Jennifer A. Leonard et al., discuss the evidence for the old world origins of new world dogs from pre-Columbian times.
Jennifer A. Leonard, Robert K. Wayne, Jane Wheeler, Raúl Valadez, Sonia Guillén, Carles Vilá, "Ancient DNA Evidence for Old World Origin of New World Dogs," Science 298 (November 22, 2002): 1613-16
Mitochondrial DNA sequences isolated from ancient dog remains from Latin America and Alaska showed that native American dogs originated from multiple Old World lineages of dogs that accompanied late Pleistocene humans across the Bering Strait. One clade of dog sequences was unique to the New World, which is consistent with a period of geographic isolation. This unique clade was absent from a large sample of modern dogs, which implies that European colonists systematically discouraged the breeding of native American dogs.