This is attributable to a simple and obvious fact: any given tonnage, or biomass, of herbivores can never support as large a tonnage of predators over an extended period. Walking dinosaur costume What is not so obvious is that the exact ratio of predator to prey should depend on the predator’s metabolic rate. Ectothermic predators eat only a seventh to a tenth as much as endotherms of similar size, so a given biomass of herbivores can support more predatory ectotherms than predatory endotherms. Animatronic dinosaur In quantitative terms, ectothermic spider and insect communities have “predator/prey ratios” of 50 percent or more. In sharp contrast, mammalian predators such as shrews, weasels, wolves, and the big African carnivores make up only a few percent of the herbivore’s biomass.
Robert Bakker realized that this may offer away to measure the metabolic rates of extinct animals. Animatronic dinosaur costume He surveyed a wide array of fossil conununities. Sure enough, such primitive reptile predators as the fin-backed dimorphodonts had biomasses 25 to 65 percent those of the reptiles and amphibians they fed upon. In fossil mammal populations, predator/prey ratios clustered around a scant 5 percent.26 This has long been known in a general way. Predatory finback reptiles are a dime a dozen in many collections, while good mammalian carnivores are the prize centerpieces of a museum’s fossils. There are exceptions to this. So-called predator traps, such as the saber-tooth cat- and wolfrich La Brea Tar Pits, have preferentially enticed, killed, and preserved enormous numbers of mammalian predators. But these are isolated cases, easily identifiable in the record. Normal fossil endothermic predator/prey ratios are much smaller, some ten times less, than those of ectothermic predators.