When the ice melted the Holarctic clade spread south and east, while the Nearctic clade spread north, the two meeting in central Canada.
Aubry’s data reveal more than just the distribution of foxes in pre-history, it also elucidates the relatedness of the animals currently inhabiting North America (see: Taxonomy).
Briefly, the creature that taxonomists currently think gave rise to modern-day dogs was a medium-sized (about the size of a coyote) grassland predator of North America called that appeared during the late Eocene, some 36 mya.
The caniforms subsequently diverged into three lineages (which we call subfamilies): the Hesperocyoninae (‘western dogs’); the Borophaginae (‘bone-crushing dogs’); and the only one still around, the Caninae, which includes the dogs, wolves, foxes, etc.
At some point -- by current thinking, around 42 million years ago (mya), during the mid-Eocene -- it appears that the carnivorans split into the two groups, or suborders, that we recognise as cat-like (Feliformia) and dog-like (Caniformia).Fox domestication Living with the wild: interacting with wild foxes Interaction with other Species Small and Medium-sized Mammals Livestock Gamebirds Arctic Foxes and other Carnivores Deer Native Animals in Australia Plants and Invertebrates Questions and Answers Evolution and Early Distribution: Dogs and cats are Carnivorans, that is, they’re members of the taxonomic order Carnivora (note this is different to simply being a carnivore, or meat-eater, which is not a taxonomic grouping), which is one of 29 orders within the class Mammalia.The evolution of carnivorans appears to have been a gradual process that happened in both North America and Eurasia, making it difficult to infer when it all started.Recent genetic work by Keith Aubry and his colleagues at the Pacific Northwest Research Station in Washington, however, has revealed new information on the spread of the Red fox in North America.Aubry’s data suggest that this species first reached North America during the Illinoian glaciation that lasted from roughly 300,000 to 130,000 years ago; during the next 30,000 years (the Sangamon interglacial period) the foxes spread south from Alaska, across what is now the contiguous USA.