Kangaroo rats have large back legs for several key reasons:
Jumping: Powerful hind legs enable bipedal locomotion, helping them leap great distances to evade predators and navigate desert terrain.
Burrowing: Strong legs are essential for digging burrows that provide shelter and help conserve water.
Energy efficiency: Large, muscular legs help conserve energy while hopping through arid environments where water is scarce.
Essentially, their legs are a perfect adaptation for desert life, supporting speed, burrowing, and efficient movement.