Dimetrodon

prehistoric · sail-backed · synapsid · permian

Massive back sail. Dimetrodon had tall spines sticking up from its backbone that created a dramatic sail-like shape across its back. Scientists think this sail may have helped it absorb heat from the sun or look impressive to other Dimetrondons.

Different sized teeth. Unlike many ancient reptiles, Dimetrodon had teeth of various sizes in its jaws, kind of like modern mammals do. This shows it was actually an early relative of mammals, not a true reptile.

Range of sizes. Some Dimetrondons were as small as a large dog at 5 feet long, while the biggest ones stretched over 15 feet and weighed as much as a grown bear. Most were somewhere in the middle of that range.

Red Beds fossils. Most Dimetrodon skeletons have been dug up from ancient rock formations called the Red Beds in Texas and Oklahoma, though scientists have also found them in Germany. These fossils are 290 to 270 million years old.

Four-legged walker. Dimetrodon walked on all four legs and couldn't rear up on its hind legs like some other creatures could. Its body was built low and sturdy for moving along the ground.