Dimetrodon mileri

Dimetrodon Temporal range: Cisuralian, 295–272 Ma PreЄ Є O S D C P T J K Pg N
Skeleton of D. incisivum, Staatliches Museum für Naturkunde Karlsruhe
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Family:	†Sphenacodontidae
Subfamily:	†Sphenacodontinae
Genus:	†Dimetrodon Cope, 1878
Type species
†Dimetrodon limbatus Cope, 1877 (originally Clepsydrops limbatus)
Species
See below
Synonyms
Genus synonymy Embolophorus Cope, 1878 Theropleura Cope, 1880 Bathyglyptus Case, 1911 Eosyodon Olson, 1962 Species synonymy Clepsydrops limbatus Cope, 1877 Clepsydrops gigas Cope, 1878 Clepsydrops natalis Cope, 1878 Dimetrodon gigas Cope, 1878 Dimetrodon incisivus Cope, 1878 Dimetrodon rectiformis Cope, 1878 Embolophorus dollovianus Cope, 1878 Dimetrodon semiradicatus Cope, 1881 Clepsydrops macrospondylus Cope 1884 Dimetrodon platycentrus Case, 1907 Theropleura grandis Case, 1907 Bathyglyptus theodori Case, 1911 Dimetrodon maximus Romer, 1936 Eosyodon hudsoni Olson, 1962

See below

Dimetrodon (ⁱ/daɪˈmiːtrədɒn/; meaning "two measures of teeth") is an extinct genus of 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 described 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 "stem-mammals" or "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.