Recently I’ve photographed both eastern cottontail rabbits (Sylvilagus floridanus, Leporidae) and snowshoe hares (Lepus americanus, Leporidae). On the surface both of these animals look rather similar:
Despite the similarities, however, these animals feature a number of differences. First, rabbits and hares have different numbers of chromosomes and can’t interbreed (cottontails also have different numbers from true rabbits, and they can’t interbreed either). Rabbits tend to have smaller, more compact bodies, while hares are larger, lankier, and more athletic-looking. Rabbit young are born hairless, sightless, and helpless. Their mothers keep them hidden to protect them from predators, either in underground warrens or surface nests, depending on species. Young hares are born fully-developed on the ground and are capable of moving around to an extent.
These are just some of the more obvious differences between these animals. I suspect those who study rabbits and hares can point out many more.