First, unicorns are not real: here is Wikipedia's article on the subject: Unicorn. Second, you posted this in Archaeology, but it actually belongs in Zoology, specifically in Cryptozoology (Wait, What is cryptozoology?). read more
But narwhals aren’t the only animals passed off as unicorns: In 1663, German naturalist Otto von Gü ericke made the first-known reconstruction of Pleistocene mammals, labeling his awkward creation a two-legged “unicorn.” (His unicorn “horn” is said to be a mammoth tusk, although some sources say he used a narwhal horn atop mammoth and woolly rhinoceros bones). read more
However, there are no fossils of unicorns. Horses, however, have an extensive fossil record. Several unicorn skeletons have been discovered, but all have also been discovered fakes. read more