Abstract: 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.

Abstract: Unusual compound trace fossils of bored bone within coprolites provide direct fossil evidence for successive exploitation of dinosaur tissues by vertebrates and invertebrates. These specimens are best described as matrix-supported conglomerates of dinosaur bone, and were found as float in the Brushy Basin Member of the Jurassic Morrison Formation in the San Rafael Swell of eastern Utah. The high concentration of bone, absence of sorting, paucity of inorganic clasts, and presence of microcrystalline phosphate point to a fecal origin, and the contents and large size of the coprolitic masses indicate that they were produced by a large theropod. Several fragments of bone in the coprolites have been conspicuously bored. Casts formed by separation of lithified fill from some of the cylindrical boreholes reveal bullet-shaped termini; this distinctive morphology suggests that the cavities were utilized for protection. Inasmuch as pupating larvae of dermestid beetles make the closest modern analogs of comparable boreholes in bone, we deduce that ancestors of modern dermestids may have bored the Jurassic bone. Although these are the first reported fossils of boreholes in coprolites, a number of examples of bored bone have been described from the Mesozoic and the late Cenozoic. Such trace fossils may reflect changing patterns in the availability of large-bodied vertebrate carcasses over time. It is not clear whether the bone fragments were bored before or after theropod consumption, but it is likely that the bone borers opportunistically exploited bone found in theropod feces. These compound traces reveal complex trophic interactions linking dinosaurs and insects, whereby refractory dinosaur tissues were exploited and recycled in a Jurassic ecosystem.