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Eocasea martini: Scientists Discover Oldest Known Ancestor of Land Herbivores

For years, scientists have been trying to figure out how small carnivores evolved into land based herbivores. With the discovery of the earliest known ancestor of land herbivores, researchers may be able to get to the bottom of the mystery.

A researcher from the University of Toronto in Mississauga, Canada has discovered an ancient lizard-like animal that may be the ancestor of land herbivores. The ancient animal, which lived approximately 300 million years ago, is a member of the Caseid family. Scientists have named the new caseid Eocasea martini.

Caseids are an extinct group of very early herbivores that lived during the Permian period. Caseids are also considered to be synapsids, a larger group that also includes mammals. Some early synapsids were known to have reptile like features. One of the most well-known examples of a synapsid with reptile-like features is the Dimetrodon. 

"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 Robert Reisz, a professor from the University of Toronto's Department of Biology. "These herbivores in turn became a major food resource for large land predators." Reisz is a co-author of the study on E. martinipublished in the online journal PLOS ONE.

One of the most surprising aspects of E. martini is the fact that it was a carnivore. This came as a big surprise for the researchers because all other known examples of caseids are herbivores. E. martini is the oldest known caseid to date and the fact that it ate other animals may prove to be the missing piece of the puzzle needed to understand how land herbivores evolved. 

"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 Jörg Fröbisch from the Museum für Naturkunde and Humboldt-University in Berlin. "This shows that caseid synapsids were much more ancient than previously documented in the fossil record." Fröbisch is also a co-author of the study.

E. martini walked the Earth around 80 million years before the dinosaurs did. The ancient animal was also relatively small weighing just around 4.4 lbs. The scientists analyzed a partial skull, a hind limb and a large section of the animal's backbone. They determined that E. martini may have fed on ancient insects.

"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," Reisz said. "When the ability to feed on plants occurred after Eocasea, it seems as though a threshold was passed."

"Multiple groups kept re-evolving the same herbivorous traits," Reisz added.


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