It's been several decades since ecologists realized that graphing the diet-size relationship of terrestrial mammals yields a U-shaped curve when aligning those mammals on a plant-to-protein gradient. As illustrated by that curve, the plant-eating herbivores on the far left and meat-eating carnivores on the far right tend to reach sizes much larger than those of the all-consuming omnivores and the invertebrate-feasting invertivores in the middle.