Re: Pterosaur Question

[pharrinj@PLU.edu]

On Sun, 14 Jan 1996, Amado Narvaez wrote:

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

                     <snip>
> 
>       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?

Actually, from what I've seen, pterosaurs have a better-defined head on 
the femur than many phytodinosaurs (sauropodomorphs/ornithischians), 
albeit set at an obtuse, rather than a right, angle to the femoral shaft.

>       2) Did plesiosaurs, mosasaurs, and ichthyosaurs also lack the
>               ball/socket arrangement?

All tetrapods have ball-and-socket hip joints.  It's just a question of 
how well-defined the head of the femur is.


> 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?

Important point:  plesiosaurs and ichthyosaurs (and placodonts and 
nothosaurs) weren't archosaurs.  I don't think anyone's exactly sure 
what they were, but they were most likely somewhere on the line leading 
to lizards.  Mosasaurs, on the other hand, were true lizards, related to 
the Komodo dragon.  The only Mesozoic marine archosaurs were two lineages 
of crocodiles adapted to the sea.  Personally, I think pterosaurs might 
as well be classified as dinosaurs, but there are many wildly differing 
opinions on the subject.

 
> (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?)

I think the main reason they were clumsy on the ground is because of 
those enormous heads and necks.  I know you will get many opinions on 
this subject, though.

> 
> Thanks from me and my "constituents" for any enlightenment.
> 
> ----- Amado Narvaez
>       anarvaez@umd5.umd.edu
> 

     Nick Pharris
     Pacific Lutheran University
     Tacoma, WA