The+Sciuridae+Family

The sciuridae family dates back to the earliest squirrel, //Douglassciurus jeffersoni//, that originated in the Northern Hemisphere around 36,000,000 years ago. It's skeletal and dental structure were very similar to modern day squirrels. The difference in which classifies modern day squirrels from the //Douglassciurus jeffersoni//is the jaw muscle and skull shape (sciuromorphous zygomasseteric system). The common tree squirrel is actually considered a "living fossil." (Living fossil- An unofficial term for any living classification of organism that seems to be the same as a species known from fossils and has no living relatives.)