A zoologist analyzes the jawbones of an extinct mammal and concludes that it was an herbivore. The zoologist most likely came to this conclusion based upon the .

Shape and structure of teeth.

Explanation:

The structure and shape of teeth varies from species to species and it greatly reflects the mode of nutrition in them.

For example, Carnivores have  long sharp pointed teeths with long canines as they need to pierce and tear the raw flesh.

The omnivores exhibit different types of teeth  like molars, premolars, canines and incisors with different shapes and size because they feed on both plants and animals and are required to cut, tear and chew their food.

Herbivores lack the canines, but have sharp and large incisors along with large molars as they need to cut their food and grind them properly.