friday dino and not-dinos

i did a stegosaurus, and two animals that, while popularly thought of as dinosaurs, are not. dimetrodon was a pelycosaur, a synapsid more closely related to mammals than to true reptiles. pteranodon was a pterosaur (pterodactyl), who, like the dinosaurs, belonged to a group called the archosaurs (dinosaurs and birds, crocodilians, pterosaurs).