Everyone knows what a dinosaur is, don't they? Don't they?
The chances are they probably don't. See, those pterodactyls that filled the prehistoric skies, they weren't dinosaurs. Nor were the vast ocean-going reptiles, the long-necked plesiosaurs and the fish-like ichthyosaurs. And as for sail-finned beast such as Dimetrodon and Edaphosaurus, they were more closely related to mammals than the 'terrible lizards' of yore.
No, for a creature to be considered a dinosaur it has to meet some very strict criteria. A particularly significant characteristic is that, unlike lizards whose legs sprawl beneath them, dinosaurs had a distinctly upright stance. In having legs held directly beneath the body, dinosaurs can be identified as belonging to the same group of animals - archosaurs - as crocodiles and modern birds.
As for the other things that remove dinosaurs from the rest of the reptiles, they've been outlined by the acclaimed American scientist Sterling J Nesbitt and consist of unique bone formations in the skull, neck, arms, legs and vertebrae. I could list all of these but it would mean breaking out terms like 'astragalus' and 'ischium'. Safe to say, there are 12 distinct physiological differences between dinosaurs and all other reptiles.
So, there you are then - dinosaurs aren't what you might have been lead to believe they are. And with current research suggesting that they might have been warm blooded and even fur-covered, the behemoths of the ancient world weren't the sluggish, lumbering oafs they're so often depicted as, either.