@Brook V: Actually..there was this whole thing with crap..I can't even remember what the "element" was that they used, but it filled these big sacs that the dragons had inside of them. (And yes, wings are an important part of their ability to fly, but if it was just their wings they would easily tire from propelling several tons of weight through the air by pumping their wings constantly. Therefore they wouldn't be able to fly long distances. -- Think about it. A bird's ability to "soar" for x ammount of time is the only reason they're able to fly long distances for long periods of time. I'm trying to think of how a dragon could have that ability.)

Oh..and something I forgot to respond to : If a dragon has bones like a bird's or cartilage instead of bones, they would be as breakable as a bird. Which means that using them for combat would be impossible. Both dragon and rider would be too easily crushed and killed.