Field work from last summer focused on late Eocene nodules and concretions in SW Montana terrestrial strata. We found that most concretions and nodules are actually burrow complexes in paleosols. Many of these paleosols are developed in massive to blocky mudstone that contain pedogenic features characteristic of Inceptisols but there are also some with more mature features that are classified as Alfisols. Rhizoliths, rhizocretions, rare rhizohaloes, a variety of dung beetle traces including Coprinisphaera, wasp and beetle cocoons assigned to Fictovichnus, and soil bee cells assigned to Celliforma are often associated with the mammal burrow complexes.
Several potential tracemakers may have produced these larger burrow complexes based on the fossil assemblages reported for the burrowed strata. Mammalian carnivores recovered from similar-aged strata include Ursids (Parictis), Amphicyonids (Brachyrhynchocyon), Canids (Hesperocyon), and Creodonts (Hyaenodon) are potential burrowers. Rodents and rabbits appear to be too small to have made the burrows, but small artiodactyls may be possible. Tortoises may also be potential burrowers, and their remains are abundant in these strata.
Our in-progress work will be reported in more detail at the joint Northeastern-NorthCentral GSA meeting in Theme Session 4 – Bio-landscaping: Advancing Ichnological and Biogeomorpological Research. A link to our abstract is: https://gsa.confex.com/gsa/2025NE/meetingapp.cgi/Paper/408864