For a long time, rabbits were taxonomically classed within the order Rodentia, a large (about 40070 of the total) body of mammals that are commonly called rodents. The order Rodentia includes not only the common mouse and rat but also gerbils, hamsters, lemmings, porcupines and beavers, to name only a few others. Today zoologists consider rabbits, hares and some closely related animals to form an order of their own, the order Lagomorpha. Blood tests show that there is a lesser relationship between rodents and rabbits than previously had been thought to exist. Rodents are characterized by having teeth that grow throughout life. The teeth of rabbits, unlike man’s and like rodents’, are permanent and do not grow continuously. Another distinction is the presence of a bone called the bacullum in the sheath of the penis in males; it is present in rodents but not in lagomorphs.
The order Lagomorpha contains two families, the family Ochotonidae and the family Leporidae. Ochotonidae contains one genus and 13 species; Leporidae contains 9 genera and approximately 50 species. Members of the family Ochotonidae are small burrowing animals that don’t look too much like rabbits. They are commonly known as pikas. They are furry, with short ears and no tail, and are found mostly in Asia, though two species are found in North America. They are also known as whistling hares because of the sharp bark or whistle that they make. The differences between rabbits and bares are slight, and there is much confusion by way of common names, the one being the name for the other, and vice versa. The only generally recognizable difference is that hares are larger than rabbits, but this is very basic.