Toronto: Scientists have identified the earliest ancestor of land-dwelling plant eaters, and the creature dating back 300 million years, surprisingly, was a meat lover.
New research from the University of Toronto Mississauga demonstrates how carnivores transitioned into herbivores for the first time on land.
Previously unknown, the 300-million-year old fossilised juvenile skeleton of Eocasea martini is less than 20 cm long.
Found in Kansas, it consists of a partial skull, most of the vertebral column, the pelvis and a hind limb.
By comparing the skeletal anatomy of related animals, researchers 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," said Jorg Frobisch of the Museum fur Naturkunde and Humboldt-University in Berlin.
Eocasea is also the most primitive member and was carnivorous, feeding on insects and other small animals.
Younger members were herbivorous, clear evidence that large terrestrial herbivores evolved from the group`s small, non-herbivorous members, such as Eocasea.
"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," Robert Reisz, a professor in the Department of Biology, said.
Researchers also found that herbivory, the ability to digest and process high-fibre plant material such as leaves and shoots, was established not just in the lineage that includes Eocasea. It arose independently at least five times, including twice in reptiles.
"Multiple groups kept re-evolving the same herbivorous traits," said Reisz.
The five groups developed the novel ability to live off plants in staggered bursts with synapsids such as Eocasea preceding reptiles by nearly 30 million years.
This shows that herbivory as a feeding strategy evolved first among distant relatives of mammals, instead of ancient reptiles - the branch that eventually gave rise to dinosaurs, birds, and modern reptiles.
The research is published online in PLoS One.