The anatomy of Arctotherium is, at least superficially, almost the same as that of extant bears. There are differences in bone size and morphology from extant bears. The body plan has not changed in a very long time for bears because it is a very successful body plan. During the species exchange of the Great American Interchange the ancestors of Arctotherium and their competitors such as Smilodon were very successful in their invasion of South America. The portions of the anatomy that ultimately made Arctotherium successful, within the ursine body plan, were the robust limbs and strong but versatile cranium and teeth. As with extant bears, Arctotherium likely, as we have seen in papers, had an omnivorous diet. An omnivorous diet allows an animal like Arctotherium maintain the high caloric intake that a body of its size would require during times when either vegetation or prey animals might be scarce. A flexible diet is a winning characteristic in an invasive species as it allows it to expand into any niche that it can muscle itself into. Not having any natural predators or being a nearly 2 tonne bear certainly helps as well.