You are in the dry floodplains of North America, 280 million years ago.

The air in the early Permian valley was thick, humid, and smelled intensely of wet ferns and sulfur. You crouched behind a sturdy coniferous tree, your breath catching as the rustling in the undergrowth grew louder.

Through the mist, they appeared—a herd of Edaphosaurus, perhaps twenty individuals. They were magnificent, plodding herbivores about 10 feet long, far from the agile dinosaurs that would rule millions of years later. Instead of speed, they possessed a heavy, low-slung armor, giving them a confident, slow movement.

What struck you most was the sheer visual impact of their dorsal sails. These were not just skin stretched over spines like their cousin, Dimetrodon. The sails on these Edaphosaurus were complex, lined with intricate crossbars that looked like wooden scaffolding, which they seemed to use to catch the warming morning sunlight.

A mother moved past your hiding spot, her small head—unusually small for her body—grinding away at a tough fern with specialized, peg-like crushing teeth. Beside her, a smaller juvenile moved, its own sail still growing. You watched as the herd gathered, resting underneath the taller conifer trees to escape the rising heat of the sun, using their impressive sails to regulate their temperature.