Photo of Giraffes Giraffa camelopardalis, Honolulu Zoo PJ 2009
Especially strange animals like the Australian platypus were long assumed to be a fake animal put together by the taxidermists and brought back to England, or when the western civilization realized that there actually exists black swans in Australia, which until then had been considered to be creatures of myths. Other beasts that fairly recently became acknowledged as real was the gorilla which until explorers actually captured one and brought it with them had been considered African superstitious stories about large dark haired apes living high up in the Deep unaccessible African mountain jungles.
Other mythological beasts might have similar history being now branded as cryptids, and described in a side note in anecdotal paper on cryptozoology. If you liked this entry you would probably also like The Mermaid of Finnmark.