Mastodons
The American mastodon (scientific name Mammut americanum) roamed North America from at least 3.75 million to 11,000 years ago. Mastodons, along with mammoths and modern elephants, are members of the order Proboscidea. As adults they stood between 2.5 and 3 meters (8-10 feet) at the shoulder and weighed betweeen 3500 and 5400 kilograms (4-6 tons).
Mastodons became extinct approximately 11,000 years ago. Today, paleontologists are trying to understand why.
Mammoths
Three species of mammoths (genus Mammuthus) lived on the mainland of the United States at the end of the last Ice Age. These were the Columbian mammoth (M. columbi), Jefferson's mammoth (M. jeffersonii), and the woolly mammoth (M. primigenius). Of these, Jefferson's mammoth and the woolly mammoth have been identified from the midwestern U.S.
As adults these late-occuring mammoths stood between about 3 and 3.7 meters (10-12 feet) at the shoulder and weighed between 5500 and 7300 kilograms (6-8 tons).
Approximately 1.5 to 1.8 million years ago the first mammoths entered North America. These mammoths came from Eurasia, crossing the Bering Strait at a time when sea level was lower than today. The first mammoths from Eurasia belonged to a species called M. meridionalis. The descendants of this species of mammoth included both the Columbian and Jefferson's mammoths. The woolly mammoths evolved in Eurasia and came over the Bering Strait much later (perhaps less than 500,000 years ago). Approximately 11,000 years ago all species of mammoths went extinct in North America.
