How could I not have done the Irish Elk (Megaloceros giganteus) yet? I have, to date, mentioned it twice.
Oh, right. Deer just are not very weird until you start going prehistoric with them. This giant deer is dead. It's pushing up daisies. It has CEASED to BE. THIS is an EX-DEER!
The Irish Elk, AKA the Giant Deer, lived around 400,000 years ago. Like the aurochs, it was a Pleistocene megabeast. It was not related to any modern elk; it was a HUGE deer, getting approximately 7 feet high at the shoulder. An antler spread of up to twelve feet from tip to tip made a male of the species even more imposing and majestic than that one shot in Bambi.
Then Disney sequelled the hell out of it.
The Irish Elk is one of the "textbook standards" for a very specific type of extinction: Its sexually-attractive antlers eventually got so huge that they killed the species. Its rack was either so big that it actually impeded movement, or a climate change simply made that headgear impossible to sustain. Essentially, it was like that overly-decorated cell phone that your best friend has; y'know, the one with so much shiny junk on it that you wonder how the eff it works.
I've seen worse.
Humans played a minimal part in its extinction; after all, we also had cows to deal with back then. The Irish Elk and humans shared space for a good long time; it's not like humans suddenly went around killing these weird giant deer that they had never seen before. Again, the hugeass antlers likely hindered the deer when they tried to avoid hunters. Either way, that headgear was their downfall.
Now, when I say "Irish Elk'd" in an entry, you will know what I mean. Those horns are pimpin', but they ultimately killed the deer.