The Gray Fossil Site was once an ancient sinkhole lake surrounded by a dense forest of hickory, oak and pine trees, scientists say. The giant flying squirrels may have migrated east on the land bridge that connected Eurasia to North America, alongside saber-toothed cats, deer, shrews and a host of other animals, according to the study.

These giant flying squirrels had a lightweight build, weighing around three pounds – and were quite agile in the treetops.”