Paleontologists unearthed the oldest ancestor of land-dwelling herbivores with the discovery of a 300-million-year-old skeleton, shedding light onto plant eaters' emergence on land, a study said Wednesday.
A partial fossil of the animal, called Eocasea martini, is "the first link between carnivores and herbivores, the transition," Robert Reisz, the article's principal author and professor at Canada's University of Toronto Mississauga, told AFP.
Eocasea was a carnivore, but had certain skeletal features that indicate it was a close relative of herbivores, Reisz said.
Only part of the skull, most of the vertebral column, the pelvis and a hind limb of the eight-inch (20-centimeter) animal were discovered when it was unearthed in the US state of Kansas, according to the study published in the scientific journal PLOS ONE.
Eocasea, which lived 80 million years before the dinosaur age, was part of a group of animals called synapsids, which included the first terrestrial herbivores and large top predators. The group eventually evolved into modern mammals.
Before herbivores emerged, terrestrial mammals ate each other and consumed insects, according to the study, which was co-authored by Jorg Frobisch of the Museum fur Naturkunde and Humboldt-University in Berlin.
The arrival of herbivores "was revolutionary to life on land because it meant terrestrial vertebrates could directly access the vast resources provided by terrestrial plants," Reisz said.
In turn, the herbivores, which grew and multiplied, became an important source of food for large predators.
Eocasea therefore initiated a process that resulted in the structure of our modern ecosystem where a large number of herbivores support fewer and fewer top predators, Reisz said.
Herbivory evolved five separate times in different animal lineages, Reisz added.
"When the ability to feed on plants occurred after Eocasea, it seems as though a threshold was passed," Reisz said.
"Multiple groups kept re-evolving the same herbivorous traits," allowing them to digest the cellulose in plants.
"If you look at dinosaurs they started as carnivores and then there are a lot of herbivore dinosaurs," Reisz said.
But, Reisz added, scientists are still puzzled why the evolution from carnivore to herbivore didn't happen earlier, and why it happened separately in several different animal lines.