Re: How were the Pterodactyls able to fly when they weight more than birds?

  Pterodactyls (pterosaurs) may not have necessarily weighed more than 
birds of equal dimensions.  However there were some forms that reached 
enormous proportions.  How they were able to fly is simply a matter of 
physics.  

   One must look at the surface area of the wing(s) or protagium (skin 
between the hind legs and fore limbs).  This skin when pulled taut will 
form a basic wing shape.  If you were to take a plane (bird, pterosaur, 
etc.) wing and cut it to view the cross section you will see a shape like 
this:


   As you can see from the diagram the air moves faster over the top of 
the wing than it does on the underside.  As the air going over the top 
speeds up the molecules become separated (due to the longer distance 
relative to the air under the wing). This makes the air on top of the wing 
less dense (and less pressure).  Because of the difference in pressure 
there is pressure (force) exerted upwards on the wing causing it to be 
lifted upwards.

   The pterosaurs had a similar shape to their "wings" as planes and birds 
have.  They can have HUGE body sizes and still have enough lift to fly 
(maybe without even moving "flapping" their "wings").  Also, there are 
great variations in the sizes of the pterosaurs.  Some with wing spans of 
5+ meters, down to ones with wing spans of 50cm or less (twice an 
albatross to about the size of a crow).  

Another point to keep in mind would be that pterosaurs had VERY VERY light 
bones, even lighter than birds today! they were hollow and strong.  This 
would greatly reduce their weight and make flying even easier.  But heavy 
things can fly too (Just look at a C5 Galaxy).

Cheers