Characteristics of animals in the tundra?

Answer 1

Short, sturdy limbs, stocky body, small ears, thick coat or other layer to keep warm, the ability to hibernate during winter, white or light coloring, heat-exchange system to keep warm blood near the core and colder blood in the extremities.

Answer 2

Well, tundra has few trees and a short growing season. So, I would expect the herbivores to be small or migratory. Predators would likely be few in number, and possibly hibernate.