Things we lost... Caribbean monk seal.

The Caribbean monk seal was a peaceful seal, very similar to its Mediterranean "cousin". It lived in big colonies among Cuba, the Netherlands Antilles and Jamaica. 
In 1494, Christopher Columbus saw them for the first time and he immediately ordered to kill eight of them to feed the ship's crew. 
Since then, the population of Caribbean seals had a meltdown; for centuries, the crews of European ships en route between Europe and the New World have been hunting them for their meat and their fur. 
It definitively became extinct during the 50s of 1900. 

(Thanks to Lorenzo S. for helping me writing this post)