Zoologist: Plants preferentially absorb heavy nitrogen from rainwater. Heavy nitrogen consequently becomes concentrated in the tissues of herbivores, and animals that eat meat in turn exhibit even higher concentrations of heavy nitrogen in their bodily tissues. We compared bone samples from European cave bears of the Ice Age with blood samples from present-day bears fed meat-enriched diets, and the levels of heavy nitrogen present in these samples were identical. Thus, the prehistoric European cave bears were not exclusively herbivores.
Bone samples from present-day bears fed meat-enriched diets exhibit the same levels of heavy nitrogen as do their blood samples would most strengthen the zoologist's argument.