Evidence for dromaeosaurid scavenging on Albertosaurus (Dinosauria: Tyrannosauridae)

Abstract

Abstract Direct evidence of trophic interactions in the fossil record (e.g., feeding traces, stomach contents) are key to understanding predator–prey relationships between extinct species and reconstructing ancient ecosystems. Recently discovered associated cranial material of an immature Albertosaurus sarcophagus from the Upper Cretaceous (uppermost Campanian–Maastrichtian) Horseshoe Canyon Formation (Alberta, Canada) represents the smallest associated Albertosaurus skull discovered to date. Osteohistological analysis of an associated limb element indicates the individual was at least eight years old at time of death. The specimen preserves two sets of unhealed tooth marks on the mandible. Tooth and denticle mark spacings were studied to identify the potential trace maker. We apply a new method to account for rake angle in tooth and denticle marks to improve the estimation of inter- and intra-mark spacing. Our results reveal that the tooth marks are most consistent with those produced by dromaeosaurids. Given that the tooth marks display no signs of healing, they represent the first documented evidence of a dromaeosaurid feeding/scavenging on tyrannosaurids. Dromaeosaurs and immature tyrannosaurids likely participated in reciprocal predation/scavenging within the carnivorous dinosaur guild. The Albertosaurus specimen and its preserved traces expand our understanding of dromaeosaurid diet and interspecific interactions and provide insight into the skull morphology of young Albertosaurus individuals.