300-Million-Year-Old Fossil Sheds Light on Herbivore Evolution

A 300-million-year old fossil of Eocasea martini has helped researchers understand the evolution of herbivores.

Researchers at University of Toronto Mississauga analyzed the bones. The team found that the Eocasea martini was a tiny meat-eating mammal, which lived some 80 million years before the age of dinosaurs.

Researchers identified the ancient species using a partial skull, backbone and hind limb, Livescience reported. The skeletons were found some two decades ago in Hamilton Quarry in southeast Kansas

The current research is important because it helps scientists learn how tiny carnivores transitioned into large herbivores.

"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," said paleontologist Robert Reisz, a professor in the Department of Biology and one of the study authors. "These herbivores in turn became a major food resource for large land predators."

For the study, researchers compared bones of E. martini and skeletons of related animals. The team discovered that the two-kilogram (4.4 pounds) juvenile E. martini was a caseid and belonged to an ancient group of vertebrates called Synapsid.

Modern mammals belong to one branch of the Synapsida. The group involved both large predators and early terrestrial herbivores.

According to the researchers, Eocasea was an ancient member of Synapsida and was a small, insect-eating animal. Animals that appeared later in the group evolved into plant-eaters.

"Eocasea is the first animal to start the process that has resulted in a terrestrial ecosystem with many plant eaters supporting fewer and fewer top predators," Jörg Fröbisch of the Museum für Naturkunde and Humboldt-University in Berlin, one of the study authors said in a news release.

What's even more interesting is that herbivory or the ability to digest plants didn't evolve just once, but occurred independently roughly five times in the past. Also, researchers found that trait must have evolved at least twice in reptiles.

"When the ability to feed on plants occurred after Eocasea, it seems as though a threshold was passed," said Reisz. "Multiple groups kept re-evolving the same herbivorous traits."

The evolution of herbivory also changed the size of animals. Reisz and colleagues looked at the size of animals in the evolutionary tree and found that four of the five herbivore groups grew large during the Permian Period.

The study is published in the journal PLOS One.