Dimetrodon (/daɪˈmiːtrədɒn or daɪˈmɛtrədɒn/, meaning "two measures of teeth") is an extinct genus of non-mammalian synapsid that lived during the Cisuralian (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 neural spine 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 of Texas and Oklahoma. More recently, fossils have been found in Germany. Over a dozen species have been named since the genus was first erected in 1878. Dimetrodon is often mistaken for a dinosaur or as a contemporary of dinosaurs in popular culture, but it became extinct some 40 million years before the first appearance of dinosaurs. Reptile-like in appearance and physiology, Dimetrodon is nevertheless more closely related to mammals than to modern reptiles, though it is not a direct ancestor of mammals. Dimetrodon is assigned to the "non-mammalian synapsids", a group traditionally called "mammal-like reptiles". This groups Dimetrodon together with mammals in a clade (evolutionary group) called Synapsida, while placing dinosaurs, reptiles and birds in a separate clade, Sauropsida. Single openings in the skull behind each eye, known as temporal fenestrae, and other skull features distinguish Dimetrodon and mammals from most of the earliest sauropsids. Dimetrodon was probably one of the apex predators of the Cisuralian ecosystems, feeding on fish and tetrapods, including reptiles and amphibians. Smaller Dimetrodon species may have had different ecological roles. The sail of Dimetrodon may have been used to stabilize its spine or to heat and cool its body as a form of thermoregulation. Some recent studies[citation needed] argue that the sail would have been ineffective at removing heat from the body due to large species being discovered with small sails and small species being discovered with large sails, essentially ruling out heat regulation as its main purpose. The sail was most likely used in courtship display with methods such as threatening rivals or showing off to potential mates.
Dimetrodon
Prehistoric Creatures
for Prehistoric Creatures in Dino-Riders
Suggested by alecgroskreutz1
The Valorians were a species of peaceful humanoids that lived on the planet Valoria until they were invaded by the predatory Rulons. A group of Valorians lead by Questar attempted to escape the Rulon invasion using a spaceship equipped with their "Space Time Energy Projector" (S.T.E.P.); however, something went wrong. They were sent back in time and space, to the planet Earth 65 million years back to the age of the dinosaurs. Unknown to them, the Rulon flagship, the Dreadlock, locked in with a tractor beam, was also sent back through time when the S.T.E.P. was activated. After successfully landing on prehistoric Earth, the Valorians used their AMP ("Amplified Mental Projector") necklaces to telepathically communicate with the dinosaurs they encountered and eventually befriended them. On the other hand, the Rulons - led by the warlord Krulos - used brainwashing devices known as brain-boxes to control dinosaurs for their own needs. The Rulons then launched an attack on the Valorians, who called upon their dinosaur friends to assist them in fighting back. After ultimately defeating the Rulons, the Valorians renamed themselves Dino-Riders.
