The mammal with the largest antlers of any extant deer is the moose, Alces alces. Its antlers are broad and palmate, shaped somewhat like open hands, rather than the narrower, branching form typical of many other deer.
Only male moose normally grow antlers. They begin developing in spring under a living covering called velvet, grow rapidly during the summer, and are shed after the autumn breeding season. Age, nutrition, health, and subspecies all affect their size. Mature Alaskan bulls can have antler spans of about 1.8 meters, with recorded antler weights reaching roughly 36 kilograms.
Moose use antlers mainly for display, dominance contests, and fighting rivals. Their size can signal a male’s condition, but the number of points is not a simple age calculator; beam diameter and overall development are more useful indicators.
The extinct Irish elk had even larger antlers, so the word “extant” matters here. Among living deer, however, the moose is the clear answer. In Eurasia, the same species is commonly called the elk, which can create confusion with the North American elk, or wapiti.