Dinosaur herbivory and plant evolution: what fossils can test

Dinosaurs fed on Mesozoic plants, but the phrase “dinosaurs shaped plant evolution” can mean two different things. Fossils may show that an animal ate a plant or damaged a leaf. Demonstrating that a plant lineage evolved a trait in response to dinosaur feeding requires a further line of evidence linking the two evolutionary histories. The first claim is easier to establish than the second.

What was on the menu?

For most fossil herbivores, researchers infer diet from teeth, jaw mechanics, wear and the plants preserved in the same region. Those clues can indicate broad feeding modes, but they rarely identify every species consumed. Coprolites add direct evidence when they contain recognisable plant tissue. Even then, the producer may be uncertain unless the digestive fossil is associated with a skeleton or other diagnostic material.

A rare exception is a 95-million-year-old sauropod specimen of Diamantinasaurus matildae from the Winton Formation in Queensland, Australia. Its mineralised gut contents, or cololite, preserve parts of several plants. Researchers identified conifer material, seed-fern remains and flowering-plant leaves. The specimen provides direct evidence that this individual ate a mixed selection of plants and had access to more than one feeding height.

One cololite is a snapshot, not a complete lifetime diet for the genus. It cannot show how often the animal ate each plant, whether it preferred particular species, or how its feeding changed with season. Still, it replaces a broad assumption about sauropod herbivory with evidence from an actual meal.

Plant damage and evolutionary response

Fossil leaves can preserve holes, margin feeding, mines and other damage. These traces document herbivore activity and allow comparisons among plant communities. They do not always identify the animal that caused the damage, and multiple kinds of insects and vertebrates may produce similar marks.

Across the Mesozoic, plants and herbivorous dinosaurs changed in diversity and anatomy. That timing led researchers to test whether the two groups coevolved. A major review of herbivorous dinosaurs concluded that, despite several floral transitions, strong evidence for direct plant-dinosaur coevolution had not been found. A broad overlap in time is not enough: both groups must be represented well enough to demonstrate that changes in one track changes in the other.

This caution does not mean dinosaurs had no ecological impact. Large herbivores consumed vegetation and moved nutrients, and their local feeding could influence plant structure. It means that a claim such as “cycads evolved armour to resist sauropods” needs more than an image of a dinosaur browsing a cycad.

What can be said with confidence?

The evidence supports a varied relationship. Dinosaurs ate plants from multiple lineages; feeding traces and digestive remains document some of those interactions; and herbivores were important members of terrestrial food webs. The fossil record does not yet reveal a universal, reciprocal arms race between dinosaurs and plants.

Plant communities also changed with climate, soils and continental geography. Those factors affected both plant availability and dinosaur distributions. A useful reconstruction therefore combines animal anatomy, direct food remains, plant fossils and geology instead of assigning every botanical change to herbivory. For a wider view of ancient vegetation, read about plant life through the Mesozoic and dinosaur feeding evidence.