Pelycosaur synapsid (composite)

One of the only large plant eaters around, a lone Edaphosaurus moves through dense vegetation, including Calamites, a treelike horsetail.
LIGHT, ENERGY, AND LIFE
The sun powers life. Plants use sunlight to make food. Animals get their energy from eating plants or other animals. Decomposers and detritivores return nutrients to the soil.

This was as true in the early Permian as it is today. But few large plant eaters roamed the Earth 290 million years ago. In fact, Edaphosaurus and Diadectes were among the only large herbivores of the day.