Carbone, Samuel T. Turvey and Jon Bielby found that Tyrannosaurus would have been unable to compete as an obligate scavenger against smaller theropods and it would have been necessary for it to primarily hunt large prey. In addition, a study by Graeme D. Ruxton and David C. Houson in 2004 found that vertebrates would need to be large bodied and capable of soaring flight to be obligate scavengers. This study also suggested the evolution of a terrestrial obligate scavenger was unlikely even with the absence of birds because for terrestrial carnivores there is a lack of strong selection pressure towards becoming an exclusive scavenger. The study further adds that it may always be more advantageous for terrestrial carnivores to be able to retain the flexibility of obtaining food through hunting and scavenging. A census study of the Hell Creek Formation published by John Horner, Mark B. Goodwin and Nathan Myhrvold in 2011 found that because of their relative abundance, tyrannosaurs were more like hyenas: opportunistic feeders that dined on more than just live prey and a specific group of dinosaurs. Riley Black, however, held that this research did not overturn Tyrannosauruss image as a predator, noting that research has found that spotted hyenas obtained a majority of their food from hunting; scavenging as little as 5% in some locations. He also noted that the census is an imperfect depiction of the area's ecology since various biases in collecting and preservation may have affected the results. For example, Tyrannosaurus may have regularly destroyed the skeletons of Edmontosaurus which it preyed upon. Horner, Goodwin and Myhrvold's study, according to , actually shows what most palaeontologists believe; that Tyrannosaurus was an opportunistic carnivore; an animal that both hunted and scavenged. However, the energetic importance of scavenging in Tyrannosaurus may have been mainly restricted to juvenile individuals as a recent study has shown that multi-ton theropods would have gained little energy from scavenging after accounting for the energy expended from foraging. Most paleontologists accept that Tyrannosaurus was both an active predator and a scavenger like most large carnivores. David Hone of Queen Mary, University of London, for example, wrote in his blog that ancering that it was either predator or scavenger in various papers has been unsatisfactory because it was most likely both. Switek also wrote that Tyrannosaurus was undoubtedly a predator and a scavenger, and that researchers have objected to the idea that