Narwhal

Few treasures brought home from their travels by sailors in ancient times caused more wonderment than the horn of the fabled unicorn. But the sailors' tall tales were eventually found out and the unicorn's horn proved to be the no less extraordinary upper left tooth of the narwhal (Monodon monoceros). The tusk can grow up to 3m long, and is used for fighting other males, usually over a female but often just in a display of strength. Most adult males have battle-scarred heads, and sometimes the hollow tusk breaks. Narwhals, which eat fish, krill and squid, stay close to the pack ice and it is not unknown for them to get trapped beneath it and die.