The burrows of the miocene beaver palaeocastor, Western Nebraska, U.S.A

Abstract

Daimonelix is a name given to terrestrial lebensspuren of the late Oligocene—early Miocene beaver genus Palaeocastor, and is not a plant or fresh-water sponge as was originally believed by Barbour. Palaeocastor belongs to a lineage of castorids always found in upland habitat, never near evidence of ponded water. Daimonelices are found in high concentrations in the Harrison Formation of western Nebraska and eastern Wyoming, which represents a semiarid, upland paleoenvironment of sandy substrate. Assignment of a large sample of contemporaneous Daimonelix to the species P. fossor is based on a series of incisor width measurements and on mean shaft diameters. The remarkable preservation of daimonelices, which permits detailed analysis of events in beaver burrow construction, is shown to be due to rapid silicification of plant roots invading the burrows. Some aspects of Palaeocastor ecology and ethology are also clarified. The spatial distribution of Daimonelix consists of scattered towns of high burrow density. One such colony is shown in a detailed paleogeographic map. Criteria for time equivalency of such burrow aggregations are established. The entoptychine gopher Gregorymys, the carnivore Zodiolestes, and the larger beaver P. magnus are also shown to be occasional inhabitants of Palaeocastor fossor colonies.