Edaphosaurus was one of the first herbivorous reptiles. Do not confuse this creature with dimetrodon, because he was a carnivore, whereas this guy eats plants. Also, dimetrodon had a more symetrical spine. In this picture there is also seymouria, a land anphibian. He’s the orange, yellow and white bloke with no spine.
In the BBC’s “Walking with Monsters” it depicts dimetrodon killing one of these beasts. A close observer would have noticed it killed a youngster, probably because an adult was as large and as strong as a dimetrodon.