In 1577, the English explorer Martin Frobisher led an expedition of 150 men to the northern reaches of Canada, in search of a passage to India and a fortune in gold. As they surveyed the islands near the coast, they came across something Frobisher could never have anticipated: a unicorn fish.

“Upon another small island here,” Frobisher wrote in his journal, “was also found a great dead fish, which, as it would seem, had been embayed with ice, and was in proportion round like to a porpoise, being about twelve foot long, and in bigness answerable, having a horn of two yards long growing out of the snout or nostrils. This horn is wreathed and straight, like in fashion to