A Mokele Mbele, now commonly found in the CONGO rain forest..

 A Mokele Mbele, now commonly found in the CONGO rain forest.

The legend of the long-necked, water-loving reptilian beast dwelling deep in the African jungle was widely known of by sailors who ported in the area. 

So, when a Portuguese crew returning from the second globe found a few juveniles of this Creature had stowed away on their ship, they made sure to release them back into what they thought was their natural habitat when they stopped by Angola.

The thing is, the locals made up the Mokele Mbele as a joke because they thought white sailors would believe anything. 

They have no idea what these things are or where they came from.