A newly discovered 300-million-year-old meat-eating mammal ancestor is the oldest known member of a line that gave rise to rhinoceros-size herbivores.
The lizardlike animal, dubbed Eocasea martini, was a caseid. Caseids were a primitive group of synapsids, an umbrella term that includes mammals and their close relatives. Ancient nonmammalian synapsids, including caseids, looked reptilian — the famous fin-backed Dimetrodon was a synapsid — but were an entirely different branch of life from reptiles and birds.
"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.
The discovery of the new species is important, because E. martiniappears to have been a carnivore, Reisz told Live Science. Weighing less than 4.4 lbs. (2 kilograms), the little caseid probably chowed down on insects.
"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."
Waiting to be found
Reisz and his colleagues identified the new species from a partial skull and skeleton, including most of the backbone and one hind limb. The fossil came from Hamilton Quarry in southeast Kansas, the site of an ancient lagoon famous for plant and fish specimens.
"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 would become E. martiniwas first found more than two decades ago by paleontologist Larry Martin of the University of Kansas. It sat in storage at the university's Dyke Museum of Natural History for years, until Reisz borrowed it to prepare it for study.
Written By: Stephanie Pappas
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