Irish Elk is neither exclusively Irish, not is it an elk.
It's the largest deer that ever lived.
Reliable estimates of their total antler span range up to 12 feet.
It evolved during the glacial period of the last few million years and became extinct in Ireland around 11000 years ago (but may have survived to historic times in continental Europe).
Why did such huge antlers evolve? What was the adaptive advantage they provided?
They served as "visual dominance-rank symbols". Mostly for display/ritualized combat, not as weapons.
If the antlers are adaptive, why did the deer become extinct?
The giant deer flourished in Ireland for a very brief warm period (between two colder epochs) of about 1000 years, 12000 to 11000 years before the present. They were well adapted for the glassy, sparsely wooded, open country of this time but probably could not adapt fast enough for the subarctic tundra that followed, or to the heavy forestation that developed after the final retreat of the ice sheet.
Darwinian evolution decrees that no animal shall actively develop a harmful structure, but it offers no guarantee that useful structures will continue to be adaptive in changed environments.
Ever Since Darwin: Reflections in Natural History by Stephen Jay Gould
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