Dinosaurs overshadowed mammals for most of the Mesozoic, but evidence of actual dinosaur-mammal interactions are very rare. On the mammalian score, a specimen of the relatively large Cretaceous mammal Repenomamus robustus described
In Utah's Grand Staircase-Escalante National Monument, within the 80-million-year-old rock of the Wahweap Formation, paleontologists have discovered evidence that small predatory dinosaurs dug down into the soil to reach the burrows of small mammals. As reported in the journal
The first trace fossil type was made by a digging dinosaur, probably a maniraptoran similar in form to Deinonychus and Troodon. At first glance it doesn't look like much—just a lumpy bit of sandstone—but if you look carefully, a claw impression and numerous downward-arcing grooves can be seen. It appears that the dinosaur was repeatedly sticking its foot into the hole and raking out sediment, a behavior consistent with the idea that these dinosaurs probably did not use their arms to dig because their feathers would have gotten in the way or been damaged.
The second group of traces, found near the claw marks, preserve mammal burrows and dens. Networks of branching, winding burrows connect to bulbous chambers where mammals found refuge, and these underground structures are very similar to those made by small, social mammals living today. Based upon the close association of these structures with the claw marks, and especially the correspondence between deeper burrows and deeper dig marks made by dinosaurs, the researchers hypothesize that the predatory dinosaur was trying to get at the mammals.
Together the scratches and burrows tell of ancient interactions we could only previously infer on the basis of bones. It most have been terrifying for those small mammals, hearing the predatory dinosaur scratching deep into the ground in the hopes of catching them.
Edward L. Simpson, Hannah L. Hilbert-Wolf, Michael C. Wizevich, Sarah E. Tindall, Ben R. Fasinski, Lauren P. Storm and Mattathias D. Needle (2010). Predatory digging behavior by dinosaurs Geology, 38, 699-702 : 10.1130/G31019.1