(
Glaucomys sabrinus) gliding (
Glaucomys volans) skeleton at the
NMNH. The styliform cartilage attached to the wrist supports the wing membrane. The direction and speed of the animal in midair are varied by changing the positions of its limbs, largely controlled by small
cartilaginous wrist bones. There is a cartilage projection from the wrist that the squirrel holds upwards during a glide. Possible origins for the styliform cartilage have been explored, and the data suggests that it is most likely homologous to the carpal structures that can be found in other squirrels. The wrist also changes the tautness of the
patagium, a furry parachute-like membrane that stretches from wrist to ankle. The tail is
dorsoventrally (from the back to the front) flattened to help control the surrounding air whilst it is gliding.
Similar gliding animals The
colugos,
Petauridae, and
Anomaluridae are gliding mammals which are similar to flying squirrels through
convergent evolution, although are not particularly close in relation. Like the flying squirrel, they are
scansorial mammals that use their patagium to glide, unpowered, to move quickly through their environment.
Evolutionary history Prior to the 21st century, the evolutionary history of the flying squirrel was frequently debated. This debate was clarified greatly as a result of two molecular studies. These studies found support that flying squirrels originated 18–20 million years ago, are monophyletic, and have a sister relationship with tree squirrels. Due to their close ancestry, the morphological differences between flying squirrels and tree squirrels reveal insight into the formation of the gliding mechanism. Compared to squirrels of similar size, flying squirrels, northern and southern flying squirrels show lengthening in bones of the lumbar vertebrae and forearm, whereas bones of the feet, hands, and distal vertebrae are reduced in length. Such differences in body proportions reveal the flying squirrels' adaptation to minimize wing loading and to increase maneuverability while gliding. The consequence for these differences is that unlike regular squirrels, flying squirrels are not well adapted for quadrupedal locomotion and therefore must rely more heavily on their gliding abilities. Several hypotheses have attempted to explain the evolution of gliding in flying squirrels. One possible explanation is related to energy efficiency and foraging. Gliding is an energetically efficient way to progress from one tree to another while foraging, as opposed to climbing down trees and maneuvering on the ground floor or executing dangerous leaps in the air. Furthermore, take-off and landing procedures during leaps, implemented for safety purposes, may explain the gliding mechanism. While leaps at high speeds are important to escape danger, the high-force impact of landing on a new tree could be detrimental to a squirrel's health.
Fluorescence In 2019 it was observed, by chance, that a flying squirrel
fluoresced pink under UV light. Subsequent research by biologists at
Northland College in Northern
Wisconsin found that this is true for all three species of North American flying squirrels. At this time it is unknown what purpose this serves. Non-flying squirrels do not fluoresce under UV light. ==Taxonomy==