The northwestern wolf (Canis lupus occidentalis), also known as the Mackenzie Valley wolf, Alaskan timber wolf, or Canadian timber wolf, is a subspecies of gray wolf in western North America. Arguably the largest grey wolf subspecies in the world, it ranges from Alaska, the upper Mackenzie River Valley; southward throughout the western Canadian provinces, aside from prairie landscapes in its southern portions, as well as the Northwestern United States. Taxonomy This wolf is recognized as a subspecies of Canis lupus in the taxonomic authority Mammal Species of the World (2005). The subspecies was first written of by Scottish naturalist Sir John Richardson in 1829. He chose to give it the name occidentalis in reference to its geographic location rather than label it by its color, as it was too variable to warrant such. According to one source, phylogenetic analyses of North American gray wolves show that there are three clades corresponding to C. l. occidentalis, C. l. nubilus and C. l. baileyi, each one representing a separate invasion into North America from distinct Eurasian ancestors. C. l. occidentalis, the most northwestern subspecies, is descended from the last gray wolves to colonize North America. It likely crossed into North America through the Bering land bridge after the last ice age, displacing C. l. nubilus populations as it advanced, a process which has continued until present times. Along with C. l. nubilus, C. l. occidentalis is the most widespread member of the five gray wolf subspecies in North America, with at least six different synonyms. Description Northwestern wolves are one of the largest subspecies of wolves. In British Columbia, Canada, five adult females averaged 42.5 kg or 93.6 lbs with a range of 85 lbs to 100 lbs (38.6 - 45.4 kg) and ten adult males averaged 112.2 lbs or 51.7 kg with a range of 105 lbs to 135 lbs (47.6 - 61.2 kg), with a weight range for all adults of 38.6 kg to 61.2 kg (85 - 135 lbs). In Yellowstone National Park, adult females were average about 40 kg (90 lbs) and adult males average about 50 kg (110 lbs), with a mean adult body mass in winter of . More recent studies have reported the average range of height and weight in the north-west of the United States, both sexes were between tall at the shoulder. Here the weight of males was reported at between , while