differed from modern wolves by 1 to 10 mutations, and all belonged to haplogroup2, indicating its predominance in this region for over 40,000 years, both before and after the Last Glacial Maximum. A comparison of current and past frequencies indicates that in Europe haplogroup2 became outnumbered by haplogroup1 over the past several thousand years, but in North America haplogroup2including the Beringian wolfbecame extinct and was replaced by haplogroup1 after the Last Glacial Maximum. However, a 2016 study did not support the existence of two wolf haplogroups. A scenario consistent with the phylogenetic, ice sheet size, and sea-level depth data is that during the Late Pleistocene the sea levels were at their lowest. A single wave of wolf colonization into North America commenced with the opening of the Bering land bridge 70,000YBP. It ended with the closing of the Yukon corridor that ran along the division between the Laurentide Ice Sheet and the Cordilleran Ice Sheet 23,000YBP during the Late Glacial Maximum. As wolves had been in the fossil record of North America but the genetic ancestry of modern wolves could be traced back only 80,000 years, the wolf haplotypes that were already in North America were replaced by these invaders, either through competitive displacement or through genetic admixture. The replacement in North America of a basal population of wolves by a more recent one is consistent with the findings of earlier studies. The Beringian wolves are morphologically and genetically comparable to Late Pleistocene European wolves. One study found that ancient wolves across Eurasia had a mDNA sequence identical to six Beringian wolves (indicating a common maternal ancestor). These wolves included a wolf from the Nerubajskoe-4 Paleolithic site, near Odessa, Ukraine, dated 30,000YBP, a wolf from the Zaskalnaya-9 Paleolithic site, in Zaskalnaya on the Crimean Peninsula, dated 28,000YBP, and the "Altai dog" from the Altai Mountains of Central Asia dated 33,000YBP. Another wolf from the Vypustek cave, Czech Republic, dated 44,000YBP had a mDNA sequence identical to two Beringian wolves (indicating another common maternal ancestor). The Beringian wolves are phylogenetically associated with a distinct group of four modern European mDNA haplotypes, which indicates that both ancient and extant North American wolves originated in Eurasia. Of these four modern haplotypes, one was only found in the Italian wolf and one only found among wolves in Romania. These four haplotypes fall, along with those of the Beringian wolves, under mDNA haplogroup2. Ancient specimens