What it looked like
The dimetrodon weighed about 250 kg. It had a large sail-like flap of skin along its back, full of blood vessels. It was held up by long, bony spines, each of which grew out of a separate vertebra. This flap might have been used to absorb and release heat, for impressing a mate, or for making it look much larger than it was to frighten away predators.

The Dimetrodon is not a dinosaur, and is probably more closely related to us than to the dinosaurs. It is a Pelycosaur, which had many things in common with mammals, and is among the relatives of warm-blooded mammals.

What it ate
Dimetrodon was a carnivore with a huge head and mouth. It had large, powerful jaws, and two types of teeth - sharp canines and shearing teeth. It probably ate other pelycosaurs (its close relatives), and insects. It could leave its cold, sluggish state much earlier after sunrise than the pelycosaurs with no sails and catch and eat them.

How it moved around
Dimetrodon walked on four legs that sprawled out to the sides (unlike the dinosaurs, whose legs came from under their bodies). They were probably very fast runners.

How it probably behaved
Dimetrodon was a carnivore during the Permian period, living mainly in swampy areas. Unlike other pelycosaurs with no big fin on their back, they warmed up earlier after sunrise and cooled off more efficiently in the heat of the day. This, and their large and powerful jaws gave them the advantage over others, giving them dominance.

 A view of what the world looked like in the Permian era, before the dinosaurs.

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