Dimetrodon

*Dimetrodon grandis*

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***Dimetrodon*** (pronounced /daɪˈmiːtrədɒn/; meaning "two measures of teeth" ) is an extinct genus of synapsid that lived in the Cisuralian (Early) Permian period. The name *Dimetrodon* refers to a range of animals under the genus, and it currently includes up to 20 subspecies in it, but the name is synonymous amongst them.

As a synapsid, it was more closely related to mammals than to true reptiles such as lizards and snakes. It is classified as a pelycosaur, which is an informal grouping composed of basal or primitive Late Paleozoic synapsids. Fossils of *Dimetrodon* have been found in North America and Europe.

## Description and Paleobiology

### Skull

*Dimetrodon* was a carnivore and had two types of teeth in its mouth, like a mammal, shearing teeth and sharp canine teeth. Its name, in fact, means "two measures of teeth". This genus was one of the first with different-shaped teeth, and the teeth could for kill prey, then tear them to bits. It has a large skull with temporal holes at the back of each eye on the side, a unique trait of a synapsid skull. This made possible new attachment sites for jaw muscles, which could run fast and let the animal chew.

In a 2001 study on the biomechanics of the dinosaur *Albertosaurus's* teeth, William L. Abler saw that examined *Dimetrodon* teeth had serrations so fine as to look like a crack in the tooth. Though *Albertosaurus* had similar serrations, the base of each serration included a round void which would have functioned to distribute force over a larger surface area. These voids would not let the "crack" formed by the serration to spread through the tooth. *Dimetrodon* was found to lack adaptations to stop "crack" spreading.

### Legs

The strong legs of *Dimetrodon* were spread beside the body. Based on the construction of the legs, it was a fast and smoothly moving animal, especially compared to its solidly built, herbivorous relatives. The shape of the hip bones, the hind legs and the joints between the vertebrae can be seen.

### Sail

*Dimetrodon's* most recognizable feature was a sail on its back, not unlike that of *Spinosaurus*. It is thought to have been used to regulate its body temperature. It would be able to pump blood into the sail and the sun would heat it. Then *Dimetrodon's* blood would go back into its body, warming the creature.

## Species

The genus Dimetrodon currently includes several more or less recognized types:

Many species have been described by Edward Drinker Cope during his expeditions in 1880. Romer Alfred Sherman described a few species in the 1930s and 1940s. Most of the type specimens from the collection of which Cope based his descriptions were not released from the matrix. Reassessment after his death led to different conclusions on these specimens, including on the construction of the skull.[17] The status of some of the species described by Cope is questionable, namely *D. fritillus*, *D. gigas*, *D. incisivus*, *D. rectiformis,* and *D. semiradicatus*. There is a broad subdivision into species with a long skull from the Early Permian and species with a short head from the later parts of the Permian.

## Paleoecology

Fossils are known from the United States (Texas, Oklahoma, New Mexico, Arizona, Utah, and Ohio) and Germany, areas that the first parts of the Permian were part of the supercontinent Euramerica. Most fossil finds are part of lowland ecosystems, during the Permian would have been vast wetlands. In particular, the Red Beds of Texas is an area ofthe great diversity of fossils of *Dimetrodon* species and other species from the Early Permian. The fossils date from 290 to 270 million years ago, which means it lived from the Cisuralian to the Guadalupian period. *Dimetrodon* probably developed from a *Sphenacodon*-like ancestor. The climate of the Late Carboniferous (Pennsylvanaen) and Early Permian (Asse Lien, Sakmarien, Arti Skiing) resulted in warm, humid ecosystems in subtropical and tropical zones, consisting of vast wetland areas. In additio,n there were large ice sheets on the Southern Hemisphere that stretched to about 30° south. The fauna was concentrated in this period therefore in tropical and subtropical zones. Aquatic and semi-aquatic tetrapods dominated, while land predators as *Dimetrodon* were largely water-fed animals. The Early Permian had a drier and hotter climate where deserts began to develop. This led a climate change causing major extinction of the tetrapods, thus clearing the way for the development of therapsids. *Dimetrodon* was replaced as an apex predator by carnivores as *Biarmosuchia* and *Dinocephalia*.

## JPInstitute.com Description

Dimetrodon is commonly mistaken for a dinosaur, but it was in fact NOT a dinosaur at all. It was one of a number of animals known as Mammal-Like Reptiles that dominated the late Permian period. It was a large meat-eater that lived primarily in swampy areas and had a very interesting feature - a large sail on its back. Dimetrodon disappeared at the beginning of the Triassic Period.

Unlike other pelycosaurs that did not have fins, Dimetrodon was able to warm up in the morning and cool off more efficiently during the heat of the day due to its sail. This method of controlling its body temperature, along with its large and powerful jaws, gave this predator a distinct advantage over the other large carnivores, making it the dominant land predator. In fact, its ability to warm up faster would have enabled it to catch and eat the slower, non-finned Mammal-Like Reptiles.

Dimetrodon is easily distinguished from dinosaurs as its legs were positioned on the side of its body while dinosaurs had their legs under their bodies. Even with this body structure, it was probably a very fast runner. It had a large head with very strong jaws and two types of teeth -sharp fang-like teeth for ripping and tearing in the front and smaller cheek teeth in the back that were designed for shredding the meat.

## Links

http://web.archive.org/web/20040806075558fw\_/http://www.jpinstitute.com/dinopedia/dinocards/dc\_dimet.html#

## References

Template:References

1. ↑ R & Demar Barghusen HR. (1972) "Mechanics and the Evolution of the synapsid jaw". *Evolution*, 26(4):622-637.
2. ↑ HR Barghusen. (1973) "The adductor jaw musculature of *Dimetrodon* (Reptilia, Pelycosauria)". *Journal of Paleontology*, 47(5):823-834.
3. ↑ 3.0 3.1 3.2 3.3 Alberto tooth abs 84
4. ↑ *The illustrated encyclopaedia of dinosaurs and prehistoric animals*. D & B Palmer Cox. Second Edition; Könemann, 2000, p. 184.