Another, more specific criticism suggests that theropods may not have preserved as well as herbivorous dinosaurs. Walking dinosaur costume If so, then the predators would appear to be rarer than they really were. But in fact, it has just been found that the opposite is true. As I explained in Chapter 4, predatory dinosaur bones are denser than those of herbivorous dinosaurs of equal size. Animatronic dinosaur costume This probably made theropod bones more resistant to rot, and more likely to be incorporated into the fossil record, than those of other dinosaurs. Not only that, but Philip Currie finds that when exposed today by erosion, theropod bones disintegrate much more slowly than the herbivore bones.27 It is difncult, perhaps impossible, to tell exactly how much this alters the preservation rates of predatory dinosaurs vis-d-vis the herbivores. But it does mean that the dinosaur predator/prey ratios we find are probably higher than the true values, perhaps by as much as half or more.
This may help explain another perplexing thing about predator/ prey ratios. In modern marrunal communities, P/P ratios are extremely low, only 0.2 to 1.5 percent. Because dinosaur P/P ratios are consistently higher, it has been argued that the dinosaurian predators had a higher metabolic rate than modern carnivores. 28 This sounds fair enough, except that fossil mammal P/ P ratios are also higher than today’s, running from 1.5 to 9 percent! Part of the problem is that the number of predator remains found at a given fossil locale is so low that fluctuations around the true value are to be expected. Realistic dinosaur model Another part of the problem stems from the fact that modern conununities are not unspoiled. lnterference and competition from man has suppressed the nurnbers and species of predators. Even in big game parks, poachers often compete with the carnivores, and they are not counted in the predator/prey ratios! Past mammal communities often had many more species of really big, powerful predators than to today’s, able to kill more of the population’s herbivores. Perhaps most importantly, mammal carnivores also have the relatively denser bones found in theropods. So they too may be more numerous in the fossil record than they really were. Hence, in both dinosaur and extinct mammal faunas the origin al P/P ratios may have been closer to, but stitl higher than, the modern range.