Probable Dung Beetle Burrows Associated with Daemonelix (Beaver Burrows) in the Miocene Harrison Formation, Nebraska, U.S.A.

Numerous distinctive invertebrate burrows have been found closely associated with Daemonelix, the helical burrows of the extinct Miocene beaver Paleocastor. The invertebrate burrows are simple, cylindrical, unbranching structures that extend directly from the Daemonelix wall. Casts of both Daemonelix and the invertebrate burrows have been preserved by silification of roots around the burrow walls. These unusual vertebrate-invertebrate trace-fossil associations have been observed at two different localities in the Harrison Formation in northwestern Nebraska.

Forty-seven invertebrate burrows were found, with most located on the shaft of the Daemonelix. The recurrent nature of the association and the abundance of invertebrate burrows suggest that the invertebrate burrow makers sought an association with Paleocastor for a specific resource. Resources available and exploited by invertebrates in modern vertebrate burrowing communities include shed fur, stored food, carrion, insect prey, a stable environment, and dung.

The physical characteristics of the invertebrate burrows and comparisons with modern burrowing vertebrate communities suggest that the availability of dung was the most probable reason for this association. Dung would have been an abundant and reliable resource in the Paleocastor community, and the external morphology of the associated invertebrate burrows is consistent with modern dung beetle burrows. No associated fossil dung material has been found, but many modern dung beetle feeding burrows contain dung only in the ends, or are empty if the dung has been consumed. This rare burrow-to-burrow association provides evidence of ancient vertebrate-invertebrate interactions and sheds light on the complexity of the Paleocastor community.