Re: The Effects of Dromaeosaur Predation

[Amtoine Grant <rascienz@shaw.ca>]

On 21-Aug-08, at 10:19 PM, Tim Williams wrote:

> Scott Selberg wrote:
>
>
> > Jonas Weselake-George's request for ornithopod forelimb movement  
> > got me thinking about an old theory of mine. It has always struck  
> > me that considering the build and posture of Iguanodon, the spiked  
> > thumb would not be a very effective weapon against a large  
> > theropod like an allosaurid. However, given the proper mobility in  
> > the shoulder and elbow, the spikes would be very effective for  
> > peeling a dromaeosaur off of the animals flanks. Obviously there  
> > are many other factors involved, but I've always found it  
> > interesting that right when large dromaeosaurs become common,  
> > allosaurs decline and large herbivores with unprotected flanks are  
> > largely replaced by herbivores like armoured titanosaurs,  
> > nodosaurs, and perhaps iguanodontids that were designed for flank  
> > protection. Also, when tyrannosaurs came to the fore and  
> > dromaeosaurs are somewhat relegated to small game hunting, large  
> > herbivores with relatively unprotected flanks again come to the  
> > forefront. Again, I realize that there are many other factors  
> > involved and other things going on at that time, but I think that  
> > the effects of the radical new approach that dromaeosaurs brought  
> > to predation may have had a much bigger effect on herbivore  
> > evolution than is generally considered.

Iguanodont thumb spikes being primarily used for defense has always  
truck me as illogical as well. The only way to utilize them would be  
expose & let the attacker close to the most vital parts that should  
be protected(neck, stomach). And rearing up on two legs to do so I  
assume would decrease pivotal speed, a serious problem if ever  
dealing with more than one attacker at a time. For close inter- 
species combat, however, they are ideal.
It is very interesting to observe, given the assumed difference in  
allosaurid vs dromaeosaurid predation methods, the allosaurs in JFC  
leaping onto the sides of the Camarasaurus in the "raptor" method.