Origin and genetics[edit]
The gray fox appeared in North America during the mid-Pliocene epoch 3.6 million years ago (AEO) with the first fossil evidence found at the lower 111 Ranch site, Graham County, Arizona with contemporary mammals like the giant sloth, the elephant-like Cuvieronius, the large-headed llama, and the early small horses of Nannippus and Equus.[8] Genetic analyses of the fox-like canids confirmed that the gray fox is a distinct genus from the red foxes (Vulpes spp.). Genetically, the gray fox often clusters with two other ancient lineages, the east Asian raccoon dog (Nyctereutes procyonoides) and the African bat-eared fox (Otocyon megalotis).[9] Chromosome number is 2n=66.[10] Faunal remains at two northern California cave sites confirm the presence of the gray fox during the late Pleistocene.[11] Genetic analysis has shown that the gray fox migrated into the northeastern United States post-Pleistocene in association with the Medieval Climate Anomaly warming trend.[12] Recent mitochondrial genetic studies suggests divergence of North American eastern and western gray foxes in the Irvingtonian mid-Pleistocene into separate sister taxa.[13]
The gray fox's dwarf relative, the Channel Island fox, is likely descended from mainland gray foxes.[14] These foxes apparently were transported by humans to the islands and from island to island, and are descended from a minimum of 3-4 matrilineal founders.