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Giant vegetarian species evolved from tiny carnivore: Study

According to a new report in the journal PLOS ONE, a tiny carnivore living about 300 million years ago was the ancestor of a group of very large herbivores. The study, carried out by paleontologist Robert Reisz, a professor of Department of Biology at the University of Toronto, Mississauga, was based on a 6.5-inch long fossilized creature found in what is now Kansas.

The creature, which is called a caseid, lived on a diet of insects and other small animals. The caseid belonged to a group of four-legged terrestrial vertebrates (Synapsida) that evolved into mammals and mammal-like reptiles.

“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 Reisz in a press release. “These herbivores, in turn, became a major food resource for large land predators.”

The newly discovered creature, which has been named Eocasea martinis, evolved over a period of time into caseid herbivores weighing over 1100 pounds. In order to do this, the species had to be able to digest and process high-fiber plant material.

“When the ability to feed on plants occurred after Eocasea, it seems as though a threshold was passed,” said Reisz. He said that the same ability evolved in at least five separate instances over the course of Earth’s history.

“Our results demonstrate for the first time that large caseid herbivores evolved from small, non-herbivorous caseids,” said Reisz and colleague Jörg Fröbisch of the Museum für Naturkunde and Humboldt-University in Berlin, in an abstract to the report.

They note that this is first of three documented occurrences of herbivores evolving from carnivores, while at the same time greatly increasing in body size. This pattern is consistent with what is seen in modern terrestrial ecosystems where many large plant eaters support fewer and fewer top predators, Reisz said.