The question of whether the familiar, bushy-tailed squirrel is classified as a rodent is a frequent point of curiosity for many people observing backyard wildlife. Biological classification can often seem overly complex, yet it provides a precise framework for understanding the relationships between different animal groups. Understanding where the squirrel fits helps clarify the broad diversity of the world’s mammals.
The Definitive Answer
Squirrels are classified as rodents, belonging to the Order Rodentia. This vast order encompasses a wide array of mammals, including rats, mice, porcupines, and beavers. The squirrel specifically falls into the family Sciuridae, which includes tree squirrels, ground squirrels, and flying squirrels. Recognizing squirrels as members of this order places them within the largest group of mammals, accounting for approximately 40% of all mammal species globally.
Defining the Order Rodentia
The classification of squirrels within the Order Rodentia is fundamentally determined by their unique dental structure. The defining characteristic of all rodents is the presence of a single pair of continuously growing incisors in both the upper and lower jaws. These teeth are specialized for gnawing, which is reflected in the Latin origin of the order’s name, rodere, meaning “to gnaw.” The incisors are rootless, growing throughout the animal’s life, which necessitates constant use to keep them worn down.
These specialized teeth are structured with a thick layer of enamel only on the front surface. As the rodent gnaws, the softer dentine on the back surface wears away faster than the hard enamel on the front. This uneven wear creates a razor-sharp, chisel-like edge that constantly self-sharpens and functions effectively for chewing through tough materials like nuts and bark. Rodents also lack canine teeth, resulting in a large gap, known as a diastema, between their incisors and their cheek teeth.
Squirrels Versus Similar Mammals
The precise classification of rodents helps distinguish squirrels from other small mammals that are often mistaken for them, such as rabbits and hares. Rabbits and hares belong to a separate order called Lagomorpha, even though they share the feature of continuously growing incisors. The primary anatomical difference lies in the number of upper incisors; rodents possess only one pair in the upper jaw, while lagomorphs have two pairs. The second, smaller pair of upper incisors in lagomorphs, often called “peg teeth,” are located directly behind the larger front pair.
Other small animals like shrews and moles are also not rodents, belonging instead to the order Eulipotyphla. These animals lack the characteristic continuously growing incisors of both Rodentia and Lagomorpha, solidifying the dental structure as the critical factor in biological classification.