Allen's Rule of latitudinal variation in Rabbucks (Ungulagus spp).

    50 Million Years after the Age of Man, the rabbit was left with no major grazing competitors and quickly evolved to occupy the position once held by deer. Variation in Rabbucks follows Allen's Rule: as compared with the temperate Common Rabbuck, the Arctic Rabbuck has a chunk body and relatively short extremities (note the ears and legs) whereas the Desert Rabbuck is more slenderly built.