Norwegian Lundehund

Six toes on each foot, ears that fold shut and a neck that bends back towards the spine: every oddity of the Lundehund was shaped by centuries of scrambling into cliff crevices after puffins on Norway's coast. When puffin hunting died out the job went with it, and distemper outbreaks around the Second World War and in 1963 left the breed rebuilt from a handful of closely related survivors. The world population has since recovered to roughly 1,500, and Norway's breed club now runs a controlled outcross to other Nordic spitz breeds. Ask any breeder about Lundehund syndrome, an incurable gut disorder the bottleneck left behind.