The opossum is a marsupial of the order Didelphimorphia endemic to the Americas. The largest order of marsupials in the Western Hemisphere, it comprises 110+ species in 19 genera. Opossums originated in South America and entered North America in the Great American Interchange following the connection of the two continents. Their unspecialized biology, flexible diet, and reproductive habits make them successful colonizers and survivors in diverse locations and conditions. In the United States and Canada, the only species found is the Virginia opossum. It is often simply referred to as an "opossum", and in North America they are commonly referred to as possums.