This is one of the things that really annoys me about Disney...
Notice that Aladar doesn't have the correct bone structure at all for an Iguanodon. I heard somewhere that Disney modeled him on a horse. Now, I know there were a few things they had to change for the movie for the sake of the story, but I don't think that was a huge plot point.
(Disney DID consult paeleontologists, but apparently ignored everything they said!)