One of the largest deer to ever roam the planet, the Irish Elk one lived throughout Eurasia, although its namesake comes from the many specimens found in the bogs of Ireland. Their study by Georges Cuvier was a key moment in extinction as a concept, as before this time, the idea of extinction was not common place. He was the first to challenge the thought that the Irish Elk had living specimens, asserting that perhaps they were wiped out.

They were massive, standing at nearly 7 feet tall (2.1 meters) at the shoulders and holding antlers that were as large as 12 feet (3.65 meters) from tip to tip, weighing 88 pounds (40 kg) alone. It’s estimated that they grew as large as 1,543 pounds (700 kg).

Their extinction is much debated. The argument over their massive antlers trumped all other theories, proposing that sexual selection drove their antlers to be too large, thus killing the species. However, further study showed that the antlers were always proportional to the body size no matter how much females preferred larger antlers during the rut.

One theory suggests a change in the nutritional quality and quantity of their foliage led to a decrease in female reproduction and in a condition similar to osteoporosis. Climate change in the last glacial period was the driving force behind the changing foliage.

However, the youngest specimen, found in Siberia, showed no signs of nutritional stress, leaving a mystery to their eventual demise.

Extinction Date: About 7,700 years ago