This 2015 video is called Channel: 4 Extinct: The Irish Elk. This species is also called giant deer.
It is from the last ice age, a time when the North Sea was still a plain, where, eg, giant deer grazed. In the Netherlands now, North Sea sand is used to build the Zandmotor, an artificial island to prevent flooding.
In the Zandmotor sand, someone recently found that deer molar, and brought it to the natural history museum in Rotterdam. There, scientists discovered there were Ice Age plant rests on that molar.
Eg, remains of Artemisia plants were found on the molar. That is not a plant which covered a large part of the land during the Ice Age, but it does contain a lot of calcium. “That is exactly what one needs to build up enormous antlers”, says [paleontologist] Mol.
So far, paleontologists had never paid attention to plant rests on giant deer fossils. Meanwhile, 30-40 other giant deer molars with plant rests have been discovered in the Rotterdam museum collection.
Maybe other museums will start to investigate their collections as well, to find out what exactly giant deer ate.
The scientific report, Giant deer (Megaloceros giganteus) diet from Mid‐Weichselian deposits under the present North Sea inferred from molar‐embedded botanical remains, was published here.