Long before the dinosaurs, there was a genus of animals called Synapsids. They weren’t dinosaurs, or even reptiles, despite their appearance—they were more closely related to mammals of today.
The largest and most iconic Synapsid was dimetrodon, the enormous lizard-looking creature with a sail on its back. It roamed the ancient United States during the Permian period, over 250 millions years ago. It was the top predator of its time, feeding on fish and small reptiles. Their size ranged anywhere from 5 feet to nearly 18 feet in the largest species, and they could weigh between 60 and 550 pounds. Their teeth were uniquely shaped like teardrops.
Of course, the most unique aspect of these creatures was their enormous sail. Researchers disagree on what function this sail served—some say it was for display purposes for finding mates, while others argue that it was meant to help the animal regulate its body heat. Since Dimetrodon was a proto-mammal, not a mammal like we know today, the sail could be thought of as a sort of primitive way of being warm-blooded.
If the largest extinction event of all time had not happened, life on Earth would have been very different—these synapsids would have continued evolving, and the age of dinosaurs may never have happened. It’s fascinating to consider that our mammalian ancestors had such a good start before a disaster wiped them out for a while, leaving another genus to evolve in their place. In The Sixth Event, I portrayed these ancient ancestors of ours as pretty intelligent—but of course, there’s no way to tell what sort of behaviors they really had. Unfortunately, mysteries of a creature that lived 250 million years ago tend to stay buried.