12,000 years ago
The Ice Age glacier diorama depicts a relatively recent phenomenon: the Wisconsin glacial episode, specifically the advance and retreat of this massive ice sheet's Des Moines Lobe, which started about 24,000 years ago. The Des Moines Lobe's effect on the north-central Iowa landscape still can be seen in everything from the lakes and river system the lobe formed to the productive soils it deposited. When the glaciers melted back some 12,500 years ago, a change in climate occurred. Many Ice Age mammals moved farther north, like the musk ox and reindeer, or they became extinct, like the mammoth. The Giant Ice Age Sloth,Megalonyx jeffersonii, the famed "Giant Claw" discovered by Thomas Jefferson, stood almost ten feet tall and weighed 2 to 3 tons, as much as a small elephant. It grazed Iowa's woodland during a geologic period called the Pleistocene when huge glaciers of ice covered most of Iowa. Sloths were herbivores who used their claws for food gathering, defense, and possibly to climb trees. They became extinct about 9,500 years ago, along with mammoths, giant beavers, camels, and many other large ice age mammals living in Iowa. Besides the climate change, early Paleoindians may have hastened the sloth's demise since they would have found the huge, sluggish creature an easy prey.