Bull elk after sunset, Yellowstone National Park. Tourists passing through may hear the word "Wapiti" now and then, which is a Native American word for these animals from the Shawnee meaning "white rump." Those antlers are made of bone, can spread over 4 feet, and weigh over 20 pounds. These antlers are amongst the fastest growing tissues in the animal kingdom, and can grow up to 1 inch per day!