Living between 286 and 270 million years ago, dimetrodon inhabited swampy regions of North America and Europe. Measuring about 12 feet (4m) long, this predator featured a sail-like spine on its back.

such as geodes and fossils of dimetrodon footprints that are 295 to 272 million years old, begin to wash up. These riches are what many rockhounds are after. Dimetrodons were mammal-like reptiles that ...