No. Tetrapods and reptiles diverge well before dinosaurs. All dinosaurs are diapsids as compared to mammals, which are synapsids. A dimetrodon (the one with the big sail) is not actually a dino and is more closely related to humans than it is to dinos.

To expand on this concept, all dinosaurs and humans are technically considered bony-fishes as they are nested within the bony-fishes clade, osteoicthyes, but thats probably spelled wrong (this recently was used as a way of protecting some types of animals in a law that is supposed to protect fish as a category), and all birds are technically dinos, so when we refer to non-avian dinos, it just means dinosaurs excluding the birds!