Temporal range: early Permian
|Dimetrodon grandis skeleton at the |
National Museum of Natural History
Dimetrodon 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, from red beds in Texas and Oklahoma. The largest known species of Dimetrodon is D. angelensis at 4.6 metres (15 ft) and the smallest is D. teutonis at 60 centimetres (24 in).
Dimetrodon was a carnivore, probably the top predator in its environment. Its main feature is the large sail on its back formed by elongated spines extending upwards from the vertebrae. The spines would be joined by skin. The general opinion of palaeontologists is that it was a temperature-regulating device. The idea is that the animal could warm up in the early morning by placing itself broadside to the Sun, and later could cool off in the shade, or arrange for its body to get less sunlight. At this stage in evolution, no land animals were homoiotherms. Very likely the sail was also used for sexual or territorial signalling. In which case, the skin would be coloured. This, of course, is supposition, but it does make sense of the animal's most extraordinary feature.
In evolutionary terms, Dimetrodon was a synapsid, a line of land animals which eventually gave rise to the mammals. It was not on the direct line of descent, but a good example of the evolutionary grade typical of Permian synapsids.
- "The Kungurian Age". Palaeos. Retrieved 29 September 2013.
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- Florides G.A. et al 2001. Natural environment and thermal behaviour of Dimetrodon limbatus. Journal of Thermal Biology 26 (1): 15–20. 
- Benson R.J. 2012. Interrelationships of basal synapsids: cranial and postcranial morphological partitions suggest different topologies. Journal of Systematic Paleontology 10 (2).