It's pedantic to point this out I'm sure but despite it's little plastic avatar regularly appearing in sets of dinosaur figures Dimetrodon wasn't a dinosaur, it was in fact a very distant cousin/ancestor of mammals, and predated the first according-to-Hoyle dinosaurs by 40-60 million years..
(Coincidentally my hostname convention for naming computers was/is in fact based on extinct animals, and I'd usually name PowerPC-based machines running *nix after synapsid/therapsid (mammal-like) reptiles... which lead to horrors like having to memorize how to spell "Estemmenosuchus".)