Edmontosaur had also survived a tyrannosaur attack and that this was further proof that Tyrannosaurus were predators. Kenneth Carpenter (1998) had also described another specimen of the hadrosaurid Edmontosaurus annectens (in some newspapers it is misidentified as the similar Hadrosaurus) from Montana as having healed supposed tyrannosaur-inflicted damage on its tail vertebrae; having some of its caudal neural spines mutilated. The fact that the damage seems to have healed suggests that the Edmontosaurus survived a tyrannosaur's attack on a living target, i.e. the tyrannosaur had attempted active predation; however, the damage is ambiguous and not directly attributable to Tyrannosaurus. Another Edmontosaur specimen that is suspected to have survived a tyrannosaur attack had also been previously identified by Bruce Rothschild and Robert DePalma in an article published in the journal "Cretaceous Research". This specimen is described to have fossilized skin showing scars and tooth induced traumas on the skull in the form of large tooth drags, with size and spacing that leaves only Tyrannosaurus as the only likely assailant. Phil Bell of Pipestone Creek further stated that the skull injuries were consistent with tyrannosaur-bitten bones. There is also evidence for an aggressive interaction between a Triceratops and a Tyrannosaurus in the form of partially healed tyrannosaur tooth marks on a Triceratops brow horn and squamosal (a bone of the neck frill); the bitten horn is also broken, with new bone growth after the break. It is not known what the exact nature of the interaction was, though: either animal could have been the aggressor. Since the Triceratops wounds healed, it is most likely that the Triceratops survived the encounter and managed to overcome the Tyrannosaurus. Paleontologist Peter Dodson estimated that in a battle against a bull Triceratops, the Triceratops had the upper hand and would successfully defend itself by inflicting fatal wounds to the Tyrannosaurus using its sharp horns. Various studies have also taken into account the ecosystem that Tyrannosaurus lived in. Some researchers argue that if Tyrannosaurus were a scavenger, another dinosaur had to be the top predator in the Amerasian Upper Cretaceous. Top prey were the larger marginocephalians and ornithopods. The other tyrannosaurids share so many characteristics that only small dromaeosaurs and troodontids remain as feasible top predators. In this light, scavenger hypothesis adherents have suggested that the size and power of tyrannosaurs allowed them to steal kills from smaller predators. However, a study published in 2011 by Chris