What this actually means for the structure of the foot is a question that is still being researched today. It would seem that an accessory navicular is commonly related to pes planus. Frederick Kidner, in 1929, first theorized that the presence of an accessory navicular could be the cause of pes planus.
Successful as they are, Eastern Gray Squirrels live only 11-12 months on average, but some individuals have survived more than ten years in the wild. Factors affecting survival include the severity of winter, abundance of food, and parasites.
Fox squirrels are approximately twice the size of gray squirrels. They range in length from 20-26 inches (including tail) with an adult weight range from about 2 to 2 1/2 pounds. Fox squirrels that survive to become adults live an average of 3 to 4 years. Individual animals have been known to live as long as 12 years.