Though that works, to be more concise you may want to replace Siigonis with Qah, which means hide or scales. 

Now T-Rex has a proper, three syllable dragon name:  Thurqahjun

I'm a bit late here, but "thur" means a more righteous ruler, whereas "drog" is someone who rules by force. If there's one thing I know about T-Rex, it's that it was a nasty beastie. The word "drog" might be more appropriate for them, although "Drogqahjun" doesn't roll off the tongue quite as nicely.