Category: Dinosaur

Dimetrodon (di-metro-don) was a large carnivorous reptile that lived during the Lower Permian (about 298-270 million years ago) of what is now the southwestern US. Recently, specimens have been found in Europe. Although it is often thought of as a dinosaur, probably because of its large size and carnivorous habits, it lived at least 40 million years before the first dinosaurs appeared on Earth. In fact, it is much more closely related to the ancestors of mammals, although there is little mammal-like about its structure or habits.



Genera and Species

Classification: Pelycosauria, Sphenacodontidae.

Species: There are presently 11 recognized species of Dimetrodon, but most of these cannot be distinguished by their anatomy. Many species can be distinguished only by their size, stratigraphic occurrence, or geographic occurrence. A more careful study of the many skeletons of Dimetrodon will likely show that most of these ‘species’ are slight variants that belong to Dimetrodon natalis, D. milleri, D. limbatus, or D. grandis.


Dimetrodon is a large quadrupedal animal with a sprawling posture like a modern crocodile, but unlike a modern crocodile, had a tall, narrow skull with huge canine teeth and a single opening on each side behind the eyes that marked it as a mammal-like reptile. Its most conspicuous feature is a tall ‘sail’ projecting from its back. The sail was composed of skin supported internally by greatly elongated bony spines growing from the tops of the vertebrae.


Dimetrodon shows a lot of variation in size depending on the species, but it is possible that many of these ‘species’ are simply very small or very large individuals of one of at most a half dozen valid species.

Length: 1.7-4.6 m (5.6-15.1 feet)

Weight: 28-250 kg (62-551 pounds)


Dimetrodon, like all modern reptiles are ‘cold blooded’ – in other words, they can’t produce their own body heat like a bird or mammal. However, it has been suggested that they were able to warm their bodies by exposing their ‘sail’ to the sun’s rays, and so were able to be more active than a standard cold blooded reptile. The ‘sail’ may also have been used for display or species recognition (A closely related animal, Sphenacodon, was very similar to Dimetrodon except it didn’t have a sail); perhaps this was how these creatures identified another member of their species. It may even have helped attract mates.

History of Discovery

The first specimen of Dimetrodon was described by E. D. Cope in 1878. Many more Dimetrodon specimens were collected in the subsequent years, and in the early 20th Century, another paleontologist, E. C. Case, described several more species. Beginning in the 1920s, the famous vertebrate paleontologist A. S. Romer began a multi-year collecting program in Texas, during which he amassed an enormous collection of Dimetrodon bones and skeletons, which became the basis for a classic work on pelycosaurs. As a result of the efforts of these three paleontologists, Dimetrodon is one of the best known of the early reptiles.


Dimetrodon lived in lowland areas where rivers, ponds, and swamps were common. The food web at the time was very closely tied to the water, where most of Dimetrodon’s food originated. It was a top predator, feeding on other reptiles and large semi-terrestrial amphibians that were common at the time.


  1. Knol, R. (2013, January 7). Early Permian. Retrieved May 22, 2014, from http://www.dinosaurcollectorsitea.com/EarlyPerm.html.

  2.  Dimetrodon. (n.d.). Retrieved May 22, 2014, from http://www.prehistoric-wildlife.com/species/d/dimetrodon.html.

  3. Romer, A.S., and Price, L.W. 1940 Review of the Pelycosauria. Geological Society of America Special Paper 28.

  4.  Steyer, S. (2012). Earth before the dinosaurs. Bloomington: Indiana University Press.