First, contrary to what many investigators have postulated, the beasts probably had to have been cold-blooded, because the costs of maintaining a constant body temperatureówhich is to say, being warm-bloodedóat that size would have necessitated unrealistic hunting success (up to 10 times that of a lion) and a means of cooling down to avoid overheating.

The second requirement derives from the observations that meat-eating species have more extensive geographic ranges and lower population densities than vegetarians do, and big carnivores range over bigger areas than small ones do. For gigantic theropod species to succeed, the researchers argue, they would have needed continent-size landmasses to sustain populations large enough to avoid extinction. Third, titans-in-the-making had to be released from the ecological pressure of competing with other large species for foodóthrough the extinction of rivals or the hunting of different prey, for example.