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One of the most abundant wild mammals living in moderate latitudes is the common squirrel. Squirrels thrive in almost every habitat, from tropical rainforest to semiarid desert. They avoid only the cold polar regions and the driest deserts. Squirrels are also one of the very few mammals that thrive in cosmopolitan areas. Some wild squirrels have even become pets of a sort, or at least comfortable around people, if the human is patient and not aggressive towards the animal (Rose, 2014). As two of the leading squirrel authorities observed, “one can only marvel at how well adapted squirrels are to exploiting a forested environment” and, one could add, an urban environment as well (Steele and Koprowski, 2001, p. 11).

Their diversity is enormous and the squirrel family includes, not only tree and ground squirrels, but also flying squirrels, chipmunks, marmots, groundhogs and prairie dogs, all which deserve a separate paper. Many of the 273 squirrel species live in North America where they have very few enemies. This paper covers only tree squirrels, which nest and live in trees and have bushy tails to help them balance while running up and down trees. Ground squirrels live on the ground, have shorter, less bushy tails, and their fur is usually brown-gray with gray and white dots.

Extremely Well-Designed

Squirrels are very well designed for their terrestrial and arboreal life. Growing up in Michigan, I remember tree squirrels moving on the ground by a “hopping run” travel mode to scurry up a tree. Their sharp claws enable them to run down the tree about as fast as they can run up it. Their trademark is their slender bodies with very long, very bushy tails. The term ‘squirrel’ derives from the bushy tail, which is one of their more-defining traits. Their large eyes give them excellent vision, allowing them to jump from one limb to another limb of the same tree, or even to other trees. They are one of the few mammals, aside from primates, that have color vision (Steele and Koprowski, 2001, p. 7).

Their excellent sense of touch uses the vibrissae (whisker-like hairs) on their strong flexible limbs as well as their heads. This system allows then to navigate telephone wires with ease, even while running on a wire almost as rapidly as they run on the ground. Their tail is central to maintain balance on telephone wires high up the ground as well as in trees. Its function is similar to how a tightrope walker uses a pole to balance. They can also use their long tail, which is 40 percent of their body length, to protect their face and body from dogs, raptors, and other predators.

The blood vessels in the tail serve as an efficient thermoregulation system, opening blood circulation to the tail to cool the squirrel, and closing it to retain heat. Raising their tail over their body affords them the ability to enjoy the cool shade it provides. It also serves as a warm blanket that greatly helps to keep them warm during cold winter nights. Lastly, their tail is critical in communicating to other squirrels and potential predators (Steele and Koprowski, 2001, pp. 7, 13, 122, 124) .

Their Diet

Squirrels are herbivorous, subsisting on seeds and nuts, but some will eat insects and even very small vertebrates (Steele and Koprowski, 2001, pp. 38-40, 42, 44-47). They have large incisor teeth designed to crack open their diet of walnut, acorn, hickory and other nuts. Their constant gnawing helps them to keep their teeth razor sharp. Both tree and ground squirrels live in the same area year-round, including the cold winters. A motivation to write this paper is to understand how squirrels survive the ferocious winters where I live. Ground squirrels live on, or in the ground, and not in trees, and hibernate during the winter. Their heart rate and breathing rate slows down greatly and their body temperature falls below zero in preparation for hibernation.

In contrast, gray tree squirrels rely on sheltered nests made from twigs and leaves, or dens in trees like woodpeckers, to sleep. In the winter they sleep in their nest or den and rely on fat reserves, and stored food to survive the long, cold winters (Cheevers, 2020). Also, in preparing for winter, they maximize their food consumption and body mass. They venture out during the morning and evening only if their food supply is low. They prepare for the winter by storing acorns and other nuts, berries, and tree bark in shallow holes near the trees where their nest is located. Squirrels use spatial memory to locate stored food, and often bury their food near landmarks to aid them in remembering where they stored it (Jacobs and Liman, 1991).

Evidence for Squirrel Evolution

Evolutionists believe that squirrels evolved about 36 million years ago from some hypothetical “more primitive rodent” (Thorington and Ferrell, 2006, p. 23). Previously, the earliest squirrel fossil evidence was found in western North America Darwin-dated to about 36 million years ago. A nearly complete skeleton was discovered in 1975 which “is surprisingly like that of a modern tree squirrel” (Thorington, and Ferrell, 2006, p. 23). The skeleton of the find, determined to be a D. jeffersoni breed squirrel, was “discovered in early Oligocene deposits of Wyoming, [and] represents what may be the oldest fossil squirrel known… Except for minor differences in joint construction, the skeleton is strikingly similar to that of Sciurusniger, the living fox squirrel. It differs from extant ground squirrels in the more gracile proportions of its long bones and asymmetry of foot construction. This early member of the squirrel family was clearly an arboreal squirrel, with morphology, and presumably habits, very similar to those of extant Sciurinae.” (Emry and Thorington, 1982). The bones that were examined were judged to be “identical” to modern squirrels (Emry and Thorington, 1982, pp. 9, 10, 19, 20).

The newest discovery after 1975 was a squirrel-like creature from China Darwin-dated over 200 million years old. The fossils were discovered by private collectors and amateur paleontologists in the fertile fossil province of Liaoning (Choi, 2014). The phylogeny [evolutionary relationship] of the fossils found “remains unsolved and has generated contentious views on the origin and earliest evolution of mammals.” (Shundong et al., 2014). As two of the leading experts of squirrels observed, “biologists consider tree squirrels to be living fossils because they remain virtually indistinguishable from European and North American specimens that lived more than 5 million years ago.” (Steele and Koprowski, 2001, pp. 11-12). Squirrels are only one of hundreds of examples of living fossils (Eldredge and Stanley, 2012).

Many examples of variations within the genesis kind exist, such as documented by Steele and Koprowski (2001, pp. 102-104), but I have been unable to locate any evidence for the evolution of squirrels from a non-squirrel. In short, the origins concern is not of variations within the genesis kind, but the evolution of the first squirrel from a non-squirrel. From what is known, the first squirrel was very close to identical to modern squirrels. And if a local squirrel is making off with seed from your bird feeder, just reflect that they are all wonderful creations!


Cheevers, Carrie. 2020. How do squirrels prepare for winter? Spectrum News, November 11. https://spectrumlocalnews.com/tx/san-antonio/weather/2020/11/11/how-do-squirrels-prepare-for-winter-

Choi, Charles Q. 2014. Ancient squirrel-like creatures push back mammal evolution. Live Science. https://www.livescience.com/47774-ancient-squirrels-push-back-mammal-evolution.html

Emry, Robert, and Richard W. Thorington, Jr. 1982. Descriptive and comparative osteology of the oldest fossil squirrel. Protosciurus (Rodentia: Sciuridae). Washington, D.C. SMITHSONIAN INSTITUTION PRESS, Number 47.

Emry, Robert, and Richard W. Thorington, Jr. 1984. The Tree Squirrel Sciurerus carolinensis  as a living Fossil. In: Eldridge, Niles, and S.M. Stanley. Living Fossils. New York, NY: Springer-Verlag.

Eldredge, ‎Niles, and S.M. Stanley. 2012. Living Fossils. New York NY: Springer-Verlag.

Jacobs, Lucia, and Emily Liman, 1991. Grey squirrels remember the locations of buried nuts.

Animal Behaviour. 41 (1): 103-110, January.

Pope, Joyce. 1992. Living Fossils (Curious Creatures): Animals Unchanged by Time. Austin, TX: Steck-Vaughn Library.

Rose, Nancy. 2014. The Secret Life of Squirrels. New York, NY: Little Brown.

Shundong, Bi, et al., 2014. Three new Jurassic euharamiyidan species reinforce early divergence of mammals. Nature. 514 (7524): 579-584, September 10; doi: 10.1038/nature13718. Epub.

Steele, Michael A., and John L. Koprowski. 2001. North American Tree Squirrels. Washington, D.C.: Smithsonian Institution Press. .

Thorington, Richard W., and Katie E. Ferrell. 2006. Squirrels: The Animal Answer Guide. Baltimore, MD: Johns Hopkins University Press.

Jerry Bergman
July 2021

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