The mule deer and the white tail deer are the two longest surviving deer species of North America.
The black tailed mule deer has existed for over 2 million years! The white tail deer beats out the black tailed mule deer, having existed for 3.5 million years, but both speak volumes about their ability to adapt to a changing world. This length of time is unprecedented in the deer family. Most other similar species (moose, reindeer, etc..) have only been around for thousands of years.