Scientists have determined that a 300-million-year-old carnivore was the ancestor of a large group of herbivores.

The lizard like creature, named Eocasea martini, or E.martini, was a caseid, according to LiveScience.com. Caseids were a primitive group of synapsids, which includes mammals and close relatives.

Ancient non-mammal synapsids, like caseids, looked a lot like reptiles still around today, but were made from a "different branch of life" from birds and reptiles, according to LiveScience.

The discovery is noteworthy because E.martini was likely a carnivore.

"It's within this side of vertebrate evolution that we have the first plant-eating animals," said study leader Robert Reisz, a paleontologist at the University of Toronto, according to LiveScience.

E.martini weighted less than 5 pounds, and ate mostly insects, according to Reisz.

The paleontologist and his colleagues identified the new species after examining a skeleton and partial skull.

"All other members of this group, the caseids, are plant eaters," Reisz said. This one, the oldest, isn't. We see a transformation within the group from an insectivorous animal to a plant-eating animal."

Fossils came from Hamilton Quarry in southeast Kansas. The spot is a well-known ancient lagoon famous for its vast amount of plants and fish.

"There are very few terrestrial vertebrates coming out of that locality, but each one has turned out to be very important scientifically," Reisz said.

The specimen that eventually became E.martini was first discovered over two decades ago by Larry Martin from the University of Kansas. It was stored at the university's Dyke Museum of Natural History until Reisz borrowed it, according to LiveScience.com

"Nobody paid much attention to it," Reisz said. "It's a tiny little animal."

The anatomy of the animal showed that it was a caseid, but lacked a barrel-shaped rib cage that later members of the group had.

A broad rib cage means it was a plant eater, since animals that live off of planets need large guts to break down leaves and stems, according to LiveSceince.com.

The species helped Reisz and his colleagues understand how some animals started out as insect eating creatures before becoming meat eaters.

"What's really interesting is that this is not the only group that it happened to," Reisz said. "Other groups seem to have been doing this roughly at the time."

Research was published this week in the journal PLOS ONE.

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