Robert Bakker argued in The Dinosaur Heresies that cold-blooded predators need much less food than warm-blooded ones because of their lower metabolism, meaning that a given mass of prey can support far more cold-blooded predators than warm-blooded ones; the ratio of the total mass of predators to prey in dinosaurs was much more like that of more recent warm-blooded species than that of recent and fossil cold-blooded ones; therefore, predatory dinosaurs had to be warm-blooded, and since the earliest dinosaurs, such as Herrerasaurus, were predators, all other dinosaurs must therefore be warm-blooded.
However, Bakker’s argument has since been criticized and is no longer taken seriously: estimates of dinosaur weights vary greatly, and even a small variation could make a huge difference in the calculated predator-to-prey ratio; Bakker’s sample may not have been representative, as he obtained his numbers by museum specimens which have a bias towards rare or well-preserved specimens and therefore do not represent what actually exists in fossil beds; there are no published predator-to-prey ratios for large cold-blooded predators because such animals are rare and mostly occur only on relatively small islands (such as with the Komodo dragon); the concept assumes that predator populations are limited by the availability of prey animals, though other factors such as cannibalism or the predation of one predator by another could make their actual populations lower than those imposed by the supply of prey; ecological factors can reduce the predator-prey ratio, such as a given predator only preying on a particular species of prey or disease; and it is difficult to say what actually preys on what when it comes to fossil animals that cannot be observed in action.
