predators such as canids and hyaenids (hyenas). He also cited other extinct animals such as the Diatryma (also known as Gastornis) and Phorusrhacids. Gregory S. Paul cited thylacines as another example. Tyrannosaurus had large olfactory bulbs, suggesting a highly developed sense of smell which could sniff out carcasses over great distances, as modern vultures do. Because vultures are primarily scavengers, it has been suggested that such a highly developed sense of smell may imply that tyrannosaurs were as well. However, Farlow and Holtz have noted that a good sense of smell could also be used to detect live prey as well as for behaviors unrelated to food acquisition. Darla K. Zelenitsky, Francois Therrien and Yoshitsugu Kobayashi also discussed the Tyrannosauruss sense of smell in their 2009 study and stated that it was not an indication of a particular feeding strategy the animal was using (predator versus scavenger), but indicate that tyrannosaurids such as Tyrannosaurus were active during low light conditions and may have used their sense of smell to search for food and navigate through large home ranges. In a 2013 lecture, Holtz. also noted that like Tyrannosaurus, wolves and raptors such as Velociraptor also had a good sense of smell. Others have argued that the primary scavenger hypothesis is implausible because the only modern pure scavengers are large gliding birds, which use their keen senses and energy-efficient gliding to cover vast areas economically. However, researchers from Glasgow concluded that an ecosystem as productive as the current Serengeti would provide sufficient carrion for a large theropod scavenger, although the theropod might have had to be cold-blooded in order to get more calories from carrion than it spent on foraging (see Metabolism of dinosaurs). They also suggested that modern ecosystems like Serengeti have no large terrestrial scavengers because gliding birds now do the job much more efficiently, while large theropods did not face competition for the scavenger ecological niche from gliding birds. However, further research by the same scientists found that the evolution of a terrestrial obligate scavenger was unlikely (read more on Ruxton & Houson's 2004 study below). Tyrannosaur teeth could crush bone, and therefore could extract as much food (bone marrow) as possible from carcass remnants, usually the least nutritious parts. Karen Chin and colleagues have found bone fragments in coprolites (fossilized feces) that they attribute to tyrannosaurs, but point out that a tyrannosaur's teeth were not well adapted