Flying squirrels’ relatives date back to the Eocene period, which was between 38 and 55 million years ago. Tree squirrels were first, about 30 million years ago. Followed by tree squirrels, between 28 and 2.5 million years ago. Flying squirrels are not well represented in the fossil records mostly due to their fine bone structures not preserving well. However, teeth are found and dentition characteristics are made, but it can be very difficult. In order to figure out the fossil record and evolutionary history of these animals, specialists must be highly educated.
It is believed that the two species of flying squirrels, northern and southern flying squirrels, migrated to North America via the Bering Land Bridge, which connected North America to Siberia. Northern flying squirrels are more adapted to temperate, mixed coniferous- deciduous forests (Vernes, 2001). It is believed that southern and northern flying squirrels have adapted to the different niches they inhabit. Evidence of this can be found by comparing the baculum of each squirrel. The baculum is a small supporting bone of the penis that aids in the mating process and is present in many mammal species. The northern flying squirrel’s baculum is structurally more comparable in shape to the Asian genus Hylopletes than that of the southern flying squirrel’s (Patterson, 2001). All of these differences can be linked back to the separation of the two species, also known as the process of speciation. "By modifying habitats and creating bridges and barriers between land masses, climate change and tectonic events [land mass movements] are believed to have important consequences for diversification of terrestrial organisms," wrote two Duke University evolutionary biologists in a paper posted on the Feb. 20, 2003, edition of Science Express, the online version of the journal Science (Basgall, 2003).
There is also evidence to support that flying squirrels have specialized adaptations to cold weather and have been seen to increase in local population numbers during cold months. Another interesting correlation is that enhanced longevity is linked to flying or gliding habits (Holmes and Austad, 1994).
Basgall, M. (2003). Squirrels' Evolutionary Family Tree Reveals Influence of Climate, Geology. Duke University.
Holmes, D. J., & Austad, S. N. (1994). Fly now, die later: life-history correlates of gliding and flying in mammals. Journal of Mammalogy, 224-226.
Patterson, S. (2000). Flying Squirrels. FlyingSquirrels.com
Pennycuick, C. J. (2008). Modelling the flying bird (Vol. 5). Elsevier. Figure 2 photo.
Vernes, K. (2001). Gliding performance of the northern flying squirrel (Glaucomys sabrinus) in mature mixed forest of eastern Canada. Journal of Mammalogy, 82(4), 1026-1033.