Temporal range: Cisuralian to Guadalupian (Asselian to Roadian),
Dimetrodon incisivum 01.jpg
Skeleton of D. limbatus, Staatliches Museum für Naturkunde Karlsruhe
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Clade: Synapsida
Family: Sphenacodontidae
Subfamily: Sphenacodontinae
Genus: Dimetrodon
Cope, 1878
Type species
Dimetrodon limbatus
Cope, 1877

See below

Genus synonymy
  • Bathygnathus
    Leidy, 1854
  • Embolophorus
    Cope, 1878
  • Theropleura
    Cope, 1880
  • Bathyglyptus
    Case, 1911
  • Eosyodon
    Olson, 1962
Species synonymy
  • Bathygnathus borealis
    Leidy, 1854
  • 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

Dimetrodon (/dˈmtrədɒn/ (listen)[1] or /dˈmɛtrədɒn/,[2]) 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 (Mya).[3][4][5] 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, its 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.[6][7] 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.[4] Dimetrodon is assigned to the "non-mammalian synapsids", a group traditionally – but incorrectly – called "mammal-like reptiles",[4] and now known as stem mammals. This groups Dimetrodon together with mammals in a clade (evolutionary group) called Synapsida, while placing dinosaurs, reptiles, and birds in a separate clade, the 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.[8] Some recent studies 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.[9][10]

  1. ^ "Dimetrodon". Lexico UK English Dictionary. Oxford University Press. Archived from the original on 2020-03-22.
  2. ^ Dimetrodon. Dictionary.com. Dictionary.com Unabridged. Random House, Inc. http://www.dictionary.com/browse/dimetrodon (accessed: February 12, 2018).
  3. ^ "Dimetrodon". Paleobiology Database. Retrieved 23 August 2012.
  4. ^ a b c Angielczyk, K. D. (2009). "Dimetrodon is Not a Dinosaur: Using Tree Thinking to Understand the Ancient Relatives of Mammals and their Evolution". Evolution: Education and Outreach. 2 (2): 257–271. doi:10.1007/s12052-009-0117-4.
  5. ^ Huttenlocker, A. K.; Rega, E. (2012). "The Paleobiology and Bone Microstructure of Pelycosauriangrade Synapsids". In Chinsamy, A. (ed.). Forerunners of Mammals: Radiation, Histology, Biology. Indiana University Press. pp. 90–119. ISBN 978-0-253-35697-0.
  6. ^ "Famous Prehistoric Animals That Weren't Actually Dinosaurs". Feb 17, 2021. Archived from the original on 2021-04-07.
  7. ^ Black, Riley. "The Dimetrodon in Your Family Tree". Smithsonian Magazine. Retrieved 2021-12-05.
  8. ^ Cloudsley-Thompson, J. L. (2005-01-19). Ecology and Behaviour of Mesozoic Reptiles. Springer Science & Business Media. ISBN 978-3-540-22421-1.
  9. ^ Fiesta, Enrique; Davidson, John (2015-01-10). Dimetrodon - Permian Predator. Mendon Cottage Books. ISBN 978-1-310-19617-1.
  10. ^ Zachos, Frank; Asher, Robert (2018-10-22). Mammalian Evolution, Diversity and Systematics. Walter de Gruyter GmbH & Co KG. ISBN 978-3-11-034155-3.

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