Paleocastor is the name given to a genus of early beaver that lived in North America during the late Oligocene and Early Miocene. Unlike modern beavers, Paleocastor was not an aquatic mammal. They lacked many of the specialized adaptations (like a large flat tail) that are commonly associated with beavers. Instead, they have a more more generalized rodent skeletal morphology. Additionally, they also lived in corkscrew shaped burrows which have been preserved in some of the most fascinating ichnofossils I've ever seen.
|Paleocastor burrows, Harrison Formation (Miocene), Agate Fossil Beds National Monument, Nebraska (James St. John)|