Megalonyx jeffersonii, commonly known as Jefferson's ground sloth, was a large prehistoric mammal that roamed North America. It was an herbivore with long claws and a robust body, adapted for foraging in forests and open woodlands.

M. americanum, commonly known as the American mastodon, was native to North America. Its geographical distribution ranged from Alaska and the Yukon in the north, southward through most of the United States, and into parts of Mexico. Fossil evidence has been found as far east as the Atlantic coast and as far west as the Pacific coast.

The American mastodon primarily inhabited deciduous and mixed woodlands, swamps, and marshy areas. These environments provided the cool, moist conditions that were favorable for their survival. The climate during the time of the mastodons was generally cooler and wetter than it is today, often associated with the late Pleistocene epoch.

As herbivores, mastodons primarily fed on shrubs, trees, and other vegetation available in their woodland habitats. They were well adapted to browsing and were likely important for maintaining the structure of their ecosystems by influencing the composition and distribution of plant species. Their presence in diverse environments suggests a degree of adaptability to different ecological niches within their range.