After the live weights were determined for all the common species, I made a census of the total meat available, the total weight represented by all the fossils from the habitat under study. Some times these calculations profoundly changed the traditional picture of predator-and-prey relations. For example, in the floodplains haunted by Dimetrodon, the commonest prey were smallish, flat-bodied amphibians, including the boomerang-headed Diplocaulus. Paleoecologists had traditionally reconstructed these ecosystems with Diplocaulus in the role of chief meat-supplier to the fin-backed predator.(dinosaur costume) However, most Dimetrodons were medium-sized and big animals, between twenty and a hundred pounds in weight. Diplocaulus weighed only a pound or two on average, at best a Permian hors d’oeuvre for the bigger animal. All the Diplocaulus carcasses together didn’t amount to enough meat to keep even one mated pair of Dimetrodons alive and healthy. The two large species of prey, Eryops and the Diadectes, were only one tenth as common as Diplocaulus, but those animals were a hundred times heavier, on average. An adult Eryops or Diadectes weighed about two hundred pounds, heavier than most adult Dimetrodons. So most of the meat supply for Dimetrodon came from the rarer but bigger species. This illustrates an important general rule: Large predators obtain most of their food from large prey.
Armed with new confidence in this method of predator-prey analysis, I returned to my primary goal—evaluating the dinosaurs’ metabolism. Thanks to a census by a Canadian paleontologist, a complete count of the very rich dinosaur beds in the Judith Delta and later sediment was available. These formations yield Late Cretaceous fauna, duckbill and horned dinosaurs, and other plant-eat-ers, all of which were hunted by the tyrannosaurids. If orthodoxy were correct, tyrannosaurs should have been as common as Dimetrodon had been hundreds of millions of years before. But, if my hypothesis were right, dinosaurs would show the same low predator-to-prey ratio as fossil mammals. To compare these dinosaurs to warm-blooded mammals, I calculated predator-to-prey ratios from some recent publications that supplied counts for saber-toothed cats and hyenalike hunters found in South Dakota. When I calculated the body weight of each fossil saber-tooth and of its prey and added all the columns of data, the final ratio between the mammal predators and their total available prey proved nearly identical to the tally for dinosaurs both the tyrannosaurs and the mammals added up to between 3 and 5 percent of the weight of their prey.
The case for warm-blooded tyrannosaurs was beginning to look good. If only one dinosaur habitat had the same predator-to-prey ratio as one fossil mammal habitat, the case for warm-bloodedness would obviously have been weak. But, in fact, dozens of fossil dinosaurs and dozens of fossil mammals from the full variety of sediments exhibited the identical range. (realistic dinosaur costume)This consistent pattern had only one logical interpretation: Dinosaurs and mammals were fundamentally similar in their metabolic needs and both had a much higher metabolism than cold-bloods like the fin backs.