My point was that back in the 1800s they thought Iguanodon looked like that picture (a giant lumbering iguana) because the tooth looked like a big iguana tooth and that's all they had from the "world around them" to go by.

More complete evidence has since revealed that the probably looked more like this:

[image|http://upload.wikimedia.org/wikipedia/commons/e/e0/Iguanodon.jpg||||]

Also, other leading theories as to the purpose of Pterosaur crests are that the were used to regulate body temperature, for aerodynamics, or a combination of all three.