I can't believe these actually existed...
Steller’s Sea Cow
We still call manatees “sea cows,” but they weren’t the only ones. Discovered in 1741 by Georg Steller, sea cows were much bigger than manatees or dugongs. Their average size was thought to be about 26 feet long and they were estimated to weigh around three tons!
While living sea cows were found in the Commander Islands (in the Bearing Sea), there is evidence that the species was once very wide-spread. Unfortunately, it only took about three decades after their discovery for sea cows to go extinct. Their docile, trusting nature made them easy targets for hunting and their valuable meat, fat, and skins made them desirable prey. The last sea cow was thought to be killed in 1768, though there are unsubstantiated accounts that people have seen them in the wild since.
Also known as the “giant deer,” Irish elks have the unique distinction of being the largest deer to ever walk the Earth. Despite the name, the Irish elk was not exclusive to the areas that became Ireland, rather the best preserved remains were discovered on the island.
It’s unclear exactly what led to the extinction of the giant deer as the most recent remains have been dated to about 8000 years ago, but there are a few different popular theories…
Irish Elk, continued
The first theory is overhunting by ancient humans, but it’s almost impossible to verify hunting rates from limited remains. The more likely theory is that they had a maladaptation (an evolutionary adaptation that negatively affects survival) resulting from orthogenesis that caused them to die off or initiated an evolutionary split that led to their modern day relatives.