Why Rabbits Aren't Actually Rodents
According to Britannica, of the more than 4,600 mammal species thought to roam the Earth, nearly half are rodents, making them the largest mammalian order. So if you had to pull a random milkable animal out of a hat and guess which kind it was, "rodent" would be your best bet. Unless, of course, that mammal is a cat or — much more surprisingly — a rabbit. As it turns out, the critter we're most likely to to associate with hats that aren't filled with lice doesn't actually belong to the rodent family.
"But how can this be?" you must be asking with an exasperated gasp. "Everyone knows that Mickey Mouse and the Easter Bunny must be brothers from different mothers! They even look like they were fathered by the same milkman." In reality, there's nothing brotherly about them. Per the Society of Vertebrate Paleontology, rabbits and mice belong to distinct "sister groups." While mice and about 2,000 other species of animal are classed rodents, rabbits are lagomorphs. Also included in the latter category are hares and Pikas, which presumably should make Pikachu a lagomorph as well.
Rabbits and rodents are similar...but different
Lagomorphs and rodents are superficially similar, so much so that, as the University of Texas at El Paso notes, they both used to be classified as rodents. After all, both rodents and lagomorphs are equipped with "ever-growing incisors and a diastema (space) separating the incisors from the cheek teeth." But "no rodent has more than a total of two upper and two lower incisors, whereas lagomorphs have a total of four upper incisors."
Another notable difference is species diversity within the two groups. Lagomorphs and rodents hopped and scurried (respectively) down very different evolutionary paths. The bunny trail led to fewer species because long-eared carrot-munchers had to compete with hoofed animals like horses, cows, pigs, and deer. As a result, there are fewer than 100 separate lagomorph species, and they tend not to vary very much in terms of size or physical traits. Bunnies aren't the only animals that are easy to confuse with rodents. Bats, which are often referred to as flying mice (in fact, the German word for "bat" is "fledermaus," which literally means "flying mouse"), are classified as Chiroptera, not rodents.