regions, but a substantial breeding population occurred on isolated Sable Island, 100 miles southeast of Nova Scotia and 500 miles due east of Portland, Maine, until the early Colonial period. Abundant walrus remains have also been recovered from the southern North Sea dating to the Eemian interglacial period, when that region would have been submerged as it is today, unlike the intervening glacial lowstand when the shallow North Sea was dry land. Fossils known from San Francisco, Vancouver, and the Atlantic US coast as far south as North Carolina have been referred to glacial periods An isolated population in the Laptev Sea was considered by some authorities, including many Russian biologists and the canonical Mammal Species of the World, to be a third subspecies, O. r. laptevi (Chapskii, 1940), but has since been determined to be of Pacific walrus origin. Anatomy While some outsized Pacific males can weigh as much as , most weigh between . An occasional male of the Pacific subspecies far exceeds normal dimensions. In 1909, a walrus hide weighing was collected from an enormous bull in Franz Josef Land, while in August 1910, Jack Woodson shot a walrus, harvesting its hide. Since a walrus's hide usually accounts for about 20% of its body weight, the total body mass of these two giants is estimated to have been at least . The Atlantic subspecies weighs about 10–20% less than the Pacific subspecies. Male Atlantic walrus weigh an average of . The Atlantic walrus also tends to have relatively shorter tusks and somewhat more flattened snout. Females weigh about two-thirds as much as males, with the Atlantic females averaging , sometimes weighing as little as , and the Pacific female averaging . Length typically ranges from . Newborn walruses are already quite large, averaging in weight and in length across both sexes and subspecies. All told, the walrus is the third largest pinniped species, after the two elephant seals. Walruses maintain such a high body weight because of the blubber stored underneath their skin. This blubber keeps them warm and the fat provides energy to the walrus. The walrus's body shape shares features with both sea lions (eared seals: Otariidae) and seals (true seals: Phocidae). As with otariids, it can turn its rear flippers forward and move on all fours; however, its swimming technique is more like that of true seals, relying less on flippers and more on