Cenozoic Era

Illustration of <em>Castoroides</em> in New Jersey, by Charles R. Knight
Illustration of Castoroides in New Jersey by Charles R. Knight, 1904

66 Million Years Ago - Present Day

The Cenozoic Era began after the impact of an asteroid wiped out the dinosaurs, enabling mammals to proliferate, flourish, and grow in size. One example is the giant beaver, Castoroides. Most fossils of Castoroides have been found in states bordering the Great Lakes, from Illinois to Ohio, but their fossils range from Alaska to Florida, dating from more than one million years ago to 11,000 years ago. Humans arrived in Illinois around 12,000 years ago, in time to hunt megafauna from mammoths to giant ground sloths as Ice Age glaciers receded.