Aboriginal hunters from Arctic Canada have a couple of names for what they say is an extremely rare polar bear that is huge, narrow-bodied, fast-moving and lithe: "tiriarnaq" or "tigiaqpak," meaning "weasel bear." Now the thawing and rapidly eroding Chukchi Sea coastal permafrost has produced evidence that one of these legendary weasel bears — or some other strange kind of bear — roamed Arctic Alaska centuries ago. A huge, fully intact and unusually shaped polar bear skull emerged in 2014 from an eroding archaeological site about 13 miles southwest of Utqiaġvik (Barrow). It is one of the biggest polar bear...