Evolution

• Marmots are ground squirrels.Jupiterimages/Photos.com/Getty Images
  
  Squirrels are classified as tree, flying and ground. These types evolved during the animals' migration to Europe, Asia, Africa and South America. Tree and flying squirrels showed up in Eurasia 30 million years ago, traveling over land bridges like those where the Bering Strait is now. These land masses disappeared below sea level periodically. When land resurfaced, no trees would be present. This ultimately produced the ground squirrel. Africa collided with Eurasia about 18 million years ago. Migration and diversification of squirrels from Eurasia began shortly after this event. Squirrels entered South America less than 3 million years ago over the Isthmus of Panama. All South American squirrels, except one type, are believed to have one common ancestor from North America.