A mystery in the sandstone
In the late 19th century, settlers and ranchers in Sioux County, Nebraska, began finding enormous, screw-like fossils weathering out of the hillsides. These structures, some descending nearly 3 meters (9.8 feet) into the ground, were perfectly symmetrical spirals. They became known as "The Devil's Corkscrews." Paleontologist Dr. Erwin Hinckley Barbour of the University of Nebraska began a formal investigation in 1891. His initial hypothesis was that the fossils, which he scientifically named Daimonelix ("Devil's Helix"), were the remains of giant freshwater sponges or the taproots of unusual ancient plants. This plant theory was supported by the discovery of fossilized plant-like fibers within the structures. For decades, the true origin of the thousands of Daimonelix scattered across the area was a subject of intense scientific debate.
The fossils are primarily found within the Harrison Formation, a layer of fine-grained sandstone deposited during the Miocene epoch, roughly 20 to 23 million years ago. Other paleontologists, including the famous Edward Drinker Cope, soon challenged the plant-origin theory. Cope suggested the corkscrews might be the fossilized burrows of a large, ancient rodent. The turning point in the debate came when the fossilized skeletons of small animals were found inside the terminal chambers of the corkscrews. This discovery provided strong evidence that the structures were not plants, but the homes of an extinct creature.
The beaver behind the burrow
The skeletons found within the Daimonelix belonged to Palaeocastor, an extinct genus of land-dwelling beaver. Unlike its modern, dam-building relatives, Palaeocastor was a fossorial, or burrowing, animal, comparable in size to a modern prairie dog or muskrat. These ancient beavers lived in large colonies similar to today's prairie dog towns.
Detailed studies in the 1970s by paleontologists Larry Martin and Deb Bennett confirmed the burrow theory. They discovered that the inner walls of the Daimonelix spirals had scrape marks. These marks perfectly matched the size and shape of the incisor teeth of Palaeocastor, proving the beavers dug the elaborate structures with their teeth, not their claws. A complete Daimonelix consists of the vertical spiral shaft and a more horizontal living chamber at the bottom, which often slopes upward to prevent flooding. The spiral design itself may have helped maintain a stable temperature and humidity inside the burrow as the Miocene climate became warmer and drier. The plant fibers Barbour originally found were likely roots that grew into the burrow after it was abandoned, which then helped in the fossilization process.