Studies using mitochondrial DNA have indicated that the wolves of coastal south-east Alaska are genetically distinct from inland gray wolves, reflecting a pattern also observed in other taxa. They show a phylogenetic relationship with extirpated wolves from the south (Oklahoma), indicating that these wolves are the last remains of a once widespread group that has been largely extirpated during the last century, and that the wolves of northern North America had originally expanded from southern refuges below the Wisconsin glaciation after the ice had melted at the end of the Last Glacial Maximum. These findings call into question the taxonomic classification of "C.l. nulibus" proposed by Nowak. Another study found that the wolves of coastal British Columbia were genetically and ecologically distinct from the inland wolves, including other wolves from inland British Columbia. A study of the three coastal wolves indicated a close phylogenetic relationship across regions that are geographically and ecologically contiguous, and the study proposed that "Canis lupus ligoni" (Alexander Archipelago wolf), "Canis lupus columbianus" (British Columbia wolf), and "Canis lupus crassodon" (Vancouver Island wolf) should be recognized as a single subspecies of "Canis lupus".