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.
Dimetrodon species2DB15

Description and Paleobiology


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.[1][2]

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.[3] 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.[3] These voids would not let the "crack" formed by the serration to spread through the tooth.[3] Dimetrodon was found to lack adaptations to stop "crack" spreading.[3]


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.[4]


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.

Dimetrodon in The Land Before Time

Dimetrodon only appears in one entry in the Land Before Time franchise, and that is in the original 1988 film, Land Before Time. First, some Dimetrodon appear in a brief shot during the Great Earthshake, fleeing and being tossed by a wave of rock and debris. Later, an individual of a different species is seen while Littlefoot, Ducky, and Petrie are hiding in the "Big Underground", and as it passes them it flicks its tongue out similarly to that of a snake or lizard, and hisses.

There are a couple of inaccuracies with their appearance in the movie: One is that Dimetrodon did not live at the same time as the dinosaurs. However, many dinosaurs from different times and places appear in The Land Before Time, which could excuse this. The second inaccuracy is how the Dimetrodon that passes the children sticks its tongue out to taste the air like a snake which it likely did not do as it was a close relative to mammals rather than reptiles.

Recent studies have shown that Dimetrodon's sail had the neural spines partially exposed at the tips, and that its walking gait was semi-erect like that of a crocodilian. However, these are more recent studies and such findings were not readily available when the film was in the pre-production stages.



  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.
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