Old Earth Ministries Online Earth History Curriculum

Presented by Old Earth Ministries (We Believe in an Old Earth...and God!)

This curriculum is presented free of charge for use by homeschooling families.

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Chapter 8 - The Permian Period

Lesson 43: Dimetrodon


   Dimetrodon (pronounced /daɪˈmɛtrədɒn/, meaning "two measures of teeth") was a predatory synapsid ("mammal-like reptile") genus that flourished during the Permian period, living between 280265 million years ago (Artinskian to Capitanian stages). It was more closely related to mammals than to true reptiles such as lizards. It is classified as a pelycosaur. Fossils of Dimetrodon have been found in North America and Europe.

     Dimetrodon was an apex predator, among the largest of its day. It grew to up to 3.5 metres (11 ft) in length. The name Dimetrodon means "two-measures of teeth", so-named because it had a large skull with two different types of teeth (shearing teeth and sharp canine teeth), unlike reptiles. It walked on four side-sprawling legs and had a large tail. Dimetrodon may have moved in a manner similar to present-day lizards.


Chapter 8 - The Permian Period


 Lesson 40 - Permian Overview

 Lesson 41 - The Permian Extinction, Part 1

 Lesson 42 - The Permian Extinction, Part 2

 Lesson 43 - Species In-Depth, Dimetrodon





     The most distinctive characteristic of Dimetrodon was the spectacular sail on its back (other pelycosaurs such as Edaphosaurus, Ianthasaurus, and SphenacodonDimetrodon also had this anatomical feature). The sail, which may have been supplied with numerous blood vessels, may have been used to regulate body temperature; the extra surface area provided by the sail may have allowed the animal to warm up or cool off more rapidly than without a sail. This adaptation might have been important because it would have given the animal a head start over its prey in the morning, thus providing more time to hunt cooler, slower prey. The sail may also have been used as a display in mating rituals and to warn off other predators. The sail was supported by neural spines, each one sprouting from an individual vertebra. Assuming a rich blood supply to the sail, Bramwell and Fellgett (1973) calculated that a 200 kg Dimetrodon would heat up from 26C to 32C in 205 minutes without a sail and in only 80 minutes with a sail.

Relationship with Modern Mammals

     As a synapsid, Dimetrodon was distantly related to modern mammals. Synapsids were the first tetrapods to evolve differentiated (or heterodont) teeth. Whereas reptiles hardly chew their food - they mostly gulp it down - synapsids like Dimetrodon developed teeth to help shear meat into smaller pieces for easier digestion. These 'two-measure teeth' eventually gave rise to the various kinds of teeth present in modern mammals.

In Popular Culture Today

     In many popular culture references, Dimetrodon is often erroneously seen as a dinosaur or as living alongside dinosaurs.

     A composite of Edaphosaurus and Dimetrodon fossils went on display in 1907 in the American Museum of Natural History, New York, presented by the curator of vertebrate paleontology Henry Fairfield Osborn and illustrated in the pages of Scientific American (May 1907) as "Naosaurus", by the great scientific illustrator Charles R. Knight.

     Dimetrodon has also been featured in various television programs. In the 1974 television program Land of the Lost, a very large Dimetrodon (about 26 feet or 8 metres long) named "Torchy" first appeared in the Season 3 episode "Cornered". Somehow, Torchy could breathe fire and would often eat coal to stoke his internal furnace, leading him to fight with the show's female Allosaurus, "Big Alice", and winning.

     A Dimetrodon was briefly seen in The Land Before Time. It is shown sporting a forked tongue common to snakes.

     In the television documentary Walking With Monsters (called Before the Dinosaurs in the United States), baby Dimetrodon were shown hatching with sails, fully independent. In fact, no Dimetrodon eggs have yet been found and it is entirely possible that the sail, which would be hard to store in an egg, was either absent or not rigid upon hatching. Hatchlings were portrayed sprinting towards trees after hatching in order to escape cannibalistic adults, behaviors based on the modern Komodo Dragon. Dimetrodon was also shown as having an egg-laying style similar to the modern crocodile, though no evidence regarding Dimetrodon reproduction has ever actually been found.

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Source: Dimetrodon