The formation of the Isthmus of Panama, about 3 Mya, joined South America to North America, allowing canids to invade South America, where they diversified. However, the most recent common ancestor of the South American canids lived in North America some 4 Mya and more than one incursion across the new land bridge is likely. One of the resulting lineages consisted of the gray fox ("Urocyon cinereoargentus") and the now-extinct dire wolf ("Aenocyon dirus"). The other lineage consisted of the so-called South American endemic species; the maned wolf ("Chrysocyon brachyurus"), the short-eared dog ("Atelocynus microtis"), the bush dog ("Speothos venaticus"), the crab-eating fox ("Cerdocyon thous"), and the South American foxes ("Lycalopex" spp.). The monophyly of this group has been established by molecular means.