Limbs and niche partitioning

[NJPharris@aol.com]

In a message dated 9/29/99 6:01:38 PM Pacific Daylight Time, 
mbonnan@hotmail.com writes:

> One thing that has always intrigued me about dinosaurs is this idea: 
perhaps 
>  because they have relatively stiff joints and limbs that tended to move in 
>  relatively restricted planes, could this be a reason (among many) for why 
>  dinos got so big?  In other words, maybe one of the problems with getting 
>  huge is that if you have multiple degrees of freedom in your joints, you 
>  have problems going beyond a certain size because of all the torques, 
>  stresses, etc.  If you are ancestrally constrained, perhaps it is easier 
for 
> 
>  you to get big?

I've wondered this myself in the past (and there are probably some old posts 
of mine on the subject floating around the archives).  This may also be why 
dinosaurs were not particularly effective at producing small-mammal-sized 
forms (at least not until the advent of advanced flight and hopping 
locomotion opened up new niches for small birds), since flexible limbs and 
spines are probably more effective than dinosaur-type limbs and spines for 
skittering along the ground and in the trees.

So maybe the mammals and the dinosaurs were specialized for different niches: 
 the dinosaurs with their stiff limbs, were better at producing large, 
ground-based forms, while mammals, with their flexible limbs and spines, were 
more suited to occupying the fossorial, scansorial, or arboreal small-animal 
niches (which a great many mammals still occupy to this day).

--Nick P.