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Evolution in the Great Lakes

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Notable Fossil Finds:

  • In 1897, a mastodon skeleton was found near Boaz, Wis. Spear points found in it suggest it was probably killed by early human hunters. (See it at the Geology Museum at the University of Wisconsin.)

  • In 1958, a 300-million-year-old sea creature -- perhaps transparent in appearance -- was found in Illinois. Later named the Tully Monster, this foot-long soft-bodied marine animal has no recognizable relatives, and no one knows how it swam or what it ate.

  • In 1938, a young giant beaver skeleton was discovered by workers excavating a road in St. Paul, Mich. The animal lived about 10,000 years ago, and was estimated to be 250 pounds, or about half its potential size.

  • The Gunflint and Mesabi Iron Ranges of Minnesota contain 2-billion-year-old fossil bacterial formations called stromatolites. These layered mounds represent life's earliest ecosystems.

  • In 1919, a massive trilobite -- more than a foot long -- was discovered by workers excavating the Huffman Dam near Dayton, Ohio. Most trilobites are only inches in length. A 16-inch fossil was later discovered in Montgomery County, Ohio.

  • Fossil teeth of rhinoceroses and a three-toed horse from the Miocene epoch (23-5 million years ago) have been found in western Iowa. Younger elephant bones have also been discovered there.

Endangered Species:

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

 Gray wolf

Gray wolf (land mammal)
  • Appearance: Coal-black to snowy-white in color, with longer legs and larger feet than most dogs (4-5 feet long, 50-140 pounds)
  • Habitat: Wolves live in packs over territories from 50 to 1,000 square miles in size; they are highly adaptive to climate extremes and can live most anywhere
  • Threat: Human hunting
  • Fast fact: Until their protection in 1973, gray wolves had been exterminated in all lower 48 states except Minnesota. Wolf reintroduction programs, though controversial, have restored populations to several states in this region.

Indiana bat (land mammal)
  • Appearance: Black-haired, with distinctive pink lips (most bats have dark lips)
  • Habitat: Dispersed widely across the countryside when not hibernating in caves
  • Threat: Human disturbance during hibernation, or changes in cave climate
  • Fast fact: When bats are awakened from hibernation, they quickly burn fat reserves meant to sustain them through winter.
Karner blue butterfly (insect)
  • Appearance: Males are dark blue/silvery, with narrow black margins around its wings; females are gray/brown on outer wing portions, blue on the top, and have irregular orange crescents inside a black border (one-inch wingspan)
  • Habitat: Caterpillars eat only wild lupine leaves; adults feed on plant nectar
  • Threat: Habitat loss (from man-made and natural causes), collectors
  • Fast fact: This species has two hatching periods. Caterpillars emerge from eggs in April, feed, then pupate. These butterflies then mate and lay eggs in late-summer that won't hatch until the following spring.
Hine's emerald dragonfly (insect)
  • Appearance: Emerald-green eyes and a metallic green body, with yellow stripes on its side (three-inch wingspan)
  • Habitat: Marshes rich in calcium carbonate
  • Threat: Development of wetland habitats, pollution, and pesticides
  • Fast fact: While adults may live only four to five weeks, the development, or nymph, stage can last several years.
Piping plover (bird)
  • Appearance: A beige and white body, with a short black bill and yellow legs
  • Habitat: Beaches and sandflats, where they nest and feed on crustaceans, molluscs, and insects
  • Threat: In the past, hunting; today, development and recreational use of beaches
  • Fast fact: In 1991, only 16 pairs were counted in the Great Lakes region.
Kirtland's warbler (bird)
  • Appearance: Blue-gray head and upper body, with a yellow underside (six inches)
  • Habitat: Its highly specialized breeding requirements restrict it to areas with large stands of 8- to 22-year-old jack pine trees
  • Threat: In the past, extensive logging; today, wildfire prevention policy, which replaces jack pines with red pines or hardwood trees
  • Fast fact: In 1987, only 167 singing males were counted; today, there are more than 1,000.


Take a giant step back, to 2 billion years ago. Look around at what will later be the Great Lakes-Big Rivers region, and you'll see no plants or animals, only the sea and perhaps some beaches. In shallow waters are mounded formations called stromatolites. These are actually colonies of bacteria or algae, which live as mats layered one on top of the other. You can find fossil stromatolites today in northern Michigan and Minnesota.

Limestone and coal beds, which formed from the organic remains of reefs and plant life, respectively, tell us that tropical conditions prevailed over all of what is now North America from about 550-250 million years ago. It was in the southern hemisphere back then, drifting toward the equator. Shallow seas covered the region, with trilobites, sea scorpions, and plantlike animals called crinoids among the thriving marine life. When sea levels dropped, forested swamplands formed in coastal areas. Giant insects and some of the earliest amphibians lived in these habitats.

Fossil fishes, sharks, and marine invertebrates suggest much of the region was probably flooded by water when dinosaurs roamed the planet. The occasional fossilized bone indicates that at least some dry land harbored animal life.

Lakes, rivers, rolling hills, and fertile plains -- these are lasting reminders of the region's most recent geological activity. Glaciers flowed down from the north at least four times during the last Ice Age. They covered nearly all of the region before retreating. As they advanced, they scoured the surface. As they melted, rushing waters filled depressions, cut river channels, and flooded lowland areas. The rugged scenery of the Driftless Area in Illinois and Wisconsin -- land left untouched by glaciers -- provides a glimpse at what the region looked like prior to the Ice Age.

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