Arctic Tundra: Musk Oxen
Musk oxen are hoofed mammals found in the arctic reaches of North America, Greenland, and Siberia. They are large animals with an outer coat of long hollow guard hairs and inner coat of fine, thick underhair, or qiviut. These layers insulate them against the extreme cold of the arctic tundra. They use their large, sharp curved horns for defense. They travel in herds and, when threatened, will stop and form a circle. The young calves are pushed inside the circle, and the adults form a defensive ring. Some paleontologist propose that this is how dinosaurs like Triceratops might have protected their young.
credit: Jerry L. Hout, U.S. Fish and Wildlife Service