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Name means: Two Measure Teeth


Species: angelensis, booneorum, borealis, dollovianus, gigashomogenes, grandis, limbatus, loomisi, macrospondylus, milleri, natalis, occidentalis, teutonis

Range: Early to mid-Permian (Artinskian-Kungurian, 290-273 MYA) from Oklahoma, Texas, Utah, New Mexico, Prince Edward Island (Canada), Germany

Size estimate: 5-15 ft length, 60-550 lbs

Discovery: Edward Drinker Cope, 1878

Classification: synapsida, sphenacodontia, sphenacodontidae, sphenacodontinae


Often confused with dinosaurs, Dimetrodon predated them by tens of millions of years. Its striking profile made it irresistible to the authors and illustrators of books about dinosaurs. Like many of the popular meat-eating dinosaurs, it may also have played the apex predator role in its ecology. Yet as reptile-like as it appears, Dimetrodon is a stem mammal. Its close relatives gave rise to mammals themselves millions of years later.


Dimetrodon shows several features that made it one of the top predators of its time. The teeth that inspired its name come in different sizes and shapes. Scientists call this condition “heterodonty.” Though known in reptiles like Tyrannosaurus, Heterodontosaurus, or the crocodilian Malawisuchus, by far the most common heterodonts are mammals. Heterodont teeth gave Dimetrodon an advantage in catching and eating prey. It could bite animals into smaller pieces, which in turn allowed it to develop a stronger bite. Since its skull didn’t need to expand to swallow prey larger than its head, it could grow more rigid for greater bite power. Later species of Dimetrodon developed saw-like edges along their teeth to make them sharper.


The function of its sail remains unknown. Theories that it acted like a solar panel to control its body heat have some backing from the fossil record. However, the sail may not have changed the surface area of the animal enough to make it effective on its own. Another theory that has gained support in recent years says Dimetrodon used its sail for display. Different sail shapes among the various species of Dimetrodon might provide evidence for this theory. Perhaps the oddest fact in the mystery of Dimetrodon’s sail stems from the sails of unrelated animals in its same environment. The plant-eating stem mammal Edaphosaurus and the amphibian Platyhystrix both grew spinal sails. Later archosaurs like Arizonasuchus, Spinosaurus, and Ouranosaurus also sported fins on their backs. These fins may have grown as responses to the same evolutionary pressures. Even so, each group developed different design specifics for their sails. Dimetrodon’s spines showed a unique groove towards their tips. This groove gave them a cross-section like an I-beam for greater strength. The length or even presence of the groove may have changed as the animal grew older.

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