Dimetrodon meaning "Two-measures Tooth" is a carnivore meat-eating pelycosaur mammal-like reptile, an ancestor of the mammals, that lives during the Permain Period, long before the dinosaurs evolved.
The Dimetrodon has a large sail-like flap of skin along its back, dense with blood vessels. The sail was supported by long, bony spines, each of grew out of a separate spinal vertebra. The sail may have been a thermoregulatory structure, used to absorb and release heat. The sail mayhave also been used for mating and dominance rituals, and/or for making it look much larger than it was to predators. Dimetrodon had sharp teeth and clawed feet.
In The Rite of Spring segment, a pair Dimetrodons were seen, one was yawning and the other one was eating a Nothosaurus. Even though they were carnivores, they lived with herbivorous dinosaurs. One was seen when the Tyrannosaurus Rex arrived in the thunderstorm. One Dimetrodon was running away along with a Parasaurolophus, a Triceratops, a Dimorphodon, and 2 lizards from the Tyrannosaurus Rex hunting and chasing them.
One Dimetrodon was seen after the Stegosaurus' death from been killed by the T-Rex along with a group of herbivorous dinosaurs (A Parasaurolophus, Triceratops, Corythosaurus and a Diplodocus) looking and watching. There were no Dimetrodons seen again at the end of the segment, But they most likely became extinct in the drought of starvation, and dehydration.
In real life
Dimetrodon (meaning "two measures of teeth") is an extinct genus of synapsid that lived during the Early Permian, around 295–272 million years ago (Ma). It is a member of the family Sphenacodontidae. The most prominent feature of Dimetrodon is the large sail on its back formed by elongated spines extending from the vertebrae. It walked on four legs and had a tall, curved skull with large teeth of different sizes set along the jaws. Most fossils have been found in the southwestern United States, the majority coming from a geological deposit called the Red Beds in Texas and Oklahoma. More recently, fossils have been found in Germany. Over a dozen species have been named since the genus was first described in 1878.