Burrow fossils are the remains of burrows - holes or tunnels excavated into the ground or seafloor - by animals to create a space suitable for habitation, temporary refuge, or as a byproduct of locomotion preserved in the rock record. Because burrow fossils represent the preserved byproducts of behavior rather than physical remains, they are considered a kind of trace fossil.
A primary example is Palaeocastor ('ancient beaver') is an extinct genus of beavers that lived in the North American Badlands during the late Oligocene period to early Miocene.
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.
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 where the "screws" were situated; the deposits in which they occur were laid down in immense freshwater lakes in the Miocene Epoch, 20 million years ago.
In 1892, Dr. Barbour proposed that the devil's corkscrews were the burrows of large rodents.
The dispute on its real identity ceased when a fossilized beaver was discovered in one of them.