Palaeocastor
Palaeocastor ('ancient beaver') is an extinct genus of beavers that lived in the North American Badlands during the late Oligocene period to early Miocene. Palaeocastor was much smaller than modern beavers. There are several species including Palaeocastor fossor, Palaeocastor magnus, Palaeocastor wahlerti, and Palaeocastor peninsulatus. Habitat Some members of this genus made corkscrew-shaped burrows and tunnels. Like many early castorids, Palaeocastor was predominantly a burrowing animal instead of an aquatic animal. Fossil evidence suggests they may have lived in family groups like modern beavers and employed a K reproductive strategy instead of the normal r-strategy of most rodents. Based on size and habitat, Palaeocastor fossor has been compared to a black-tailed prairie dog (Cynomys ludovicianus). "Devil's corkscrews" The discovery of Palaeocastor sprang from the discovery of devil's corkscrews in the plains of Sioux County, Nebraska, as a tree-sized, screw-like underground formation. Its basic form is an elongated spiral of hardened earth material that inserts into the soil as deep as . These puzzling structures first came to notice through Dr. E. H. Barbour of the University of Nebraska around Harrison, Nebraska, in 1891 and 1892. Then he described it as giant freshwater sponges. This identification was influenced by the surroundings