Re: Stego/Ankylo limbs

[Dinogeorge@aol.com]

In a message dated 96-01-31 00:19:14 EST, longrich@phoenix.Princeton.EDU
(Nicholas R. Longrich) writes:

>       Were those limbs really just for grasping? Psittacosaurs have 
>decently powerful front arms, that seem at least as useful for walking on 
>the ground as a kangaroos, so they could have had some practice. And what 
>about ornithopods? Even ornithopods only partially quadrupedal seem 
>to have erect forelimbs.
> Iguanodon had bipedal ancestors (dryosaurs? or somebody else?) 
>but doesn't seem to have had a problem with walking on 
>erect front limbs, at least part time, and, neither does Tenontosaurus, 
>which is a modified hypsilophodont. 

I wouldn't be at all surprised if _Stenopelix_, _Psittacosaurus_, and company
used their short forelimbs for locomotion now and then, as the mood hit them.
The hands, or what is known of them, had relatively short digits
(particularly digits IV and V) and probably had to be used together to do any
kind of serious grasping. But they were lightly built, relatively small
dinosaurs that did not (yet) have a serious graviportal problem. They didn't
_need_ to keep their forelimbs on the ground most of the time to support the
weight of their forequarters. We know, of course, that this became less and
less true for their larger and larger descendants.

The duckbilled dinosaurs had a rather longer evolutionary history of
facultative quadrupedality--back through iguanodontians and camptosaurians to
somewhere in the Jurassic--so I'd expect them to have had more highly
derived, more erect forelimbs, and indeed they did.