The origins of Dire Wolves seemed to have become somewhat confused at some point. There has been discussion in the past as to where these wolves came from and how they became as large, as a population and individually, in North America. As with many animals in North America it appears that that the origins lie in a movement over the Bering land bridge into North America from Asia during the Quarternary period. The animal that actually made the journey was a somewhat different canid known as Canis armbrusteri. During its fanning out into different packs throughout the central plains of North America the animals began to differentiate appreciably and eventually C. armbrusteri disappeared as a recognizable species and was effectively replaced by C. dirus which arose from these new adaptations and speciation events. The Dire Wolf packs moved into the South American continent as they continued to differentiate from C. armbrusteri and two subspecies (C. nehringi and C. dirus) developed, but are not officially recognized as such because they are considered to be genetically identical. Two subspecies have been named in North America though. Canis dirus dirus is recognized as being larger and populating the lands east of the Rocky Mountains while the west coast and lands were populated by the smaller C. dirus guildayi. It is most interesting to note that the extant Gray (C. lupus) and Red (C. rufus) wolves are of Eurasian origin, more recently than the Dire Wolf. These two species survived through the extinction which claimed the Dire Wolf in part because they were smaller and more agile, allowing them to expand their prey selection whereas the Dire Wolf was built more for wrestling, as a pack, the larger mammoths and other megafauna that died out at the end of the Pleistocene.