📸 Dimetrodon fossil at the National Museum of Natural History (image credit: Jeff Kubina)
280 million years ago, the Dimetrodon roamed the Earth, an apex predator at the top of the Permian Period’s food chain. With its distinctly reptilian appearance, Dimetrodon is often mistaken for a dinosaur, but they were actually synapsids. This clade of amniotes was a forerunner to today’s mammals, but there’s not much of a family resemblance. With its complex and deadly teeth and striking but still mysterious neural spines, these prehistoric carnivores occupy a special place in Earth’s history, anticipating many of the evolutionary traits used by both the dinosaurs and mammals.
📸 Diagram of Dimetrodon's spines
The Dimetrodon genus can immediately be identified by its iconic spine, a huge extension of its vertebrae that could grow over 5 feet tall. The purpose of the spine sail is unknown, though speculation ranges from courtship displays to temperature regulation. More recent studies have shown that the spines lacked the necessary channels for carrying blood vessels. A study in 2012 in conjunction with NASA's Jet Propulsion Laboratory suggests the sail may have served as a spring-like energy storage device for fast locomotion, allowing for the Dimetrodon to quickly close in on prey.
📸 Individual spine
Dimetrodon was certainly not the only creature with such a spine sail. Take Spinosaurus, a dinosaur that emerged much later in the fossil record with little relation to Dimetrodon. Both animals sported the fashionable back sail due to convergent evolution, a process where two unrelated animals develop similar features and lifestyles. As with Dimetrodon, debate continues around what purpose the Spinosaurus’ eponymous spine served, though it is clear there is still much to learn about these striking anatomical features.
The Dimetrodon’s sail made the animal a sight to see, but it was their teeth that allowed them to dominate as a predator. Dimetrodon is one of the first terrestrial vertebrates to develop multiple types of teeth, including tightly compressed, recurved teeth with sharp cutting edges. Known as ziphodont teeth, scientists speculate this development was a result of a new, refined feeding style in which flesh is sheared from the bones by pulling instead of direct, bone-crushing force. Coupled with its massive skull and large jaw adductor muscle, Dimetrodon sported many evolutionary traits that allowed it to dominate as a carnivore.
📸 Dental serrations in Dimetrodon grandis (source: Brink, Kirstin S., and Robert R. Reisz. "Hidden dental diversity in the oldest terrestrial apex predator Dimetrodon.")
The Permian Period that the Dimetrodon thrived in represents a radical change to life in response to a more varied climate across the planet. It was a transition from the warm, swampy jungles of the Carboniferous Period towards a more arid climate. The supercontinent Pangea had formed into the single landmass on the planet, with an interior that held stretches of dry deserts within. In the oceans, we see the first true bony fish. On land, the evolution of amphibian life gives way to pure terrestrial animals, including Dimetrodon and the other synapsids.
During the Permian Period, terrestrial life was defined by the amniotes, who had evolved during the Carboniferous. Amniotes were the first animals to evolve an external eggshell, diverging from the amphibians by being able to reproduce without a water source. With this evolutionary feature, amniotes were able to dominate life on land and diversify, dividing into two clades, synapsids and sauropsids. The main difference between the two was in their skulls, synapsids having one temporal fenestra (an opening in the skull behind the eye) and sauropsids having two, or none at all.
📸 Dimetrodon spine next to a Spinosaurus fossil. The Dimetrodon spine is being held by a very distant mammalian relative
Superficially, synapsids and sauropsids appeared similar, but the divergence between the two would lead in very different directions, with sauropsids evolving into dinosaurs and synapsids becoming mammals. The Dimetrodon is a good example of this, the animal refining a number of traits that we humans use today, although Dimetrodon is not a direct ancestor of mammals. The genus’ teeth are similar to our own in that we also have varied shapes to our teeth that allow us to break down food effectively. Dimetrodon also had a somewhat upright posture which is also in line with mammals.
The evolutionary branches between today’s mammals and the Permian’s Dimetrodon are far apart, but the connection can be found in subtle anatomical features that appeared around 280 million years ago. The Dimetrodon is a testament to just how long evolution’s story is, that our own species is distantly related to a reptilian-like predator that crushed its prey with serrated teeth and sported massive neural spines. With these attributes, the Dimetrodon dominated the world’s food chains of the Permian Period for millions of years.
📸 Dimetrodon paleoart
📸 Dimetrodon spine fragments on display
Quite the backbone
This specimen is a fossil fragment of a Dimetrodon neural spine sail, originally featured in the Second Edition of the Mini Museum. The material was recovered from private land in West Texas, USA. This region, known as the Texas Red Beds, contains one of the most complete fossil records of the Early Permian and dates to roughly, 280,000,000 years old.
These fragments of Dimetrodon neural spine sail material vary by size, color and shape. The ancient Permian Period material is quite precious and it is rare to see in public hands.
Check out our full Dimetrodon fossil collection, with riker box specimens, several larger segments of neural spine fossils and even a complete showcase dorsal vertebra! Explore the Dimetrodon collection here!
Angielczyk, Kenneth D. “Dimetrodon Is Not a Dinosaur: Using Tree Thinking to Understand the Ancient Relatives of Mammals and Their Evolution.” Evolution education & outreach 2.2 (2009): 257–271. Web.
Brink, Kirstin S., and Robert R. Reisz. "Hidden dental diversity in the oldest terrestrial apex predator Dimetrodon." Nature communications 5 (2014).
Cowen R. History of Life. 4th ed. Blackwell Pub.; 2005.
Dial KP, Shubin N, Brainerd EL, eds. Great Transformations in Vertebrate Evolution. The University of Chicago Press; 2015.
Rega, Elizabeth A., et al. "Healed fractures in the neural spines of an associated skeleton of Dimetrodon: implications for dorsal sail morphology and function." Fieldiana Life and Earth Sciences (2012): 104-111.