Jurassic herbivore diets: teeth, isotopes and food overlap

When several large herbivores lived in the same region, they did not necessarily eat the same plants in the same way. But the popular explanation that one dinosaur browsed high branches while another stayed low is too tidy to treat as a general rule. Palaeontologists test resource use by combining jaw and tooth anatomy, microscopic wear, fossil plants and chemical signals preserved in teeth.

Teeth show how food was processed

Tooth shape can indicate whether an animal cut, stripped or ground vegetation. Tooth replacement rate and jaw movement add information about how quickly a dinosaur processed food. Microscopic scratches and pits on the enamel record contact with plant tissues or grit, although the signal can vary across a tooth and can be modified after burial.

These features describe feeding mechanics more directly than the exact species of plant eaten. A broad, low tooth does not by itself prove that its owner fed only on ferns; a powerful jaw does not identify a particular conifer. The flora shows what was locally available, and the anatomy narrows the range of plausible feeding strategies.

What calcium isotopes add

A 2025 study examined stable calcium isotope ratios in tooth enamel from five vertebrate taxa at Carnegie Quarry in the Morrison Formation: Allosaurus, Camarasaurus, Camptosaurus, Diplodocus and Eutretauranosuchus. The herbivore measurements were consistent with resource differences between Camarasaurus and Camptosaurus. Diplodocus showed values that overlapped with both the larger and smaller herbivores, rather than fitting a strict feeding tier of its own.

This is evidence for some niche partitioning, not proof that every genus had a separate menu. The dataset is small, especially for taxa represented by only one or two teeth. Calcium isotope values also respond to the plant tissues consumed and to biological and environmental factors. They do not translate directly into a list of plant species.

Different methods answer different questions

Carbon and oxygen isotopes can help compare habitat use or environmental conditions; calcium isotopes can add information about plant resources; and dental microwear can reveal the texture of foods processed shortly before an animal died. Each method samples a different timescale and may be affected by preservation. Agreement among independent evidence is more persuasive than a single proxy.

The fossil record itself is uneven. A quarry can accumulate remains from floods, droughts or many seasons. Several genera found in one formation may have lived in different places or at different times. Even at a single site, a tooth cannot tell us whether a dinosaur changed its diet as it grew or as plants became more or less available.

Competition is a hypothesis to test

Resource partitioning can reduce direct competition, but the fossil evidence does not show that every difference evolved because species were competing. Habitat, body size, digestion, plant chemistry and seasonal change can all shape diet. Similar isotope values may indicate overlap, while different values can reflect several causes besides different plant species.

The Morrison Formation is especially useful because it preserves a diverse dinosaur fauna and a broad plant record. Still, its ecosystem is not a universal model for the Jurassic. For the connected predator and prey relationships, see our overview of Jurassic food webs; for the habitat itself, read about Jurassic forests and floodplains.