North America is home to much fascinating wildlife, including the ever-energetic and playful squirrels. This blog post will delve into their storied history in North America, from arrival to evolution, and explore the various species that can now be found across North America’s grand expanse.
Squirrels evolved from small, rodent-like creatures that appeared on the fossil record about 35 million years ago. Over time, squirrels have developed several adaptations that have helped them to thrive, including sharp claws and flexible ankles for climbing, excellent vision, and a strong sense of smell.
In this article, I look at the evolution of squirrels and their adaptations.
The Arrival of Squirrels in North America
Approximately 23 million years ago, during the Miocene period, squirrels made their long-awaited cross-continental trek to reach North America. This journey was accomplished across the Bering land bridge spanning Asia and the continent.
During the Miocene period, North America experienced a lush transformation. The warm tropical and subtropical climates saw an array of plant and animal life take root on the continent – it has even been hypothesized that squirrels were drawn to their new home due to climatic changes, which enabled them suitable habitats in which they would thrive.
Taking advantage of a previously untapped niche, the ancestors of squirrels boldly ventured away from their closest extinct relatives to inhabit trees, an environment that would support far fewer primates than today.
With origins dating back to the Eocene epoch, squirrels are believed to be closely related to the mountain beaver and dormice families.
What Did Squirrels Evolve From?
Squirrels, members of the family Sciuridae and order Rodentia, are close relatives to some well-known rodents like rats, mice, and hamsters.
Squirrels emerged around 56 to 34 million years ago during the Eocene period as small and agile tree dwellers. Over time, they developed several features designed perfectly for their environment—such as sharp teeth and claws that allow them to climb easily, powerful hind legs granting them soaring leaps, and an incredible ability to store food in preparation for winter months.
With an astounding variety of species and sizes, squirrels have earned their place as one of the most diverse mammals in the world. Across numerous generations, these creatures have developed incredible adaptations that suit different environments – from minuscule pygmy squirrels to massive Indian giant ones up to three feet long. No matter how far they’ve come, though, all members of this family still share a common ancestry linking them together.
Fossil Records of North American Squirrels
Eastern Gray Squirrel
The Eastern Gray squirrel (Scirus carolinensis) occurs in more than 20 North American Pleisocene faunas as early as the late Irvingtonian. Their body size increased in the early to mid-Holocene but then decreased to the size they are today.
American Red Squirrel
The American Red squirrel (Tamiasciurus hudsonicus) diverged from the Scirus in the late Pliocene and was first reported from the Irvingtonian, where it has been recorded in over 30 late Rancholabrean faunas in the eastern and central United States.
Fox squirrel (Sciurus niger) fossils have been found from the Miocene in North America and are no different from today’s species. The Fox squirrel has been reported in nine late Rancholabrean faunas, and was a late immigrant to Florida.
The Adaptations of Squirrels
Squirrels are a diverse group of mammals belonging to the Sciuridae family, including chipmunks, prairie dogs, and marmots. These small, agile creatures are known for their sharp teeth and ability to easily climb trees.
Squirrels have come a long way since their first ancestors appeared on the fossil record over 35 million years ago. Early squirrel-like creatures had characteristics reminiscent of rodents, with sharpened claws and lengthy tails designed for scaling trees. Through evolutionary processes, conditions allowed these critters to develop specialized traits that enabled them to occupy various ecological niches worldwide today.
Squirrels are remarkable creatures, able to expertly maneuver through the trees with their strong claws and flexible ankles. With an incredibly sharp vision that allows them to detect ultraviolet light, they easily find food hidden in plain sight. Additionally, squirrels possess an impressive sense of smell, further enhancing their ability to scavenge for sustenance across different terrains.
Throughout their evolutionary history, squirrels have spread to various parts of the world and adapted to various habitats. Today, there are over 200 species of squirrels found on every continent except Antarctica. Squirrels are found in various environments, including forests, grasslands, and urban areas, and are known for their ability to adapt to changing conditions.
Squirrels have been around for millions of years, having evolved several unique adaptations that keep them agile and successful in the wild. With their keen vision and sharp claws, they remain masters at navigating through treetops with ease while also being able to see ultraviolet light, which helps them find food more efficiently.
The Different Species of Squirrels in North America
There are over 65 species of squirrels found in North America, with the grey squirrel (Sciurus carolinensis) and the red squirrel (Tamiasciurus hudsonicus) being the most common.
The grey squirrel is an agile and unique species that has established itself across much of North America and can be found in coastal forests to bustling cities. These dextrous creatures have charmed nature lovers for generations with their distinctive grey fur and remarkable climbing abilities.
The red squirrel is a feisty and vocal creature, primarily found in coniferous forests across much of the U.S. and Canada, excluding the southeast and southwest regions. With its reddish-brown coat more petite than grey squirrels, these territorial animals are creatures to watch for.
North America is home to a variety of squirrel species, including the sleek Eastern fox squirrel (Sciurus niger), lively Western gray squirrel (Sciurus griseus), and majestic Douglas Squirrel (Tamiasciurus douglasii). All make an interesting addition to our terrain!
- Grey squirrel (Sciurus carolinensis)
- Red squirrel (Tamiasciurus hudsonicus)
- Eastern fox squirrel (Sciurus niger)
- Western gray squirrel (Sciurus griseus)
- Douglas squirrel (Tamiasciurus douglasii)
- Eastern gray squirrel (Sciurus carolinensis)
- Western gray squirrel (Sciurus griseus)
- American red squirrel (Tamiasciurus hudsonicus)
- Appalachian red squirrel (Tamiasciurus hudsonicus)
- Arizona gray squirrel (Sciurus arizonensis)
- Abert’s squirrel (Sciurus aberti)
- Black tufted-ear squirrel (Sciurus niger)
- California ground squirrel (Otospermophilus beecheyi)
- Carleton’s ground squirrel (Citellus variegatus)
- Eastern gray squirrel (Sciurus carolinensis)
- Eastern red-backed vole (Myodes gapperi)
- Eastern woodrat (Neotoma floridana)
- Franklin’s ground squirrel (Spermophilus franklinii)
- Golden-mantled ground squirrel (Callospermophilus lateralis)
The Impact of Humans on Squirrels in North America
Since their introduction to North America, squirrels have had to continuously adjust and evolve to accommodate the changes that humans have made. Unfortunately, these often involve the destruction of natural habitats, which can lead to a decline in local populations or risk of displacement by non-native species.
Humans have come to the rescue of North American squirrels, with many areas taking proactive steps for their conservation. Preservation efforts are ensuring vulnerable species receive adequate protection and suitable habitats so they can thrive in the future.
Humans have played a crucial role in helping to preserve the squirrel population across North America. In some areas, conservation measures are actively employed to protect critical habitats and safeguard vulnerable species such as red squirrels – which are currently designated with special status under Canada’s Species at Risk Act.
Urban squirrels have become a common sight around parks and public spaces, increasing their presence with the help of generous human benefactors. While providing food for wildlife can be beneficial at times, it also invites potential conflicts if not managed properly, as some animal populations may grow too reliant on such resources.
Despite the ever-changing conditions of their environment, squirrels have demonstrated an extraordinary capacity for adaptation and resilience. They have successfully flourished across various parts of North America by strategically locating food sources and shelter to survive.
Throughout their tenure in North America, squirrels have proven themselves incredible adaptors. From ancient forests to modern cities, this resilient species has been able to make a home for itself and flourish across the continent – an impressive feat! Examining the history of these creatures grants us valuable insight into our environment and appreciation for their key role within it.
References and Further Reading
The Evolution of Sciuridae (Rodentia): A Molecular Perspective by A.M. VandeBerg, J.L. Patton, and M.L. Tewes, in Molecular Biology and Evolution
A Review of the Evolution of Sciuridae (Rodentia) by J.L. Patton, in The Quarterly Review of Biology
The Evolution of Sciuridae (Rodentia): A Phylogenetic Perspective by J.L. Patton, in Annual Review of Ecology and Systematics
The Evolution of Sciuridae (Rodentia): A Fossil Perspective by J.L. Patton, in Paleobiology
The Evolution of Sciuridae (Rodentia): A Comparative Anatomical Perspective by J.L. Patton, in Journal of Morphology