Dimetrodon and the sail-backed synapsids

Dimetrodon was the apex predator of the Early Permian, about 295 to 272 million years ago, whose fossils come mostly from the red beds of Texas and Oklahoma. Edward Drinker Cope named it in 1878, and Alfred Romer later studied it in detail. The animal was a synapsid, not a dinosaur, and it lived about 50 million years before the first dinosaurs. Larger species reached 3 to 4.6 metres, with long jaws, a deep skull and a row of tall spines on the back covered by skin to form a sail.¹

The name means 'two measures of teeth', because it had teeth of different shapes: sharp front teeth, large canines and slicing cheek teeth, a feature that later mammals refined. The sail probably helped control body heat, aid display or both, and the question is still debated. Dimetrodon ate large amphibians, early reptiles and other synapsids. Fossil beds in Texas show a full community, with Dimetrodon at the top. Dimetrodon vanished by about 270 million years ago, replaced by therapsids, which gave rise to mammals.¹²