What in the world is it? It’s not a dinosaur that’s for sure. It’s of the genus Dimetrodon, and lived during the Permian Period, 280 to 265 million years ago, predating dinosaurs by a good 35 million years. More closely related to mammals than to reptiles, Dimetrodon measured about 1o feet long, and had two types of teeth, hence the name Dimetrodon, which means Di (two)- metro(measure)-odon(tooth). Having a variety of tooth types, with multiple cusps, is a characteristic of mammals, not reptiles, to name just one of the many differences between the two groups. And finally there’s the NEW T-Shirt that tells the world that you know that it’s NOT a dinosaur. Unfortunately, the vagueness of the shirt may lead the uninitiated to think that you’re declaring that you’re not obsolete just yet.