamy jungle they roamed.

Look at the ground we stand on. This surface is part of the Poleslide Member of the Brulé Formation, laid down during the early years of the Oligocene Epoch. Thirty million years is a good approximate age for this spot, although, climb a little way up a slope and we subtract a few million years; drop down into a gully and we add a few.

Look now to the high ridge on our left. It is capped by sandstone made from sediments that collected in a streambed; hence it is called channel sandstone. For as long as those tough rocks are up there, they protect the ridge from erosion. Obviously though, great chunks of the channel sandstone have been undercut in the past, broken off, and rolled down the slope. This sandstone, containing many fossil bones and teeth which washed into the stream, probably is the youngest Oligocene layer which survives here, only about 23 million years old.

Shall we walk the Fossil Exhibit Trail now? Along the way we wil see plaster replicas of fossils which were found here. Real fossils are not exhibited. Read The History of the Fossil Exhibit Trail of this booklet if you want to know why.

Guide to the Fossil Exhibit Trail

  1. Merycoidodon, a member of the oreodont family.
    The oreodonts died out about 5 million years ago; what we know about them comes entirely from studies of their fossil remains. They were stocky, about the size of sheep. But their long tails, short legs, and upper and lower pairs of fang-like teeth made them look very different from sheep, or pigs, or from any other familar animals. One things is sure - the oreodonts are the most commonly fossilized North American mammals of the Oligocene Epoch. Merycoidodon, commonly fossilized in the Badlands, is considered typical of the oreodont family. By their numbers, and by indications of a facial gland which appears to have been identical to scent glands used by some modern animals to mark territory, we know they were sociable, running in herds.

    Another indication of group interaction in the oreodonts is well developed vocal equipment (larynx) discovered fossilized in a specimen of a related genus. An encounter with a herd of the plant eating Merycoidodon, jostling for position as they browsed, may have been a noisy experience; an experience, however, which we may be content to imagine!

    The oreodonts (close relatives to camels) have been found only in North America. Some, like the genus Leptauchenia, have been regarded as aquatic because their eyes are high on their skulls, as are those of alligators.

  2. Mesohippus, the Ogilocene horse - and a coprolite of a predator.
    If the oreodonts, known only by their fossils, are difficult to imagine as living animals, the horses of the Ogilocene are easier to visualize. Though small, they resembled the horses of the genus Equus that are alive today.

    The horse of the Oligocene, Mesohippus and the very similar Miohippus, already had the leggy grace of Equus, though not the size. Mesohippus was little larger than a collie dog, and had three toes per foot (the middle toe longer and bigger than the others), rather than the single toe of Equus. Three toes supported the animal better than one when traveling through swampy places.

    Mesohippus did not always outmanuever its predators, of course. We know that because often its fossilized skulls, as well as those of other grazing mammals, are found in the Badlands without a trace of the remainder of the skeleton, evidence that predators and scavengers devoured or hauled off the more easily crunched bones. A further clue of the activities of predators during the Ogilocene here is the coprolites (fossil feces) often found in association with skulls of herbivores.

    Feces of bone-crunching predators and scavengers are highly mineralized because of the calcium in the bones they ingested. That is why these feces are more frequently fossilized than the mineral-poor, rarely fossilized feces of plant eaters.

  3. Hyracodon, an Oligocene rhinoceros.
    The Hyracodons, smaller than today's rhinos, were trim and speedy like the horses of their time. But eventually they died out, leaving the field to the ponderous rhinoceroses which survived them, some still hanging on in greatly reduced numbers in Africa and southeast Asia. Indeed, the living rhinos may soon join the hyracodonts in extinction. Increasingly, their wild places are cleared for farms. Also, they are hunted for their horns, valuable because they are reputed to restore sexual vigor to those who have lost it.
  4. Subhyracodon, the ancestor of the modern rhinoceros - and fossil boluses of bung beetles.
    Big and supported by heavy legs, Subhyracodon was not the sort of animal that could run swiftly over the plains. Its teeth were built for grinding tougher plants than those eaten by its small fleet relative, Hyracodon. But both were plant eaters; they contributed daily to the droppings that littered the Oligocene prairie.

    Droppings of plant eaters were rarely fossilized in the same shape as when they fell. But marble-sized balls of dung, called boluses, were frequently fosillized after burial by the dung beetles.

    Coprolites fossilized in the shape as when they fell, and fossilized dung beetles boluses, both are trace fossils. By trace fossil it is meant that, while the body of the plant or animal was not preserved, some trace of it was, not only proving the plant or animal's existence, but often telling something about how it lived.

    Thus, the fossilized boluses in this exhibit prove that beetles that rolled dung here in the past. They are also evidence of the mammals which produced the dung, and even of the plants which were eated by mammals.

  5. Hyaenodon, a hyaena-like mammal - and fossil seeds of hackberry.
    Predators like Hyaenodon are much less numerous as fossils than the herbivores they preyed upon. The reason is straightforward. Every pound of a predator takes about ten pounds of plant eater to support it; a pack of Hyaenodons required a population of hundreds of Oreodonts to keep them fed.

    Robust jaws indicate that the Hyaenodons, like the modern hyaenas that live in Africa, specialized in crushing the bones of their victims, and the victims of other predators as well, for the marrow inside.

    The white pea-sized objects beside the Hyaenodon skull are hackberry seeds. they are almost as rich in calcium as bone, and that is why, in contrast to other plants, they were commonly fossilized in the Badlands formations, Hackberry has survived the tens of millions of years that have elapsed since the Oligocene, and still abounds in the Badlands. in fact, its present range includes most of the United States and parts of Canada.

  6. Stylemys, a land turtle - and snails.
    Turtles were plentiful in the Badlands during the late Eocene and Oligocene. Great land tortoises lumbered over the landscape. Periodically they were drowned by the muddy floods that swept down from the western highlands and fossilized. The turtle populations bounced back after the floods. Safe from most predators, they had evolved armor, a defensive strategy pioneered hundreds of millions of years earlier by the quite unrelated snails.

    Land snails also were abundant here during the Oligocene, and their shells were frequently fossilized. yet these fossils shells are rarely seen. As soon as one is exposed by erosion, rainwater dissolves it. this frees the coil of claystone, called a cast, which filled the shell when a flood buried it.

  7. The giant pig Archaeotherium - and plant roots.
    A long robust head and sturdy tusks fitted the giant pig for rooting. Scratches on their tusks, presumably made by sharp grains of sand clinging to the roots the Archaeotherium ate, have been accepted as evidence that they fed on underground parts of plants - even as do their distant relatives, the pigs of our breakfast table. Like the living pigs, Archaeotherium was omniverous, that is, it ate plants and animals as the opportunity arose.

    Because Archaeotherium was large and had fearsome tusks, we doubt that most predators dared to risk a clash with a full grown adult. They are thought to have been very agressive, perhaps fighting among themselves. many of their fossil bones show healed injuries.

    Here and there in the Oligocene Badlands, conditions were right for the fossilization of plant roots. that such fossils even exist here has only recently been recognized.

    The roots and other evidence prove that the Badlands formations consist mostly of fossil soils, one stacking atop the other as one layer of mud after another was deposited and converted into soil, only to be covered with fresh mud by the next flood. One scientist counted 87 fossil soils from the earliest of the Badlands formations to the most recent.

    The rain-eroded buttes may look desolate, but they are not. Every rain frees from their flanks fossil plants and animals of an ancient landscape.

The Fossil Exhibit Trail Story

In the late 1950's, park planners struggled with the problem of how to exhibit the park's fossils in the field. It seemed obvious how to do it. Find an area rich in fossils, remove enough of the Badlands rock so that visitors could clearly see the fossils, and build a trail connecting the specimens.

But it was not that easy. Even at the most promising site, the site of the present trail, the variety and quality of fossils accessible to a trail simply were not there. Marvelous things were found, but nature had not placed them with a fossil exhibit in mind.

Three suitable in situ specimens (specimens in the place where they were fossilized) were found, but not enough to justify a trail. Reluctantly, the planners decided to bring in genuine fossil skulls, found elsewhere in the same formation and place them along the trail where such fossils might have been found, had we been so lucky.

From the beginning it was recognized that the fossils on the trail would have to be protected from climate and human erosion. They were housed in concrete boxes with strong plastic domes. And so, the trail was constructed and opened to the public in the spring of 1962. Immediately - a big problem! Vandals and thieves smashed domes and damaged or hauled off exhibit fossils faster than it was practical to replace them. If the trail were to be kept open, it had to be with plaster casts of the fossil skulls - casts made and painted to the most exacting museum standards. And so they were installed.

The casts, worthless on the market, and impossible to remove without shattering, have not been immune to vandals, nor have the domes escaped damage, but with constant attention, the park has kept the trail in operation since 1962.

In 1985, fossil seeds, roots, coprolites, snails and beetle boluses were added to the exhibits in order to better portray the Oligocene environment. All of these fossils are commonly found in the area, and are frequently associated with fossils of the species exhibited.

Despite departures from a true in situ exhibit trail (which never existed), the trail winds through Badlands formations where real fossils lie just beneath the surface (as they do throughout the park). The result is a view of Oligocene life more immediate than could be achieved in a museum.

Since its very inception, the Fossil Exhibit Trail has been immensely popular. In 1980, the Secretary of the Interior, Cecil D. Andrus, designated it a National Recreation Trail in the National Trails System.

It is illegal to remove fossils, or any other geologic specimens, from a National Park.
Text by Jay Shuler.
From the brochure published by the Badlands Natural History Society.

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© 1995 Karen M. Strom