A pair of adult Dimetrodon battle it out.
Herbivorous Edaphosaurus in the Permian Period.
These were the strange sail-backs, of the Early-Mid Permian Period (290-270 million years ago) They were relatively huge for their time, and had succeeded in conquering the land, and all competition. The Pelycosaurs would hold this title for over 20 million years. Dimetrodon, the largest and most famous of them all, was about the size of a large-Lion. It even preyed on other Pelycosaurs, such as the herbivore Edaphosaurus, as well as anything else it could catch. Other than this, they probably like to fight with each other, as depicted on the screen. The large sails on their backs, were evolved to exploit the sunlight. Turned to the sun when it rise each ancient morning, the sail would act like a solar-panel, providing energy for the reptile. If too hot, they would simple either find shade so that the rays of the sun were not being absorbed, or they would turn themselves away from the sunlight at an angle.