Virginia Opossum (Didelphis virginiana) is the only marsupial (family Didelphidae) found in North America north of the Rio Grande River. A solitary and nocturnal animal about the size of a domestic cat, it is a successful opportunist and is found throughout Central America and North America from coast to coast (introduced to California in 1910), and from Costa Rica to southern Canada; it seems to be still expanding its range northward. Its ancestors evolved in South America, but were enabled to invade North America in the Great American Interchange by the formation of the Isthmus of Panama about 3 million years ago. The Virginia Opossum is often seen near towns, rummaging through garbage cans, or lying by the side of the road, a victim of traffic.