Dimetrodon Fossil range: Early–Middle Permian, 280–265 Ma PreЄ Є O S D C P T J K Pg N
Dimetrodon grandis skeleton at the National Museum of Natural History
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Superclass:	Tetrapoda
Class:	Synapsida
Order:	Pelycosauria
Suborder:	Eupelycosauria
Family:	Sphenacodontidae
Genus:	Dimetrodon Cope, 1878
Species
D. angelensis Olson, 1962 D. booneorum Romer, 1937 D. dollovianus Cope, 1888 D. fritillus Cope, 1878 D. gigas Sternberg, 1942 D. giganhomogenes Case, 1907 D. grandis Case, 1907 D. limbatus Cope, 1877 D. loomisi Romer, 1937 D. macrospondylus Cope, 1884 D. milleri Romer, 1937 D. natalis Cope, 1877 D. occidentalis Berman, 1977 D. platycentrus Case, 1907 D. teutonis Berman, Reisz, Martens & Henrici, 2001
Synonyms
Bathyglyptus Case, 1911 Embolophorus Cope, 1878 Theropleura Cope, 1878 (in partium)

Dimetrodon (pronounced /daɪˈmɛtrədɒn/, meaning "two measures of teeth") was a predatory synapsid ("mammal-like reptile") genus that flourished during the Permian period, living between 280–265 million years ago (Artinskian to Capitanian stages). It was more closely related to mammals than to true reptiles such as lizards. It is classified as a pelycosaur. Fossils of Dimetrodon have been found in North America and Europe.

Contents 1 Description 1.1 Sail 2 Relationship with modern mammals 3 In popular culture 4 Gallery of species 5 See also 6 References

[edit] Description

Dimetrodon was an apex predator, among the largest of its day. It grew to up to 3.5 metres (11 ft) in length. The name Dimetrodon means "two-measures of teeth", so-named because it had a large skull with two different types of teeth (shearing teeth and sharp canine teeth), unlike reptiles.^[1] It walked on four side-sprawling legs and had a large tail. Dimetrodon may have moved in a manner similar to present-day lizards.

[edit] Sail

The most distinctive characteristic of Dimetrodon was the spectacular sail on its back (other pelycosaurs such as Edaphosaurus, Ianthasaurus, and Sphenacodon also have this trait). The sail, which was dense with blood vessels, was probably used to regulate body temperature; the surface area would allow it to warm up or cool off more efficiently. This adaptation was important because it would give the animal more time to hunt prey. The sail may also have been used in mating rituals and to warn off other predators. The sail was supported by neural spines, each one sprouting from an individual vertebra. Bramwell and Fellgett (1973) calculate that a 200 kg Dimetrodon would heat up from 26°C to 32°C in 205 minutes without a sail and in only 80 minutes with a sail.^[2]

[edit] Relationship with modern mammals

As a synapsid, Dimetrodon was distantly related to modern mammals. Synapsids were the first tetrapods to evolve differentiated (or heterodont) teeth. Whereas reptiles hardly chew their food, simply gulping it down, synapsids like Dimetrodon developed teeth to help shear meat into smaller pieces for easier digestion. These 'two-measure teeth' eventually gave rise to the various kinds of teeth present in modern mammals. Dimetrodon was not a dinosaur.

[edit] In popular culture

In many popular culture references, Dimetrodon is often erroneously seen as a dinosaur or as living alongside dinosaurs.

A composite of Edaphosaurus and Dimetrodon fossils^[3] went on display in 1907 in the American Museum of Natural History, New York, presented by the curator of vertebrate paleontology Henry Fairfield Osborn and illustrated in the pages of Scientific American (May 1907) as "Naosaurus", by the great scientific illustrator Charles R. Knight.

Dimetrodon has also been featured in various television programs. In the 1974 television program Land of the Lost, a very large Dimetrodon (about 26 feet or 8 metres long) named "Torchy" first appeared in the Season 3 episode "Cornered". Somehow, Torchy could breathe fire and would often eat coal to stoke his internal furnace, leading him to fight with the show's female Allosaurus, "Big Alice", and winning.

A Dimetrodon was briefly seen in The Land Before Time. It is shown sporting a forked tongue common to snakes.

In the television documentary Walking With Monsters (called Before the Dinosaurs in the United States), baby Dimetrodon were shown hatching with sails, fully independent. In fact, no Dimetrodon eggs have yet been found and it is entirely possible that the sail, which would be hard to store in an egg, was either absent or not rigid upon hatching. Hatchlings were portrayed sprinting towards trees after hatching in order to escape cannibalistic adults, behaviors based on the modern Komodo Dragon. Dimetrodon was also shown as having an egg-laying style similar to the modern crocodile, though no evidence regarding Dimetrodon reproduction has ever actually been found.

[edit] Gallery of species

D. gigashomogenes	D. grandis	D. loomisi	D. milleri
D. natalis	D. limbatus

[edit] See also

• Sphenacodon - a pelycosaur closely related to Dimetrodon.
• Spinosaurus - a dinosaur with a sail on its back.
• Evolution of mammals

[edit] References

1. ^ Palmer, D., ed (1999). The Marshall Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals. London: Marshall Editions. p. 187. ISBN 1-84028-152-9. 
2. ^ Bramwell, C. D.; Fellgett, P.P. (1973). "Thermal regulation in sail lizards". Nature 242: 203–205. doi:10.1038/242203a0. 
3. ^ Both came from Permian strata in Texas.

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