Pterosaur Question

[Amado Narvaez <anarvaez@umd5.umd.edu>]

I was re-reading Spinar and Currie's _The Great Dinosaurs_ and in the 
early section about defining dinosaurs is the statement:

        Some of the most important characteristics used to define
        the Dinosauria are found in the hind limb. This is because
        dinosaurs were more efficient walkers than more primitive
        cousins like thecodonts, crocodiles and pterosaurs (flying
        reptiles). The upper leg bone (femur) has a ball-like head
        that fits into the hip socket and brings the leg under the body.

I have two questions about the statement:
        1) Does this mean pterosaurs did not have a ball/socket pelvic
                arrangement?
        2) Did plesiosaurs, mosasaurs, and ichthyosaurs also lack the
                ball/socket arrangement?

Often the popular books on dinosaurs exclude pterosaurs and marine 
dwelling reptiles of the Mesozoic from the Dinosauria because they didn't 
live on the land. That may be true of plesiosaurs, but it's a weak 
argument for pterosaurs, especially if I'm going to try to convince the 
kids at my school (and colleagues) that birds are dinosaurs.

So, the two questions above can probably be summarized as one:

        What specific characteristics exclude pterosaurs and marine 
                dwelling archosaurs from the Dinosauria?

(On another tangent: There was a lot of discussion a while back about 
pterosaur locomotion, but isn't part of the reason they were less 
efficient walkers due to the awkwardness of dealing with the wings?)

Thanks from me and my "constituents" for any enlightenment.

----- Amado Narvaez
      anarvaez@umd5.umd.edu