Data from: Mammal-bearing gastric pellets potentially attributable to Troodon formosus at the Cretaceous Egg Mountain locality, Two Medicine Formation, Montana, U.S.A.

Fossil gastric pellets (regurgitalites) have distinct taphonomic
characteristics that facilitate inferences of behavioural ecology in deep
time, despite their rarity in the fossil record. Using the taphonomic
patterns of both extant and fossil small mammals from more recent geologic
deposits as a guide, we assess the taphonomy of three unusual
multi-individual aggregates of mammal skeletons from paleosols at Egg
Mountain, a dinosaur nesting locality from the Upper Cretaceous Two
Medicine Formation, Montana, USA. One aggregate consists of two
individuals of the multituberculate Filikomys primaevus. This specimen is
characterized by brecciated crania, articulated postcrania, and an absence
of digestive markings, all suggestive of a non-predatory origin. Two
additional aggregates consist of three and eleven individuals,
respectively, primarily of the marsupialiform Alphadon halleyi. High
proportions of crania and indigestible elements (e.g. teeth), extensive
disarticulation and breakage, digestive corrosion patterns, and the
absence of a phosphatic ground mass are indicative of regurgitalites and
align with features of extant prey in diurnal raptor gastric pellets. We
interpret these specimens as the oldest known mammal-bearing
regurgitalites. The discrepancy in taphonomic features implies behavioural
separation between the two mammalian taxa at the locality. Abundant shed
teeth and nesting evidence at the locality favors Troodon formosus as the
predator responsible for the regurgitalites, congruent with previous
inferences of a small-bodied prey diet, manipulation of prey during
feeding, heightened metabolic processes, and potential nocturnality for
this taxon.