How carnivores evolved into herbivores 300 million years ago revealed

Researchers have found the earliest ancestor of land herbivores, a 300-million-year old fossilized juvenile skeleton of Eocasea martini that is less than 20 cm long.

Paleontologist Robert Reisz, a professor in the Department of Biology, said the evolution of herbivory was revolutionary to life on land because it meant terrestrial vertebrates could directly access the vast resources provided by terrestrial plants.

He said these herbivores in turn became a major food resource for large land predators.

By comparing the skeletal anatomy of related animals, Reisz and colleague Jorg Frobisch of the Museum fur Naturkunde and Humboldt-University in Berlin, discovered that Eocasea martini belonged to the caseid branch of the group Synapsid. This group, which includes early terrestrial herbivores and large top predators, ultimately evolved into modern living mammals.

Eocasea lived nearly 80 million years before the age of dinosaurs. "Eocasea is one of the oldest relatives of modern mammals and closes a gap of about 20 million years to the next youngest members of the caseid family," says Frobisch. "This shows that caseid synapsids were much more ancient than previously documented in the fossil record."

It's also the most primitive member and was carnivorous, feeding on insects and other small animals. Younger members were herbivorous, says Reisz, clear evidence that large terrestrial herbivores evolved from the group's small, non-herbivorous members, such as Eocasea.

The research is published online in PLOS ONE.