When the Badlands Weren’t so Bad
A six-horned rhinoceros with tusks ambles along, startling a group of tiny horses which in turn spook a ground-nesting bird off its nest. Peace quickly returns to the meadow at the edge of a lush forest. It’s a warm, sunny day in the Oligocene Epoch, some 30 million years ago. A couple volcanoes are smoking in the Rocky Mountains far to the west. But the plumes are visible only to sharp-eyed eagles and hawks soaring overhead. About fifty years ago, a volcanic eruption had dumped a blanket of ash on the forest, killing most of the trees and animals. But no living animal in the area had even been born yet.
The Badlands
The White River Badlands is a spectacular burial ground for mammals that lived during the late Eocene and Oligocene epochs, which ended over twenty million years ago. The Badlands were hardly bad back then; rather, it was an area of lush forests.
During this period, Nature experimented with large herbivores, or plant-eaters. They eventually evolved into two great groups of ungulates, or hoofed mammals. Even-toed ungulates include such “cloven-hoofed” species as deer, antelope, sheep, goats, cattle, bison, camels, and pigs. The odd-toed ungulates are the rhinoceroses, tapirs, and horses.
During the Eocene and Oligocene, rhinoceroses and animals that resembled rhinoceroses were very abundant and diverse. They sported a great variety of horns and were the largest animals of the time, though some species were small.
The most spectacular Badlands fossils represent rhinoceros-like titanotheres, including Brontotherium. This beast carried two broad, blunt horns growing side by side on the nose, resembling a giant slingshot. Fossils of broken ribs are probably evidence of Oligocene sparring matches.
The tiny Hyracotherium, or eohippus — the “dawn horse” launched another group of odd-toed mammals. Over millions of years, they became larger and their toes became fewer. Today horses have a single hoof on each foot and are big enough to ride. Mesohippus was a horse that lived during the Oligocene.
Perhaps more abundant than rhinos and horses combined were various species of oreodons. They were so numerous that the rocks in which their bones are found are sometimes called “oreodon beds.” The most common species in the Oligocene Badlands, Merycoidodon was about the size of a sheep.
Today, only a few species of horses and rhinoceroses survive, while oreodons are extinct. But animals related to oreodons survived and evolved into the great diversity of even-toed hoofed mammals that are among the most familiar animals today. They include the bison, cattle, pronghorns, elk and deer that graze South Dakota’s grasslands even today.
Among the Badlands’ biggest mysteries is the chalicothere, a large creature with horse-like teeth and claws on its feet that could be retracted, similar to cats. What would this bizarre plant-eater have evolved into if it had not become extinct?
Geology & Fossils
The Missouri River divides South Dakota into two great regions. Western South Dakota includes the Badlands and Black Hills.
Eastern South Dakota
This region was covered by Ice Age glaciers, which removed much of the fossils from this region, burying others under tons of debris.
West Dakota
Some 200 years ago, Lewis and Clark crossed the Missouri River near the South Dakota-Nebraska border. They found themselves on the edge of an ocean prairie that came to be known as the Great Plains.
Today, some of the stone-capped buttes that tower over the Great Plains like lonely sentinels are named Turtle Butte. Native Americans had associated some of these landforms with turtles. Others may have been named by white pioneers for fossils of giant tortoises they found nearby. Today, South Dakota’s turtles are mostly small “mud” turtles — with an occasional prehistoric-looking snapping turtle — that swim in the small lakes, farm ponds, and streams that dot the land.
The biggest turtles yet discovered are buried beneath the Great Plains. Archelon grew to lengths of more than ten feet and had flippers. This sea turtle which lived more than 65 million years ago during the Cretaceous Period, when ancient seas covered much of the Great Plains. Other giant marine reptiles whose remains are abundant in South Dakota include lizard-like mosasaurs and long-necked plesiosaurs.
But South Dakota wasn’t completely underwater during the Cretaceous. Cretaceous dinosaurs that are well represented in South Dakota include hadrosaurs (or duck-billed dinosaurs), the hard headed Pachycephalosaurus, Tyrannosaurus and Triceratops.
In fact, the most famous tyrannosaur in the world is probably a South Dakotan specimen named Sue. Discovered in 1990, it’s the most complete skeleton ever found. Evidence of healed-over scars on its face, along with other injuries, indicate it may have fought with another Tyrannosaurus. Sue gained even more fame as it became the center of a legal battle involving its discoverer, a rancher, Native Americans and the FBI. Sheez!
But the Triceratops had already been adopted as South Dakota’s state fossil. Its remains are especially abundant in the Hell Creek Formation near Mud Buttes. These are located west of the community of Belle Fourche, the geographic center of the United States.
South Dakota is also known for its fossil cycads. Sometimes growing as large as trees, these plants evolved during the Triassic Period, then became very diverse and abundant during the Cretaceous. A few cycads survive today, though none are native to the United States.
The Black Hills
South Dakota’s oldest rocks are found in the Black Hills, which can be thought of as a mountainous island in a sea of grass. The Black Hills were formed during the Paleocene and Eocene eras when great blocks of ancient metamorphic and igneous rock were thrust upward. The rocks are as old as 2½ billion years, but sediments deposited in valleys in the Black Hills contain fossils, including some dinosaurs — like Barosaurus. Discovered in the Black Hills, this long-necked sauropod is one of South Dakota’s best known souvenirs from the Jurassic Period.
South Dakota’s Chinese Connection
George Washington was the first person to introduce the Chinese ring-necked pheasant to North America. Today, Washington’s likeness is carved on the face of Mt. Rushmore, South Dakota’s most famous landmark. And the ring-necked pheasant is South Dakota’s state bird!
With its gaping mouth and enormous bill, the paddlefish looks like a prehistoric monster, and it is. Paddlefishes live only in the Missouri River and its tributaries and in China. Why is their range so far apart?
Fossils tell us paddlefishes lived during the Cretaceous Period, when the continents were arranged quite differently. As continents drifted apart, they certain species were “stranded” on opposite sides of oceans. The American alligators’s closest relative also lives in China, while tapirs are found in both tropical America and tropical Asia.
South Dakota Geologic Map
(Courtesy South Dakota Geological Survey)To see the map, click here.
Eastern South Dakota
Eastern South Dakota was shaped by the Pleistocene Epoch, or “Ice Age.” Beginning about 2 million years ago, continental glaciers moved generally southward across North America, covering eastern South Dakota several times. As each ice sheet advanced, it transported large volumes of rock debris frozen into the lower layers of ice. Thick, heavy glaciers scoured and smoothed off the terrain. Thinner ice sheets overrode obstacles rather than planing them. As the ice melted, sediment called glacial drift was left behind.
The boundary between the tan color and the light green on the left is formed by the Missouri River. The funny-colored oblong area surrounded by green spots at top right is the James River Valley, a souvenir of ancient Lake Dakota. Learn more about East Dakota’s Ice Age heritage.
West Dakota
If you want to look for fossils in South Dakota, just remember the three colors above. Fossils of dinosaurs and marine reptiles are found in rocks representing the Cretaceous Period. Shale and chalk are laid down in water, so that’s where you’d find fossils of sea turtles, ammonites, etc. Sandstone and clay are land deposits; look there for Tyrannosaurus, Triceratops and cycads. Learn more about South Dakota’s Cretaceous Rocks, and why they’re responsible for the gold rush that turned the Black Hills into a tourist mecca and confined its original inhabitants to Indian reservations!
Orange represents sediments laid down during the early part of the Age of Mammals (Tertiary). The large orange area at the bottom of the map is the White River Badlands, which is known for its fossils of large mammals that lived during the Oligocene Epoch (part of the Tertiary). At the top of the map is another badlands area with Tertiary rocks. It merges with the North Dakota Badlands. Learn more about South Dakota’s Tertiary Rocks, and why they may have kept the Black Hills looking 40 million years young!
Some fossils of older dinosaurs have been found in the blue area encircling the Black Hills at bottom left. Those rocks were laid down during the Jurassic and Triassic periods. The lighter blue represents rocks laid down during the Paleozoic Era, long before dinosaurs evolved.
The reddish center, which represents the core of the Black Hills, indicates 1) igenous rocks (granite, rhyolite, phonolite), which are hardened lava (molten rock that flows to the surface) or magma (molten rock that remains underground) and 2) metamorphic rocks (schist, slate, quartzite) which are formed under great pressure. Igneous rocks don’t contain fossils, and any fossils in metamorphic rocks have usually been destroyed. What makes these rocks interesting is their great age more than two billion years! Two small areas of Precambrian rocks are also found in eastern South Dakota. Learn more about South Dakota’s oldest rocks.
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