The males of the Cervidae (deer) family, such as elk, moose, deer, and caribou, grow antlers on their heads. Caribou are the only species in which the females also have antlers. Antlers are branched structures made of bone. Most antlered animals shed them annually in the fall or winter and then grow new antlers in the spring. Horns, unlike antlers, don't fall off but continue to grow throughout the animal's life. Further, horns aren't branched, nor are they made entirely of bone. Horns contain a bony core that is covered with a sheath of keratin, similar to the material of fingernails. Horned animals, which include sheep, cows, bison, and goats, are in the Bovidae family. In many Bovidae species, both females and males have horns. Which organizational structure does this text primarily use? for ixl