Evolution title
portion of frog image
Evolution in the Moutain-Prairie

More on endangered species | Fossil collecting | Educational standards | Other regions

Notable Fossil Finds:

  • In 1857, the rarest, oldest, and first sauropod dinosaur in the western United States was discovered in southern Utah at the bottom of the Morrison Formation. Sauropods were large, herbivorous, four-legged creatures that lived over a 100-million-year span.

  • In 1911, researchers discovered the remains of a mosasaur, a huge aquatic reptile, in the Smoky Hill Chalk formation in western Kansas. At 50 feet long, it was one of the largest mosasaurs found in North America. (See it at Kansas University's Museum of Natural History.)

  • Since 1971, nearly 100 complete rhinoceros skeletons have been uncovered in Nebraska's Ashfall Fossil Beds, along with dozens of horses, camels, turtles, and cranes. Volcanic ash buried these animals 10 million years ago.

  • Fossil Lake in Wyoming contains fossils of more than 20 kinds of fish, 100 varieties of insects, and a large number of plants. Skeletons, teeth, fish scales, and even skin have been preserved in rock layers 45-50 million years old.

  • In 1877, the backbone of the first-known Stegosaurus was discovered near Morrison, Co.

  • In 1952, a 90-million-year-old fish was discovered preserved in chalk near Fort Hays, Kan. Inside its body was an undigested smaller fish, also well preserved.

  • A giant Ultrasaurus, a carnivorous Torvosaurus, pterosaurs, and other fossils have been discovered in Dry Mesa Quarry near Delta, Co. Scientists first found the site in 1971. (See the fossils at the Museum of Western Colorado.)

  • The Cleveland-Lloyd Dinosaur Quarry in Utah has yielded more than 30 complete dinosaur skeletons, 12,000 bones, and several eggs. Most of the bones are from the dominant Jurassic carnivore, Allosaurus. (See these fossils at the College of Eastern Utah Prehistoric Museum.)

  • The Mancos Shale formation in Utah has large fossil ammonites, marine invertebrates that lived inside coiled shells. Some specimens are more than a 18 inches in diameter.

  • Alamosaurus, a giant, four-legged plant-eating dinosaur, was found on the Wasatch Plateau in central Utah. It is thought to have been the only sauropod dinosaur left at the great extinction 65 million years ago.

  • Several Utahraptors have been found in the Cedar Mountain formation near Arches National Park, Utah. These sickle-clawed carnivores probably hunted in packs. (See them at the College of Eastern Utah Prehistoric Museum.)

  • In 1922, the largest-known mammoth skeleton was discovered in Lincoln County, Neb. It stood 14 feet tall at the shoulder and was probably not yet full-grown. (See "Archie" at the University of Nebraska State Museum.)

  • An ancient nesting ground with as many as 20 fossilized dinosaur eggs was found on what is now called Egg Mountain in Montana. The discovery suggests dinosaurs exercised parental care and that they might have been warm-blooded.

  • In 1993, what may be the only known fossilized dinosaur heart was discovered in northwestern South Dakota. The heart was found in the chest cavity of a 13-foot-long plant-eater that lived 66 million years ago.

  • In 1998, the bones of five Tyrannosaurus rex individuals, including perhaps the biggest ever, were discovered in Garfield County in eastern Montana. The first Tyrannosaurus fossil was also found here in 1902. Of the 20-odd ever found, the most complete specimen, named Sue, was unearthed in South Dakota's Badlands in 1990.

Endangered Species:

Photo of American burying beetle The following animal and plant species are among those listed in the federal government's register of endangered species in this region.

 American burying beetle

American burying beetle (insect)

  • Appearance: Shiny black body, with orange-red markings on its wing covers and one just behind its head, this beetle also has orange facial markings and orange tips on the antennae (1.5 inches)
  • Habitat: Lives where carcasses are found, though prefers grasslands and open hardwood forests
  • Threat: Lack of carcasses, pesticides
  • Fast fact: To reproduce, these beetles need the rotting flesh of small or medium-sized birds or mammals. A breeding pair buries the carcass, mates, and the female lays eggs in a nearby tunnel. Larvae feed on the carcass before emerging from the ground.

Black-footed ferret (land mammal)

  • Appearance: These long, slender weasels have short yellow-beige fur, a brown head, a black mask around the eyes, black feet and legs, and a black-tipped tail
  • Habitat: Prairie dog colonies; they feed primarily on prairie dogs by night and use their burrows as shelters
  • Threat: Habitat loss to farming, prairie dog elimination tactics, disease
  • Fast fact: Reintroduction sites must be free of rabies and plague, or else these diseases could wipe out entire prairie dog colonies and thus hurt ferret recovery.

Pallid sturgeon (fish)

  • Appearance: This toothless fish possesses a flattened, shovel-shaped snout; bony plates; and a long, reptile-like tail (up to six feet long, weighing 80 pounds)
  • Habitat: River systems that include the Missouri River, the Yellowstone River, and the Mississippi River
  • Threat: Damming and other diversions that alter the flow of water or its temperature
  • Fast fact: Pallid sturgeon are one of the largest, ugliest, and oldest fishes in the region, having evolved from fishes that lived 70 million years ago.

Topeka shiner (fish)

  • Appearance: Silvery in color, with a well defined dark stripe along its side, and a dark wedge-shaped spot at the base of the tail fin (less than three inches)
  • Habitat: Small prairie streams in pools with clear, clean water
  • Threat: Changes in water quality, accelerated soil runoff, which causes sedimentation
  • Fast fact: Because this small minnow is reliant on clean water, it serves as an indicator of the general health of the ecosystems in which it lives.

Eskimo curlew (bird)

  • Appearance: Dark brown body with a lighter breast and a pale-white throat with brown streaks, the curlew's distinctive curved bill is two inches long (11-14 inches)
  • Habitat: Eskimo curlews spend winters in the treeless plains of Argentina, then migrate north to the tall grass prairies of the Mississippi Valley. They breed in the arctic tundra.
  • Threat: Because of its low population (35-150 individuals), it is particularly vulnerable
  • Fast fact: By the 1900s, this bird, which once numbered in the millions, was thought to be extinct due in large part to heavy hunting along its migratory path.


The Mountain-Prairie region has arguably the most impressive fossil heritage in North America. As far back as 1.7 billion years ago, blue-green algae communities formed mounds that later hardened, and these "stromatolites" can now be found in Wyoming and Montana.

Prairie states, which are flood-prone, have a strong record of ancient marine life, including ancestors of squid, clams, and snails. Limestone, a by-product of marine life, underlies much of Kansas, for example. The formation of the Rockies, beginning about 300 million years ago, lifted the land around them, so land animals feature prominently in the fossil record of the drier Mountain states.

Shallow seas covered the center of North America on and off through the dinosaur age (225-65 million years ago). The elevated canyons and mesas of the Colorado Plateau, however, have produced some of the best-known dinosaur fossils. The Morrison Formation, home to Dinosaur National Park, is a fossil-rich rock layer from the Jurassic period, during which the world's largest-known dinosaurs lived.

In the time following the dinosaur extinction 65 million years ago, sea levels dropped. Weathering of the Rocky Mountains sent large volumes of sediment on to the Great Plains. Then, about 30 million years ago, sustained volcanic activity in the mountains sent ash eastward, covering the landscape and snuffing out life. From the plant and animal life preserved in these thick deposits, we can interpret such things as climate, and have come to know that the region was warmer then than it is today.

Beginning about 2 million years ago, Ice Age glaciers advanced from Canada well into the Mountain-Prairie region. The land-altering effect of the moving glaciers can still be seen in the small depressions, or "prairie potholes," that spot the region's northern landscape.

Explore Evolution online at www.pbs.org/evolution
Back to your local station's home page