The answer to whether a squirrel is in the rat family is scientifically “no,” though the confusion is understandable since they share a close genetic background. Squirrels and rats are not classified within the same family, which is a specific grouping in biological taxonomy. Their relationship is much broader, placing them together at a higher level of classification, but their separate evolutionary paths resulted in distinct physical and behavioral traits.
Shared Identity: The Rodent Order
Squirrels and rats are fundamentally linked because they both belong to the Order Rodentia, the largest group of mammals globally, encompassing approximately 40% of all mammal species. This group includes diverse animals such as beavers, porcupines, hamsters, mice, and capybaras. The single, unifying characteristic defining every member of this order is their specialized dental structure, which is adapted for gnawing.
All rodents possess a single pair of large, chisel-shaped incisors in both their upper and lower jaws that grow continuously throughout their lives. The front surface of these teeth is covered in hard enamel, while the back is softer dentine. This structure causes the back to wear away faster, constantly maintaining a sharp, self-sharpening edge. This continuous growth necessitates constant gnawing to wear the teeth down. Additionally, all rodents lack canine teeth, leaving a noticeable gap, known as a diastema, between the incisors and the molars.
The size of the Rodentia order requires a breakdown into different families, which is where squirrels and rats diverge. This separation reflects millions of years of evolution that led them to adapt to different habitats and lifestyles. Although they share the same fundamental dental design, differences in body shape, tail structure, and behavior place them into separate family groups.
The Squirrel Family (Sciuridae)
Squirrels belong to the family Sciuridae, a diverse group consisting of approximately 280 species. This family is found across the Americas, Eurasia, and Africa, occupying habitats from forests to grasslands. Sciurids are characterized by their climbing adaptations, though many species are strictly terrestrial. The family includes:
- Tree squirrels
- Chipmunks
- Marmots
- Groundhogs
- Prairie dogs
The most recognizable physical trait of many squirrels, especially arboreal species, is their long, bushy tail, used for balance and communication. Tree squirrels also have long, muscular legs and sharp claws that aid in agility and the ability to scale trees quickly. Conversely, ground squirrels, such as marmots, are more robust with shorter, stouter limbs for digging burrows, and their tails are typically less bushy.
The typical diet for most sciurids centers on nuts, seeds, and fruit, though their eating habits are opportunistic. They consume a range of items, including fungi, insects, eggs, and small vertebrates. Specialized forms, such as flying squirrels, possess a furred membrane of skin (a patagium) that extends between their wrists and ankles, allowing them to glide between trees.
The True Rat and Mouse Family (Muridae)
The true rats and mice belong to the family Muridae, one of the largest families of mammals in the world. This successful family contains over 1,383 species, including the common house mouse and the genus Rattus (true rats). Murids are found on every continent except Antarctica and have adapted to a vast range of environments, from tropical forests to tundras.
Unlike the bushy-tailed sciurids, murids typically have slender bodies, pointed snouts, and long tails that are generally hairless or covered in scales. This difference in tail structure is a clear distinction between the two families. The majority of murids are terrestrial, living on or under the ground, although the family does include some arboreal species.
Murids are known for their generalized, omnivorous diet and high reproductive potential. Species like the Norway rat (Rattus norvegicus) and the black rat (Rattus rattus) are highly adaptable to human environments, leading to their widespread distribution. The Muridae family’s success is due to its ability to fill a wide array of ecological niches.